Sciencemadness Discussion Board

Has anyone made a EBW setup.

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Forumdude - 23-2-2013 at 00:19

I have looked around and there isnt much information on how to make one of these or how many volts and joules ect and what kinds of wire will work for the actual EBW and the wires leading from it.


Phantom - 23-2-2013 at 01:51

http://www.sciencemadness.org/talk/viewthread.php?tid=15317
https://www.sciencemadness.org/whisper/viewthread.php?tid=12...


Forumdude - 23-2-2013 at 12:01

Thank you so much! I searched EBW on here and those pages didnt come up.

Forumdude - 23-2-2013 at 12:07

Thing is though I have no electrical experience and I have no clue as to what they are discussing

Ral123 - 23-2-2013 at 12:28

I like your sense of humour :D

hissingnoise - 23-2-2013 at 12:37

Yeah, that is funny . . .

Fuse - 25-2-2013 at 06:45

I've built one, some videos posted on youtube with "Freepatentsonline" nick.

franklyn - 26-2-2013 at 02:15

Seems you need to read a lot more on this topic.

A Guide to Explosives Firing
www.dtic.mil/dtic/tr/fulltext/u2/a322055.pdf

If you want a second opinion _
www.amateurpyro.com/forums/topic/414-ebws-capacitor-discharg...

_______________________________________________________


While on the topic I thought this an interesting development , it's a device that
amplifies the power from a normal blasting machine producing a pulse to fire EBW's.

Blasting Machine Power Multipliers for EBW's
www.teledynerisi.com/1techtopics/pdf/0295.pdf
www.teledynerisi.com/products/0products_2fs_page43.asp

The above would be used for example with a blasting machine like this_
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=26117...

.

Blasting Machine.jpg - 41kB

Fuse - 26-2-2013 at 05:02

http://www.youtube.com/watch?v=IXMDltOiNpU

With this I detonate ETN directly :D

Ral123 - 26-2-2013 at 10:55

Are these things reliable? In a way you use electrical energy in the battery to do the job of the primary. How many joules you put in each shot? Did you make experiments with other secondaries?

Fuse - 27-2-2013 at 01:37

The energy stored in the capacitor is 8J, from that you can transfer about 0,5-1J into exploding wire
(see http://www.dtic.mil/dtic/tr/fulltext/u2/609449.pdf).

Reliability is 100% for me; at the moment more than 50 test never failed.
Unfotunately I never tried with others primary.
In the future I will try to detonate a very insensitive material like AN-AL.
(see patent US 3,156,186)
If it works I can remove every type of primary :D

Ral123 - 27-2-2013 at 04:41

Nice, I'd use azide with the wire for critical applications to be sure. Interesting, 1J makes that thing explode, and with enough force to initiate the ETN. I wonder how will it perform in winter at -20, specially if the ETN has previously been a little melted from the heat of the sun near a window :P

Forumdude - 9-3-2013 at 23:16

Sorry I've been away but this is great information haha and and Fuse I have stumbled apoun your videos in the past ! Great stuff!

EBW HV Power Supply from Handheld Bug Zapper Rackets

Hennig Brand - 8-4-2015 at 14:50

I have two hand held bug zappers that were given to me which had mechanical problems of some sort but the power supplies still work fine (is it a bad sign that people keep giving me their old junk?). I also have 6 X 1000V, 1uF film capacitors which I removed from a large burned out VFD (variable frequency drive) for large induction motor speed control found at a scrap yard years ago. I discovered that once the ca. 400V capacitors were removed from these bug zapper power supplies that they could easily charge a several uF capacitor up to 1000V and that two of these in series could easily charge up to 2000V. I haven't tried going much higher except by accident the 3X2 capacitor bank of 6X1000V, 1uF capacitors (total 2000V, 1.5uF) was charged up to about 2200V once. Another 1000v, 1A diode (1N4007), was added in series with each of the two rectifier diodes present on each PS output.

So far I only have 40 gauge copper to make bridge wires and only RG6 coax (cable/satellite television cable) and/or speaker wire for transmission. Charged up to 2000V the 1.5uF capacitor bank can easily detonate ETN through 1ft of 18 gauge speaker wire, however, attempting the same thing with 12ft of RG6 coaxial cable resulted in failures.

I am just getting my feet wet with this, but decided to post since I think it is interesting.



Bug Zapper.jpg - 239kB Two Bug Zappers in Series (1).jpg - 284kB Two Bug Zappers in Series (2).jpg - 259kB

I know I should have bypass resistors in parallel with the two sets of series connected capacitors and on the rectifier diodes to ensure even distribution of charge/voltage. I ordered some high voltage, high ohmic value, bleeder resistors today but they will be a while getting to me.

Ideally 4 or even 6kV would be much better than 2kV and if the bridge wire was closer to 50 gauge the power requirements would be much less than they are now using a 40 gauge bridge wire. I think I have some heavy coaxial stored in a shed that was used by someone for Ham radio, which could be a big improvement in the transmission department.

Another couple of bug zapper rackets and I am good to go for 4kV. :D

Does anyone know exactly what type of capacitor this is? The warning on it is a bit ominous and for good reason I guess. A couple of these in series would be 12uF and could be charged to about 4kV. Now that is one hell of a jolt! I came into possession quite a few years ago of a lot of used 1970s electronics and electrical equipment from personnel carriers, etc, when they were being refurbished; a certain piece, of which I had a few dozen I think, had one of these big HV capacitors buried deep inside.

Big HV Capacitor.jpg - 487kB


[Edited on 9-4-2015 by Hennig Brand]

24uF Capacitor Charged To 1600V Discharged Through 12ft RG6 Coax Into 40 Gauge Copper Bridgewire Initiates ETN

Hennig Brand - 9-4-2015 at 06:55

I hooked up the big 2kV, 24uF capacitor this morning to the bug zapper HV power supply. A 40 gauge copper bridge wire, about 1.5-2mm long was connected at the other end of 12ft of RG6 coaxial cable. Wrapped around the bridge wire in a bit of plastic wrap was about 50mg of loose, crystalline, ETN. The 24uF capacitor was only charged to 1600V because the bug zapper power supply took almost a full minute to even charge it up that much (batteries are old, so replacing them could make a big difference). There was a huge bang when the wire was touched to the charged capacitor and on inspection the plastic wrap was seen to be blown away and the bit of circuit board/spacer which held the bridge wire was broken away from the solder joints.

Capacitor Energy = 1/2CV^2
Energy = 1/2*0.000024F*1600V^2
Energy = 30.7 Joules

If two were hooked in series and charged to 4000V:

Energy = 1/2*0.000012F*4000V^2
Energy = 96 Joules !!!

I am still just learning, but this amount of capacitance is likely way overkill even with a 40 gauge bridge wire, also, at least 4000V would be much better than 2000V for long cable runs. It should be no problem initiating ETN through 100ft of cable with the right capacitor(s) and cable. I used a half to a full foot of 18 gauge speaker wire on either end of the RG6 coaxial for this test, so a section of consumable wire of some sort could be made as part of each EBW cap assembly with the idea that it would be consumed/destroyed in the blast.

Large Cap EBW.jpg - 299kB Vaporized BW Detonated ETN.jpg - 172kB

I suppose three of these capacitors hooked in series, with appropriate bypass resistors, would have 8uF of capacitance and could be charged as high as 6000V which would be about right probably.

Energy = 1/2CV^2
Energy = 144J !!!


Remote Control of EBW Power Supply Charging and Firing

The big limitation to these systems is the transmission cable, which must be kept as short as possible for practical purposes. I see no reason why heavy cables need to be run all the way back to the operator/shot firer. The power supply, capacitor(s) and firing switch/mechanism could all be fairly close to the blast in a tough enclosure or even buried. Small signal, light gauge, wiring could be run to the distant operator/shot firer so that charging and firing could be controlled as well as voltage/charge monitoring all from a distance. In fact if desired all that needs to be relatively close to the blast is the capacitor(s) and the firing mechanism, the power supply could charge the capacitors through a fairly light copper pair from a distance.


[Edited on 9-4-2015 by Hennig Brand]

markx - 9-4-2015 at 09:25

You need a beefier power supply for the cap. Using this bug zapper is like trying to fill a pool with a bucket :)

E.g. a topology like this one:

http://www.hvlabs.hu/inverter/fcsinverter.gif

The IR2153 or 21531 are selfresonating drivers that can be tuned in on the sweet spot of the transformer and operated in halfbridge or push pull mode. They are cheap and quite reliable, requiring very limited amount of external parts, but one has to limit the current through the chip Vcc leg to max 5mA. This can be done via a resistor of appropriate size if the supply voltage is fairly constant. With a battery though, I would suggest a sepic converter for that job. It is very annoying when the circuit draws big amps from the battery dropping the voltage below the UVLO treshold of the driver chip (9,5-10V) and the circuit starts to softswitch itself on and off. Then one tries to decrease the limiting resistor value and the chip gives off the ghost when a fresh battery with higher voltage is connected...
A sepic converter will feed a stable voltage of appropriate value to power the chip independent of the input voltage from the battery and eliminates the overcurrent problem very efficiently.
The output of the transformer can be driven through a simple voltage multiplier to get the required kV.

Hennig Brand - 9-4-2015 at 14:27

Thanks, not a bad idea. You know though, the two series connected bug zappers have no problem charging up 1.5uF to 2000V, from just a couple of 1.5V AA cells, in well under 10 seconds. The last capacitor used really is a beast at 24uF and 2000V. Would be pretty funny to have an EBW power supply made with eight or ten series/parallel connected bug zapper power supplies. :D They are only $3-4 dollars each new IIRC and the first two were given to me broken so they were free. Pretty sure the transformers in them could handle more current so I could probably crank them up some. :D

Here is a power supply I have used in the past that works great and is not picky at all about component choice (pretty much any transistors that can handle the voltage and current within reason). I built a stun gun eight years ago or so and used the front half of one of these circuits when I built it (up to and including T1). It made a simple and tough little HV supply.


Stungun 2.png - 11kB

Stun Gun 3.png - 9kB

The circuits were taken from the following website which also has some assembly instructions.

http://chemelec.com/Projects/Stun-Gun-1/Stun-Gun.htm

I think it was probably the second one I used, but like I said before component choice is flexible. I wound my own transformers, or rewound I should say T1 from a salvaged switching supply transformer. Some voltage multiplier stages after T1 and you have everything you need. What you suggested could be a better solution, but it doesn't have to be too sophisticated and I kind of like working with garden variety discrete components such as transistors, capacitors, resistors, etc.


[Edited on 9-4-2015 by Hennig Brand]

markx - 10-4-2015 at 01:56

I'm sure both options will work just fine....and usually whichever one is simpler will do a better job.

And then there are the days when simple stuff gets kinda out of hands :D :D :

WP_20141112_005[1].jpg - 1.4MB

WP_20141112_012[1].jpg - 1.3MB WP_20141112_007[1].jpg - 1.2MB

WP_20141102_001[1].jpg - 1.4MB

Hennig Brand - 10-4-2015 at 06:11

Looks very nice. Is that an EBW power supply?

Also, forgot to mention that there were high ohmic value bleeder resistors across the original HV storage capacitors on the bug zappers' outputs. These resistors as well as the original ca. 400V capacitors were removed so that the zapper supplies could be used to charge 1000V capacitors.

As was mentioned already, with two AA, 1.5 volt cells, the two series connected bug zapper power supplies took about a minute to charge the 24uF capacitor up to 1600V. The two AA batteries (3V total) were replaced with a small sealed lead acid battery (4V) which enabled the bug zapper supplies to charge the 24uF capacitor up to the full 2000V in 30-40 seconds. I was just going to add more AA batteries in series/parallel to get higher voltage/current capability, but this lead acid battery was sitting right on the table looking at me already. Components (transistors and transformers) were monitored for excessive heating during charging and were found to get only slightly warm if at all. These bug zapper supplies could probably be run from even higher supply voltages.

Almost like my brother knew what I needed when he dropped off the battery a couple of days ago which he said came out of a junked handheld spotlight (like the ones used for jacking deer).


Sealed Lead Acid Battery.jpg - 346kB


I have some RG-213 stored in a shed, but will have to dig it out to know for sure how much. It can be bought for $1/foot or less sometimes if you can make a deal with some of the Ham radio nuts (have heard of it being sold sometimes for as little as 50 cents per foot). Here is a picture of RG-213. It is a very heavy coaxial with 12.5 gauge center conductor I believe and very heavy braided shielding. According to the literature RG-213 is very suitable for use as EBW transmission line. The table was taken from "Explosives Engineering", by Cooper.

RG-213 Heavy Coaxial.png - 61kB Impedances of Common EBW Detonator Cables.jpg - 49kB


[Edited on 10-4-2015 by Hennig Brand]

High Voltage/High Current Relay

Hennig Brand - 11-4-2015 at 07:10

This relay which I built in the last hour or two is extremely crude, but something much more refined could be easily built. Other than the foot long piece of 1/2" brass rod purchased for $5 everything else was from the junk pile. The idea is that the capacitor(s) can be charged through the low current normally closed contact (brass wood screw) and then once charged the solenoid could be activated which would dump the high current pulse through the 1/2" brass contact and into the transmission line and bridge wire thereby initiating the cap. Of course the relay could also connect the capacitor(s) to some other more efficient switching mechanism which could then dump the stored charge into the transmission line and bridge wire. The relay can be operated remotely using a length of light gauge wire.

Here is a picture of the crude high voltage/ high current relay and also a tiny video of it in operation.

High Voltage High Current Relay.jpg - 279kB

Attachment: Relay in Action.mp4 (9.2MB)
This file has been downloaded 1174 times


The solenoid is much bigger than it needs to be. It is rated for 120V and when kept mostly retracted it generates lots of force even when powered by only an 18V cordless drill battery pack (as was done in the video). Also from reading some of the Tesla coil sites, it seems that contacts with large, smooth surfaces with the right curvature can really reduce inductance and losses at a spark gap. I tried for 1" brass rod for contacts, but all I could locate yesterday was 1/2".


The pivot screw has been replaced with a pivot bolt which looks a little less foolish and will work better and for longer too. The spring was also positioned so that a little more tension was put on the contacts in the normally closed position. Picture below.

Relay Improved.jpg - 260kB


[Edited on 11-4-2015 by Hennig Brand]

Triggered Spark Gap Switch

Hennig Brand - 12-4-2015 at 04:54

From the little bit I have learned about it so far, trigatrons appears to be much more controllable, more reliable, faster and more efficient than passive spark gaps (non-triggered spark gaps).


Here is a snip-it from the Wiki page on trigatrons:

"
A trigatron is a type of triggerable spark gap switch designed for high current and high voltage, (usually 10-100 kV and 20-100 kA, though devices in the mega-ampere range exist as well). It has very simple construction and in many cases is the lowest cost high energy switching option. It may operate in open air, it may be sealed, or it may be filled with a dielectric gas other than air or a liquid dielectric. The dielectric gas may be pressurized, or a liquid dielectric (e.g. mineral oil) may be substituted to further extend the operating voltage. Trigatrons may be rated for repeated use (over 10,000 switching cycles), or they may be single-shot, destroyed in a single use.

A trigatron has three electrodes. The heavy main electrodes are for the high current switching path, and a smaller third electrode serves as the trigger. During normal operation, the voltage between the main electrodes is somewhat lower than the breakdown voltage corresponding to their distance and the dielectric between them (usually air, argon-oxygen, nitrogen, hydrogen, or sulfur hexafluoride). To switch the device, a high voltage pulse is delivered to the triggering electrode. This ionizes the medium between it and one of the main electrodes, creating a spark which shortens the thickness of non-ionized medium between the electrodes. The triggering spark also generates ultraviolet light and free electrons in the main gap. These lead to the rapid electrical breakdown of the main gap, culminating in a low resistance electric arc between the main electrodes. The arc will continue to conduct until current flow drops sufficiently to extinguish it.

The triggering electrode is most often mounted through a hole in the center of the positive main electrode. The undrilled main electrode is the negative electrode. When switching high currents, the electrodes undergo considerable heat stress, as they are directly involved in the electric arc. This causes the surfaces to undergo gradual vaporization, so some designs incorporate methods to easily adjust the distance between the electrodes or to actually replace the electrodes. The main electrodes are typically fabricated from brass, or alloys of copper and tungsten for longer electrode life."


Found a good website with lots of technical data sheets for triggered spark gaps. Attached are a couple of related ones from the site.

http://www.reb3.com/


Attachment: Specifications for Spark-Gap Switches.pdf (951kB)
This file has been downloaded 1684 times

Attachment: Application Information for Spark-Gap Switches.pdf (326kB)
This file has been downloaded 2301 times


Here is a good DIY HV page with some simple firing circuits for trigatrons and where I found the link to the above commercial site:

http://hotstreamer.deanostoybox.com/ross/projects/Pulse/puls...


Here is a good electrical engineering journal article on trigatrons:

Attachment: Triggering in trigatron spark gaps - A fundamental study.pdf (1.8MB)
This file has been downloaded 854 times



Threaded Switch Doesn't Bounce

The reason attention is being put on designing a triggered spark gap is because normal switches and relays have a variety of problems, such as switch bounce, which can cause erratic behavior especially with such high currents and short pulse durations where perfect switching is vital to performance. With the exception of not having timing as precise as with a trigatron, I think I may have a fairly simple solution for spark gap switching. One of the electrodes could be fixed and the other could be set into an electrically insulated track and moved towards the other electrode until arc over occurred firing the EBW. Timing would be awful compared to a trigatron, but how much does 1 or 2 seconds delay matter for general purpose blasting? Unlike a true static spark gap, where firing voltage/charge is somewhat uncertain, the capacitor(s) could be charged up to the desired level with the electrodes far enough apart to not result in premature firing and then when desired the movable electrode could be threaded into firing position.


[Edited on 13-4-2015 by Hennig Brand]

nux vomica - 12-4-2015 at 22:01

Here's a link to a US co that manufactures ebw switches don't think you could buy off them but they have data sheets on line cheers nuxy.
http://www.highenergydevices.com/products/three-electrode%20...

jock88 - 13-4-2015 at 12:49


Get Cooks book as it has lots of info.

Some reading on EBW's attached.

Attachment: ebw.rar (1.8MB)
This file has been downloaded 880 times


Screw Triggered Spark Gap

Hennig Brand - 13-4-2015 at 13:15

Thanks, that site looks interesting. There are also at least a few sites online with peoples' descriptions of how they have built their own. They aren't terribly complicated and I probably will eventually build one.

Here are a couple pictures of the "Screw Gap". It works, but I have not tested it yet with proper transmission cable, proper EBW and explosives in a cap.

Screw Gap (1).jpg - 243kB Screw Gap (2).jpg - 258kB


Thanks for the reading material Jock88.

edit:

Static Gap

A plain old static gap with a threaded adjustment for width would be the simplest thing, however, at these relatively low voltages the spark gap is very narrow especially with large curved electrodes which are used because they are much more efficient than fine point contacts. A very narrow gap and slight changes in the surface of the contacts (any kind of roughness or buildup) could make the gap fire early and wear or other changes could cause the gap to fail to fire. Since energy is proportional to the capacitor(s) voltage squared the gap would need to be very carefully adjusted in order to get good results.

I used the calculator from the following site, which is apparently based on empirical data, to get data points for the attached graph which was made in Excel. The other graph, showing higher voltages, came from the site linked to above regarding stun gun HV PS circuits.

https://www.cirris.com/learning-center/calculators/50-high-v...


Arc Distance In Air versus DC Voltage.jpg - 44kB Arc Length Versus Voltage.png - 18kB



Here is the same graph as above, but this time with extrapolated values from 3000-6000V.


Arc Distance versus DC Voltage (400-3000V) Plus Extrapolated Values from 3000-6000V.jpg - 46kB



Ok, I just found the following appendix from the article, "Electrostatic Discharge: Understand, Simulate, and Fix ESD Problems, Third Edition
Published Online: 22 SEP 2009", which has tables giving break over voltages for spherical and pointed contacts. This looks like a decent reference.


Attachment: Spark Over Voltages (Wiley).pdf (429kB)
This file has been downloaded 908 times


[Edited on 14-4-2015 by Hennig Brand]

jock88 - 14-4-2015 at 12:04


I wrongly give a book name above in my last post as Cook. That should be Cooper. There is a very useful chapter on EBW's.

Also the compressed .rar file in my last post needs to be decompressed and the starting point for reading the whole 'web page' is the file called EBW_INFO.HTML


The attached file is from 'Twospoons' from this thread:
http://www.sciencemadness.org/talk/viewthread.php?tid=10874

May help in spark gap firing.

Jock88


Attachment: swinging cascade.pdf (59kB)
This file has been downloaded 597 times

[Edited on 14-4-2015 by jock88]

Simple Trigatron Trigger Pulse Generator From Bug Zapper Power Supply

Hennig Brand - 15-4-2015 at 02:50

Yeah, I knew you meant Cooper. Thanks for that compressed file, it has a lot of good stuff in it. I have been mulling the triggered switch thing over for the last couple of days. Just about ready to give something a try.


I already linked to this page earlier, but after looking at the one-shot trigatron pulse generator on that page I got a couple of ideas.

http://hotstreamer.deanostoybox.com/ross/projects/Pulse/puls...

Here is an image of the one-shot pulse generator from that page:


Trigatron Trigger Pulse Generator (SCR One Shot).png - 3kB



In order to keep things really simple the SCR was replaced with a static spark gap and the AC input and voltage doubler stage were replaced with the ubiquitous bug zapper power supply. A single bug zapper supply, with proper adjustment, can easily charge a suitable capacitor to over a 1000 volts if needed. The capacitor is charged through the primary winding of the transformer until the breakover voltage of the spark gap is reached which then arcs over and dumps the stored charge through the transformer primary very rapidly which transfers the pulse by electromagnetic induction to the transformer secondary and the trigatron trigger electrode.


Simple Trigatron Trigger Pulse Generator.jpg - 56kB


If more precise firing times are required replace the static spark gap with an SCR. Multiple circuits like this could be fired simultaneously using SCRs. SCRs are sensitive to overvoltage, with ones I have commonly seen being rated for max 400V or sometimes 600V, so the capacitor and charging circuit would need to be designed carefully so as not to create an over voltage situation unless very high voltage SCRs could be obtained. A pulse capacitor charged to a lower voltage and a transformer with lower turns ratio (more voltage gain) would be needed.

I avoided winding a transformer by taking one from a switching supply, which seems to have a couple windings with a turns ratio (# turns in primary/# turns in secondary) of 1/2-1/4 (estimated by spark gap length at secondary). This transformer is not designed to be used at several thousand volts, but so far it seems to be holding up just fine. When I actually get it put together more properly I will post a picture or two.

BTW, a couple people have mentioned capacitor charging current limiting resistors. They are not needed when using the bug zapper supplies, since the transformers themselves are made to be current limiting (or it just happened that way maybe).

I am pretty sure I can get by with just three bug zapper power supplies, as long as I go no higher than 3-4kV and a few uF of capacitance. Two in series to charge the capacitor bank and one to fire the trigatron. If I was more clever, or motivated, I probably wouldn't even need the third one, but they are only $3 each at the local dollar store anyway.


[Edited on 15-4-2015 by Hennig Brand]

markx - 15-4-2015 at 12:58

The last "single pulse" circuit with the spark gap will generate a very high frequency hv ac on the transformer secondary (the capacitor and primary winding form a LC resonant circuit as the gap fires and shorts the cap through the inductance)....it is actually the most classic setup for spark triggered tig welder arcstarters. The high frequency ac is transferred to the welder circuit by an air core transformer. In fact the resonant ac is usually of such high frequency that it will flow by the semiconductor junctions (paracitic capacitance of the junction will conduct it) and will not harm them. It will also not produce a classic electric shock in you body if you should touch the secondary while the gap fires. Actually one can barely feel it due to the skin effect....it still can burn your skin if enough power is applied.

Hennig Brand - 15-4-2015 at 14:36

Interesting, it should work fine then. I have seen the same thing done with stunguns, which is where I got the idea. The stun gun I made this way sure had one hell of a bite to it though. It is current not voltage that does the damage and the arc starter probably had very low current as well as high frequency. From what I have seen, it takes very little current to trigger a trigatron as well. The above linked to website suggested using a 1uF, 400v, pulse cap before the automotive ignition coil, they were using, which would then boost the voltage up to as high as 30kV, so the current was really very low and it sounded from the description that an even smaller capacitor could probably be used with good results. Those guys were playing with some big capacitor banks and trigatrons too (coin shrinking, etc).

Thought I would mention that from what I have read so far voltages below the main electrode (capacitor(s)) voltage are normally used to fire the trigatron and that using voltages well above are not needed and can actually cause problems.


[Edited on 16-4-2015 by Hennig Brand]

aga - 15-4-2015 at 14:57

Sorry if i have this backwards, but you guys just want a localised high voltage pulse no ?

Why is it necessary to waste all that energy along long wires ?

Why not incorporate some cpu power/battery nearer to the device you want to detonate, and put that in control of the detonation ?

The wire, or wireless part of the system would be standard comms stuff.

Hennig Brand - 15-4-2015 at 16:31

Unless you are going to replace the capacitor bank and main high voltage & high current switch with every shot fired there needs to be at least some distance between the main power module and the blast. Yes, the capacitor bank discharge (the switch) could be controlled remotely through small gauge wire. That is how it is done by the professionals when they need to put more distance between them and the blast than is practical with the heavy low loss lines from what I understand. There is a page in that compression file, posted by Jock88, which shows or describes a commercial blasting box being controlled remotely by wire, but there still always needs to be at least some wire between the box and the blast unless you don't mind losing it as I said (preferably low resistance, low inductance, HV wire for low losses).

A battery or regular power supply can't supply nearly a large enough di/dt. There needs to be a massive pulse of current with extremely fast rise time to get a shock wave from the exploding wire capable of initiating a secondary explosive. I think you are thinking of regular low voltage resistive type electric detonators. And in that case I would use/have used one or more long extension cords and a cordless drill battery. Even from a couple hundred feet away or more it works perfectly since an amp or less is all that is needed to fire them properly. However, we are then back to using primaries again.


1200V, 25A SCR

It seems higher voltage SCRs are not that hard to get and they can be quite affordable too. I think I will be replacing the spark gap in the trigatron trigger pulse generator with one of these SCRs either set up as a one shot for precise firing times or set up for repetitive pulses triggered by a DIAC.

http://www.ebay.com/itm/10-pcs-NEW-ST-TYN1225-SCR-25A-1200V-...


Constructing Bridgewire Heads

It can be a bit challenging attaching the bridgewires to the lead posts/wires when constructing a bridgewire head. One of the big problems I have noticed was that solder will tend to flow out onto the copper bridge wire when soldering. I found a good webpage which describes methods to effectively prevent solder from flowing where it is not wanted.

http://www.ganoksin.com/borisat/nenam/solder-flow-clb.htm

Here is a copy/paste from there:

"
While goldsmiths normally strive to have their solder flow easily, there are times you don't want it to flow, such as spilling over a decorated surface, if it 'freezes' a mechanism, or if it threatens to open a gap in a seam soldered earlier in a construction.
The best way of not melting earlier seams is to learn heat control and use heat sinks creatively to suck heat from the immediate area where the threatened join is. I use small blocks of steel for this purpose. Repair jewelers sometimes use stacks of copper pennies as heat sinks - but make sure they are pre-1974 or so ( as later ones have zinc cores which can melt out suddenly with unfortunate consequences. A solder's melting temperature rises every time it is heated so there is the (admittedly mostly mental) assistance of earlier seams melting at a higher temperature than the same solder you are using again for a join.

Heat sinks won't work well with silver objects, as silver conducts heat so rapidly. Instead, for silver constructions and for especially delicate jobs a solder flow retardant can be really useful. A paint-on solder flow retardant is easiest to use.

There are commercial solder flow retardants, but I've never needed to use them. Here are some of the ways that goldsmiths use to prevent solder flowing.

Polishing Machine Rouge: Some people use a little rouge powder from the polishing machine dust mixed with a small amount of oil which works well. Jeff Demand of Toronto likes to make a heat the rouge until it melts and then paint it on.

Pencil Lead: a graphite stick or soft pencil will leave a barrier that solder won't flow across. Pencil leads also work to line up tube sections when constructing a hinge. Liquid graphite lubricant that can be found in for automotive supply stores can be used.

Scrap of Rubber: One can take a small piece of rubber (vulcanized mold chunk, a slice off a piece of an old torch hose etc) and, holding it in tweezers, rub it on the metal part to be protected while it is hot. The rubber melts on with a truly nasty smell (use ventilation) and leaves a brown slimy coat on the metal. This too works well.

Yellow Ochre: Old timers used yellow ochre with water. I find that it has a tendency to "bleed" into the flux and make the soldering problematic. It is somewhat better mixed with a little oil instead of water but I find it difficult to remove from the piece and do not use it.

Maalox® and "White-Out": My favorite is Papermate© correction fluid. There are solvent based and solvent-free water based versions. In my experience the water based version does not come off the metal after soldering as easily as the solvent based one. I like the solvent based one for this reason.

I wrote to the Papermate company listing all the metals, chemicals and temperatures that their product would come in contact with in standard use by metalsmiths. In their return letter no mention of chemical interactions with the white pigment was made and they felt the main danger lay in the solvent used: 1.1.1. trichloroethylene which is a mutagen and carcinogen. This leads me to think that the white material is something inert (chalk). 1.1.1. trichloroethylene breaks down when heated to form chlorine gas, hydrogen chloride and phosgene gas, all highly toxic. Their lab ran evaporation rate tests and found that because it skins over the solvent does not evaporate as quickly as they had thought. About twenty minutes after application the solvent will for all intents and purposes have evaporated. There is a safety problem here: it would be wise to use water rather than solvent based materials. Ceramist's 'kiln wash' might work in the same way.

I have a suspicion that Papermate® and similar products are mostly calcium carbonate, what print makers call 'whiting;' and what the rest of us call 'chalk'. The cheapest source by volume for chalk in solution is probably Maalox® though I have not yet tried it as a solder flow retardant.
Robert Kaylor of Boise, Idaho uses China White, a standard graphic artists material made mostly of chalk as an effective solder flow retardant. It comes as a liquid in a tube or in a dry cake which one uses like a water color cake with a brush and a little water. "

I think I will be using White-out to prevent the bridgewire from getting soldered in the middle and then removing it with solvent after soldering. I solvent wash would be a good thing after soldering anyway I think.


[Edited on 16-4-2015 by Hennig Brand]

pcb bridge wire

nux vomica - 16-4-2015 at 15:00

Hi everyone I might have an idea that I think will make fabricating the bridge wire part more easier and more consistent .
We make a small round circuit board with two pads to connect the wires to then have the bridgewire connecting between the pads the bridgewire can be etched as small as needed and it can be gold plated and you can stencil resist over areas where you want to keep the solder if you make a double sided board you can connect on one side of the board and the via will connect to the bridgewire side

Cheers nuxy



Hennig Brand - 16-4-2015 at 16:28

I think the bridgewire should be up on posts with low density fine secondary explosive all around it. I was thinking along similar lines as you for a while though. The other thing is that the bridge wire is normally 0.001 inch to 0.003 inch in diameter; 40 AWG is actually slightly bigger than 0.003 inch in diameter and that is tricky enough to deal with. Gold has less than half the tensile strength of copper, so it must need very special handling equipment especially when it gets down to 0.001 inch.

Bridge Wire Plug.jpg - 15kB


Then again maybe I am not right, here is a document showing the bridgewire positioned more or less right up against the plug.


EBW (High Temperature Model).jpg - 48kB

Attachment: High Temperature EBW Detonator.pdf (317kB)
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[Edited on 17-4-2015 by Hennig Brand]

jock88 - 17-4-2015 at 13:41

Quote: Originally posted by markx  
The last "single pulse" circuit with the spark gap will generate a very high frequency hv ac on the transformer secondary (the capacitor and primary winding form a LC resonant circuit as the gap fires and shorts the cap through the inductance)....it is actually the most classic setup for spark triggered tig welder arcstarters. The high frequency ac is transferred to the welder circuit by an air core transformer. In fact the resonant ac is usually of such high frequency that it will flow by the semiconductor junctions (paracitic capacitance of the junction will conduct it) and will not harm them. It will also not produce a classic electric shock in you body if you should touch the secondary while the gap fires. Actually one can barely feel it due to the skin effect....it still can burn your skin if enough power is applied.


This would work OK so long a the 'ubiquitous bug zapper device' is dc (not ac). I don't know what they are?

As far as the 'best' wire to use, there was a patent put up on the board that had no bridge wire at all. The patent was restricted at the time because it was when the bomb was being developed. It was filed in (about 44) and published in the seventies (about).
I'll have a look for if some time.

[Edited on 17-4-2015 by jock88]

Hennig Brand - 17-4-2015 at 13:56

The bug zappers have a tiny flyback transformer in them, which produces AC, but the output is rectified to DC with HV diodes (the diode(s) also come with the zappers). It has to be DC because the energy is stored in a capacitor like a coiled spring waiting for the unsuspecting bug to get between the conductive mesh contacts and then to ride the lightning. :D

0.3g of ETN Initiated With 40 Gauge Copper EBW

Hennig Brand - 17-4-2015 at 15:12

EBW Head:

A half inch or so of hot melt glue stick was sliced off on a cutting board, drilled once and then drilled a second time, for lead wires, using a previously made jig/spacer made from a piece of circuit board to give precise hole spacing. The bridge wire was ca. 40AWG copper of about 2 to 2.5mm length. The white-out solder flow retardant worked beautifully preventing any solder from flowing out onto the middle of the bridgewire. It could also be easily removed with acetone which made it very soft so that it could be gently wiped away. A fine cotton swab soaked in acetone would likely be effective and gentle. Once a few tricks are learned EBW head construction is not that difficult. The EBW head was pressed into the fluffy ETN with light finger pressure only.


Charge:

0.3g of ETN pressed in three increments into a 7.6mm Al casing; 0.1g at about 30lbs, 0.1g at about 15lbs and 0.1g with only finger pressure to remove voids and settle the ETN. The ETN was very light and fluffy, the result of rapid precipitation from dilution of a well mixed solution in methanol with water.


Transmission Line:

12ft of RG-6 coax (satellite/cable television coax) and 1ft of 18AWG speaker wire. Total 13ft of transmission line.


Capacitor Bank:

6X 1uF, 1000V connected to give 0.67uF and 3000V. The bank was charged to only 2300V for this test. The voltage divider allows a much lower and very safe proportional voltage to be monitored with a regular multimeter/volt meter and from a distance with a fine sensing wire if desired. The voltage divider also doubles as a bleeder resistor ensuring that the capacitor bank is fairly quickly discharged after use.


Switching:

Switching was accomplished by the very crude and inefficient method of touching the center conductor of the coax to the speaker wire connected to the capacitor bank.


Target:

Ca. 2.6mm steel plate.


Results:

It was a very loud boom, which I could tell clearly even though I was wearing earmuffs (I was only 10ft away of course). The result, in terms of steel penetration & shattering, would have been better if the bottom increment(s) of ETN had been pressed to much higher density with a press and of course if more ETN had been used. This test was simply proof of concept.

Very large capacitors are not needed at all. The most important thing is to have low impedance cable that isn't too long, good low inductance & resistance connections and high voltage. I have 100ft of RG-213 ordered which I will have soon, as well as enough new pulse capacitors to make a low ERS capacitor bank of 1.2uF and 4000V. I don't think I will have any trouble initiating these homemade EBW detonators through 100ft of RG-213 since it is a very low loss cable.


BTW, a good source of ca. 40AWG copper magnet wire is the little door and window alarms which are often available at dollar stores and hardware stores, etc. Don’t let the small size fool you, the inductor that is in them holds a lot of magnet wire. About ten years ago I decided to make a 2-3V relay from a reed switch and the magnet wire on one of those inductors. It seemed like I was winding for hours though I guess it couldn’t have been; it was really surprising how long the wire was that makes up those windings. The insulation can be easily burned off with a low flame of a small butane torch. Even a mini butane torch can melt the fine copper wire if care is not used.



1.jpg - 264kB 2.jpg - 253kB 3.jpg - 277kB 4.jpg - 506kB 5.jpg - 200kB 6.jpg - 183kB 7.jpg - 157kB 8.jpg - 201kB


[Edited on 18-4-2015 by Hennig Brand]

nux vomica - 17-4-2015 at 18:03

Hi I've drawn up a drawing of how I see the bridgewire head made from a fiberglass pcb cheers nuxy



ebw pcb.jpg - 157kB

Hennig Brand - 17-4-2015 at 18:37

Interesting ideas. I can see the third one working, but I think it would be very difficult for most amateurs to accurately and precisely make 0.001-0.003inch diameter strips in comparison to just obtaining some fine gauge wire with consistent diameter.

nux vomica - 17-4-2015 at 19:07

I realise that most people would be put off making there own pcb,s but I have made them at home that had all smt components on them I made the uv resist transparency's and the solder paste stencils myself.

Also there is a lot of free programs online (eagle cad is one) for free that you can draw up your board then send it off to a pcb manufacture in china and get it fabricated very cheaply nowadays.

I've got a cnc router at home so I can mill the board, I've got some carbide bits that are .5mm in dia , but I admit the stencil for the green resist coat is a bit more challenging to fabricate.

cheers nuxy.

jock88 - 18-4-2015 at 13:38


You can purchase very fine Nichrome wire. It may the more resistant to corrosion for a more long term device. Copper is somewhat reactive with a very thin wire(or is it?).
The extra resistance of the tiny piece of Nichrome would be irrelevant.

Energy Injected to the Wire During the First Current Pulse

Hennig Brand - 18-4-2015 at 14:10

The following snip-it and table were taken from, "Electric Explosion of Wires as a Method for Preparation of Nanopowders" by Yu A. Kotov. The article is attached below as well.

"
The energy W injected to the wire during the first current pulse was found to be

W = (hb * W0 * S^2 * Z)^0.5


where W0 = 1/2CVo^2 is the stored energy, J; Vo is the capacitor charging voltage, kV; Z = (L/C)^0.5 is the circuit characteristic impedance, Ohm; L is the discharge circuit inductance, μH; C is the capacitance, μF; S = 1/4 * pi * D^2 is the wire cross-sectional area, mm2 (D being the wire diameter, mm); hb has the dimensionality of A^2 * s / mm4 and represents the pre-explosion specific ‘action’ or thermal toughness of the material heated with a current pulse (Anderson&Neilson, 1959; Cnare & Neilson, 1959; Cnare, 1961). This notion was used earlier (Rudenberg, 1950) for calculation of safety fuses. The obtained hb values (Anderson & Neilson, 1959; Cnare&Neilson, 1959; Tucker&Neilson, 1959; Cnare, 1961; Kotov et al., 1990) are given in Table 1."



Sublimation Energy and Specific Action of some Metals.jpg - 95kB


Attachment: Electric Explosions of Wires as a Method of Preparation of Nanopowders.pdf (208kB)
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hb(Copper) / hb(Gold) = ca. 4

All other things being equal, it seems as though it takes roughly four times the energy to explode a copper bridgewire than it takes for a gold one. Of course, all other things being equal, a change in the diameter of the bridge wire by a factor of two would change the burst energy by a factor of sixteen.

Quote: Originally posted by jock88  

You can purchase very fine Nichrome wire. It may the more resistant to corrosion for a more long term device. Copper is somewhat reactive with a very thin wire(or is it?).
The extra resistance of the tiny piece of Nichrome would be irrelevant.


Nichrome is much more corrosion resistant, but is not very suitable other than that from the few things I have read (very high resistivity for one). Copper is quite suitable, except for the corrosion issue and its much lower density than gold as well.


[Edited on 19-4-2015 by Hennig Brand]

jock88 - 18-4-2015 at 14:58

"All other things being equal, it seems as though it takes roughly four times the energy to explode a copper bridgewire than it takes for a gold one."

Since nickle has a value closer to gold (and assuming chromium's figure is not too bad) then nichrome should not be too bad?



Patent of spark gap detonator (no wire 'ebw') attached.

The filed and publication dates are very different.

Attachment: US3955505.pdf (188kB)
This file has been downloaded 620 times

[Edited on 18-4-2015 by jock88]

Hennig Brand - 18-4-2015 at 16:31

40 gauge nichrome wire resistance at 20C = ca. 70 ohms/ft
40 gauge gold wire resistance at 20C = ca. 1.49 ohms/ft
40 gauge copper wire resistance at 20C = ca. 1.05 ohms/ft


I = V / R
Initial current flow = voltage of capacitor(s) / resistance of system

Using nichrome resistance wire would add a lot of unwanted resistance to the system which would greatly decrease current flow for a given voltage.

Even a 2mm long nichrome bridge wire (40 gauge) would add about 0.46 ohms of resistance to the system, while 100ft of RG-213 cable only adds about 0.3 ohms of resistance. The tiny 2mm long nichrome wire could easily have more resistance than the whole rest of the system!



Attachment: Initiation of Exposives by Exploding Wires I (Effect of Circuit Inductance).pdf (1.7MB)
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Attachment: Initiation of Explosives by Exploding Wires II (Effect of Circuit Resistance).pdf (1.1MB)
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Attachment: Initiation of Explosives by Exploding Wires III (Effect of Wire Diameter).pdf (1.1MB)
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Attachment: Initiation of Explosives by Exploding Wires IV (Effect of Wire Length).pdf (755kB)
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Attachment: Initiation of Explosives by Exploding Wires V (Effect of Wire Material).pdf (1.3MB)
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Attachment: Initiation of Explosives by Exploding Wires VI (Further Effects of Wire Material).pdf (1.2MB)
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Attachment: Initiation of Explosives by Exploding Wires VII (Effect of Energy Termination).pdf (1.2MB)
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Attachment: Initiation of Explosives by Exploding Wires VIII (Effect of Moderate Voltage Levels).pdf (865kB)
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[Edited on 19-4-2015 by Hennig Brand]

Hennig Brand - 19-4-2015 at 11:21

This has some useful information in it, though quite general.

Attachment: High Voltage Surge Generators - HV Engineering Chapter 8.pdf (207kB)
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From "Military Explosives" page 8-17, regarding compatibility of PETN and copper.

"
At temperatures up to about 50°C, dry PETN does not react with copper, brass, aluminum, magnesium, magnesium-aluminum alloys, stainless steel, mild steel, mild steel coated with acid proof black paint, and mild steel plated with copper, cadmium, nickel or zinc. Wet PETN does not react with stainless steel, and aluminum is affected only slightly after long periods of storage. However copper, brass, magnesium, magnesium-aluminum alloys, mild steel, mild steel coated with acid-proof black paint, and mild steel plated with cadmium, copper, nickel or zinc are affected. PETN is used in the explosive core of industrial detonating fuses, in the charge of commercial blasting caps, and as the entire explosive charge in exploding bridge wire detonators."


[Edited on 19-4-2015 by Hennig Brand]

markx - 19-4-2015 at 22:23

I see you still refuse to show mercy to this mangled corpse of a witness plate....hasn't the poor bastard suffered enough already? :D :D :D

Cool capacitor bank btw...

jock88 - 20-4-2015 at 02:00


It's a very holy plate.

Hennig Brand - 20-4-2015 at 13:26

I am going to use it for a strainer when I am done. ;)
No, seriously, it seems when I go looking for a witness plate that one keeps turning up. Just like a bad penny! :D


Here are a couple snip-its which show how even relatively small increases in explosive density make initiation of secondary explosives by EBW much more difficult. The first snip-it is from Cooper and the second is from "Exploding Wires Vol 4".


PETN Density Effect EBW (Cooper).jpg - 77kB PETN Effect of Density (Exploding Wires Vol 4).jpg - 87kB


[Edited on 21-4-2015 by Hennig Brand]

aga - 20-4-2015 at 13:34

Sorry if this sounds dense.

To detonate [whatever] are you just looking for a hot wire, or a Very hot wire that gets very hot very fast, or an Extremely hot wire that gets hot extremely fast ?

I know nothing about explosives, but do know about wires getting hot.


[Edited on 20-4-2015 by aga]

Hennig Brand - 20-4-2015 at 13:42

The following are the first ten pages from one of the RISI technical sections from their site. Read page three for a good basic description of the difference between regular low power electrical igniters and exploding bridge wire secondary explosive initiators.

Attachment: page1.pdf (28kB)
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aga - 20-4-2015 at 14:06

WOW.

Thanks for the references.


Hennig Brand - 20-4-2015 at 14:16

You are welcome.

EBW Failure using 0.67uF cap Charged to 2400V fired Through over 51ft of RG-6 Equivalent Cable

Hennig Brand - 21-4-2015 at 07:49

I was fairly sure that this wouldn't work, but I tried it anyway. A half gram of ETN was pressed in a 7.6mm aluminum casing with over 100lbs of force with a lever press and then another 0.2g was added loose on top. The copper bridgewire EBW head was made in the same way as last time and was gently pressed into the loose ETN just enough to remove voids and lightly compact it. Fifty feet of RG-6 and 1ft of 18 gauge speaker wire was used as transmission line. The 0.67uF capacitor bank was charged to 2400V and wires touched together to fire the EBW. There was no detonation and on closer inspection about 1/3 to 1/2 of the ETN was gone and the EBW head, which had been lightly glued in place, had been blown out of the cap. It seems as though the ETN was ignited and built up just enough pressure to pop out the EBW head. It was a fairly long run of fairly light cable and the capacitor bank was only charged to 2400V, so this is to be expected.

In the last day or so I made a graph generating spreadsheet in Excel using what I think are the appropriate pulsed power equations. According to "Explosives Engineering" by Cooper, EBWs typically require several hundred amps at very fast rise rate, in the neighborhood of 200A/usec. Using the numbers from each test I made a couple of graphs, one for the successful attempt from earlier and one from this past failure. It is very clear why this last test failed when looking at the graph. So far change in bridgewire resistance was not accounted for when making the graphs. I may post the spreadsheet soon so that others can use it. I think it could be a great tool for analysing EBW systems and should lead to greater understanding, control and reproducibility. BTW, one of the key equations from Cooper is incorrect.

Ironically the RG-213 came in about an hour or so after I did the test with the RG-6. As can be seen from the images, RG-213 is a much heavier coaxial cable than RG-6. The white cable below is 50ft of RG-6. The black cable in the box is 100ft of RG-213.

I also made the main electrodes for a trigatron a couple of days ago which are shown below.


Cap In Place.jpg - 272kB No Detonation (1).jpg - 264kB No Detonation (2).jpg - 277kB 50ft of Rg-6 Coaxial.jpg - 491kB 100ft of RG-213 Coaxial.jpg - 231kB RG-213.jpg - 321kB Brass Trigatron Electrodes.jpg - 324kB EBW Current Versus Time Graphs.jpg - 64kB


[Edited on 21-4-2015 by Hennig Brand]

Burst Action of EBWs

Hennig Brand - 21-4-2015 at 15:54

The copper magnet wire from the window/door alarm inductor was carefully measured with a micrometer and without insulation it is actually only about 1.5mil (0.0015 inch in diameter). We know from the reference a couple posts ago that the "burst action coefficient" (Kb) is about four times higher for copper than for gold. Burst action is a function of only the bridgewire material and the bridgewire diameter and is easy to calculate using the following equation from Cooper:

Gb = Kb * D^4

For a 1.5mil gold bridgewire (Cooper):

Gb = 0.022 A^2s/mil * (1.5mil)^4 = 0.11 A^2 s


Adjusting for 1.5mil copper:

Gb = 4* [0.022 A^2s/mil* (1.5mil)^4] = 0.45 A^2 s

Burst action is the area under the curve of current squared versus time. As a crude approximation a straight line was assumed and the value for current was squared at points along the current versus time plots and then the area of the triangles were calculated.

The area under the curve of both graphs for the first 2 microseconds, corresponding to the graphs from the last post, were measured and the burst action calculated.

For 13ft RG-6 coax, 2300V, 0.67uF Gb = 0.846 A^2 s

For 51ft RG-6 coax, 2400V, 0.67uF Gb = 0.081 A^2 s

It is obvious that the 51ft coax test would never have made the calculated burst action or at least not in a short enough time to generate a shockwave effective for secondary explosive initiation.



[Edited on 21-4-2015 by Hennig Brand]

Distributed-Parameter Method for EBW System Analysis

Hennig Brand - 22-4-2015 at 15:12

The equations given in Cooper are for the common lumped-parameter method for analysing pulsed power systems. Besides the fact that one of his equations is wrong, according to what I have been reading this method is very inaccurate except for cases with essentially no transmission line. So what I have presented above is likely very inaccurate. I found a good article yesterday in "Exploding Wires Vol. 2" outlining a simplified distributed-parameter method that is reported to provide analytical results very close to actual results in most cases. I am not going to attempt to explain it here, because it would be a waste of time since the author did such a great job of it. I have attached the section from the text below, as well as the Excel sheet I spent the day working on which is based on the final simplified equations from the article.

It is a work in progress, but the results produced by the spreadsheet seem reasonable at this point. When values are input for the same type and length of wires, the reflection times seem to agree fairly well with the times from the graphs in Cooper's book, but the currents still seem a bit high. This method does assume a constant voltage source, which the author states is normally a reasonable assumption for the short times (considerably less than one RC time constant) normally involved to bring a wire to explosion. An assumption used in this method that also could result in at least slightly higher currents, "For most purposes, the wiring and transmission lines used in exploding wire work can be treated as lossless lines, that is, R~0 because provision is made for carrying very high currents and G~0 because good insulating materials are used between the wires to prevent high-voltage breakdown." Another factor which results in higher currents, especially in the early stages before wire explosion, is the constant high value for bridge wire resistance used. According to the article maximum resistance is normally used for this method. Five ohms was used throughout for bridgewire resistance, since maximum values for gold bridgewires can apparently go as high as 10 ohms. Lowering bridgewire resistance does bring the currents closer to what is seen in the graphs in Cooper.

The new graphs are attached.


EBW Current Versus Time (Distributed-Parameter Method).jpg - 65kB


For the 13ft RG-6 graph, burst action (0.45A^2s) is reached in about 0.62 microseconds with a burst current of 1240 amps. This test was of course successful in practise as well. For the 51ft RG-6 graph burst action is reached in about 1.41 microseconds at a burst current of about 800 amps. The time was longer until burst and the current was also lower at burst in comparison to the first graph. The second test was a failure in practise, but the switching losses could have been huge since switching was accomplished by the very crude method of touching too small gauge (18 gauge) wires together by hand.



Attachment: Effects of Transmission Lines in Applications of Exploding Wires (Section from Exploding Wires Vol.2).pdf (719kB)
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Attachment: EBW Current Versus Time (Distributed Parameter Method) - Spreadsheet and Graph.xlsx (65kB)
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[Edited on 23-4-2015 by Hennig Brand]

Comparing Gold and Copper EBWs - Bridgewire Inertia and Resistance

Hennig Brand - 24-4-2015 at 10:49

I did some more thinking last night about how to compare copper EBWs to the more well documented gold EBWs and I think I have it sorted out pretty well.

It is all about bridgewire inertia (Newton's first law) which is directly proportional to bridgewire mass. Since gold is about 2.15 times as dense as copper, in the solid and liquid forms, bridgewires made of gold will have about 2.15 times the inertia or ability to resist motion for the same dimensions.

From "Initiation of Explosives by Exploding Wires" Part 5 and 6, it can be seen from the graphs that gold at 2mil diameter and 100mils length has a maximum resistance of about 7.8 ohms and copper of the same dimensions has a maximum resistance of about 3.7 ohms. This means that copper requires about 7.8 / 3.7 = 2.11 times more I^2, for the same power dissipation, since power dissipated in the wire is I^2R (P=I^2R) and the resistance of gold and copper increase in a similar way to their maximum values.

Adding these two values together produces a 4.26X increase in I^2/t that is needed for copper to build up the same energy level in the wire before inertia is overcome to produce a bridgewire explosion of similar intensity.

Commercial EBW systems produce a nominal current rise of 200A/usec for a 1.5mil gold bridgewire (Cooper, RISI).

In order to build up to the same energy level and produce a bridgewire explosion of similar intensity as is produced in the case of a 1.5mil gold bridgewire the current rate of rise would need to be about (4.26 I^2)^1/2 per usec or 2.06*200A/usec which gives an average current rise rate of 413 A/usec for a copper bridgewire of 1.5mil diameter. Since this would be for an EBW of commercial quality and consistency this value should be seen as an absolute minimum for most homemade EBW detonators.


Updated Spreadsheet

The spreadsheet has been updated. The big changes are that it now calculates burst action for a specific size and type of wire, produces an I^2 versus t graph, gives the area under the I^2 versus t step function, automatically determines at what time burst action is met or exceeded and displays the average rate of current rise over that time period.

The crude method used in the last couple of posts to determine the time and current when burst action was reached was a simple approximation. Here are the new accurate values obtained from the updated spreadsheet:

For 2300V, 0.67uF, 13ft RG-6, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 1356 A
Time at or above Burst Action = 0.65 usec
Average rate of Current Rise = 1356A/0.65usec = 2086 A/usec
Detonation from test

For 2400V, 0.67uF, 51ft RG-6, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 876 A
Time at or above Burst Action = 1.54 usec
Average rate of Current Rise = 876A/1.54usec = 569 A/usec
No detonation from test

While the current rate of rise is theoretically about 38% above what is needed, for the second test, the crude homemade equipment used could have easily necessitated using a much higher current rate of rise. Many things can effect whether a EBW detonator will function property or not. Explosive type, crystal size, surface area and density are big ones too, which were assumed equal to the PETN used commercially in this example. The goal here was simply to develop a system which would allow reasonably accurate predictions of EBW performance and allow much more informed comparison to be made when testing.



Attachment: EBW Current Versus Time (Distributed-Parameter Method) - Spreadsheet and Graphs.xlsx (95kB)
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[Edited on 25-4-2015 by Hennig Brand]

jock88 - 24-4-2015 at 13:32

40 gauge nichrome wire resistance at 20C = ca. 70 ohms/ft
40 gauge gold wire resistance at 20C = ca. 1.49 ohms/ft
40 gauge copper wire resistance at 20C = ca. 1.05 ohms/ft


The above is data given by Hennig.

Assuming a 2mm long bridge wire this means that for 40 gauge wire you have:

nichrome 0.46 ohms
gold 0.0099
copper 0.077

Does this 'extra' resistance make much of a difference given the resistance quoted in the last post given that?:
Quote for book:
From "Initiation of Explosives by Exploding Wires" Part 5 and 6, it can be seen from the graphs that gold at 2mil diameter and 100mils length has a maximum resistance of about 7.8 ohms and copper of the same dimensions has a maximum resistance of about 3.7 ohms.

Is this 'maximum resistance' they speak of the resistance when the wire is red hot (just before breakage)?

I am not too well up with the maths etc btw.

Perhaps I am a bit obsessed with the anti corrosion (and cheapness over gold) that nichrome would provide.


I find it strange that Pt is never mentioned/used in EBW's.


Do you have the book or series of books 'Exploding wires'?
I have never seen them uploaded here though I think they were sought. Perhaps I missed them.

http://www.abebooks.com/book-search/title/exploding-wires/us...




There is another read here on exploding wires?

http://www.osti.gov/scitech/servlets/purl/4114397


put .pdf onto url for the pdf

J88



[Edited on 24-4-2015 by jock88]

Hennig Brand - 24-4-2015 at 14:24

The resistance of copper, gold and platinum starts out very low and then increases very rapidly in the final fraction of a microsecond before biridgewire explosion. I have attached the resistance versus time graphs from "Initiation of Explosives by Exploding Wires" for gold and copper. Those documents have other graphs for several other metals if you want to look as well.


Increase in resistance with temperature (wiretron.com)

°F .......°C......NiCrA........NiCrC

68 .......20.......0 .............0
600.....315 .....3.3% .......5.2%
1000....538 ....6.3% .......8.6%
2000...1093....6.0% .......10.5%


So ironically it looks as though nichrome ends up having too little resistance when it counts. Higher resistance at the start is only part of the problem, what is even worse is that its resistance rises only slightly with temperature. Inertia again plays a major role. Nichrome wire will tend to rise in energy level more gradually instead of explosively. With proper function, gold and copper bridgewires obtain most of their energy in the last few tens of nanoseconds before wire explosion (P=I^2R). Also, nichrome's density is even a bit lower than copper which is undesirable (inertia again). I believe nichrome may have other problems too, but I would need to look into it more.

I have never tried it, so I don't know for sure, but nichrome doesn't come highly recommended from the few things I have read. It will undoubtedly work, but it might require a blasting box that is very large (more power). Platinum is used commercially from what I have read, but gold is more common. The amount of gold is so small in an EBW that commercially the cost is not a big concern. It is much harder for an average experimenter to obtain gold in a cost effective way though.

I am in the process of trying to collect the four volumes of "Exploding Wires". They were published in the 60s, as was a lot of the reading material on EBWs.


Copper EBW Resistance.jpg - 74kB Gold BW Resistance.jpg - 81kB


[Edited on 25-4-2015 by Hennig Brand]

Comparing Gold and Copper EBWs (Revisited) - Heats of Vaporization

Hennig Brand - 25-4-2015 at 08:35

Something else of significance which I am still trying to wrap my head around is the effect of bridgewire material heat of vaporization on bridgewire energy/current rise requirements.

If comparing bridgewires of equal volume a copper bridgewire takes about 26% more energy to vaporize (if my calculations are correct).

edit:
So far this actually doesn't look to be of great significance. The area under the gold and copper power versus time graphs from "Initiation of Explosives by Exploding Wires V & VI" were found. At least from their tests, it turns out that the fraction of total energy used up in the phase change is only different by about 2-3% between gold and copper. The phase change energy was higher for copper, but then so was the total energy. They more or less cancelled each other out, at least for those tests.

Here is the excel sheet were that was used to compare the two graphs from the articles:


Attachment: Energy to Bridgewire Gold versus Copper.xlsx (14kB)
This file has been downloaded 596 times


Here is something a little humorous. I picked up four bug zappers at the local dollar store for $3 each. It turns out that they are of the lower voltage variety only putting out about 850-900 volts. For fun I hooked all four in series with at least 4kV worth of diodes on the output terminals. The capacitor bank was made from salvaged pulse capacitors. The eight of them hooked together give a capacitance of 0.5uF and a voltage of 4000V. The four series connected bug zapper supplies can charge the bank up to about 3200V in about 10-12 seconds. I guess I need another bug zapper so I can charge them up to 4000V. Actually, the 4000V bank probably shouldn't be charged much over 3200V anyway. In any case these bug zappers are really the weakest I have seen so far. Three of the zapper supplies I had before would easily produce more voltage than four of these. Anyway $15 in these weak bug zappers can get you a 4kV supply. I guess I really should just build a decent HV supply, other than winding the transformer there really is nothing to it. Actually a suitable transformer could likely be ordered very easily if the tedious process of (re)winding a transformer was preferred to be avoided.

Four Bug Zapper Supplies 3200V.jpg - 271kB


[Edited on 25-4-2015 by Hennig Brand]

jock88 - 25-4-2015 at 14:37

The resistance at break time (when or what exactly 'break time' is I don't really know) is overcome by a very large voltage appearing accross the gap. I think the whole thing is very hard to analyze due to nonlinearities etc. I don't know much about it myself.

If you look at the table at the bottom of the attached document (it was contained in the attached web page way above) it shows a voltage of 10.5KV accross the ebw.
Since it is possible to get these things to work with NO wire, I wonder just how important the wire (or type of wire) actually is.

For a hv supply would not a oil fired ignition transformer + voltage double (or tripler) do the job?


Weak bug zappers are outlawed when I come from from an animal welfare point of view. Only bug zappers of a minimum 1/2CV^2 are allowed on sale. The cheap one leave the bug riding the lightning too long before death and are very cruel!

Attachment: tucker_2.pdf (205kB)
This file has been downloaded 776 times

[Edited on 25-4-2015 by jock88]

Hennig Brand - 25-4-2015 at 18:36

I believe break time is referring to when the wire bursts. It can be very violent if enough energy is dumped in fast enough or it can be very gently like a hot wire igniter if not enough energy is dumped into the wire in a short enough time. In order to make a shockwave capable of initiating secondary explosives the rate of energy deposition has to be high enough that the inertia (mass) of the bridgewire can hold it back enough to build up to a very energetic release/shockwave.
From Cooper, " The attainment of burst does not depend on the shape of the current trace, but occurs at the time and current where the area under the current squared versus time curve equals the burst action. Attainment of burst is necessary but not sufficient to form the shock that will detonate the initial pressing." So wire burst or break is necessary but it can happen at too low an energy level to initiate the explosive.

With a big enough HV power supply anything is possible probably, even no wire at all. Maybe with a big enough Tesla coil we wouldn't even need transmission line. ;)
It really isn't that hard to get a good approximation of what is going on if a few reasonable assumptions are made. It does take a bit of time and a little math knowledge to go through it, but that article I posted with the first version of the spreadsheet explains it very well. I am definitely not a math wiz, but I am not too bad either and I spent a day sorting through it.

You are referring to voltage drop across the bridgewire which gets very high as the wire approaches explosion because the resistance spikes and current pulses have stepped up to a high value too (Ohm's law, V=IR). If you look at the first test results, from a few posts ago, the model gave a peak current of 1356A and if we assume a peak resistance of 4ohms we get V=1356A*4ohms= 5424V across the bridgewire before burst. As you can imagine, much higher voltages are easily possible as well, such as when higher voltage capacitors are used, shorter and/or more efficient transmission line and also if a different bridgewire material is used which has a higher final resistance such as gold (about double the final resistance of copper).

A couple people have mentioned small consumer grade inverters with added voltage multipliers, such as a Cockcroft–Walton generator, which would likely be one of the simplest alternatives with the most complicated part being "off the shelf". Even the smallest automotive inverters are way overpowered though for any normal sized EBW capacitor bank. I suppose that being a little bit overpowered is not a big concern though.

Regarding bug zappers, I think what they may have done is reduced the voltage and made the capacitance larger. I could compare the capacitors later. The sparks from these zappers seem weaker as well though.

0.5uF, 4000V Capacitor Bank Charged to 4000V in Under 10 Seconds From 2 Bug Zapper Supplies

Hennig Brand - 26-4-2015 at 08:46

I went back to the two older bug zapper supplies, because they put out more voltage and current. Four of the pulse capacitors from the other bug zapper supplies were used to make two voltage doubler stages, one on each bug zapper output. Separate halves of the main 4000V capacitor bank (2000V) were connected as C2 for the two voltage doubler stages. Each bug zapper supply now charges up half of the capacitor bank to 2000V for a total combined capacitor bank voltage of 4000V. These two bug zapper supplies can now easily charge the 0.5uF, 4000V, capacitor bank up to 4000V in under 10 seconds. Two bug zapper supplies can be made to function as an effective EBW system power supply.


4kV Supply From Two Bug Zapper Rackets.jpg - 263kB Voltage Doubler Circuit.jpg - 70kB


Observation:
Replacing all tiny gauge wiring that typically comes with these zappers with even the small solid conductors from telephone cable greatly increases performance.


Quote: Originally posted by Hennig Brand  
I believe break time is referring to when the wire bursts. It can be very violent if enough energy is dumped in fast enough or it can be very gently like a hot wire igniter if not enough energy is dumped into the wire in a short enough time. In order to make a shockwave capable of initiating secondary explosives the rate of energy deposition has to be high enough that the inertia (mass) of the bridgewire can hold it back enough to build up to a very energetic release/shockwave.
From Cooper, " The attainment of burst does not depend on the shape of the current trace, but occurs at the time and current where the area under the current squared versus time curve equals the burst action. Attainment of burst is necessary but not sufficient to form the shock that will detonate the initial pressing." So wire burst or break is necessary but it can happen at too low an energy level to initiate the explosive.


What I should have said was wire burst can happen at a power level that is too low. However, because of the inertia of the wire and the fact that the wire's resistance will end at a higher value, with a higher current rate of rise, the energy contained in the wire at burst will in fact also be higher.


[Edited on 27-4-2015 by Hennig Brand]

0.6g of ETN Initiated by 1.5mil Cu EBW using 3700V, 0.5uf, capacitor discharged through ca. 51ft of RG-6 Coaxial Cable

Hennig Brand - 29-4-2015 at 04:40

The 0.6g of ETN was pressed into the 7.6mm Al casing in three increments. About 0.2g was pressed with a lever press at about 100lbs of force, about 0.2g was pressed firmly by hand and about 0.2g was poured in loose and then only very gently compressed just to settle and remove large voids. The copper bridgewire was ca. 1.5mil in diameter and ca. 100mil in length. The 0.5uF capacitor bank was charged to ca. 3700V before the small capacitor (0.15uF, 800V) on the third bug zapper supply was discharged through the primary winding of the trigger transformer sending a HV trigger pulse from the transformers secondary winding to the trigger electrode of the trigatron thereby discharging the main stored charge through the firing leads and bridgewire almost instantaneously. The trigger transformer used is a repurposed switching power supply transformer, salvaged from an old power supply. The trigger electrode/conductor and insulation/spacing were provided by a section of high voltage wire (40kV) connecting the flyback transformer and CRT anode from an old television. About 150 ohms worth of resistors were put in series between the trigger pulse generator and the trigger electrode to isolate the generator from the main electrical charge. The trigger circuit was fired by simply touching two wires together, connecting the capacitor to the primary winding of the trigger transformer. The target the EBW detonator was sitting on (held in place by tape) is 1/8" steel. Even from 40+ft away it was a nice boom, however the damage to the witness plate was a bit less than hoped for. There was, however, a significant dent in the top side and a substantial scab blown off the back side proving that there was definitely a detonation. A significant amount of the 0.6g of ETN may have been used up during the time it took to accelerate from low velocity to high velocity detonation.

The fireset can obviously be made much more compact. The three bug zapper supplies could be made to fit into something not much bigger than a large package of cigarettes probably. The trigatron could be made 5-10X smaller; when I get around to it I am going to make a nice compact trigatron in a small (plastic?) enclosure.

Found a good use for the tiny vise that was given to me a while back. It really makes soldering the bridgewires much easier. I kind of wish I hadn't spent over $100 on 100ft of RG-213 since for my purposes RG-6 seems to be adequate. To get similar results as this test at 102ft, instead of 51ft, the RG-6 coax could simply be doubled (connect shield to shield and center conductor to center conductor at both ends). Connecting two lengths in parallel basically halves the inductance and resistance.

EBW Soldering.jpg - 243kB
Cap In Position.jpg - 274kB EBW Fire Set.jpg - 267kB
Witnes Plate Top View.jpg - 300kB Witness Plate Bottom View.jpg - 230kB


Here is the graph produced using the previously posted, distributed parameter method, spreadsheet.

Current Versus Time Graph.jpg - 34kB


Here are the numbers from the last test, which failed, and this successful test for comparison purposes.

For 2400V, 0.67uF, 51ft RG-6, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 876 A
Time at or above Burst Action = 1.54 usec
Average rate of Current Rise = 876A/1.54usec = 569 A/usec
No detonation from test

For 3700V, 0.5uF, 51ft RG-6, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 1039 A
Time at or above Burst Action = 1.15 usec
Average rate of Current Rise = 1039A/1.15usec = 903 A/usec
Detonation confirmed

Of course this test used a trigatron, triggered spark gap, while switching for the previous tests was done by simply touching two 18gauge wires together, so it is really not a fair comparison.


[Edited on 29-4-2015 by Hennig Brand]

[Edited on 25-9-2015 by Bert]

10g of ETN Putty Explosive Initiated With Custom Made EBW Detonator

Hennig Brand - 7-5-2015 at 13:33

Well the bug zappers are no more. After about three successful tests I noticed that the bug zapper supplies were charging the capacitor bank up to lower and lower voltages until they wouldn't even charge the bank up to 2000V anymore. The amount of current being drawn from those zapper supplies was really a lot more than what they were designed for. I am currently working on a compact switching supply operating at fairly high frequency, but for now I came up with a simple solution for a power supply that is very tough and basically free. I located four discarded microwave ovens which provided me with everything needed to make a power supply. I obtained a transformer, four HV capacitors and four HV diodes. The transformer was run with a hundred watt light bulb in series with the primary to limit current which was latter changed to two 75ohm, 50W, resistors in series. The four diodes and capacitors were configured as two voltage doublers with the diodes run in opposite directions. This gave one output that was 2000+V and one output that was -2000+V. The two outputs together gave a potential difference of well over 4000V (without load). This supply is very robust and free, but the efficiency is low especially since half the power going to the system is dissipated in the current limiting resistors. A properly matched transformer could double the efficiency. Efficiency is not a big concern for me at the moment, anyway, since the amount of energy used is so small and this isn't a commercial product. The system draws about 50W of which about 26W is dissipated in the current limiting resistors. It can charge the 0.5uF capacitor up to 4000V in under ten seconds. A small automotive inverter fed by a 12V lead acid battery was used to feed the transformer, though the unit could have just as easily been plugged into a standard wall plug for this test.

The detonator was made about a week ago. The 7.6mm casing contained about 0.7g of ETN, 0.5g pressed at 100lbs, 0.1g hand pressed, 0.1g left almost loose. The ca. 1.5mil copper bridgewire was about 100mil long. The blasting cable used was 50ft of RG-6 and 2-3 feet of 18 gauge speaker wire. The main charge was 10g of 80% ETN putty explosive. The target was 1/8 inch wall thickness square tubing. The 0.5uF capacitor bank was charged to about 3800V before the trigatron was fired. Detonation was immediate, as it has been for all the successful tests. Both 1/8 inch sides of the tubing were penetrated.

I am going to get a tough little plastic toolbox to house the whole fireset. Much bigger and heavier than a commercial fireset, but it is tough as nails and free. Still working on a more compact version.

A safety note: None of the capacitors stay charged for more than a few seconds after power is removed from the circuit. The main pulse capacitor bank has 10Mohm bleeder/bypass resistors across each capacitor in the series string. The microwave oven capacitors have internal bleeder resistors, which drain them in a few seconds. All in all it is a fairly safe system....did I mention free. :D

Note, all microwave oven capacitors may not have internal bleeder resistors, but I think most do.


1.jpg - 234kB 2.jpg - 249kB 3.jpg - 253kB 4.jpg - 268kB 5.jpg - 272kB 6.jpg - 266kB 7.jpg - 269kB 8.jpg - 265kB 9.jpg - 266kB 10.jpg - 267kB


[Edited on 8-5-2015 by Hennig Brand]

nux vomica - 7-5-2015 at 16:25

I've managed to get my setup up and running but I still need to make some etn this weekend to fully test it most parts are from fleabay the high voltage generator looks like its meant for a tazer cos it produces nice sparks between the electrodes at 3 volt supply.
I used 10 400v 10 uf capacitors in series for 4000 v 1 uf and a spark switch to fire them I also like found that a peizo bbq igniter will fire the switch ok so that realy simplifys that part now I just need the new router bits to turnup so I can mill some mini pcb,s cheers nuxy.



20150503_172802.jpg - 1.2MB

jock88 - 7-5-2015 at 16:44


@ HB
You appear to be inadvertently making tractor parts!!!

http://www.ebay.ie/itm/Massey-Ferguson-Tractor-Drawbar-Stays...

Hennig Brand - 7-5-2015 at 18:38

Nux Vomica,
I like what you did with the housing for the sparkgap switch. I will do something similar when I get around to miniaturizing my fireset. Those capacitors you have are not the right thing though, unless I missed something. They are high ESL and ESR and not designed for pulse applications. Also when you add capacitors in series ESL and ESR increase just like resistance with resistors. I know I have caps in series too but they were salvaged and they are pulse rated caps. It is best to get high voltage, low capacitance pulse rated caps with low ESL and ESR and put them in parallel as much as possible. Your setup might still work with a short low inductance blasting cable but they are relatively slow caps from what I have seen. Interested to see how your charging circuit works out. If it is for a tazer it will put out very low current but you may be able to do somthing with it still. Some good ideas you have there. Yeah, if properly adjusted even very weak sparks will fire the gap. Interesting that a piezo igniter works. I though about using one and then decided not to try it. It may work but it is very underpowered. I think there are advantages to more trigger pulse power.

Those poor bug zapper supplies, after doing a couple of simple calculations after the fact it was obvious that I was seriously abusing them. The 60Hz stuff is working great but it is just so big and heavy. A much smaller 60Hz transformer than the MOT could be used but I used what I had. If I wanted to charge to 8000V or even 10 000V this system could easily be made to do it too. I am trying to learn about modern switching power supplies. They are small, light, powerful and efficient.


Jock88,
That is starting to look like a drawbar isn't it. :D


[Edited on 8-5-2015 by Hennig Brand]

nux vomica - 7-5-2015 at 19:16

The capacitors were advertised as low impedance and low esr I suppose you cant trust sellers on ebay though, the power supply doesnt seem to have any trouble pushing the voltage over 4000v i have to shut the power off quickly cos it shoots up fast, im trying to think of a voltage limiting circuit that shuts the power off at a set voltage.
yeah a pezio dosent seem to have much spark in it but it will fire the switch every time that i have clicked it.
cheers nuxy.

20150503_172816.jpg - 1.2MB

[Edited on 8-5-2015 by nux vomica]

Varmint - 8-5-2015 at 03:32

The piezo is perfectly adequate to fire the gap, all you need is a plasma channel to allow the lower voltage higher current to blast through.

If you were to concentrate on a creating a very high energy trigger, at some point you'd be putting so much energy in that the trigger itself would serve the entire purpose on it's own (EWB).


Hennig Brand - 8-5-2015 at 08:54

Those capacitors could very well be low ESR, as in low ESR for that type of capacitor. Look at typical values for the different cap types from the following Wiki link. The pulse caps (film type) I recently bought are advertised as having 0.005 ohm ESR and when I connect them in parallel it gets even lower.

http://en.m.wikipedia.org/wiki/Equivalent_series_resistance

Going with a very low ESR value of 1ohm each for the 10X10uF electrolytics in series charged to 4000V that gives on RC time constant of 10 useconds (time to discharge to 37% of initial voltage) even before considering other circuit resistances and inductances. Much too slow.


A high voltage resistor (I just used regular 1/4 watt resistors in series) can be used to limit current but normally more importantly it isolates the charging circuit from the capacitor bank at discharge which would otherwise be basically a short circuit siuation for the supply.

I guess as long as the gap fires for our purposes delay and jitter are not a big concern. As far as the trigger pulse alone firing the EBW this is not possible at least with my setup. The adjacent electrode, which is the main electrode with the trigger electrode in its center, is common (negative) ground. The negative side of the capacitor bank is connected to it through the blasting line and bridgewire and so is the negative side of the trigger transformer. I have fired the trigger circuit many times with everything connected without a charge in the main capacitor bank and it had no effect on the bridgewire.

Edit:
The piezo igniter might be better than I thought. From the bit of digging I have done the performance of the switch relating to trigger pulse seems to be mostly related to voltage.


[Edited on 9-5-2015 by Hennig Brand]

Hennig Brand - 9-5-2015 at 10:18

I think not being able to accurately and precisely control trigger pulse voltage and probably energy level would likely be unexceptable for a commercial system. How much of a problem it could possibly be for us I don't know.

The following was taken from the trigatron spark gap chapter of the text "Gas Discharge Closing Switches".

"
-Charging Voltage Dependence.
As would be expected, closing delay and jitter decrease with increasing charging voltage. Trigatrons are normally operated with charging voltages in the range of ~80-90% of static self-break, VSB. Triggering at voltages down to less than 50% of VSB is easily achieved, and operation below 5% of VSB has been reported. For charging voltages less than about 70-80% of VSB the closing delay and jitter generally increase rapidly with decreasing voltage, approaching times in excess of 10 us below 50% VSB. M. D. Williams (1969) studied the effect of charging and trigger voltage on delay and jitter of a standard trigatron design. For operation in air, with VSB = 20.5 kV using a 17 kV trigger pulse, he reports delays ranging from 140 ns for 15 kV charge to about 60 ns for 20 kV. Jitter varied from about 30 to 7 ns over this same range.

-Trigger Pulse Dependence.
Also as expected, closing delay and jitter decrease with increasing trigger pulse voltage. In the study mentioned above, M. D. Williams reports delay and jitter data as a function of trigger voltage for voltages between 14 and 20 kV. He finds a much weaker dependence on trigger voltage than on charging voltage, with delay remaining almost constant over this range, and jitter varying between 10 and 6 ns. The dependence of closing characteristics on trigger pulse risetime and duration are not well documented. Delay and jitter generally decrease with decreasing risetime, and the jitter is often somewhat less than the risetime. The pulse duration should be at least as long as the formative and transit time for a streamer. Risetimes in the 5-20 ns range, and durations longer than 20 ns are commonly used. The dependence of these characteristics on the impedance of the trigger generator is similarly poorly documented. Delay and jitter apparently decrease with decreasing impedance, although it is common practice to put a 100-1000 ohm resistor between the generator and the trigger pin for isolation of the generator from the main charge. Papadias (1970) found that the minimum charging voltage for which a trigatron could be triggered decreased with increasing energy in the trigger pulse. Guenther (1989) reports that besides trigger voltage, rise time and duration, trigger energy is a very important factor in reducing delay and jitter."


[Edited on 10-5-2015 by Hennig Brand]

Hennig Brand - 10-5-2015 at 14:00

I spent the last few hours making a smaller trigatron. The tubing used is food grade vinyl I believe (it was part of a wine/beer brewing kit) and is an excellent insulator. Not exactly sure how well the tubing is going to respond to high voltage discharges, but it should be fine I think especially since it is only one discharge every now and then, not constant repetitive discharges. The tubing fits the electrodes like a glove, in fact it is a little difficult to get them apart once together. Half inch brass rod was used as the starting point. Here are a few pictures.


Trigatron (1).jpg - 197kB Trigatron (2).jpg - 146kB
Trigatron (3).jpg - 147kB Trigatron (4).jpg - 154kB
Trigatron (5).jpg - 230kB



I have been calling the caps I purchased metal film type when actually they are metal foil type which are far superior from what I have read. Here is a data sheet for the caps I bought. They are the same ones many of the Tesla coil people love to use. Probably bigger and tougher than they need to be for this application.


Attachment: High Pulse Capacitors Data sheet Type 942C.pdf (134kB)
This file has been downloaded 679 times


[Edited on 10-5-2015 by Hennig Brand]

Bert - 11-5-2015 at 04:36

;)I am waiting for the home brew krytron design...

image.jpg - 158kB

Or your LASER pulse switched sprytron?

Quote:
Sprytrons can be also triggered by a laser pulse. In 1999 the laser pulse energy needed to trigger a sprytron was reduced to 10 microjoules.


[Edited on 11-5-2015 by Bert]

Hennig Brand - 12-5-2015 at 06:04

Now you're just getting fancy. I am just a meat and potatoes kind of guy. ;)

For non repetitive, low demand, applications such as these I think the trigatron is just fine. Some of these other devices do give lower delay and jitter and operating life from the bit I have read. Operating life is not a big concern for us though, since EBW triggering is not a high frequency application. Unless doing multiple shots where the shots need to be timed perfectly, the small amount of delay and jitter of a well made and adjusted trigatron is likely more than accurate enough for us. I guess the laser triggered devices are extremely precise with very low delay and jitter.

Spartan - 13-5-2015 at 07:42

Has anyone try to connect a mobile phone to the EBW detonator something like this video:
https://www.youtube.com/watch?v=LrSdQjlUND8

Do you think it's possible? If it is safe i think it's a good idea, you avoid to use to long wires.

Hennig Brand - 13-5-2015 at 08:15

That is not a radio controlled EBW it is a radio controlled hot wire igniter. However, yes, it would be possible to remotely charge and trigger an EBW fireset. I enjoy that particular YouTuber's videos, but I don't think I like how he made a switch from the vibrator motor. I would have taken the vibrator motor right out and used the power wires to drive a relay or transistor. Wires are safer than radio control, especially if the radio control system is not well designed and encoded. Heavy wires are only needed between the fireset and detonator, the fireset can be controlled by fairly fine wires. To be honest, I don't think it is fair to call the wires heavy anyway in many cases. The RG-6 coaxial I have been using it not heavy at all and it tends not to tangle much either.

Spartan - 13-5-2015 at 08:58

Quote: Originally posted by Hennig Brand  
That is not a radio controlled EBW it is a radio controlled hot wire igniter. However, yes, it would be possible to remotely charge and trigger an EBW fireset. I enjoy that particular YouTuber's videos, but I don't think I like how he made a switch from the vibrator motor. I would have taken the vibrator motor right out and used the power wires to drive a relay or transistor. Wires are safer than radio control, especially if the radio control system is not well designed and encoded. Heavy wires are only needed between the fireset and detonator, the fireset can be controlled by fairly fine wires. To be honest, I don't think it is fair to call the wires heavy anyway in many cases. The RG-6 coaxial I have been using it not heavy at all and it tends not to tangle much either.


Thanks, you are right you use heavy wires only between fireset and detonator, i am unfamiliar with electricity.

[Edited on 13-5-2015 by Spartan]

Hennig Brand - 13-5-2015 at 10:43

Don't worry about it, it is an entertaining video anyway.

ecos - 15-5-2015 at 00:38

Quote: Originally posted by Spartan  
Has anyone try to connect a mobile phone to the EBW detonator something like this video:
https://www.youtube.com/watch?v=LrSdQjlUND8

Do you think it's possible? If it is safe i think it's a good idea, you avoid to use to long wires.


I have a friend who lost his hand because of mobile phone !
he made similar setup but he received an advertisement sms while the wires were connected to detonator !

another one made similar setup and when he turned on the phone it played the startup tone and he was severely injured.

avoid such mobile phones setup ! really risky.

jock88 - 15-5-2015 at 01:38


Also the mother in law may send you a text at the appropriate time if she knows what you are up to.

You would need to put a tone decoder (dual tone would be better) on the output of the phone set it up so that pressing the (say) 4 will give an output at the other end.

Hennig Brand - 15-5-2015 at 03:28

Tone encoding works well, I made a radio controlled switch from a pair of GMRS radios a few years back. The receiver had a tone decoder and also a timer which when activated disconnected the output to the igniter for a minute or so allowing time to safely make connections and retire to a safe distance before the system became active (I suppose the timer could have also disconnected the input to the encoder from the radio receiver). The tone generator at the transmitter was an mp3 player. The tones were made with a computer tone generator program and then saved as an mp3 file and put on a free mp3 player (someone got it for subscribing to something IIRC, very cheap mp3 player). The system could be used with any audio transmitter receiver pair. I built it just for fun, and other than a few tests I have always used wires or fuse when doing any serious blasting (wires are best).

Regarding controlling an EBW fireset, the system could be charged and fired from a single control. One control could charge the capacitor bank and fire it. A comparator could be used to automatically fire the EBW when the voltage of the capacitor bank rose to a set value. A suitably low proportional voltage could be made available for the comparator using a voltage divider. When the voltage rose above the set point and the comparator changed state it could send the trigger pulse to the trigatron and fire the EBW.


[Edited on 15-5-2015 by Hennig Brand]

Varmint - 15-5-2015 at 06:55

The wise engineer would make it a pass-key, where a specific sequence is sent, even wiser would be to time encode the key string.

i.e. lets say the pass string is DTMF 27639. The decoded DTMF is sent to a microcontroller and the first 2 chars are expected in 1 second, the 3rd char 3 to 5 seconds later, the last two characters keyed within one second, sent greater than 3, but less than 5 seconds after the 3rd character. Bad sequences cause a lockout of a programmed duration, or in fact failsafe the system requiring a physical reset.

Seem complex? Well, you want the largest margin of safety you can engineer, or at least I would if I were working in that area. Bad se

EBW Capacitor Bank Charging Circuit (555 Inverter Based)

Hennig Brand - 15-5-2015 at 07:06

Thanks for the radio control encoding tips. I was aware that a lot more sophistication and safety could be added, but to tell the truth I never made it past using two tones at once. Always meant to go back and make it more sophisticated though. Electricity/electronics is just one of my hobbies, I went through Chemical Engineering.

First off I will say that Markx was right when he said I needed a beefier power supply than those bug zappers and his suggestion for a circuit was a good one. The post by Markx earlier in this thread can be found here:

http://www.sciencemadness.org/talk/viewthread.php?tid=23466#...

I have ordered some of the IR2153 and 21531, but they will take a couple of weeks to get to me (paid a lot more for the 21531, oh well live and learn). In the mean time I have been working on a 555 inverter circuit. The IR2153 is superior as a mosfet driver, but the 555 can be made to work and it is a much more common IC.

I used the circuit found here:
http://www.eleccircuit.com/220-volts-power-inverter-using-ne...

However, I was not interested in driving a big, heavy, slow 50 or 60Hz transformer or using a voltage multiplier with big capacitors as is required with such low frequencies. In order to bring the frequency of the astable circuit from 50Hz up to about 15kHz C1 was changed to 1nF, R1 was changed to 1kohm and R2 was changed to 47kohm. This also kept the duty cycle just slightly over 50%. The only part I used that was exactly the same as specified was the 555 timer IC. I was hesitant to go higher in frequency because I was only using a regular 555, not the faster cmos variety and I was only using slow 1N4007 diodes not one of the faster types such as UF4007.

The transformer was wound on a plastic bobbin which came with the salvaged pot core used. The ferrite pot core is 3019P, 3C8 material (presently called 3C81 from what I have read). The primary is 18 turns 26AWG bifular wound in two layers to give a center tap. The secondary was wound in 10 layers, with each layer having about 40 turns of double insulated 40AWG magnet wire. A layer/strip of printer paper just slightly wider than the bobbin winding surface was wrapped on between each layer which added insulation between layers and also gave a nice flat, smooth, surface to wind on. There are better commercial insulating papers available for winding. Apparently I had the primary hooked up out of phase yesterday because it took about 15seconds to even charge the capacitor bank up to 2000V and I was having some trouble with the upper transistor heating, but the heat sinks I was using yesterday were also tiny and the run times were longer so I am not sure that it is related. Today I changed the transformer primary winding wiring around and now the circuit charges up the 0.5uF capacitor bank to 4000V in about 5 seconds. I should also mention that there is 40Mohms of resistance across the capacitor bank as a bleeder and bypass network and that there is 1Mohm (10X 100kohm resistors) between the capacitor bank and the power supply. So the supply is putting out much more than what would be needed to charge the capacitor bank without these extra loads.

The heat sinks are just what I could find lying around and are not even matched. More than big enough for the 5 second run time though. The pot core was found on a piece of industrial electronics in a scrap yard. It looks to have been sitting out in the snow and rain for several years. The old windings were removed before the new windings were put on.

The battery pack I am using is made up of a mix of old AA batteries and so is not ideal. The circuit draws about 0.7-0.8A, from the little battery pack, which pulls it down to about 7-7.5Volts. The output from the transformer is about 500-550V which is fed into two six stage half wave voltage multipliers made up of 3kV 10nF ceramic caps and 1N4007 (1A, 1000V) diodes. The diodes for the two multipliers are run in opposite directions from one another. The voltage across the two multiplier outputs is greater than 6000V with no load.



Inverter, Voltage Multiplier & Capacitors.jpg - 259kB Inverter.jpg - 286kB Voltage Multiplier.jpg - 285kB
220-volts-power-inverter-using-NE555-and-MOSFET.jpg - 61kB Stacked Villard Cascade.jpg - 25kB



Found some mounting hardware. It looks a little less amateurish without the pink elastic band. :D

555 Inverter Circuit (500V Output).jpg - 250kB


[Edited on 15-5-2015 by Hennig Brand]

Varmint - 15-5-2015 at 12:10

Henning:

The rectifiers aren't at odds with the chopping frequency, but the conduction to off recovery time.

That's not to say the 1N4007s are inadequate, just that it might require further analysis if your efficiency is below expectation, especially if they are getting warmer than might be considered normal considering the forward drop vs average current.

Hennig Brand - 15-5-2015 at 13:51

So when it takes them longer to change state, than a faster diode, they dissipate heat and even if it is not enough heat to destroy them it lowers overall circuit efficiency. I am not yet sure exactly how high a frequency designers would use a regular rectifier diode such as the 1N4007 in a voltage multiplier circuit. They seem to be working lovely at 15kHz, but 15kHz isn't really all that high as switching supplies go.

Quote: Originally posted by Varmint  
Henning:

The rectifiers aren't at odds with the chopping frequency, but the conduction to off recovery time.


I see what you mean, but the amount of times the diode has to change state per unit time is the frequency.


[Edited on 16-5-2015 by Hennig Brand]

Ferrite Transformer & Voltage Multiplier Design Guides

Hennig Brand - 19-5-2015 at 06:59

Ferrite Transformer:

Here is a good straightforward method for ferrite transformer design. Also attached is the Magnetics 2013 catalogue with specifications for most common core sizes and types.


Attachment: Ferrite Transformer & Inductor Design - MagneticsFerritePowerDesign2013.pdf (160kB)
This file has been downloaded 436 times

Attachment: Ferrite Core Specifications - Magnetics2013FerriteCatalog.pdf (1.9MB)
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Ferrite Transformer Design Sample Calculation:

WaAc = (Po * Dcma) / (Kt * Bmax * f)
WaAc = (5W * 500cir.mils/amp) / (0.001 * 2000gauss * 15000Hz) [used aggressive value for current density since power supply is only run intermittently]
WaAc = 0.0833

From table: 1814 Pot Core is large enough, however, since I had a 3019P core it was used.

Ac = 1.36 cm^2 [3019 effective area value from table]

Np = Vp * 10^8 / (4 * B * Ac * f)
Np = 24V * 10^8 / (4 * 2000 gauss * 1.36 cm^2 * 15000Hz) [12V DC supply voltage, which gives 24V peak to peak on transformer primary]
Np = 14.71 ---> round up to 15 turns
[Primary is double 15 (30 turns center tapped)]

Ns = Vs / Vp * Np
Ns = 500V / 24V * 15 turns
Ns = 313 turns
Secondary 313 turns

WaAc = 0.0833, Ac = 1.36cm^2
Wa = 0.0833 / 1.36cm^2
Wa = 0.06125

Kwa = NpAwp + NsAws
Wa = 0.06125, K = 0.6 for pot cores, let NpAwp = 1.1NsAws
Aws = (0.6 * 0.06125) / (2.1 * 313)
Aws = 0.000056 cm^2 or 0.0056 mm^2
Secondary: 40 AWG magnet wire

NpAwp = 1.1NsAws
Awp = (1.1 * 313 * 0.000056cm^2) / 15
Awp = 0.00129 cm^2 or 0.129 mm^2
Primary: 26 AWG magnet wire

I used a pot core, but an E core would have been fine too, maybe better in some respects. Also notice that I used a bit more turns than was really necessary when I wound the transformer above, but it works fine and the extra turns will keep the flux density down even lower. I hadn't done this calculation when I wound the transformer.


Voltage Multiplier:

Here is a voltage multiplier design guide. I made a small excel sheet, based on a couple of the equations from the guide, which allows quick half wave multiplier design comparisons to be made. Notice at low frequencies that the capacitors must be much larger in capacitance than at high frequencies. Notice how above I used 3kV capacitors for the two half wave multipliers made. Even going as low as 1kV caps probably would have been enough, since the components only need to be rated for the multiplier stage voltage which is about double the supply voltage (supply voltage is ca. 500V in the above case). Using components rated at least a little higher in value than absolutely needed is good practice though.


Attachment: Voltage Multiplier Design Guide.pdf (289kB)
This file has been downloaded 599 times

Attachment: Voltage Multiplier Excel Sheet.xlsx (10kB)
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[Edited on 20-5-2015 by Hennig Brand]

105ft of Blasting Line, 10g of ETN Putty Explosive Initiated With Custom Made ETN EBW Detonator

Hennig Brand - 21-5-2015 at 13:42

This test was performed nearly exactly the same as the last test, except that a new homemade power supply was used. The 0.5uF capacitor bank was charged to ca. 3800V before the homemade brass trigatron was triggered dumping the electrical charge through the blasting cable and bridgewire. The detonator was made using a 7.6mm id Al casing and 0.7g of ETN; 0.5g was pressed at 100lbs of force, 0.1g was hand pressed and 0.1g was put in nearly loose. The bridgewire used was 1.5mil diameter copper, about 100mil long. The witness target was 1/8 inch wall thickness square steel tubing. The blasting cable was made up of 100ft of RG-6 (standard cable, satellite, TV coaxial) and 5-6ft of 18 gauge speaker wire. The main charge was once again 10g of 80% ETN putty explosive.

The test was a complete success. Both 1/8" sides of the steel tubing were perforated in a very brisant detonation.

Right now this system is a bit inconvenient because it takes about 15 minutes to set up the modular fireset and run the line to the charge. Once all fireset components are assembled together permanently in a suitable small enclosure it should only take a couple of minutes to set up.

Being 105ft away is normally far enough for my purposes, but the distance could be doubled to 210ft with the same setup by simply using two 210ft lengths of the same cable type. Two 210ft pieces in parallel basically have half the inductance and resistance compared to a single cable of the same length and should perform similarly as a single piece 105ft long. There are also much better cables available, which would allow much longer cable runs to be made. In my opinion, however, 100ft is enough for most normal small scale blasting. If more distance is needed the blasting box could be sandbagged 100ft away from the blast and the operator could control the blasting box through long thin cable at a much greater distance away.

I used the old trigatron, in the wooden block, because I wanted to keep everything as much the same as earlier tests as possible.


100ft RG-6.jpg - 984kB Fireset 1.jpg - 425kB Fireset 2.jpg - 413kB Fireset 3.jpg - 443kB Setup 1.jpg - 1.1MB Setup 2.jpg - 1MB Setup 3.jpg - 970kB Post Blast 1.jpg - 505kB Post Blast 2.jpg - 503kB Post Blast 3.jpg - 530kB



Here is a current versus time graph generated using the "Distributed Parameter Method" Excel sheet attached earlier in this thread.

Current Versus Time Graph.jpg - 32kB

The theoretical numbers for the earlier failed test look better than this test, however the theoretical model assumed fast efficient switching. A trigatron was used in this successful test, and simple touching of 18 gauge wires was used as the method of switching for the earlier failed test. Fast efficient switching appears to be very important, but I am unable to quantify it exactly at this time.

For 3800V, 0.5uF, 105ft RG-6, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 853 A
Time at or above Burst Action = 1.85 usec
Average rate of Current Rise = 462 A/usec
Trigatron Switching
Detonation Confirmed

For 2400V, 0.67uF, 51ft RG-6, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 876 A
Time at or above Burst Action = 1.54 usec
Average rate of Current Rise = 876A/1.54usec = 569 A/usec
Switching accomplished by touching two 18gauge wires together
No detonation from test


[Edited on 22-5-2015 by Hennig Brand]

jock88 - 24-5-2015 at 14:19


How many ebw's could be put in series for a given set up or would you be better off using a bigger cap (same Voltage) and going for parallel?

Would NG be around the same sensitivity as ETN for ebw' detonators?

Hennig Brand - 24-5-2015 at 15:28

These documents give a feel for what is possible with commercial gold EBW detonators. Results would likely be somewhat different with my homemade copper EBW detonators and fireset. The specs of the capacitors used in the RISI firesets are normally 1uF and 4000V from what I have seen. It looks as though quite a few commercial detonators can be fired simultaneously in various series parallel configurations depending on cable length, etc.

I have more reading material on series parallel connecting EBWs, but I can't locate it right at the moment.


Attachment: Series Parallel Firing of EBW Detonators.pdf (29kB)
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Attachment: FS-43 Firing System.pdf (35kB)
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Nitroglycerine is a homogenous explosive not well suited to this application, at least not in its pure form. It has very low stable detonation velocities, while PETN or ETN or MHN, etc, can be initiated low order by an EBW and then quickly accelerate to high order. Progressive increase in explosive density aids the explosive in accelerating from low order to high order detonation as well, something that would be impossible to do with a homogenous explosive like NG.


[Edited on 25-5-2015 by Hennig Brand]

Much Better Cables Are Available

Hennig Brand - 24-5-2015 at 18:19

Just did a theoretical comparison between RG-6 coax and the "C" cable sold by RISI using the distributed parameter method. Using "C" cable could easily double the distance that my system would function effectively, compared to when using RG-6, everything else being equal. I would like to get some of this cable or something similar.

RG-6 Coaxial
For 3800V, 0.5uF, 105ft RG-6, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 853 A
Time at or above Burst Action = 1.85 usec
Average rate of Current Rise = 462 A/usec
Trigatron Switching
Detonation Confirmed

"C" Cable Coaxial
For 3800V, 0.5uF, 210ft RISI "C" Type Coax, Cu BW 1.5mil D, 100mil L
Current at or above Burst Action = 763 A
Time at or above Burst Action = 1.44 usec
Average rate of Current Rise = 531 A/usec


RG-6 Coaxial Versus RISI C Type Coaxial.jpg - 68kB


[Edited on 25-5-2015 by Hennig Brand]

Hennig Brand - 29-5-2015 at 03:39

Quote: Originally posted by Hennig Brand  
These documents give a feel for what is possible with commercial gold EBW detonators. Results would likely be somewhat different with my homemade copper EBW detonators and fireset. The specs of the capacitors used in the RISI firesets are normally 1uF and 4000V from what I have seen. It looks as though quite a few commercial detonators can be fired simultaneously in various series parallel configurations depending on cable length, etc.


What I said about the capacitors in the commercial EBW firesets was kind of misleading I think. More accurately, normally the commercial units I have seen described have 1uF of capacitance (in total) and are designed to be charged to 4000V. If the capacitor or capacitor bank is designed to be charged to 4000V it is likely rated for 5000V or more.

Hennig Brand - 3-6-2015 at 11:35

I was going from my memory of earlier tests when I wrote down the amount of force used to press the ETN with the lever press. I just checked today and I am easily pressing with at least 300lbs of force the way I have been doing it. I incorrectly stated that it was only 100lbs of force in several places in the last couple of pages in this thread. Here are four examples that I found. Any more that state 100lbs of force should also say 300lbs as well.

First post second line here:
http://www.sciencemadness.org/talk/viewthread.php?tid=23466&...

" A half gram of ETN was pressed in a 7.6mm aluminum casing with over 100lbs of force with a lever press and then another 0.2g was added loose on top."

It should say "with about 300lbs of force".

Same thing here:
http://www.sciencemadness.org/talk/viewthread.php?tid=23466&...

"About 0.2g was pressed with a lever press at about 100lbs of force, about 0.2g was pressed firmly by hand and about 0.2g was poured in loose and then only very gently compressed just to settle and remove large voids."

It should say "at about 300lbs of force".

And here:
http://www.sciencemadness.org/talk/viewthread.php?tid=23466&...

"The 7.6mm casing contained about 0.7g of ETN, 0.5g pressed at 100lbs, 0.1g hand pressed, 0.1g left almost loose."

And here:
http://www.sciencemadness.org/talk/viewthread.php?tid=23466&...

"The detonator was made using a 7.6mm id Al casing and 0.7g of ETN; 0.5g was pressed at 100lbs of force, 0.1g was hand pressed and 0.1g was put in nearly loose."

Maybe I am being a little obsessive, but there is a big difference between 300lbs and 100lbs.

nux vomica - 9-6-2015 at 05:32

I'm getting the closer to being able to do some proper testing now ive got new capacitors, there Epcos 5uf 1300v radial metalized polypropylene film with 0.006 ohm ESR I bought 4 so that gives me 5200v and 1.25 UF.

I had issues with mach3 on my cnc router that took time to work out so I just finished routing the board on the weekend but every thing seems to fit on okay , I built the spark switch into the board to tidy things up a bit and keep it close to the capacitors.

I've taken a short video of the piezo fireing the spark switch but thats about it so far , cheers nuxy.


20150609_181751.jpg - 1MB

20150609_185121.jpg - 954kB

[Edited on 9-6-2015 by nux vomica]

nux vomica - 9-6-2015 at 05:45

Spark switch video

Attachment: 20150609_181820_001_001.3gp (9.3MB)
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Hennig Brand - 9-6-2015 at 12:15

Looks very professional, well done. Those capacitors are far superior to what you had before for this purpose. You did a nice job of making a small tidy spark gap switch. Your setup will be quite compact that is for sure, which is a good thing.


I have a bunch of 2153 chips now so I should probably make at least one inverter using one. The inverter based on the ubiquitous 555 is working well enough for my purposes already though, at least in this application. The 2153 inverter circuit diagram below was taken from the following webpage:

http://danyk.cz/menic230_4_en.html

The 2153 datasheet has a graph allowing component choices to me made for a desired operating frequency.


IR2153 Inverter Circuit.jpg - 31kB


Attachment: IR2153 Data Sheet.pdf (156kB)
This file has been downloaded 393 times


[Edited on 9-6-2015 by Hennig Brand]

nux vomica - 10-6-2015 at 04:48

Just had a successful test used 0.030 mm dia x 1.6mm long copper bridgewire with .8 grm etn, dont know compression figures as in a rush but compressed .7 then used .1 grm loose alloy tube 8mm id x20mm long at the end of 7 meters of rg6 coax and 200mm speaker twin core.

Charged capacitors for 11seconds volt measurement would be over 4500 volts didn't have gauge just used times tested in shed then hit piezo button nice bang and a dent nearly through the 2mm s/s plate nice:D


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[Edited on 10-6-2015 by nux vomica]

[Edited on 10-6-2015 by nux vomica]

[Edited on 10-6-2015 by nux vomica]

[Edited on 10-6-2015 by nux vomica]

Hennig Brand - 10-6-2015 at 10:42

A positive result is nice. So the bridgewire was around 0.63 mils in diameter or 54 AWG right? Seems extremely thin, but if it works it works. Must be very difficult not to break when handling. Was the bridgwire copper? It would have been nice to know more about the specifics of the test, such as capacitor bank voltage prior to firing. Your assumption about the voltage could be right, but maybe not.

nux vomica - 10-6-2015 at 14:46

I made a error on the wire dia have changed it in post to 0.030 mm or 1.225 mill (1 mill is 0.0245 mm so 0.030mm / 0.0245 equals 1.225 mill ) its copper from flash transformer I cant measure voltage over 2800 volts at the moment as I am useing a 5 volt analog meter with 5 m ohm resistance and power supply wont go over that level if connected, so I have run power for set times then touched wires on cap bank to measure the voltage.
Cheers nuxy.

[Edited on 11-6-2015 by nux vomica]

Hennig Brand - 10-6-2015 at 15:05

edit: Oh I see, the power supply is low current as suspected, which could also mean that it won't take too much abuse before it becomes damaged. Good news it that it is fairly easy to build a decent power supply. It makes a nice little project in itself too.

Use a voltage divider which gives a lower proportional voltage for measuring. Even regular 1/4watt resistors can be used if enough of them are connected in series. Often times they are only rated for a few hundred volts each IIRC, but if you add ten in series the series string can easily handle a few thousand volts. High voltage resistors are also available, such as thick film resistors, if you want to go that route. I made a voltage divider that has about 40Mohms resistance and my multimeter is attached to it at the appropriate place so that 4000V on the capacitor bank reads as 25V, but it could be any voltage you choose. The meter I am using is only rated for 1000V DC so there was no way I could use it to measure the 4000V directly.

Voltage Divider.gif - 13kB


[Edited on 11-6-2015 by Hennig Brand]

nux vomica - 10-6-2015 at 15:45

Quote: Originally posted by Hennig Brand  
A positive result is nice. So the bridgewire was around 0.63 mils in diameter or 54 AWG right? Seems extremely thin, but if it works it works. Must be very difficult not to break when handling. Was the bridgwire copper? It would have been nice to know more about the specifics of the test, such as capacitor bank voltage prior to firing. Your assumption about the voltage could be right, but maybe not.

I should listen to the quote about assumption being the mother of all fuxkups. ;)

Hennig Brand - 11-6-2015 at 13:16

I have made a few assumptions in my time too and reaped the rewards. ;)

From the above picture it looks as though your power supply is being supplied by only two AA batteries. That in itself tells a lot about the limited current supplying capability of the power supply. Power supplies have losses, usually quite significant especially with small power supplies, but lets assume for a minute that yours has no losses (Power In = Power Out). Lets assume you can pull 1A from the two AA batteries at 3V. Using conservation of energy, power in is 3V * 1A = 3W, so at 4500V the current drawn could be a maximum of 3W / 4500V = ca. 0.67mA. At 4500V the 5 Mohm Volt meter would draw, 4500V / 5 000 000 ohm = 0.9mA (0.9mA > 0.67mA). I went through these same problems when I was using the bug zapper supplies.

nux vomica - 11-6-2015 at 15:21

Had another test also successful l used same setup with copper bridgewire 0.030 x 1.6mm long .7 grams etn compressed to 1.49 grams cc and .1 gram loose on top, 7 meters coax and 200mm twin speaker wire.
Haven't been able to get to electronic supply shop so don't have accurate voltage levels just charged for 11 seconds as before and pushed pezio button detonation was instantaneous and plate was more damaged than last shot :D nuxy

[Edited on 11-6-2015 by nux vomica]

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