Sciencemadness Discussion Board - Direct electrical initiation of secondary

Direct electrical initiation of secondary

gregxy - 9-10-2010 at 17:48

Wikipedia lists the amount of energy to initiate PETN as
10-60mJ, not very much energy. Disposable cameras
typically contain a 100uF capacitor charged to 300V,
the equivalent of 4.5 J much more energy than is needed
if it can be delivered to the PETN.

EBW uses this type of setup, but is difficult to set up since
a very thin bridge wire is needed and the circuit design is
tricky.

Instead I decided to try converting the secondry explosive
into a resistive mass and passing the current directly through
it. If the resistance can be made on the order
of 10 ohms, most of the energy should be transrerred
to the explosive over a period of 1mS.
The electric field within the explosive will also help
sensitize it. In the best setup the explosive would not
be resistive but would enter "dielectric break down" just
below the applied voltage.

Instead of PETN I used ETN, pressed into 1/8" diameter
plastic straws. The length of the chage was about
1/2 inch). For the contacts I used a piece
of 24 guage solid speaker wire (from radio shack).
Strip off about 1/4 inch of insulation and you have two
small copper prongs about 1/16" apart which can be
inserted into the straw and pressed into the explosive.
The current flows through the explosive in this small
1/16" gap.

The power source is a disposable camera as described
above. About 10 feet of the 24 gauge speaker wire
was used to connect the camera to the device.

My first try was with powdered aluminum
to make the ETN conductive. Unfortunately my Al powder
(325mesh from Ebay) does not conduct at all even by itself
when pressed into a tube. I think my Al is mostly
Al2O3, maybe different Al powder would work better.

Next I tried powdered graphite. By itself the graphite
gives a resistance of less than 10 ohms. Mixing about
1 part graphite to 4 of ETN (by volume) the device
had a resistance of 1bout 1k. Energizing with the
camera, the device gave a loud bang. However I do not
think it was a full detonation. My first device disappeared
completely (although it did not damage the board it was
taped to). A second device just blasted a hole in
the straw and left the ETN mostly untouched.

With some refinement I think this method can be made
to work well. A metal tube to provide more confinement
would help. The loading density and amout of graphite
(or aluminum) could also be adjusted. Too little
graphite and the resistance is too high which lengthens
the pulse. Too much graphite lowers the sensitivity
of the ETN.

The WiZard is In - 9-10-2010 at 19:02

Quote: Originally posted by gregxy

Instead I decided to try converting the secondry explosive
into a resistive mass and passing the current directly through
it. If the resistance can be made on the order
of 10 ohms, most of the energy should be transrerred
to the explosive over a period of 1mS.

The electric field within the explosive will also help
sensitize it. In the best setup the explosive would not
be resistive but would enter "dielectric break down" just
below the applied voltage.

----
The Telegraphic Journal and Electrical Review 1874
Change Of Resistance In High Tension Fuzes At The Moment Of Firing.
Abstract of a paper read before the Society of Telegraph Engineers.
By Major Malcolm, B.E.

The Chairman (Mr. LATIMEB CLABK) asked whether the compound in the fuse was in
the form of a powder or of a solid.

Prof. ABEL said that it consisted of a mixture of phosphide of copper and subsulphide
of copper, very specially prepared with a view to permanence, together with chlorate
of potash as the oxidising agent. These formed an explosive mixture, which served
also for conducting the current, and offered a very high resistance. The mixture was
compressed with great pressure. It was found that no great care was required in the
manufacture of fuses sufficiently sensitive to be fired by means of high tension
machines. The high tension fuses which had been more recently made for submarine
purposes were made somewhat more carefully. They were carefully compressed until
some clear resistance was obtained on the galvanometer, but the same care was not
necessary with ordinary high tension fuses.

See Spons' dictionary of engineering, civil, mechanical, military, and With Technical
Terms In French, German, Italian, And Spanish.
Edited By Oliver J Byrne, 1870
p.576
http://tinyurl.com/yfvkwgm

For details.

djh
----
"Problem is, "Thus shall not kill
whales" ranks among the top
commandments in the cannon
of political correctness. So when
the Makan Indian Nation speared
a whale off America's coast on
Monday, the environmentalists
practically choked on their granola
bars. But pity the animal lovers, for
this is no clear cut call. To the
average activist, interfering in
native American cultures is almost
as taboo as chopping down redwood
trees.

Wall Street Journal 20V99

DougTheMapper - 9-10-2010 at 19:29

Check this out:

http://www.youtube.com/watch?v=-EJ8EPgGRdg

The WiZard is In - 10-10-2010 at 06:42

Quote: Originally posted by gregxy

Wikipedia lists the amount of energy to initiate PETN as
10-60mJ, not very much energy. Disposable cameras
typically contain a 100uF capacitor charged to 300V,
the equivalent of 4.5 J much more energy than is needed
if it can be delivered to the PETN.

NB - The energy sited was for static/spark ignition NOT
heat.

For a theory of spark igniiton of primary explosives see :—

Title Heuristic approach to spark initiation of reactive solids
Creator/Author Searcy, J.Q.
Publication Date 1977 Nov 01
OSTI Identifier OSTI ID: 5275524
Report Number(s) SAND-77-1649
DOE Contract Number EY-76-C-04-0789
Resource Type Technical Report
Research Org Sandia Labs., Albuquerque, N.Mex. (USA)
Format Medium: X; Size: Pages: 22
Availability Dep. NTIS, PC A02/MF A01.

A conceptual model for spark initiation of reactive solids is
proposed in this report in order to focus on an understanding of
spark initiation that can lead to the development of
more-desirable components. The proposed model is a direct
extension of a model previously developed by others for initiation
of gas phase reactions, therefore a review of earlier work is
given. In the model, energy coupling from the spark channel into
the reactive solid is modeled by a two wave structure--a shock
wave, followed by a subsonic blast wave. Detonation is initiated in
most cases if the shock wave is energetic, or a deflagration is
initiated if the shock wave is weak and the blast wave is energetic.
The division of energy between the two waves is determined by
the rise-time (or frequency) of the spark during arc development.
The amount of energy delivered into the spark channel for a given
test circuit is a function of the apparent spark resistance during
arc development, and the apparent spark resistance is influenced
by the conductive nature of the reactive solid. No new data are
presented in this report, but suggestions are made for further
work that could directly impact component design.

My copy is a poor blow back from microfiche obtained years
ago from la NTIS.

In'f anyone wanted to make/post a copy they can have (if I can find it) my MF copy.

djh
----
Heraldry—
Eleven varieties of lines, other than
straight lines, which divide the shield,
or edge our cheverons, pales, and the
like, are pictured in the heraldry books
and named as engrailed, embattled,
indented, invected, wavy or undry,
nebuly, dancetty, raguly, pontenté,
dovetailed and urdy.

gregxy - 10-10-2010 at 15:38

60mJ did seem to be very small, although it is
difficult to ignite ETN with a flame, let alone a spark,
maybe this is for dust suspended in air?

The Wikipedia article also give the initiation energy
by laser as 0.5-5.2J, which matches the energy from
the drop test 12cm*2.5Kg*9.8 = 2.9J.

Working from the physics:

The critical diameter for PETN is about 1mm,
The amount of energy to raise 1 cubic mm 1000C
(enough to insure detonation)
if the density is 1.6g/cm^3 and the specific heat
of glass (my best guess at a meterial with parameters
that are "close":
glass = 0.84 J/gK
specific heat * density * volume * dT
0.84*1.6*1e-3*1000 = 1.3J

So all these values are in the "ball park"

Now how fast must the energy be delivered:

The thermal time constant assuming the parameters
for glass and a 1mm box:

Tc = Specific heat * density * 100 * dist ^2 / thermal conductivity

Tc = 0.84 * 1.6 *100 * .1 * .1 /1.05 = 1.28 Sec

So not much heat will be lost by conduction if the
pulse is < 1mS.

To create a shock wave directly however, the energy will
need to be delivered faster than it can escape
by the shock wave. I estimate this time as
the time it takes the shock wave to cross the 1mm
volume

T = 1e-3 M / 8000 M/sec = 0.12uS

Generating a pulse this short with an energy of several J
will be difficult. (A 1uF cap charged to 2000V and < 0.1 ohm
resistance) Most of the energy will be lost on the way.

However I think a sensitive material like ETN can make
the transition to full detonation without being driven
by a full shock wave.

quicksilver - 11-10-2010 at 08:32

Be VERY careful of information in Wkipedia. Think about the elemental concept: an encyclopedia that is written by the public? Very basic concept such as route of initiation (spark gap) vs the imposition of energy by means of contact was obviously not clearly stated. It might have been someone's cat at 60 mj. but you know that we're not in new territory here, "Wiki" articles very frequently has this result.
Frankly; I doubt the figures to begin with. What journal article or research was the writer quoting from? (Lord only knows...)
Be really skeptical with "Wiki" information: if the writer does not have decent notes, move on.....

There IS some stuff in past threads here with some very reasonable and well documented electrical energy levels of some materials. The "exploding bridge-wire" thread may have some factual data also. Wizard will get some solid information (as he's done for some many years now), & you know it's solid becasue the articles are sited. I don't want simply rag on Wiki but I understand your frustration because it's become so damn popular now people are taking for granted that it's factual. But logic tells you it couldn't be that low.
Some exists in the PATR. - Same subject. There MIGHT be some Los Alamos materiel on that subject due to it's popularity in commercial & military applications.

[Edited on 11-10-2010 by quicksilver]

franklyn - 12-10-2010 at 21:29

Explosive molecular compounds being electrical insulators , must be considered
as such in any scheme to cause detonation by direct action of electric current.
Heterogeneous mixtures with conductive materials require a consistency comparable
to pyrotechnic mixtures serving only to increase the contact surface for reaction ,
if ignition is the intent. Whether this can result in high order explosion depends on
the explosive itself if it is a primary. Detonation of secondary explosives requires
instantaneous extreme high energy application to succeed. A conductive admixture
is essentially a resistor which by definition serves to limit current through put.
A possible approach to the problem would be to rely on an initially ignited portion
of only explosive to act as the switch in a circuit discharging a capacitor. You can
test this idea by placing a flame so that it contacts both wire leads. The sound it
makes must be of the same intensity as an explosion or the electric source / capacitor ,
cannot serve the purpose.
http://www.sciencemadness.org/talk/viewthread.php?tid=5064#p...

.

gregxy - 13-10-2010 at 21:46

Primary -vs- secondary is more of a contimum than a discrete state.
I don't think I could ever initiate TNT or picric acid this way but
ETN is quite sensitive. I'll try my experiment using stronger confinement
and larger capacitor and see if I can get complete initiation of the sample.
Given my 1/8" diameter sample with loose packing, it is not surprising
that it failed to go off completely.

The best setup would be to leave out the graphite and use enough
voltage to breakdown (arc thru) the ETN. The problem is that
the breakdown voltage for ETN is probably 3X higher than for air so it
is difficult to avoid arcing over the top of the sample. Plus I would need
at least 3000V instead of the 300V that the camera puts out.

Once that an insulator breaks downand the breakdown region is flooded
with ionized molecules it changes from a very high resistance to a very low one.
So the main thing that limits the current and lengthens the pulse is the
resistance and inductance of the external circuit.

dann2 - 14-10-2010 at 12:41

Hello,

Quick silver wrote:
__________________________________________________
Be VERY careful of information in Wkipedia. Think about the elemental concept: an encyclopedia that is written by the public?
__________________________________________________

I'll second that!!!!!!!!!!!!!!!!!!!!!!!!!!!

Thread here:
http://www.sciencemadness.org/talk/viewthread.php?tid=13133#...

See Coopers book. http://www.megaupload.com/?d=0DIJE7NC

YOU NEED VERY VERY LOW INDUCTANCE CAPACITORS.

If setting off something like Nitro Glycerine (a secondary explosive???) then ordinary capacitors would do (so would a hammer).

If setting off PETN or RDX (the RDX must be of a particular fine crystal structure) then it won't be happening with the UTUBE stuff no matter how big and impressive sounding/looking the capacitor is. You can have a capacitor that will blow a melon (or your hand) to Kingdom-come but it will not put off the primary (RDX, PETN)

Dann2

franklyn - 15-10-2010 at 08:55

@ gregxy

Without stating how you arrived at those numbers I can tell it's just a wild guess.
There is no standard description for expressing breakdown values , but volts per mil
( V/mil ) is common . In the MKS system Megavolts per meter ( MV/m )/ 25.4 = ( V/mil )
Values for 2 mils and 50 microns are approximately equal.
1/8 inch ( if this is the intended gap ) is 125 mils. You need to multiply by 125 the
reference value of " dielectric strength " more commonly stated as " breakdown voltage "
for ETN. A reference value may not have been established.

On *.PDF index page 13 ( Figure 7 )
Dielectric Properties of Some Common High Explosives
http://handle.dtic.mil/100.2/AD404454
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD404454&Locatio...

Bibliography here on *.PDF index pages 66 & 67
" Static Dielectric Breakdown Studies of High Explosives " might serve your purpose
The Properties of Condensed Explosives for Electromagnetic Energy Coupling
http://handle.dtic.mil/100.2/ADA177885
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA177885&Locati...

Voltage Breakdown of Potassium Dinitrobenzofuroxan
http://handle.dtic.mil/100.2/AD747364
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=AD747364&Locatio...
http://www.sciencemadness.org/talk/viewthread.php?tid=1778&a...

Point here is that even if only ignited , the flame is highly conductive. As I mentioned above ,
" A possible approach to the problem would be to rely on an initially ignited portion
of only explosive to act as the switch in a circuit discharging a capacitor."
Experimental Aspects of Coupling Electrical Energy into a Dense Detonation Wave Part 1
http://handle.dtic.mil/100.2/ADA121262
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA121262&Locati...

Bibliography here at the end _
Study of Physical Chemical Transformations in Detonation Wave by Electric Conductivity Method
http://www.intdetsymp.org/detsymp2002/PaperSubmit/FinalManus...

Shock Induced Electro Conductivity in the Insensitive High Explosive TATB
http://www.intdetsymp.org/detsymp2006/downloadmanuscript.asp...

Calculation of Maximum Rate of Dielectric Heating of Explosives
http://handle.dtic.mil/100.2/ADA955144
redirects to:
http://www.dtic.mil/cgi-bin/GetTRDoc?AD=ADA955144&Locati...
I had made a brief mention about this here _
http://www.sciencemadness.org/talk/viewthread.php?tid=5064#p...

See " Sparks In Air " here
http://en.wikipedia.org/wiki/High_voltage

Some dielectric strength values charted here _
http://www.rfcafe.com/references/electrical/dielectric-const...
Physical Properties of Plastics
http://www.machinist-materials.com/comparison_table_for_plas...
Dielectric Strength of Insulating Materials
http://psyhosting.info/Ionium/Rhodium/pdf/chemical-data/diel...
Attachment: Dielectric Strength of Insulating Materials -CRC Handbook of Chemistry & Physics .pdf (876kB)
This file has been downloaded 56851 times

Related threads
http://www.sciencemadness.org/talk/viewthread.php?tid=5064
http://www.sciencemadness.org/talk/viewthread.php?tid=13719

.

franklyn - 15-10-2010 at 09:22

Quote: Originally posted by dann2

YOU NEED VERY VERY LOW INDUCTANCE CAPACITORS.

@ dann2
Available here => Pure Unobtainium

Some people believe that if you swim right after you eat a meal , you will cramp and drown.
So naturally they won't dare do so , and so the legend continues.
You will find when measuring a capacitor it will exhibit practically the same " Inductance "
as a conductor of equivalent length !

See => http://www.ivorcatt.com/2603.htm
( Self explanatory , particularly the text in red)

Next here _ http://sound.westhost.com/articles/capacitors.htm
Scroll down to 4.0 - Parasitic Inductance in Bypass Applications
and read from Figure 14 up to 4.1 - Next scroll past that and read 5.0 - ESL and ESR

.

gregxy - 15-10-2010 at 10:26

Thanks for all the helpful references!

Looking at Cooper's book, the description for the ebw fire set
is:
1uF, 2000-4000V, 50-100mOhm.

This is only 2 to 8 J of energy, about the same as the
disposable camera and certainly not enough to explode
a mellon!

The disposable camera has an electrolytic which probably
has ~1 ohm series resistance, about 10X too high but
still cabable of delivering 300A with short leads, which
is enough to fire a commercial EBW device,
(based on the descriptions in Coopers book)

Lead resistance is important, 20gauge speaker wire
has 20mOhm/foot, so with 100 feet you have 2ohms
and it becomes the dominant resistive factor.

Note digikey has 1uF 2000V caps with 5mOhm ESR
( part # 338-1182-ND) for $22.50, perfect for this
application.

dann2 - 18-10-2010 at 12:03

Hello Grexy,

I will go back to my original shout! and say no more.

"You need very low inductance capacators"

The capacitors that you mention will NOT make RDX(correct crystal size required for reliable detonation) or PETN explode when wired up to an exploding bridge wire.

Thats my understanding.
No amount of references or explanations from Franklin will change my understanding.
There was a large debate regarding the very rapid (rapid, photoflash Caps arentoo 'slow') discharge needed to do the job (explode RDX(correct crystal size) or PETN).

If you get things working (making RDX or PETN explode) with the photoflash capacitor (please) come back here and report it.
Cheers,
Dann2

[Edited on 18-10-2010 by dann2]

dann2 - 19-10-2010 at 12:11

Hello Folks,

Quote: Originally posted by franklyn

Quote: Originally posted by dann2

YOU NEED VERY VERY LOW INDUCTANCE CAPACITORS.

@ dann2
Available here => Pure Unobtainium

I INTEND TO GET SOME!!!

(low inductance caps)
You claim that the (small inevidable) inductance in the capacitor is not relevant?
See your post in this thread regarding A-bomb stuff, (5-7-2006)
http://www.sciencemadness.org/talk/viewthread.php?tid=5075
You state "Low inductance capacitors are also required"
and then a link to low inductance caps.
Bit of inconsistency in your argument me thinks, huh.

There is a (rather verbose at times) thread here where exploding wires are discussed:
http://www.sciencemadness.org/talk/viewthread.php?tid=12414

Custom Electronics has developed a line of standardized, low inductance capacitors for use in EFI and EBW applications.
If you Google "low inductance capacitors design ebw" some useful looking links come up.

Attached (suppressed at the time if you examine the filed date and the published date) is a patent for an 'EBW' detonator what contained no wire, just a gap containing secondary explosive for the spark to jump accross.

Since you are using ETN (not PETN etc as I wrongly thought) the requirements of the capacitor are not so stringent since you are getting closer to using an actual primary (as it were). Perhaps the photo flash will do the job.
Electrolytic anything will not do the job on ETN (IMO) but I could of course be wrong.

Can any good soul here come up a pspice file for examing a circuit for this type of sererio. Very high current spike 100A per micro sec), short time intervals (micro seconds) going into a low resistence............

Dann2

Attachment: US3955505.pdf (188kB)
This file has been downloaded 514 times

[Edited on 19-10-2010 by dann2]

Contrabasso - 19-10-2010 at 13:13

With all the electric methods of firing nonel shock tube the big problem is dampness letting the HV spike run away and the actual life of the tip of the electrodes. Usually the electrodes are made into a HV connector with some mouldings to place the nonel in the right place, but as the electrodes wear then reliability suffers.

dann2 - 19-10-2010 at 15:50

Hello,

If anyone wants to get into home brewing their own very low inductance capacitors (very fast discharge) then the community that are into Dye Lasers may be of some use.
They use a very fast acting flash tube (contains air at low pressure, not Xenon) which needs a very fast discharging capacitor to drive it.

Link here:
http://192.197.62.35/staff/mcsele/lasers/LasersFLP.htm

Quote from page:
+_______________________________________
The flashlamp is a simple device filled with air at low pressure. A vacuum of no lower than 20 torr is needed which may be generated from an old fridge compressor run in reverse.
The tricky part to this laser is the capacitor which stores energy to be discharged through the lamp. To make this laser work a capacitor of low internal inductance must be used. Ordinary electrolytic capacitors will not work. Consider this screen capture of an oscilloscope trace below which shows the current and voltage characteristics of a typical photoflash discharge through a xenon lamp. In this case the capacitor was rated at 350uF and was connected directly to the lamp with no external inductance inserted into the circuit (However be aware that photoflash caps have a relatively large internal inductance designed so that the impedance of the L/C circuit matches that of the lamp).
Some researchers have used extreme measures such as coaxial capacitors [2] with the flashlmp housed in the center of the capacitor disc. The parameters of a suitable flashlamp design are covered in reference [3].

The rise time of the discharge is about 100uS and the length of the light pulse about 1.1mS. The intrinsic inductance of electrolytic capacitors will not allow the fast discharge times required for this type of laser. Many solid-state lasers (such as the YAG, described on another page on this site) can use a relatively slow discharge such as this but not flashlamp-pumped dye lasers. The best bet here is to either make a capacitor of foil and plastic sheets or obtain a suitable low-inductance type. The capacitor required (as per the Amateur Scientist design) is rated at about 15 uF at 3000 Volts. Instead of a single capacitor one may use several smaller oil-filled capacitors (of about 4 uF each) in parallel. These are the type used for high-voltage power supplies such as those used for kilowatt-plus radio transmitters.

_____________________________________________________

A Google of "low inductance capacitor for air flashtube" brings up some relevant reading.

Dann2

12AX7's original "Piffle (to photoflashes)" hold's good when trying to detonate PETN

.

ETN? that's an interesting avenue.

gregxy - 20-10-2010 at 13:54

I'll do some more experiments when I get more time,
(I'm moving now so everything is in disarray).
Next time I'm going to place the ETN in an Al tube
to give better confinement and a more rigid mechanical
setup.

The analysis in Coopers book uses a lossless transmission
line model which is going to be invalid in this case. Here
both the source and the load have lower impedance (and
resistance) than the line, so the line resistance and
inductance may be the dominant factors.

I agree the 1ohm ESR in my electrolytic cap may cause problems and that caps with low resistance and inductance
would be best, but it is easiest to start with what is at hand.

[Edited on 20-10-2010 by gregxy]

franklyn - 21-10-2010 at 03:31

@ gregxy
A useful similation applet
http://www.coilgun.info/mark2/rlcsim.htm

<><><><><><><><><><><><><><><><><><><&g t;<><><><><><><><><>

Quote: Originally posted by dann2

See your post in this thread regarding A-bomb stuff, (5-7-2006)
http://www.sciencemadness.org/talk/viewthread.php?tid=5075
You state " Low inductance capacitors are also required "
and then a link to low inductance caps.
Bit of inconsistency in your argument me thinks, huh.

@ dann2

It is not the contradiction you imply. Reducing circuit inductance minimizes
switching jitter that delays firing until later than the exact intended moment.
32 separate charges of an implosion assembly all initiated within the same few
millionths of a second requires precise timing. An accurate switch such as a
Krytron is additionally needed to realize such timing.
Discussed in the second paragraph here _
http://www.sciencemadness.org/talk/viewthread.php?tid=12414#...

Quote: Originally posted by dann2

Quoted excerpts stated on that site :
http://192.197.62.35/staff/mcsele/lasers/LasersFLP.htm
" photoflash caps have a relatively large internal inductance designed "
" The intrinsic inductance of electrolytic capacitors will not allow the fast discharge times "

Strobe / photoflash lamps are only similar in operation to EBW's destructive
power levels which do not need controls to fire only once and turn off by
themselves forever. I don't know what power supply dye lasers require but
the references cited are 35 plus years old and very archaic for what is
presently manufactured. Capacitors whether photoflash or other do not have
inductance purposely " designed " in them , that statement indicates the
author misunderstood and is mis-stating something he read somewhere
( perhaps a cited reference ? ).
Describing a capacitor as " fast discharging " is meaningless without description
of circuit operation , like claiming a high performance car is the one that empty's
the gas tank soonest. It's evident that he is attributing to ESL
( Equivalent Series Inductance ) the characteristics produced by the ESR
( Equivalent Series Resistance ) of the electrolytics.
While perhaps knowledgeable of the needs for the laser , the gentleman is
entirely unknowledgeable about how to achieve this. " The rise time of the
discharge is about 100uS and the length of the light pulse about 1.1mS
This is far too long for a dye laser which usually requires rise times on the
order of microseconds and pulse lengths under 100uS."
" The most difficult part of building this laser was finding a capacitor which
must store over 100 J and discharge extremely quickly "
Alright , in other words he wants a short pulse.
Fair enough , I have no issue with this. An electrical engineer would address
the first need for a fast rise time by placing a metalized plastic film capacitor
of 1 or 2 uF of equal voltage in parallel with the electrolytic , which having
a very low ESR will actually discharge first providing the required fast rise.
The short duration cited requires some means of cutting off the discharge
at the end of an elapsed interval. See *.PDF index page 5 _ here _
http://www.lightingassociates.org/i/u/2127806/f/tech_sheets/...
More references below under Flashlamps and control circuits
Wave shaping at this power level requires utilizing power semiconductors
such as IGCT ( Insulated Gate Commutated Thyristor )
http://books.google.com/books?id=0_D6gfUHjcEC&pg=PA231
IGBT ( Insulated Gate Bipolar Transistor ) GTO ( Gate Turn Off Thyristor )
or ETO ( Emitter Turn Off Thyristor ) in an electronic control circuit.
http://books.google.com/books?id=0_D6gfUHjcEC&pg=PA236
Understandably the author wishes to avoid such hassle and utilize something
simpler utilizing little more than a capacitor providing the required pulse.
While this is in the realm of feasible ( cheap strobe lights function with a
simple relaxation oscillator ) the engineering to build a matched set of flashlamp
and capacitor in the specific operating range is practically in the category of
unobtainium.
IGBT GTO
http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT Kharagpur/Power Electronics/PDF/L-1(SSG)(PE) ((EE)NPTEL).pdf

Flashlamps and control circuits
http://www.htds.fr/doc/optronique/sourcesLumineuses/LampesFl...
http://sales.hamamatsu.com/assets/applications/ETD/Xe-F_TLSX...
http://members.misty.com/don/donflash.html
http://members.misty.com/don/xeguide.html

Unless indifferently manufactured , form factor and construction determine
characteristics of a capacitor. High voltage caps made by Vishay-Spraque , Cornell
Dubilier , Aerovox , and Duracap-Mallory are longish cylinders used in blasting machines
for bridge wires. An improved design is squat like a hockey puck. Updated links _
http://www.sbelectronics.com/power-ring-products
http://www.sbelectronics.com/wp-content/uploads/2009/11/PPC2...

This manufacturer assures 2 Joules per cubic centimeter , if so this may well
eclipse the aluminum electroyitic.

.

dann2 - 21-10-2010 at 11:38

Hello,

The 'bottle neck' for getting the charge out of the capacitor in EBW applications (for PETN anyways) is the capacitor inductance. You can make the ESR very low but the inductance will be the bottle neck that must be made low enough for the thing to work.

You need a very low inductance capacitor. Thats really all I am saying.
I presume you aggree with that as opposed to saying that the inductance of the capacitor is not really an issue?
You of course need the rest of the circuit (lines, switches etc ) up to the task.
Photoflashe Caps. will not work for PETN no matter how fancy the rest of the circuit is designed. The (homemade) caps for the Air photoflash tube are a completely different beast than photoflashes for Xenon flash tubes (they have much lower inductance).
The discharge into Xenon flashes MUST be 'relatively' slow or the light output will NOT suit the purpose of the flash in the first place (to illuminate the scene for a photograph).

Of course Grexy is using ETN (more sensitive) so photoflashes may work. I don't know.

It's surly a piece of piss to make a low inductance capacitor. (easy for me to say, as I will not be doing it). The end product may not be a pretty sight and not of minimum size and weight but who cares. Just a series of flat plates and flat insulation (no 'rolled up' designs wanted!)

For PETN EBW Capacitors we will have to agree that:
"It's the inductance stupid"
I am really only echoing what 12AX7 stated in that other thread and you (Franklyn) argued and argued and argued and supplied link after link after link to 'show' that the inductance of the capacitor did not matter. It does.

ETN is an interesting avenue and photflashes may be OK.

Dann2

[Edited on 21-10-2010 by dann2]

Contrabasso - 21-10-2010 at 13:27

Considering that every "Nonel" or Shock tube adaptor for either the Scorpion or the shrike firing machine is simple cheap and hand held, perhaps people are complicating matters a trifle!

The Scorpion uses a internal circuit that feeds a mechanical adaptor built into a 1/4 jack plug!

Someone search Blasters supply co for the details please.
http://www.blasterstool.com/blastingnonelinitiators.aspx
http://www.blasterstool.com/combo-nonelandelectric.aspx
http://www.blasterstool.com/hr1hr2l-sbsstartertip.aspx
these adaptors wear out and must be about 50c a fire which makes the shotgun primer operated initiators simple and viable.

These both initiate the HMX in the core of shocktube reliably while the electrode tips are good but they soon wear out in real use.

[Edited on 21-10-2010 by Contrabasso]

dann2 - 28-10-2010 at 09:22

Fasinating the way those tubes work. What are they coated with on the inside.

http://en.wikipedia.org/wiki/Nonel

Contrabasso - 28-10-2010 at 10:44

Apparently it's a HMX/Aluminium powder mixture at about 6g per kilometre. In the UK it's considered not explosive for storage and transport but possession could attract the wrong kind of attention unless you have a good reason (and probably COER for HE and dets anyway) as most uses for nonel are HE based so if you have nonel they want to know what and where and what the good reason for possession is.

If you think you are going to extract the HE I really doubt there is an economical method considering the light loading of powder

dann2 - 10-3-2011 at 17:16

Hello Folks,

Having kicked the subject around for some time I have come to the conclusion that I was talking a load of codswollop (that's very accurate and reliable information if anyone out there never hear of the word :p )

Just about any old capacitor will do so long as it can withstand a good voltage, say above 500V (the higher the better).

@Franklin
I said:
"For PETN EBW Capacitors we will have to agree that:
"It's the inductance stupid"
I am really only echoing what 12AX7 stated in that other thread and you (Franklyn) argued and argued and argued and supplied link after link after link to 'show' that the inductance of the capacitor did not matter. It does."

You obviously did not supply ENOUGH links :p !!!!!!!!!

<b>Anyhow, I hereby retract anything I have said in the past about needing very low inductance capacitors for this job.</b>

If you are trying to make a system with the smallest possible weight/size (ie. no cables, minimal voltage on cap. etc etc etc) then capacitor inductance will be a factor that has to be considered.
Most systems with cables are dominated by the inductance in the cables, capacitor inductance is a very small part of the total inductance of the system.
Will post some stuff that I have been going through.
Only a very small amount of the actual charge in the firing capacitor gets to blow up the wire. Most of the charge stayes in the capacitor or just flows as the explosion takes place into the great unknowns of the plasma. Tucker_1 (first link above) states that 98% of the Voltage is still on the capacitor when the bridge wire explodes!
You need special 'high surface area' PETN at a density of approx. 0.88.
Perhaps thats the problem if anyone cannot get them to work.

There is an essenital read by T. J. Tucker here:
http://www.osti.gov/bridge/purl.cover.jsp;jsessionid=AA6F4E1...

There is also another good read here:
http://www.osti.gov/bridge/purl.cover.jsp?purl=/4229184-1Ibm...

In the second document the voltage accros the exploding brige wire gets up to 10KV at 0.162 micro seconds!!
See the printout at the bottom of the document. Is this the 'freewheeling' effect of the inductance in the circuit? The capacitor is only charged to 1KV when the system is triggered.

I cobbled together the attached diagram to try and 'see' (for myself anyways) what is going on with these devices. May be useful.

Cheers,
(bear with me) Dann2

Double post

dann2 - 10-3-2011 at 17:44

Waveforms from post above going out to longer times. This will never actually get to happen as the whole system has long since blown apart.
(as stated by others in threads around)

[Edited on 11-3-2011 by dann2]

Bert - 11-3-2011 at 06:25

The small nonel units don't have any output cabling to speak of, the firing electrodes are right on the box. This simplifies things- If you want a system that can fire a remote detonator you're going to have to deal with the firing line inductance.

Nonel with shock wave in to flame output transducers is used in some display fireworks situations. Like city displays fired on building tops with radio transmitters in the vicinity, for instance.

gregxy - 11-3-2011 at 09:27

Well maybe not any capacitor but Digikey and Ebay have
large 2kV non-electrolytics that will work.

I have now been working on electrically igniting, not detonating
smokeless powder. I find the opposite problem, the pulse
needs to be stretched to 100ms to ignite it. Using a
100uf cap at 300V, the spark passes through the powder
with no ignition. But if I put a 100 ohm resistor in series then
the powder ignites.

dann2 - 11-3-2011 at 11:43

If you were to place an inductance instead of a resistance in the circuit this would slow things down and at the same time give you more power at the business end. You are using power in the added resistor.

What secondary (or is it primary, Lead Azide?) explosive is placed at the end of Nonel tubes?

Googled a bit and got the attached document.
It states that Nonel detonators contain on primary explosive. Then it goes on to state that Nonel detonators contain Lead Azide + PETN (top of page 2)
Am I reading that wrong?
http://en.wikipedia.org/wiki/Lead(II)_azide

Lead Azide is described as a sensitive primary explosive by Wiki

Cheers,
Dann2

[Edited on 11-3-2011 by dann2]

[Edited on 11-3-2011 by dann2]

Attachment: shock-tube.pdf (47kB)
This file has been downloaded 1157 times

quicksilver - 11-3-2011 at 14:44

Nonel is aluminumized HMX: single micron level (say about 2 um or smaller) depending on the tube. That's your carrier. The cap is the cap and generally is a Nonel cap that's very light on the primary with very powerfully compressed RDX/PETN set is a unique screw or bayonet attachment at the mouth. They are getting more expensive all the time.

If the advertisement says "shock-tube" that meant the patent ran out on the Nonel design and others are making it for less.

[Edited on 11-3-2011 by quicksilver]

dann2 - 11-3-2011 at 16:46

At the end of the day the detonators with this system are detonators containing a primary explosive. Why the sales literature say they or the 'system' contain no primary explosive is beyond me.
NONEL tubes will not detonate PETN (high surface area stuff) so if you want to eliminate primaries from the system it's (properly) exploding bridge wires only that will do it.

Dann2

dann2 - 20-3-2011 at 17:33

About 'slowing down' the spark I am not too sure about adding an inductance.
Perhaps just using a heavier wire will give slower heat up time.

Attached is a study that seems to show that PETN does not increase in sensitivity as particle size is decreased (specific surface area increased). Perhaps it's just this particular initiation technique that does not give easier detonation to the PETN as partical size is reduced.

Reading a book (non shock initiation of explosives) on Google books, it says that PETN of up to 30,000 cm^2 per gram is used in EBW detonators. You only get about 8000 by recrystalizing PETN from an Acetone solution added into cold stirred water.

Dann2

Attachment: PETN_Size.pdf (97kB)
This file has been downloaded 547 times

[Edited on 21-3-2011 by dann2]

gregxy - 20-3-2011 at 18:29

An inductance would work better, I tried one first, but later found a resistance would
work just as well. (The inductance needs to be large probably close to 1H to work).

The resistance of the powder before the voltage hits it is ~1k to 5k ohms, but drops
to near zero once the voltage is applied and a plasma forms.

The part I found interesting was the duration of the pulse was more important than
the power in the pulse (for igniting this power).

quicksilver - 21-3-2011 at 06:53

Quote: Originally posted by dann2

At the end of the day the detonators with this system are detonators containing a primary explosive. Why the sales literature say they or the 'system' contain no primary explosive is beyond me.
NONEL tubes will not detonate PETN (high surface area stuff) so if you want to eliminate primaries from the system it's (properly) exploding bridge wires only that will do it.
Dann2

The Nonel system actually does not contain any primaries. they are the prepared tubing (HMX +Al) and you supply a shotgun primer that fit into a spring loaded initiator similar to a fuse lighter. That is really all there is to the manual system.The tubing costs some money as it's a single use agenda. The "snapper" can be all sorts of configurations. Several are hand-held, I have seen one that is a foot-stamped "shell" but they all use the standard shotgun primer. That's all there is to them. However they can be made to "branch" via screw adapters but not as successfully as a det-cord applications (they may branch into two and two again but that's about it).
Nonel's primary purpose was to be used in simple blasting scenarios or areas where a great deal of electrostatic / electro-radiation made other methods dangerous or impossible to cover by insurance. It was never marketed to be a replacement for detcord branching/timing numeric option. TTBoMK it's not all that popular. However the use of old fashoned fuse is so limited & rare that it filled that gap. only one or two mfg make classic fuse caps anymore and Ensign-Bickford sells only two sizes of fuse since they changed hands.

Contrabasso - 21-3-2011 at 14:44

In the UK Nonel is used in preference to det cord as there is no noise issue, nonel is almost silent but detcord is LOUD.

Accepted practise is to use shocktube into special dets which have NO primary explosive.

dann2 - 21-3-2011 at 15:41

Thanks for that.

Shock tube would surely be cheaper than det-cord (guessing) apart from the noise?

Edit:
Reading from an MSDS sheet from here:
http://www.dynonobel.com/technical-library-blasting-services...
It says that the delay detonators contain 0.05 (50 micro grams!) of Lead Azide and no PETN.

A suitable detonator for detonating slurry explosives is described as a Nonel Unidet and contains Lead Azide + PETN as described in a PDF a few posts above.
Quoting:
" CHEMICAL COMPOSITION
The explosive elements of a [Nonel Unidet] detonator consist of lead azide and
pentaerithrytol tetranitrate (PETN). The delay elements consist of
various chemicals, mainly lead oxide, silicon, antimony, and
potassium permanganate."

From another brochure, a Nonel Unidet contains 1 gram of PETN with no mention of Lead Azide.

I also read:
"Recommendations for Use [Unidet]
NONEL® Unidet detonators should always be secured inside
a suitable primer, which fully encloses the detonator."

What exactly is a 'suitable primer'?

It's all as clear as mud.

Perhaps if the amount of primary in a detonator is small enough it does not have to be declared?

There is some info. on the Nonel Unidet here:
Goto bottom of page for PDF's.
http://www.oricaminingservices.com/cz/en/product/products_an...

Dann2

[Edited on 22-3-2011 by dann2]

quicksilver - 22-3-2011 at 07:50

QUOTE:

What actual explosives can you place at the 'business' end of Nonel tubes and get reliable detonation?
Can you place PETN, RDX, or plastic explosives made from these materials and get detonation?
Can you put prima cord (= PETN) at the business end?
Am I correct in saying that you NEED a primary explosive at the ('business') end of the Nonel tube or is Nonel tube capable of exploding secondary explosives?
If Nonel tubes can initiate secondary explosives could it initiate Picric acid, which is rather insensitive?

Sorry about all the questions but I cannot find a sourse that clearly states that Nonel tubes will initiate PETN (or other common secondary) directly without the use of a primary explosive.

Dann2

_____________________________________+
The detonator is a separate issue from the Nonel system. An adapter is in the form of a bayonet plug (or screw-in end) You are correct that one would exist: but not as part of the Nonel system. The shotgun priming mechanism allows a shock wave to carry though the tube to a primed charge. It is like a tiny tunnel but that wave can only do so much. - Therefore it cannot "branch" as much as even the thinnest det-cord and not many separate detonations can take place.

You COULD put det-cord at the end but it would defeat the purpose as why not use an "all det-cord" system? Cost is 2 to 3x what det-cord costs. Even the thickest det-cord is much cheaper than Nonel. The thin, common (10) det-cord costs about $400 a roll of a thousand ft. Nonel costs about $1200 plus adapter costs, etc. Generally Nonel is used in a place where one may not safely use electrical blasting: it's not that common nor is it economical.

Very pure Picric Acid, that which would "pop" in a strike on steel to steel is rather insensitive as secondary explosives go. I have no documentation of Nonel systems being used with Picric Acid. I am guessing that it would NOT be sufficient to initiate alone without a standard detonator at the end. Think of Nonel as a fuse that burns in milliseconds, yet provides enough heat and energy in emulate a flash-powder level within a cap. That is, it has SOME energy but not enough to be a detonation system with any but the most sensitive materials (NG or a primary).

So-=YES=-, you would need a cap at the end. but it is a separate issue; YES, you could initiate PETN in det-cord with the energy of the Nonel tube (PETN is fairly easy to initiate).
There is a REASON why the detonator is a separate thing. Some are made specifically for seismic readings within built up areas (cities, etc) and Nonel is the connector of choice to use with such a device (which are VERY powerful).
Nonel has many limitations. it can be used in very wet environments, yet totally underwater; it would float up. It can be ruined by "kinking" or being flattened for even somewhat short distances. The ends MUST be kept sealed as the "dusting" of HMX & Al is SO fine that a minor amount of exposure could ruin it totally for quite a ways. It needs to be cut and placed within an adapter immediately and the roll sealed (more expense for special plastic bits). Det-cord can dribble out a little PETN from the end but generally it's packed well enough so that's not an issue. SLIGHT moisture wouldn't ruin it (as in humidity) but it would ruin exposed Nonel.
Remember that the detonator is not part of the Nonel system. so that when you read the specific Nonel literature from Nobel you are reading the material that relates to the system only. There are other makers of shock tube units now as well!

[Edited on 22-3-2011 by quicksilver]

dann2 - 22-3-2011 at 12:39

Thanks for that (and your patience too!)
I once came across used Nonel tubing at a blasting site and wondered what they were. (at least looking back in time I presume thats what all the fine tubing was).
I had no idea of pricing and am very surprised to learn that det cord is so cheap compared to Nonel. One other factor that MIGHT? encourage the use of Nonel is security. If Nonel is stolen etc, it's pretty useless stuff whereas det cord is not.
Also you can run it through an area where you want zero damage/disruption in order to get your 'signal' to the explosion site. Not a good idea with detcord. (assuming you can't use electrical of course).

I have no applications or business with Nonel or Detcord etc etc and am only asking the question (Will Nonel tubing detonate PETN directly?) from an academic point of view, coming from the subject of spark initiation of PETN.

Quote:
YES, you could initiate PETN in det-cord with the energy of the Nonel tube (PETN is fairly easy to initiate).

END

It's surprising to learn that the energy coming from the end of a Nonel tube will initiate PETN as stated by yourself and Contrabasso.
I was a bit of a doubting Thomas there for a while.......

Cheers,
Dann2

quicksilver - 22-3-2011 at 15:43

I would always want you to feel comfortable discussing such a thing. It IS a fairly advanced system; with limitations and directed toward a very specific modern usage. PETN is sensitive enough so that the limited shock would most likely provide a wave of enough strength to begin the train. Think of it this way: there you have finely powdered HMX + Al, it's hot and with sufficient length you have a few grains. In such a train it would make sense that it would provide enough (HMX) to begin PETN's initiation. But here we have a situation where a great expenditure is made (the shock tubing and connectors) and to what end?
It was conceived for a niche utility. A very damp environment, a limited testing area, or a need to isolate an initiation - very often (but not only) for seismic measurement. The use of earth shock measurement is very often preformed in built-up areas. The initiation of blasting in a very wet area or the need to isolate the blast has come a long way. Would it also be appropriate for a safety blast? In most areas; yes. But methane ("fire damp") may be too much to ask of it due to the heat from the aluminum.
Shock-tube systems are very expensive. The equipment for accurate earth movement, density, and stability for building is even more so. Often times Nonel and a seismic cap are the only energetic materials needed for such purposes. It was not made to be a fuse (or cord) replacement but an enhancement for a situation that occurs infrequently.

dann2 - 23-3-2011 at 14:44

There is a good read on shocktubes here:
http://www.shocktubesystems.com/drontey.htm

They say they are used extensively in mining.

http://members.tm.net/lapointe/Wire_Explosions.html

Some exploding Cu wire stuff

[Edited on 15-4-2011 by quicksilver]

Contrabasso - 1-4-2011 at 16:20

The major HE industry benefit of shocktube is that shots can be fired without the noise of surface laid det cord. Noise and vibration are serious problems for mines and quarries.

In the SFX industry the noise issue is also critical so lots of shots will be fired electrically. and det cord will be used as the effect rather than the connector. SFX also uses the flash that shocktube makes as it dets, it's certainly used as some lightning flashes on buildings.

dann2 - 13-4-2011 at 04:46

I pasted + cobbled together the following info. on EBW's. Might be useful.

http://www.filefactory.com/file/cbbe388/n/ebw.rar

Forgot to mention when you download the .rar and extract, look for a file called EBW_INFO.HTML and go from there.
View user's profile View All Posts By User U2U Member

Dann2

_____________
Please do your best not to double post. I realize this may have occurred after the time allotted for editing however.
Thanks;
(moderator)

[Edited on 15-4-2011 by quicksilver]

quicksilver - 15-4-2011 at 06:59

Remember that the blast box is no small agenda for an effective reliable EBW. Their expense commercially reflects the need for reliable cap-discharge array or a pulse transformer that also can become rather expensive. There are methods around this (to a degree). Often the use of an automotive battery & inverter provided portability (using a transportation vehicle as a starting point for power input) but depending upon the diameter and structure of the bridge-wire itself, you may be looking at much higher quality componentry than expected. You'll want repetitive reliability in that [blast-box] energy and to actually get the wire to burst; the level of energy often gets high enough to add an element of complexity to your agenda. The commercial units I have seen were very costly. They had to provide a very potent burst that could stand up to field conditions. Wire leads become an issue as length small diameter leads will provide a degree of resistance; heavier wire become impractical at a certain level. Small-scale tests are much less demanding however. One way this was solved (commercially) was to use a "coded repeater" for wire-less transmission for distance, then a shorter length of heavy wire to the blast itself.

Testing & experimentation of just the detonator itself could be accomplished with much simpler means but you see that EBW has never been an inexpensive issue. There HAVE been designs which had such a fine bridge-wire that it posed less demands on the blast box. The finer the wire the better, to a degree. But here the demands of construct of the EBW detonator was magnified in that the wire MUST be as corrosive resistant as possible; especially as it drops below 40 awg. TTBoMK nichrome was still used but cupro-nickle became to potentially weak. Pure nickle or a nickle-chrome-ferric rust resistant wire could stand up to the potential. At minimum it must be a resistance-wire was mandatory for the focus of the energy; and / or nichrome of more that one contact point had been employed. It's not an easy thing to design with a limited budget.

I mention this only because several times I have read of the use of a non-resistance specific wire composition (single thin copper strand) and the results are generally less than optimum.

[Edited on 15-4-2011 by quicksilver]

Contrabasso - 15-4-2011 at 10:01

Please exercise due caution when attempting EBW construction and use.

The origin of the EBW was in nuclear weapons.

IF you do perfect an EBW system then "the men in boots" may get to you before the mafia and either option could be unpleasant.

[Edited on 15-4-2011 by Contrabasso]

IndependentBoffin - 17-4-2011 at 08:56

Quote: Originally posted by gregxy

A figure of 10-60mJ of energy to initiate PETN on its own is meaningless unless the test circumstances are specified. You can quite happily cook and burn a lot of secondary explosives without risk of detonation.

All explosives fundamentally initiate because of heat, e.g. friction initiation occurs when crystals rub against each other, shock initiation occurs when hot spots are adiabatically created. E.g. see Bowden, F. P. and O. A. Gurton (1949). "Initiation of Solid Explosives by Impact and Friction: The Influence of Grit." Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences 198(1054): 337-349 or "Blast & Ballistic Loading of Structures." Smith, P.D. and Hetherington, J.D. ISBN 0750620242.

Of relevance is that primary explosives are particularly sensitive because they generally start to exothermically decompose before they melt whereas secondary explosives tend to endothermically melt before exothermically decomposing.

Quote:

EBW uses this type of setup, but is difficult to set up since
a very thin bridge wire is needed and the circuit design is
tricky.

The other method used to initiate secondaries is slapper detonators.

Quote:

Instead I decided to try converting the secondry explosive
into a resistive mass and passing the current directly through
it. If the resistance can be made on the order
of 10 ohms, most of the energy should be transrerred
to the explosive over a period of 1mS.
The electric field within the explosive will also help
sensitize it. In the best setup the explosive would not
be resistive but would enter "dielectric break down" just
below the applied voltage.

Do you have a citation for the sensitisation of explosives by applied electrical fields?

Quote:

My first try was with powdered aluminum
to make the ETN conductive. Unfortunately my Al powder
(325mesh from Ebay) does not conduct at all even by itself
when pressed into a tube. I think my Al is mostly
Al2O3, maybe different Al powder would work better.

If you are going for dielectric breakdown resulting in a sudden drop in circuit resistance as your switch then you are better off with a thinner sample + high voltage rather than aluminium particles. Don't forget aluminium particles increase the thermal conductivity of the aggregate. Aluminium can sensitise ammonium nitrate because typically initiation for aluminised AN/ANFO/ANNM is by shock, which tends to be across a surface. Heat is generated by adiabatic compression along a plane, and lost along a plane. For your approach you are effectively generating heat at a point while heat flux is happening over a spherical surface. So my point is that for this approach you run the risk of your large cool mass of explosives self-quenching any hot spots you make, therefore not resulting in a self-propagating detonation.

Quote:

Next I tried powdered graphite. By itself the graphite
gives a resistance of less than 10 ohms. Mixing about
1 part graphite to 4 of ETN (by volume) the device
had a resistance of 1bout 1k. Energizing with the
camera, the device gave a loud bang. However I do not
think it was a full detonation. My first device disappeared
completely (although it did not damage the board it was
taped to). A second device just blasted a hole in
the straw and left the ETN mostly untouched.

As above. A dielectric has to be an electrical insulator.

Quote:

With some refinement I think this method can be made
to work well. A metal tube to provide more confinement
would help. The loading density and amout of graphite
(or aluminum) could also be adjusted. Too little
graphite and the resistance is too high which lengthens
the pulse. Too much graphite lowers the sensitivity
of the ETN.

You may have some better luck trying to replicate proven EBW or slapper detonators, not that I discourage experimentation. At least you know it works and it is just an implementation issue to replicate the results. After that you can try your own modifications to the working setup.

Hades_Foundation - 26-4-2011 at 13:23

Slapper chip:
http://neyersoftware.com/Papers/AIAA99/BlueChipDetonator.htm

http://www.dtic.mil/ndia/2009fuze/IVAbaginski.pdf
Nice design, slapper and sparkgap switch both on the same chip.

Someone with knowledge of / experience in photo etching and related techniques could possibly develop a reliable and reproducible slapper design.

Been busy rolling and stacking capacitors with 150 meters of aluminum foil, lot of cling film and a bunch of photocopy paper, in the believe that electrolytic caps are not suited for pulse discharge needed for EBW or slapper, and the right caps are too expensive. that's a week of my life I'll never get back. :mad:

A decent numerical model of a BW circuit would help a lot, I'm working on a spreadsheet now, hoping to get an output characteristic that doesn't differ too much from published test data.

Some toughts I had:
Putting a smaller capacitor with very low ESR and inductance parallel to big electrolytic caps could improve the time response. The idea being that such cap would do initial heating of the BW with resulting higher resistance so the slower responding larger caps would deliver their energy at a more efficient moment. Or would the net result be a longer heating curve?

I considered some low resistance shunt over the BW that would disconnect suddenly, close to the point of maximum current (a fuse basically ), resulting in a very steep rise time of the BW current.

Would be nice if some mass produced micro-electronic device contained parts suitable for a slapper device, like kapton film of the right thickness. A semiconductor with the right properties to serve as the slapper is probably to much to ask for..

Found a pdf on closing a kapton switch using an extex detonation. That's almost the exact opposite of what we want.

I wonder if the spark gap could be reliably triggered by a drop in pressure. Connecting a big syringe to it, basically. A 2 mm gap will hold more than 12kV at 1 atm but only 2kV at 0.1 atm and less than 400 volts at 0.01 pressure. Would be a low tech way to avoid insulation issues with the trigger circuit and allow the use of a simple two electrode spark gap.

IndependentBoffin - 26-4-2011 at 13:54

Instead of building your own capacitors have you tried coupling a Cockcroft-Walton generator to a Marx generator?

http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_genera...

http://en.wikipedia.org/wiki/Marx_generator

You use the former circuit to generate high voltage DC, connect it to HV capacitors on a Marx generator to produce an extremely powerful electrical pulse. I've built a 20kV version at home using consumer electronics.

I do recall reading an Instructable on how to make the above as well.

Basically the principle of a slapper detonator is to dump enough energy into the explosive, quickly enough, so that its heating is effectively adiabatic and it rises to well above the exothermic decomposition temperature of the explosive, resulting in self-sustaining detonation. Usually for stable secondary explosives there are endothermic processes prior to the decomposition temperature of the explosive that desensitise it; e.g. melting (absorption of latent heat of fusion), boiling (absorption of latent heat of vapourisation), "heat sink" plasticisers, etc. The slapper detonator achieves this by sending a small flyer plate of material that strikes the explosive, resulting in near adiabatic compression around the impact plane.

So, if you want your design to work, you must focus on:
1) Power of your capacitor banks.
2) Rate of conversion of electrical energy to kinetic energy of the slapper. This is determined by the exploding foil's geometry and materials.
3) Rate of conversion of kinetic energy of the slapper to thermal energy of the secondary explosive. Stick with PETN, ground as fine as possible (porosity = hot spots for adiabatic compression = more likely to initiate).

[Edited on 26-4-2011 by IndependentBoffin]

Hades_Foundation - 26-4-2011 at 14:58

Quote: Originally posted by IndependentBoffin

Instead of building your own capacitors have you tried coupling a Cockcroft-Walton generator to a Marx generator?

http://en.wikipedia.org/wiki/Cockcroft%E2%80%93Walton_genera...

http://en.wikipedia.org/wiki/Marx_generator

Yep, I made a cockcroft multiplier. Don't think I'll need a Marx generator, I plan on using a relatively low voltage, 3 to 4kV, and I'm starting off with a single microwave oven cap at 2kV that I can load directly from some old transformers I've put in series. ( I now regret replacing the secondary from the MOV to make an improvised spot welder... )

Building caps for that kind of voltage just wasn't worth it.

watson.fawkes - 26-4-2011 at 16:52

Quote: Originally posted by IndependentBoffin

So, if you want your design to work, you must focus on:
1) Power of your capacitor banks.
2) Rate of conversion of electrical energy to kinetic energy of the slapper. This is determined by the exploding foil's geometry and materials.
3) Rate of conversion of kinetic energy of the slapper to thermal energy of the secondary explosive.

Don't forget (4) Transmission line characteristics from the power supply to the target device. There are other threads on this overall topic on this forum. To avoid the rather great heat over light in them, please ensure that you are least somewhat familiar with what a transmission line actually means in this context. Note that the voltage pulse equation on that page clearly shows the exponential decay based on distance. (Note that this is a "high frequency" approximation and doesn't apply over long periods of time when low frequencies, like DC, predominate.) Screwing up the transmission line can negate much work elsewhere.

IndependentBoffin - 26-4-2011 at 23:46

Quote: Originally posted by watson.fawkes

Yes agreed.

Try using some thick car jumper cables?

[Edited on 27-4-2011 by IndependentBoffin]

Hades_Foundation - 29-4-2011 at 05:07

Triggering of a spark gap by lowering the pressure works nicely. I can discharge a microwave oven cap charged to 1000V trough a gap of about 1 mm by simply pulling the plunger of a syringe . The 24V 3W small lightbulb placed in series flashes brightly but the filament stayed intact at first. It failed after about ten discharges.

Really like this way of triggering, no need for adjustable electrode distance, third electrode, isolation of the trigger circuit etc. and a wide voltage range (1000 - 7000 at 1mm spacing)

Tried the thinnest wire I could find as bw, but didn't do anything. Clearly not enough energy due to low resistance compared to rest of circuit and weak capacitor. Tested up to about 1600V, discharge is quite disappointing, the usual sparks when shorting directly (without the spark gap), but that tiny little wire won't burn.
Further experiments will have to wait till new caps arrive.

Simulating in a spreadsheet is too cumbersome, I'm looking into qucs now, but the help function is rudimentary to say the least. Only good manual I found covers version 1.12 in which equation defined devices were first introduced. It's now version 1.15 but the best info the qucs website has to offer is still that six year old document. That's one of the things I hate about the free open source 'movement', they mostly write documentation at their level, understandable for people with previous experience. The main motivation often seems to be providing a free alternative for a commercial product, and knowledge of that product is implicitly assumed.

On reflection, that 'good' manual I mentioned is a relative term..

Quote:

Remember that when creating a device, it is almost always mandatory to read of have a look at on how the model is done is the technical documentation. It is very to understand the limitation, and how we can correct some data if needed. The mian pity is that a lot of commercial software are quite obscure on the real model they use and their limitation ; QUCS is quite exceptionnal on this point this the complete modeling is explain theoretically in a special technical paper.

mian pity indeed...

Hades_Foundation - 4-5-2011 at 04:37

I've been reinventing the wheel, it seems.
Woelen came up with a vacuum controlled spark gap three years ago.
http://www.sciencemadness.org/talk/viewthread.php?tid=10874
And my idea of a shunt fuse over the BW to reach high current didn't go far enough.
From 'Non-shock initiation of explosives':

Quote:

As an alternative hypothesis on the mechanisms of operation of EBW detonators, Tucker suggested that the wire simply serves as a fuse that allows current to rise to a high value before the wire forms a high-density and highly resistive plasma. Formation of this plasma establishes a high voltage across the electrodes in the detonator, and spark breakdown occurs outside the plasma, through the low-density PETN.

Not sure I agree with his explanation though, I'd think the resistivity of the plasma would still be lower than that of the PETN??

(search for 'tucker ebw spark' in google books to read more)

quicksilver - 4-5-2011 at 07:36

Total deliverable joules is the goal. Remember that's "deliverable".... A thin wire at distance creates resistance. Busting a wire in the classic fashion is not that easy of a task. I have seen commercial units and they started with an inverter (from an automotive battery for portability, etc) and were the most expensive units available. Generally speaking, several issues were addressed. wireless transmission was utilized to maintain security via coded instruction set and to minimize wire over lengthy distance. Additionally, very expensive caps / diodes were part of any voltage multiplier system. It's been tempting to use quality photo-caps but they (electrolytic-type) were not dependable for continued usage. So film caps of the "Tesla Coil / HAM radio-Type" were typically seen. The diodes were protected with resistors. Units often ran into the several thousand dollar range.
See the below PDF file for details on appropriate capasitive design.

@Hades_Foundation :

{Moderator's note: Please do your best to use one post per: this helps in many ways & is to everyone's benefit. I would have edited it into one but I saw that it was a complex issue so I left it but multi-posts can be problematic. Thanks.}

Attachment: pulse_operation_film_capacitors.pdf (116kB)
This file has been downloaded 930 times

[Edited on 4-5-2011 by quicksilver]

Zelot - 4-6-2011 at 13:09

Even though it has been said in this thread that photo-flash type capacitors are not well suited for this job, I am in possession of a rather large capacitor bank that uses many of these in parallel. It has a total energy capacity of well over 200J, probably closer to 250J. I am rather sure that this will supply enough current to vaporize a (thin) wire and initiate ETN.

What types of metal do you recommend for the bridge wire? I was thinking that a very fine grade of steel wool would work well.

After thinking about this for awhile, it reminded me of this:
http://www.jamesyawn.com/ematch/index.html
Would something like this work?

I do not have any ETN to experiment with at the moment, nor have I synthesized it before, but I do intend to acquire some erythritol within the next few days.

Slightly off topic question:
Does potassium nitrate or ammonium nitrate typically work better in combination with sulfuric ("el diablo" drain cleaner) for this nitration?

quicksilver - 5-6-2011 at 06:29

Bridge wires in general are better designed with resistance and oxidation prevention in mind: that's why ni-chrome has been long used. Unshielded steel or copper as a bridge-wire is a poor idea from both a safety and performance standpoint. Hobby Rocketry has long understood the need to use the BEST bridge wire money could buy as the entire agenda eventually got down to a few millimeters of wire.....why take any chances?

When a mixed acid is the goal, the individual solid alkali nitrates have very minor efficiency differences. There IS (and has been, several) posts describing their "order" of efficiency in this regard. A search will find several posts showing a desendng order; yet this does not mean that since NaNO3 is somewhat more efficient than another, that would be the only choice. There are several that will provide a perfectly appropriate mixed acid.

edit:

I have worked with photo-flash caps for awhile and my personal issue with them is that many are electrolytic & not designed for LONG TERM usage. They DO work very well for their design but have a limited life.
While higher quality HV polypropylene caps used in HAM & Tesla Coil applications are designed for longevity and have a self-healing design that is very valuable.
I do understand that the common photo caps can be free via disposable cameras. But by using them it should be understood from the outset that the unit has a limited life-expectancy. A great deal of work and design modification can be limited thereby.

[Edited on 5-6-2011 by quicksilver]

Zelot - 7-6-2011 at 16:36

I do realize that having a bare metal (such as steel or copper wire) in contact with energetic materials is usually a 'no-no', so I was not intending to do this. I was thinking more along the lines of using some very thin gauge magnet wire (I have a spool of extra 30 AWG magnet wire laying around from my tesla coil projects), or even simply coating a thin wire with nitrocellulose lacquer to prevent contact with the ETN. Which of these options do you feel would have a better chance?

If an EBW-type fails, I suppose I could go the route of inducing some sort of arc directly through the material. If I discharged the cap bank through some sort of a step-up transformer (most likely will be hand-wound), I could probably get a few kV.

If I fail to do this, I suppose a portable marx generator would be in order. High voltage at moderately high current should do the job, and it could easily be powered by a few D or C-cell batteries. That should be portable enough for most needs.

Has anyone done any more testing meanwhile? I am quite interested in this, as it could avoid many injuries and accidents caused by dealing with primary explosives.

quicksilver - 8-6-2011 at 05:45

Your problem here is that magnet wire does not present an element of resistance.
This is very important. The technique would be for the construction of a "thinner, finer" bridge but of the same conductive properties as your leads. This can function but it's very marginal in the placement of the largest level of heat transference when compared to a resistance wire bridge.

When a ignition design is contemplated often a great deal weighs on the consistency of it's functionality..... It HAS to work the same, the first time, every time - to the expectations of the builder. The use of the resistance wire has been proven over many, many decades to be the truly reliable means at your disposal to focus the heat / energy at the point you demand it must be. The use of the "diminished area" concept for focusing heat is very marginal in reliability. admittedly it often starts house fires but as a solid reliable vehicle for focusing energy experiments have shown that sometimes alternative conductive pathways can completely eliminate it from functionality! (Classic example is alumuminized material surrounding it or the bridge wire contacting the metallic capsule; both of which negate the "choke point" concept).

My strongest suggestion is not to use that "choke-point" method of thin copper. It will never maintain consistency: that is it's main flaw. I have experimented with this subject for quite a few years.

On another related topic, if the classic "two lead" 22awg wire is available you have generally a 1 mm gap in which to work for a fairly consistent design of arc/spark utilization. In order to maintain the integrity of the insulation, you would most likely need to drop below 1-2 ma in current & at or above 5Kv and that is a very workable criteria. Cap discharge unfortunately entails larger levels of current to be an easy design for lengthy leads demanded in such a design. But pulse transformer or flyback designs may work very well! The variables will always be resistance reflected in distance: so you're forced to start at 1 or 2 ma which would be tough for the level of insulation at the box end. but that could be overcome.

[Edited on 8-6-2011 by quicksilver]

Zelot - 8-6-2011 at 21:14

The idea of using "two lead" wire is very enticing. The spacing would be the same each time, leading to consistent detonators. I think my best be for this type of detonator would be a pulse transformer with a capacitor bank input. The output would be relatively instantaneous (maybe a few ms delay), and because of the high voltage, the length of wire to the charge would not be much of an issue. This would allow one to be far away from the site of detonation for extra safety.

I found this topic that deals with a reaction between ETN and aluminum at high temperatures that leads to detonation:
http://www.sciencemadness.org/talk/viewthread.php?tid=13502

This could be a viable option indeed! My previous detonators consisted of an x-mas tree light bulb filled with a primary (namely acetone peroxide). Discharging one photo-flash capacitor through this reliably caused detonation. If instead of AP, a mix of ETN and aluminum powder could be used, this would be great! I don't think that the Al needs to be particularly small in particle size, as from what I read on the other thread (unintentional rhyme, but I'll leave it there

) it would detonate when in contact with Al foil. Shredding some foil in a blender or coffee grinder would probably be sufficient.

quicksilver - 9-6-2011 at 05:18

Leaving it here is appropriate as per the of"practical application" rules.
However I would say that any thought in this direct demands the highest level of professionalism possible and the most lengthy planning. Tungsten does function as resistance wire but the design (a light bulb) will prove to be a problem. Ideally one must have control over all aspects of any design.

Many patents have a great deal of information in this area.

[Edited on 9-6-2011 by quicksilver]

gnitseretni - 9-6-2011 at 07:04

Anyone ever tried an ignition device out of one of those Torpedo heaters? I have one and it says output is 15KV and 130mA. Plenty of juice, yes?

holmes1880 - 9-6-2011 at 07:47

Quote: Originally posted by quicksilver

Leaving it here is appropriate as per the of"practical application" rules.
However I would say that any thought in this direct demands the highest level of professionalism possible and the most lengthy planning.

I agree 100% with you. When you hear "xmas igniters", that pretty much reduces all hope of moving forward.

Zelot - 9-6-2011 at 09:54

Quote: Originally posted by gnitseretni

Anyone ever tried an ignition device out of one of those Torpedo heaters? I have one and it says output is 15KV and 130mA. Plenty of juice, yes?

That might be too much juice! You will need some heavily insulated wires to make sure it doesn't arc over before it reaches the etn.

Quote: Originally posted by holmes1880

I agree 100% with you. When you hear "xmas igniters", that pretty much reduces all hope of moving forward.

Look, all I was saying is that the bulbs they are relatively consistent in terms of a resistive heating element. I still would like to try the other methods, especially the step-up pulse transformer to apply an arc through the etn. If this doesn't work, adding some aluminum powder might sensitize it enough, as seen in the other thread.

Even if this discussion is leaning a bit on the side of practicality, isn't it worth having? It could lead to much safer ways for the hobbyist to experiment with energetic materials.

So let's steer this back from practicality. I want this thread to stay open.

[Edited on 6/9/2011 by Zelot]