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Author: Subject: Direct electrical initiation of secondary
quicksilver
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[*] posted on 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 371 times



[Edited on 4-5-2011 by quicksilver]




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Zelot
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[*] posted on 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?




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quicksilver
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[*] posted on 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]




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[*] posted on 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.




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[*] posted on 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]




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[*] posted on 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 :D) it would detonate when in contact with Al foil. Shredding some foil in a blender or coffee grinder would probably be sufficient.




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[*] posted on 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]




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[*] posted on 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?
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[*] posted on 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.
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[*] posted on 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]




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