| Pages:
1
2
3 |
gregxy
Hazard to Others
Posts: 421
Registered: 26-5-2006
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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 1243 times
|
|
|
quicksilver
International Hazard
Posts: 1820
Registered: 7-9-2005
Location: Inches from the keyboard....
Member Is Offline
Mood: ~-=SWINGS=-~
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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 619 times
[Edited on 21-3-2011 by dann2]
|
|
|
gregxy
Hazard to Others
Posts: 421
Registered: 26-5-2006
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1820
Registered: 7-9-2005
Location: Inches from the keyboard....
Member Is Offline
Mood: ~-=SWINGS=-~
|
|
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
Hazard to Others
Posts: 277
Registered: 2-4-2008
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1820
Registered: 7-9-2005
Location: Inches from the keyboard....
Member Is Offline
Mood: ~-=SWINGS=-~
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1820
Registered: 7-9-2005
Location: Inches from the keyboard....
Member Is Offline
Mood: ~-=SWINGS=-~
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 277
Registered: 2-4-2008
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1523
Registered: 31-1-2007
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 1820
Registered: 7-9-2005
Location: Inches from the keyboard....
Member Is Offline
Mood: ~-=SWINGS=-~
|
|
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
Hazard to Others
Posts: 277
Registered: 2-4-2008
Member Is Offline
Mood: No Mood
|
|
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
Hazard to Others
Posts: 150
Registered: 15-4-2011
Member Is Offline
Mood: No Mood
|
|
| 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. |
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
Harmless
Posts: 23
Registered: 18-2-2011
Member Is Offline
Mood: No Mood
|
|
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. 
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
Hazard to Others
Posts: 150
Registered: 15-4-2011
Member Is Offline
Mood: No Mood
|
|
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]
I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
|
|
|
Hades_Foundation
Harmless
Posts: 23
Registered: 18-2-2011
Member Is Offline
Mood: No Mood
|
|
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
International Hazard
Posts: 2793
Registered: 16-8-2008
Member Is Offline
Mood: No Mood
|
|
| 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
Hazard to Others
Posts: 150
Registered: 15-4-2011
Member Is Offline
Mood: No Mood
|
|
| Quote: Originally posted by watson.fawkes | | 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. |
Yes agreed.
Try using some thick car jumper cables?
[Edited on 27-4-2011 by IndependentBoffin]
I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
|
|
|
Hades_Foundation
Harmless
Posts: 23
Registered: 18-2-2011
Member Is Offline
Mood: No Mood
|
|
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
Harmless
Posts: 23
Registered: 18-2-2011
Member Is Offline
Mood: No Mood
|
|
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)
|
|
|
| Pages:
1
2
3 |
![[*]](images/xpblue/default_icon.gif){kind=icon}
