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Exploding resisitors at 100 meteres

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Wolfram

Fri Jan 30 2009, 11:39PM

Registered Member #33 Joined: Sat Feb 04 2006, 01:31PM
Location: Norway
Posts: 971

If I understand the first post right, he is not just looking for a simple electric igniter for flammable materials, but we shouldn't go into detail about the practical use, as we want to stick to the forum rules.

From what I've read about the application, you need a very fast pulse. Some people have had success with electrolytics in certain cases, but I would not recommend it. I think your best bet would be a microwave oven capacitor charged to between 2kv and 5kv. 100m of wire is a lot, and it is a good idea to minimize the inductance. Speaker wire might work, if it stands up to the voltage, but coax would be the best if you can find 100m of it for an affordable price.

Stay safe.

Anders M.

ConKbot of Doom

Sat Jan 31 2009, 12:32AM

Registered Member #509 Joined: Sat Feb 10 2007, 07:02AM
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Posts: 329

Just for reference, Ive used an exploding bridgewire firing system to detonate blasting caps, the system used a 1uf (I believe) capacitor charged to 4 KV and used a pair of leads (like speaker wire, but high voltage insulation) for up to 30 yards, or a custom high voltage coax lead for up to 100 yards. The detonating unit used a triggered sparkgap to fire the cap into the circuit, The main issue with that distance was inductance, not resistance.

Mattski

Wed Feb 04 2009, 06:12AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

If you want something to explode, I seem to recall seeing igniters made with nichrome wire and then coated with an explosive material. The nichrome wire will make a resistor, but without the ceramic former and lacquer coating, so it will heat up something else to the ignition point easier. DIY rocketry sites are good resources for that sort of material. The usual safety precautions apply.

As mentioned by others you need low inductance to get a fast rise time in your device. Speaker wire has two parallel conductors closely spaced which minimizes inductance, twisting the two wires together should be even better. Coaxial wire would be about the best option, also most expensive.

And to answer your safety question, 82J is very dangerous. Certainly much more than enough to kill you, depending on the current path through your body. A nonfatal shock would still be remarkably painful, and it would do some serious damage not the least of which would be serious burns on the current entry and exit points.

I would recommend sizing the bleed resistor to discharge the cap within 1 minute max. The faster that time is trades off how big your power supply must be, and how much dissipation your bleeder resistor must handle, so the decision is really just up to you about how safe it will be versus how cheap and easy.

Dave Marshall

Wed Feb 04 2009, 08:27PM

Registered Member #16 Joined: Thu Feb 02 2006, 02:22PM
Location: New Wilmington, PA
Posts: 554

Just a friendly reminder to keep things squeaky clean in this thread folks. It is being watched closely by board moderators and will be closed if it goes astray.

That said, a favorite entry on my "stupid things to do when bored" list was cutting off the end of a long extension cord, connecting the wires to the leads of smallish 6-30v capacitors (The 1000uF 6.3v caps from dead PC motherboards were always a favorite) and plugging the cord in to mains. The resulting bang, shower of sparks, and cloud of smoke and confetti were always good for a laugh.

Dave

aonomus

Wed Feb 04 2009, 09:44PM

Registered Member #1497 Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801

Similar to Dave Marshall, when I get my 3.8kJ bank done, I will likely discharge my cap bank through a series inductor (current limiting) and into a SMD tantalum... in reverse.

That should be good for a nice poof. Is tantalum toxic? :D

rp181

Wed Feb 04 2009, 11:35PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

it might not be toxic, but it never does any good to breathe in smoke. Over voltage lyctics is fun, like a smoke bomb.

LutzH

Fri Feb 06 2009, 10:02PM

Registered Member #1721 Joined: Sat Sept 27 2008, 08:44PM
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Posts: 136

Just one more note on the subject:

I think an exploding wire might be more fun, what if the wire were made out of a pyrophoric metal like Magnesium, or Zirconium?

I thought about this idea to pump a solid state laser, by putting a thin Zirconium wire in a pure O2 filled tube, with a "blow out cork" at one end, so that it does not destroy your laser rod. I suppose a long thin piece of foil would work also, like in a "Slapper Detonator" except instead of initiating an explosive I would like to configure it to provide a massive pulse of visible light.

I read a few years back about a Nd:Glass laser which was pumped by off the shelf zirconium wool camera flash bars. They got over 50 Joules in a 5-10mS long laser pulse. This does go a long way to solve the energy storage problem for high power portable lasers :)

Scavies430

Sun Feb 08 2009, 02:28PM

Registered Member #1924 Joined: Sun Jan 11 2009, 09:30PM
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Posts: 12

Hey wouldn't a different capacitor to discharge into be just as good at exploding?

Jamil merali

Thu Feb 19 2009, 03:08AM

Registered Member #1577 Joined: Sun Jul 06 2008, 05:16PM
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Posts: 16

put it into a led in reverse

Cypriotica

Tue Mar 03 2009, 03:43PM

Registered Member #1811 Joined: Sat Nov 15 2008, 11:52AM
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Posts: 14

When i was 13 i used to put a towel and snorkel on my head, wear a coat and gloves and use mains voltage with 2 long metal pins with insulated handles attached on various electronic circuits... just try it around the circuit board and be careful of the caps =) This is also fine with 12 volts

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