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Re: exploding wire



Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 04:33 PM 6/12/2006, you wrote:
Original poster: "Jim Mora" <jmora@xxxxxxxxxxx>

Hello All,

Slightly off topic, but has anyone used the cd .15uf caps in banks to explode wire? If so, what voltage seemed the most success, bank configuration, and damage to our great capacitors was sustained. Terry, you may be able to field this the best if you are willing to post it. I know Bert H uses mammoth caps. Are these sizes required? Please reply off list if this too far off topic.

Here's a demo of exploding wires
http://web.mit.edu/Edgerton/www/ExplodingWire.html

They use 500 uF @ 800V to zap a shortish piece of NiCr wire. With their energies, I'm not sure they're really getting an honest explosion (as in creating a shock wave).

In my experience, it takes about a kJ to get a good explosion from a one meter long wire in the AWG 32 or finer area. Both aluminum and copper wire work. I ran 5-20 uF at 10+kV.

Exploding wires is a matter of peak powers, too.

There is a definite series of qualitatively obvious phenomena. From lowest to highest energy:
Melting
Melting into droplets with sparks  (a "pop", like a fuse burning out)
Melting and flashing over like a spark(a crackle or "flash", like any old spark, eg. from a TC)
Exploding (a distinct "bang" or "crack")

Visually, they're quite different. All of them, except the explosion, appear to "propagate" along the wire, at least in a meter long segment.

in order to explode, the wire has to liquefy, then vaporize, then ionize, before the material has a chance to move around. So, you have to put a fair amount of energy into the wire, fairly quickly. You can calculate the amount of energy required to vaporize the wire pretty easily by looking up the heat of fusion and vaporization for the material.

The dyanmics are quite interesting, because the resistance of the wire rises rapidly as it heats, so getting enough current into it quickly enough requires a substantial voltage.






Thanks for all you do,
Jim Mora