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400 Joule exploding wire problem

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Fusion

Sun Feb 11 2007, 06:46PM

Registered Member #354 Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55

I added a 6000uF 400V electrolitic to my 100 joule capacitor bank in order to improve exploding wire and I had following problem:
wire dissapeared and no spark appear. It was a lot more interesting with 100 Joule with lots os spark. Capacitor did not lost any voltage (Vini=331V, Vend=322V)
How can I improve it?
Wire was 0.1mm diameter and 10mm long.

Dr. Shark

Sun Feb 11 2007, 08:14PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I would say that maybe your wire is not exploding (ionizing) at all, but it is just breaking, possibly due to electromagnetic forces. I suggest trying a bigger wire, as 0,1mm is not really a lot of metal to take the discharge.

Fusion

Sun Feb 11 2007, 10:00PM

Registered Member #354 Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55

May be.
What about capacitor, is good for exploding wire? I would buy lots of them by tomorrow for making a 10kjoule bank.

Tesladownunder

Sun Feb 11 2007, 10:03PM

Registered Member #10 Joined: Thu Feb 02 2006, 09:45AM
Location: Bunbury, Australia
Posts: 1424

Dr Resonance says about 2kJ per foot for exploding wire, and that is about right using pulse caps which discharge in perhaps 30us.
With electrolytics discharging in 1000us you just aren't going to get that effect.

The first shot is about 2kJ and is toned down with a series inductor. Without it the flash appears to be 1 foot across in the same lighting.

Peter

1171231409 10 FT20532 Pulsecapexplodingwire35g2kjinductor

Bjørn

Sun Feb 11 2007, 10:16PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

The amount of energy contained in a capacitor does not say much about how well they work for exploding wires. The current they can deliver is much more important.

You already have enough capacitors to kill yourself several times. Take some time to learn about capacitors and electricity in general before you start playing with capacitors that are extremely dangerous.

http://wiki.4hv.org/index.php/Capacitor
http://wiki.4hv.org/index.php/Electrical_Safety

Fusion

Sun Feb 11 2007, 10:44PM

Registered Member #354 Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55

I am in the design phase. About safety I think all caps are safe if they are charged to 0 volts, so the system will advise if caps are charged. The capacitor bank will be discharged in few seconds before access them.

I measured 3.5 milliohms of the whole circuit including cap, bars and the switch, but I do not know about inductance.
I would like reduce to minimum the wire length, with 2kJ/ft, I would need a 6 feet wire

Tesladownunder wrote ...

Dr Resonance says about 2kJ per foot for exploding wire, and that is about right using pulse caps which discharge in perhaps 30us.
With electrolytics discharging in 1000us you just aren't going to get that effect.

The first shot is about 2kJ and is toned down with a series inductor. Without it the flash appears to be 1 foot across in the same lighting.

Resonance is: w^2=1/LC,, so if I would use less capacitance and higher voltage, resonance frequency would be the same, but I would not know if the wire would dissapear before catching more energy.

Inductance of a wire is (SI units): 0.0000002*L*(LN(4*L/D)-0.75) were L and D are length and diameters in meters. Inductance is in Henrys.

If I set a series inductor, a lot more energy would be stored at the inductor instead at the wire.

[Edit: Fixed double post]

Dr. Shark

Mon Feb 12 2007, 09:56AM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

If you get a good deal on the capacitors go ahead and buy them, electrolytics of this kind are useful for a lot of things.

I disagree with Peter about the necessity of pulse caps for exploding wires: Of course no z-pinch and no hard x-rays will be produced

but for a loud bang and a lot of sparks electrolytics are plenty.

I understood the policy about safety here was not to get involved in those issues at all, but since it came up: IMHO 400V electrolytics charged to rectified mains voltage is far safer than say a MOT or a high power Marzzilli flyback. 300V is just not enough to get seriously electrocuted.

Fusion

Mon Feb 12 2007, 02:51PM

Registered Member #354 Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55

After reading all I will shift to buy 390uF x 400V caps, thanks everybody
As long I bought 10x6000uF, I will make another low voltage (1200V) cap bank

I will try soft (no hard) X rays and z-pinch and perhaps gamma rays, but I do not know measure them (perhaps with scintillators)

With my 100 joule bank I measured 4-7MW UV rays after passing through thick glass. I had to put UV sensor far away with a 100ohm sensing resistor without amplifier

Dr. Shark

Mon Feb 12 2007, 03:50PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

I would favour the 6000uf caps, they are really useful for lots of things. I'd connect them im parallel though, since this gives you a reduced series resistance and inductance.

z-pinch is in a different league though, you need some serious pulse capacitors for that. Figure at least 10kV and a couple of kJ, and you wont get away with caps that have not been designed for this exact purpose.

Your numbers seem "a bit" off, assuming a discharge time of 1ms, 100J should only give a peak power of 100kW. Maybe 1% of that gets converted to UV, i.e. 1kW, of which only 1W or less is going to hit your detector.
Well, let's not argue about 10^6 orders of magnitude

Fusion

Mon Feb 12 2007, 05:54PM

Registered Member #354 Joined: Thu Mar 30 2006, 10:12AM
Location:
Posts: 55

Your numbers and mine are the same:
Peak power was 50kA*340V=17MW, but only during less than 1us, so received power was in the 1% range.
I measured that only during switching on, after that no more UV was generated, so as less farads and higher voltage may have better results.
UV was modulated to 100Mhz that may be similar to resonance of the wire.
I think UV or X ray is generated when fast electrons fall to vacuum during wire explosion, then as there is not return path they spin at high speed around copper atoms throwing exceed energy as UV/X.
So perhaps it would be better to have very low capacitor bank and switch inductance with respect wire inductance.
I simulated wire inductance by using "fasthenry" simulator (I recommend it, is free) and it seems that is better use straigh and thin wires for having more inductance every copper gram.

The problem of wire dissapear is due magnetic force can not hold copper atoms, perhaps due delay of magnetic field with respect atom blast

I have not pulse caps

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