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Re: exploding wire



Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>

What was your bank inductance? Mine is 200nH for 3 pulse caps with a 6 inch wire shorted across the output and a capacitance of 215uF measured by the ring frequency of 25kHz. Wire length varies for each cap is 21, 25 and 30 inches for the 3 caps. Individual nameplate inductance is 80 + 40 + 40nH = 160nH. I haven't tested the currents with exploding wires yet but expect them to be in the order of 50 - 100kA based on experiences with measuring can crusher currents. I did build a coaxial shunt to measure currents noninductively but the inductance still seemed to be the major issue although I wasn't aiming to have too much resistance.

Peter
http://tesladownunder.com

Original poster: Gomez Addams <gomezaddams@xxxxxxxxx>
On Jun 13, 2006, at 5:25 PM, Tesla list wrote:
..... When I still had my 5kJ / 50kV ultra-fast capacitor bank, I found very
marked differences in the nature of the explosion at different energy
levels. .... Even though my new bank has 18kJ of total energy, it's only 10kV and
the capacitors, while also low-inductance pulse caps, are more like
the Aerovox and Maxwell caps most other amateurs are using today -
low inductance, but not ultra-low inductance.  As a result, I wonder
whether I'll be able to achieve as fast rise times as I did with the
old bank.

PS: exploding wire experiments are VERY hard on pulse capacitors.
I've been considering building a low-self-inductance power resistor
from copper pipe (using a stainless steel rod for the resistive
element) to try to damp some of the high frequency oscillations
(voltage reversal) which are the most harmful to pulse caps.  The
trick is to achieve near-critical damping without drastically
harming rise time or peak current.

Somewhere around here I've got a white paper on the design and
construction of such a resistor designed to pass hundreds of
kilo-amps and to absorb peak power levels on the order of tens of
megawatts without harm.

 - Bill "Gomez" Lemieux