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Re: A new cap failure mode?
Hello Terry, all
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Friday, February 05, 1999 6:28 AM
Subject: A new cap failure mode?
>Original Poster: Terry Fritz <twf-at-verinet-dot-com>
> In an off list discussion, a topic came up that I have not seen before but
>I always assumed may be a factor in capacitor failure.
> When one places a nice safety gap across a capacitor, and it is firing for
>any reason, what is the current in the discharge pulse? Since Tesla caps
>are designed to be very low inductance and low resistance, there is very
>little limiting the current when the safety gap fires. If a cap is charged
>to say 20kV and the resistance of the mess is say 0.5 ohm - we get 40000
>amps!! That is enough to do some real internal damage to any capacitor.
>The suggestion comes up that perhaps a safety gap placed directly across a
>primary cap needs a little resistance in the circuit to keep this current
>to a "safe" level.
Hmm, this is a very interesting aspect. I had never thought of this before.
Maybe because I didnīt need to, yet. I havenīt used any kind of safety
gap across the caps. I am always testing to see how far I can push it. :o)!
The idea of a resistor in series with the cap gap posses the problem of
needing a high voltage resistor. However, they should be easy to make.
Taking a few inches of nichrome wire and winding a few turns on a plastic
former should do the trick. You could immerse this resistor in epoxy to hold
the wire in place and increase the voltage capability. Cost shouldnīt be a
problem, because you only need a small length of wire. The voltage drop
(I^2*R losses) across the resistor should not be a problem either, because
the neccessary resistance doesnīt need to be very large (a few ohms or
even less should be sufficient). As they gaps (are not supposed to) fire
continuesly, the current capabilty of the wire in epoxy shouldnīt be a
problem either. You might not even need nichrome wire. Maybe a
few (more) turns of thinner copper or steel wire could do the trick.
As you have the necessary equipment (fiber optics probes), why not give
it a try and let us know?
Coiler ideas and greets from germany,
Reinhard