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Re: A new cap failure mode?



Hi Terry,

> Original Poster: Terry Fritz <twf-at-verinet-dot-com>
> 
> Hi All,
> 
>     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.  
> 
> Comments or suggestions are welcome...
> 
>     Terry

If it *is* a problem, I'd recommend a resistance commensurate with 
tank reactance in series with the safety gap. I'd hope that Tesla caps 
are built with at least sshot ratings when operating into a short. ?

Malcolm