Re: A new cap failure mode?

To: tesla-at-pupman-dot-com
Subject: Re: A new cap failure mode?
From: Mark Finnis <mefinnis-at-medicine.adelaide.edu.au> (by way of Terry Fritz <twf-at-verinet-dot-com>)
Date: Sat, 06 Feb 1999 07:04:33 -0700
Approved: twf-at-verinet-dot-com

G'Day from down-under .......

At 20:18 4/02/99 -0700, Terry Fritz wrote:

>	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.  

To a non-EE trained hacker, there would appear to be some merit in this !!
 Perhaps the internal inductance of a rolled cap is actually a good thing,
providing ESR is low.

Obvious response is the safety gap should be in parallel with the main gap.
 Something which has been suggested before by the likes of Malcolm for the
use of async-RSGs with neons.  (long thread on this late last year)

Surely no point with a static gap system.  If there is enough V, then the
gap with the lowest breakdown V will fire.  I think we are really talking
about RSGs here, where there the gap may not fire at each presentation.

The RSG+SG would potentially improve performance, as according to Greg even
the "whimp impulses" can be seen to maintain the ion channel.  This would
be preferrable to some other limiting R element.  Why take the energy from
the cap anywhere but into the coil pair - ie. why use some other resistance
which will divert energy.

I'm building a new RSG at present and I think I just decided to incorporate
a parallel static safety gap (I have some tungsten left over !)      ;-)

What say the learned ones  ???

cheers

Mark

http://www.cobweb-dot-com.au/~dkfinnis