RE: Hmmmm...(was CDE 942c20p15k Group buy)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Lau, Gary" <gary.lau-at-hp-dot-com> 

I think we all agree on two points:
1) Over-volting a pulse cap by having no safety mechanism in place is a
bad thing.
2) Permitting a tens-of-thousand Amp discharge is worse than not
permitting it.  How frequently one may do this before damage occurs is
unclear.

Can we not agree that both bad things may be avoided by placing the
safety gap in parallel with the main gap, rather than across the cap?
Prior to a gap's firing, the gap voltage is identical to the cap
voltage, so either configuration is equally effective at clamping an
over-voltage condition.  But by having the safety in parallel with the
main gap, the discharge current is limited by the primary inductance.

Regards, Gary Lau

 >Original poster: Edward Wingate <ewing7-at-rochester.rr-dot-com>
 >
 >Tesla list wrote:
 >>
 >> Original poster: Mark Broker <mbroker-at-thegeekgroup-dot-org>
 >>
 >> By directly shorting a charged pulse-duty capacitor, severe stresses
are
 >> imposed as tens of thousands of instantaneous amperes are flowing.
If you
 >> feel absolutely compelled to place a safety gap across the capacitor,
you
 >> should also place a high voltage power resistor in series with the
gap.  To
 >> do otherwise could have equally detrimental effects on your caps as
 >> overvoltage.

 >Mark,
 >
 >Not quite true. Just ONE voltage spike of sufficient amplitude will
take
 >out a pulse cap! A safety gap firing a few times isn't likely to cause
 >any damage to a properly speced and built pulse cap. At least that's
 >been my experience and I've been running directly wired safety gaps
 >across the caps on my coils since 1991 without causing any damage. Of
 >course, if the coil is tuned properly, the safety gaps never fire
 >anyway. If the gap does fire in operation, you stop and find out what's
 >wrong. Equally detrimental? I don't think so.
 >
 >Ed Wingate RATCB