RE: Ed Wingate's Teslathon (async RSG & NST's)

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

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

Hi Ed:

I too have often wondered about the origins of advising against the use
of async rotaries with NST's.  I've not been able to simulate nor think
of a scenario that would cause a hazardous voltage to occur, as long as
a gap fires at least once per mains half-cycle.  The oft-cited rationale
is that the more fragile NST's can't stand high break rates, but this
seems backwards to me.  Higher break rates, at least with NST's, imply
smaller bangs (which shouldn't be more stressful to the NST in any
case).  More importantly, higher break rates would guarantee that the
cap is discharged at least once per mains half-cycle.  It is conceivable
that at low break rates, gap presentations may occur at or near
zero-crossings and not fire, permitting mains resonant rise across
half-cycles.  Since async gaps are typically used with a variable speed
control, if the speed was set below 120 BPS, there would be problems.

What is the low-end of your BPS speed control?  I would think that as
long as it's "significantly" above 120 BPS, there should be no danger,
but I'd bet there's nothing preventing one from turning it all the way
down.  A properly set safety gap across the RSG should protect things
regardless, although this is difficult to accurately set.

Perhaps it's simply easier to say "don't use async RSG's with NST's",
than it is to say "don't adjust your BPS to less than some TBD number"?

Gary Lau
MA, USA

 > Original poster: "Edward Wingate" <ewing7-at-rochester.rr-dot-com>

<snip>

 > P.S. I wonder how many people noticed that my new bipolar coil was
 > running an NST along with an asynchronous rotary gap? :^o
 >