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RE: NST Safety Gap Question.



> -----Original Message-----
> From: Tesla List [mailto:tesla-at-pupman-dot-com]
> Sent: Tuesday, April 18, 2000 7:29 PM
> To: tesla-at-pupman-dot-com
> Subject: Re: NST Safety Gap Question.
>
>
> Original Poster: FutureT-at-aol-dot-com
>
> In a message dated 4/17/00 10:53:58 PM Pacific Daylight Time,
> tesla-at-pupman-dot-com writes:
>
> >
> >  Greetings All,
> >
> >  I picked up a second 9kv-at-30ma NST and decided that
> >  I now will definitely need a safety gap.  So I
> >  hooked one up and paralleled the NST's.  The gap
> >  constantly fired, it did not fire when connected
> >  up to one NST directly.  So I doubled the spacing
> >  of the gap and then it still fired often.
> >
>
> Hi Bill,
>
> It sounds to me that what is happening here is that when you added
> the second NST, it made the system resonant charging sized, so
> you're getting a lot more voltage build up due to resonant charging.
> This can be "fixed" by using a larger capacitor, which will again
> reduce the voltage, but keep the power input and spark length
> the same.  However a system with a larger capacitor often works
> best with a sync gap.  Matched (resonant) systems also often work
> best with a sync gap for that matter.
>
> You can of course run the system as it is (resonant charging mode),
> but the NST's will be voltage-stressed more than in LTR mode.  I used
> the resonant mode for my TC's for years with no problems, however
> others on the list have had NST failures.  And many on the list
> are strongly "anti-reso" for NST use because of the dangers of voltage
> stress failures of the NST's.
>
> I suspect (but cannot prove), that lower voltage NST's (7.5kV, 9kV, 12kV),
> NST's can tolerate reso-mode better than 15kV NST's.  Still, it
> is probably
> safer to run in LTR mode in all cases using NST's.  (nst's are
> soooo fragile,
> and OBIT's are even worse).
>
> Regarding the safety gap, if you keep the system as is, the only thing
> you can do is to set the safety gap wide enough so it rarely
> fires.  If you
> narrow the safely gap, the output sparks will weaken, since you'll have
> to narrow your static gap too.  BTW, when I use a sync gap on my TC,
> I'm able to set the safety gap smaller than when I use a static gap.
>
> Running with wide safety gaps, it's more important to use elaborate
> safety filters, etc on the NST output; resistors, caps to ground, etc.
> These will reduce the spark output.  I've never used the elaborate safety
> systems, I only use safety gaps with my NST's.
>
> Cheers,
> John Freau
>
>

Hi John And All,

Many thanks for the elaborate discussion on the safety gap issue
I was having.  You may have nailed it, because I tried both
12nf and 16nf.  One below resonance and the other almost at
resonance.  However I have to admit that I am a little confused
now though because, my previous understanding was that a LTR cap
and tranny match would cause higher voltages.  Maybe that is with
a static gap as opposed to a SRSG, of which I only currently have
a SG.

My safety gap is in the shape of a peace sign, or the character
'Y'.  The two high voltage leads go into the top of the 'Y' and
the ground was connected to the bottom leg.  This might have a
lot to do with it too I am supposing as well.

Cheers,
Bill Parn