[Prev][Next][Index][Thread]
Re: NST Safety Gap Question.
In a message dated 4/17/00 10:53:58 PM Pacific Daylight Time,
tesla@pupman.com writes:
>
> Greetings All,
>
> I picked up a second 9kv@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