Re: spark gap spacing

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

Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jeremiah,

When you place a capacitor across an NST, it will resonant and combination can
produce very high voltages.  Maybe 5 times the NST rated voltage!  Left
unchecked, this very high voltage (and high current too) will usually damage
the NST.  However your NST sounds really strong and the MMC was the first to
go.

Assuming the MMC cap arced at 2.5 times it's rated voltage, you were probably
hitting over 30,000 volts when the capacitor snapped.

I think something else was wrong or something was not tuned right that caused
the poor performance.  Widening the gap is a common "fix" but usually damages
something.  In this case, the NST survived and the MMC is probably fine too.  A
cracked case is just from the energy being released and it will probably
self-heal and be fine unless it is obviously destroyed or smokes a lot when run
again.  You can probably replace that cap if you have more without worrying
about the rest of them.

You should set the gap at the proper voltage.  With "only" the gap connected to
the NST the output voltage will be the NSTs rated voltage.  You can then set
the gap as wide as you can while it still fires consistently.  Then it will be
set to the rated output voltage of your NST.  It should be left at that spot at
all times.

Then try adjusting the primary tap location to get the best sparks.  With a
little fiddling, you should be able to get the sparks you want.

Cheers,

        Terry


At 09:26 PM 6/8/2001 -0500, you wrote: 
>
> Hi,
> I was wanting to know how far you should set your gap?  Today i was doing
> some testing and i set my gap real close together and it was a very poor
> performance.  I noticed the more i opened up the gap the better the
> performance.  When i opened it up all the way, and i was turning up the
> variac it finally started arcing at 11.5 KV then one of the capacitors on my
> MMC blew up.  It didn't actually explode but part of the insulation popped
> off, it was kind of weird.  Why did that happen in the first place?  The caps
> i'm using are 10 .068uF 1.25 KV and the gap is an inch wide at full open.
> Thanks
> Jeremiah