Re: need some capacitor help

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Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>

Hi Russ,

A 9000 Vrms NST will have a peak voltage of 9000 x SQRT(2) = 
12700V.  That voltage will arc about 1/2 inch between sharp points in 
air and maybe a little more along a surface.  So if the arc over 
areas are less than say 3/4 inch you might want to increase the 
distance or stick some plastic in there.  If you are easily arcing 
longer than that, the voltage might be way to high.

If your NST is 30mA, it has a resonance at 8.8nF which should be 
avoided or the voltage can resonant up way too high and damage the 
caps or NST.  You value is 6.8nF which "might" be close enough to do 
that with the 30mA NST.  In that case, you might be getting very 
excessive voltages on the caps and NST.  The solution there is to go 
to a "LTR" cap size which as far safer:

9kV 30mA = 13.3nF
9kV 60mA = 26.5nF

Note: 1nf  = 1000pF = 0.001uF

The higher load of the bigger cap will keep the voltage down to the 
rating.  You can add more caps in parallel if needed.

You could also set the main gap close enough that it fires there 
instead of across the cap.  But the best solution is more capacitance.

Try not to let it short across the cap much, the current is super 
high and it might hurt the caps.

Your 20kV caps should be fine as far as voltage goes.  When you get 
it running be careful if they start to get too warm though.

Cheers,

        Terry


At 12:45 PM 11/13/2006, you wrote:


> This is my first coil and am having some problems with my capacitors 
> i have 10 20kv 680pf doorknob caps. i fitted them between 2 sheets 
> of 1/4 inch plexiglass and had them all hooked up in parrallell. 
> powering with a 9000 volt nst i had really bad sparking everywhere. 
> what would be my best set up with theeses caps is 20kv caps enogh or 
> should i put like 2 in series.
> thanks for the help
> Russ