Re: Optimum capacitor size

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

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

At 06:37 PM 6/19/2003 -0600, you wrote:
>Original poster: "by way of Terry Fritz <teslalist-at-qwest-dot-net>" 
><Esondrmn-at-aol-dot-com>
>
>In a message dated 6/18/03 12:18:18 PM Pacific Daylight Time, 
>tesla-at-pupman-dot-com writes:
>
>
>>With an asynchronous gap, you could get great results with a value of 0.01uF
>>up to 0.04uF with no problem for a 12kV/240mA power source.  Just remember
>>to keep a safety gap on the capacitors as if you have too slow a break-rate,
>>the capacitor could charge up to some serious voltage.
>>
>>The Captain
>
>
>I agree, but it is easier on the caps if you place the safety gap across 
>the rotary gap - so when it fires, the caps are discharged through the primary.

Or, if you're worried about resonance effects with the primary inductor, 
safety gap and a current limiting resistor across the cap.  A few hundred 
ohms will limit the current to a reasonable level (say, a few hundred amps, 
peak). Unless your gap is firing continuously (and it shouldn't be!), the 
resistor rating doesn't need to be all that high.  Worst case would require 
that it be rated for the source transformer power.  Time constant will be 
negligibly small (.05 uF and 100 ohms-> time constant of 50 microseconds, 
200A peak if charged to 20 kV).  I haven't measured the inductance of 
inexpensive wirewound power resistors, but it might be low enough that it's 
not a problem..  If you use wirewounds, use two in parallel, in case one fails.