Re: Spark Gap Width

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

Original poster: Mddeming-at-aol-dot-com 

In a message dated 5/25/04 3:20:49 AM Eastern Daylight Time, 
tesla-at-pupman-dot-com writes:
Original poster: "Chris Fanjoy" <zappyman-at-hotmail-dot-com>

    Perhaps this is a rather basic question, but I'm hoping someone can
enlighten this newbie. I've looked around on the web and haven't been able
to get much help.
    My specific question is, how does one determine what width of spark gap
is needed? Is there a specific guideline, such as so many mm per kilovolt?
This is for an air-cooled static gap BTW (actually several gaps in series).
    Thanks for any advice.

Hi Chris,
      For an AC powered coil, I have found a reasonable first approximation 
to be 0.5 mm/kV of rated (rms) transformer output. The precise mm/kV is 
difficult to predict. It is dependent on temperature, humidity, cleanliness 
and geometry of electrodes, altitude, barometric pressure, smog level, (and 
often moon-phase, planet alignment, size of audience, etc.etc.)
This is the quick & dirty, math-free easy way:
     Place a simple gap across your transformer without the coil tank 
circuit connected. Open the gap to where it will just not fire. Measure 
this distance. This is your critical safety gap upper limit. Your main gap 
can be set as wide as possible to give consistent operation without 
exceeding this number. In the case of a multigap, the sum of all the 
individual gaps must not exceed this limit.
     If you're into resonant rise or other run-to-destruction fetishes, 
then all bets are off.. Just go for it and use a little less gap on your 
next transformer ;^)

Hope this helps,

Matt D.