Re: Spark Gap Questions

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Hollmike-at-aol-dot-com>

Hi CJ,
    First, setting the gap spacing wider than the transformer can breach on 
it's own is a bad idea!    This will surey burn up your transformer.  I did a 
study using a high pot tester( this is meant to test capacitor standoff 
voltage and leakage).  I set a spark gap to fire at about 8kV.   When the 
spark gap is running, the voltage would drop to about 3kV.   I then hooked up 
a capacitor across the gap and turned it on again.  The firing voltage 
remained up near 8kV in this case.  Had I placed an inductor in series with 
the cap,  it would be essentially the same as a tank circuit, but it would 
operate at a different frequency than just the cap and the parasitic 
inductance of the circuit itself.  The point is that the firing voltage 
appears much higher across the gap when a cap is placed in the circuit.  
    Now, to get back to the point,  if you set your gap so that it does not 
fire at the transformer's peak voltage(9kV/.7071 = 12.7kV) or well below 
that,  then your primary system will build up even higher voltage due to the 
resonant rise.  This will surely kill your transformer.   
    I have seen suggested total (static) gap spacing for a 15kV nst be no 
more than .25 inches to insure safety for your transformer(s).   I would 
suggest starting off with a total spacing of 9/15ths of that, or about 0.15 
inches.  You can then get the tuning and all correct before adjusting the gap 
any wider.  The safety gap should be slightly wider so it does not fire 
continuously, but should fire if the main gaps fails to for any reason.  Of 
course, this all depends on the spark gap electrode geometry.  The larger the 
diameter of the gap electrodes(spheres or pipe sections, eg.), the closer the 
spacing should be.  If using a multiple static gap,  you should short out 
several at first and experiment to find the optimum number of gaps.
   As for rotary gaps,  I have little experience with them, but I would guess 
that  you want the closest spacing possible, but keeping them far enough 
apart to prevent them from hitting while running.  Many motors have a bit of 
play in the shaft which might allow the rotary electrodes to collide with the 
stationary ones.
Hope this helps,
Mike

<< 
 I have long been under the impression that the main spark gap should have a
 larger space then the transformer(s) can breach on its(their) own, but that 
the
 combined power of the transformers and the capacitor(s) can break.  Is this 
the
 case only when using static gaps? In a RSG what is the "ideal" spacing 
between
 the flying electrodes and the stationary ones. If this depends on the rest of
 the coil, I will be using 9kv 120 ma and a .03 uf single cap. Also, should 
the
 safety gaps have a bigger gap than the ones in the main gap or a smaller
 spacing? (or does this also depend on the type of main spark gap). 
  
 Thanks,
 CJ Moore >>