Re: Spark-Gap Voltages

["Jim Lux" <jimlux-at-jpl.nasa.gov> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)]

> 
> Original poster: "Barton B. Anderson" <tesla123-at-pacbell-dot-net> 
> 
> Assuming Vp of 20kv at the gap is a typical voltage for us. According to
> the table, for a 2.5cm sphere (~ 1 inch) the gap voltage is .58cm (~.23
> inch). A needle point at 20kV is 1.75cm (~.69 inch). This table seems to
> reflect static gaps well, but does a rotary gap apply? 

Not really, for the reasons that you describe below..
> 
> I typically run a .008 inch gap (total). Since a rotary gap is aligned
only
> during specified breaks (bps), it shouldn't matter what the gap spacing
is,
> as long as it is set close enough to arc and far enough apart to not come
> in contact electrodes. It appears to me that changing the gap will only
set
> when it fires as the electrodes align. 

Exactly... changing the gap will change several things:
1) The "on" voltage drop across the gap after it strikes
2) When it fires and quenches.. Smaller gap would imply longer dwell... but
I think that rotational
speed will have more effect on this.  For a 20 cm diameter (8 inch) rotor
spinning at 1800 RPM (=30 rps) the speed of the gap, roughly, will be 18
meters/second. In 1/120th second this is about 15-16 cm.  A change in the
total gap of, say, .033 cm (roughly = 1 kV) will only take about half a
degree of phase (60 Hz)...
> 
> Does anyone disagree with this? (or agree), 
> 
> Thanks, 
> Bart
> 
>