SRSG Phase Relationship

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

Original poster: "Dave Leddon by way of Terry Fritz <twftesla-at-qwest-dot-net>" <leddon-at-attbi-dot-com>

To: leddon-at-attbi-dot-com
Subject: Phase relationship

Fellow coilers,

 I'm getting close to firing up a coil with a SRSG for the first time and I
am confused about how to set the initial the phase relationship between the
line voltage and gap firing position. The SRSG is 120 bps and the tank cap
is resonant with the nst, so I need to be careful about the initial
setting. To facilitate setup I have two small magnets attached to the back
of the rotor which lie on the same radii as the two electrodes and a
stationary pick up coil which generates pulses when the magnets spin past.
I feed these reference pulses into one channel of an oscilloscope and the
output of a filament transformer into the other channel and align the peaks
of both signals by changing the position of the rotor on the motor shaft.
It occurs to me now that this might be the worst possible initial setting
because it doesn't take into account the 90 degree phase difference between
the supply voltage and the voltage in the tank capacitor.

I believe my confusion over this phase relationship stems from reading
references in the mailing list archives containing the words "adjust firing
position to the voltage peak" and making the assumption that the voltage
referenced was the line voltage and not the capacitor voltage.

To further my understanding of this timing relationship, I downloaded one
of Richie Burnett's SRSG Microsim simulation schematics and adjusted the
parameters to match my tank circuit. When I ran the simulation with the gap
configured to fire at the peak of the line voltage, the voltage in the tank
cap rapidly climbed to 400kv. But with the gap configured to fire at the
zero crossings, the voltage never rose above the original source voltage *
1.41. This pretty much confirms that I need to change the rotor phase by 90
degrees.  But the simulation also shows that precise timing of this firing
point is essential. If I adjust the firing point by more than 0.1 ms from
the zero crossing point, the simulation shows a dangerous resonant voltage
rise.  But, if I increase the firing rate from 120 to 240 bps I don't see a
resonant rise at any firing position. So maybe the best solution would be
to either double the number of electrodes or change the tank capacitance to
be something less than resonant. I'd rather not change the tank capacitance
since it comes from a single Maxwell pulse cap and it's the only suitable
cap that I have on hand.

Is there anybody in the group who can advise me on the pitfalls or
successes of running a SRSG at 120 bps with a resonant tank cap?

Thanks,
Dave
***************************************************************************