Interesting idea. If this is true then it should not be necessary to set the firing phase for a 3600 RPM SRSG for 240 BPS. Any phase setting is as good as another. All you really need is a synchronous motor.
The reason that I went with 240 BPS instead of 120 BPS was to provide some additional over-voltage protection to the transformer in case a firing point was missed. I have a protection gap but this was just another level of protection. It would be a trivial operation for me to switch to 120 BPS if it would make a difference in spark length. All I would have to do is remove 2 flying electrodes. I am not sure it would help much since JAVATC says that my caps already charge to 88% just prior to each firing point with 240 BPS. Thoughts?
Steve
----- Original Message -----
From: "Futuret via Tesla" <tesla@xxxxxxxxxx>
To: tesla@xxxxxxxxxx
Sent: Tuesday, March 27, 2018 6:23:32 PM
Subject: Re: [TCML] Unexpected RSG phase shifter behavior
Steve,
I've noticed this also for 240 bps systems. It seems that as
the phase is shifted, the capacitor charges to varying degrees
during the 2 times that it charges along the 60Hz AC cycle.
If the phase is shifted far enough, the system fires only at
120 bps but each "bang size" is larger. The result is basically
the same power throughput in any phase position. If it's running
at 240 bps, and if the cap charges more in the 1st charge event
along the AC half cycle, then it charges less during the 2nd charge
event along the AC half cycle. Conversely if the phase is adjusted
so the capacitor changes less during the 1st charge event, then
it charges more during the 2nd charge event. This can all be
seen on an oscilloscope as the phase is adjusted during coil
operation. It's possible to hear the sound change as the system
varies from 120 to 240 bps.
John
-----Original Message-----
From: Steve White <steve.white1@xxxxxxxxx>
To: Tesla Coil List <tesla@xxxxxxxxxx>
Sent: Tue, Mar 27, 2018 6:03 pm
Subject: [TCML] Unexpected RSG phase shifter behavior
I have had my big SGTC running for about 9 months now. Here are the salient specs:
* 8.6" x 39" secondary
* 9" x 30" top load
* 45 nF of primary circuit capacitance
* RSG with 4 rotating electrodes and 2 stationary electrodes, 3600 RPM, 240 breaks per second (4 per 60 Hz cycle at 0, 90, 180, and 270 degrees)
* Pole pig as power source
* 4800 watt wall power
* Maximum spark length is about 8 feet
I also built an electrical phase shifter, as others have, based on a variac and capacitors. I confirmed with my oscilloscope and an optical sensor that I can get about 0 to 90 degrees of phase shift by turning the variac knob. Before I added the phase shifter, I used an optical sensor and oscilloscope to accurately set the firing points at 0, 90, 180, and 270 degrees of each 60 Hz cycle.
My question concerns the apparent non-effect of the phase shifter on spark length. With the coil running, as I adjust the phase shift, I see no apparent change in the spark length. Does anyone have any thoughts as to why this would be? I am perfectly satisfied with the coil's performance, I just can't explain the apparent non-effect of the phase shifter.
Steve
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