I guess if the caps are charging to one polarity then switching and
charging to the other polarity before firing then that might not be
good. I guess that arrangement should be avoided. The reversal
damage depends a lot on the voltage rating of the capacitors too.
..... How close to the max spec voltage they are charging up to.
If the life of the caps is reduced from 100 years to 30 years, things
might still be OK?
John
-----Original Message-----
From: Steve White <steve.white1@xxxxxxxxx>
To: Futuret <futuret@xxxxxxx>; Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wed, Mar 28, 2018 12:19 am
Subject: Re: [TCML] Unexpected RSG phase shifter behavior
John,
After giving this some more thought, it occurs to me that if I shifted the firing points worst-case to 45, 135, 225, and 270 degrees that the 45 and 225 degree firing points would be very bad for my capacitors. At these 2 points it appears that this would cause a 100% voltage reversal on the capacitors as the charging switches polarity at the zero-crossing points of the 60 Hz sine wave. Since I use Maxwell energy discharge capacitors with about a 20% voltage reversal spec, this doesn't sound good for the life of my capacitors. 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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