Re: SRSG Phase Relationship

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

Original poster: "Sundog by way of Terry Fritz <twftesla-at-qwest-dot-net>" <sundog-at-timeship-dot-net>

Hi Dave,
         A#1 most-important-rule-you'll-ever-find - Set the safety gap, and 
*leave it!*.  This will help protect against resonant rise.  I phase my 
SRSG's using the old fashioned "tape and flourescent" method. I adjust the 
SRSG so the middle of the white "band" is lined up with the electrodes and 
bump the power (after tuning the coil with a static gap and adding a 
breakout).  If the firing is not smooth or the safety fires, I retard the 
SRSG a bit.  I used to use a nifty little IR LED and a comparator with a 
green LED on the disc before mounting the electrodes in it.  The IR LED was 
fed DC, and the comparator fed pulsed AC (1 diode and a Zeener so I got 
grabbed the very top of the AC mains).  This worked for initial phasing, 
but was otherwise pretty useless ;)  Comparator just checked if both 
outputs were high and flipped on the green LED when they were.  I'd suggest 
the flourescent method, as once you get the SRSG working, you can tweak it 
from there.  The safety gap should only fire every once in awhile.  A 
thought, you may want to put the safety gap across the main gap (as I do), 
so when it does fire you're still discharging the cap through the primay 
and limiting the surge current, and it'll have less effect on the "smooth 
running" of the coil that way (IE, streamers won't stop for a beat while 
the spark gap fires).
Hope it helps!
Shad


At 10:00 PM 3/1/02 -0700, you wrote:
>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
>***************************************************************************