[TCML] Phase tuning gadgets and when to set the gap to discharge.

[Jeremy Scott <supertux1@xxxxxxxxx>]

Hi all,

I designed and built a simple circuit to help adjust the phase of SRSG's.

It's a timing light (white LED .. fancy) that pulses at 120 pps at each AC zero crossing.  The pulse width is less than a millisecond or so with 
half of it before and the other half after the zero crossing. Kind of like
an inverted rectified full wave if you can imagine that. 

It uses a 120VAC to 9VAC power adapter/transformer that I found in my junk box for the signal and power. It's a fairly simple two-transistor circuit.

Turn the lights out, shine it at a rotary spark gap, and you can see if the electrodes line up like they should and if your motor is truly synchronous.

So I used it on the propeller gap of my first coil which was tuned right but never worked very well. Hah. Way out of sync. Not at the zero crossing and not at a peak, but somewhere in between.

I tried it with the SRSG phase adjust variac thing as discussed previously on this list and turns out the adjuster isn't doing anything. (Anyone know the proper size capacitor for one of those small square oriental motors?)
So now I know why my first coil sucked and I can fix it!

So I guess I got a few questions, now that I can visually see at which point in the AC cycle the gap is firing at. 

1. So now that I can actually see and adjust the timing, when is the best time to have the gap fire, theoretically? (I know practically, it's 'whatever' ... adjust it while running until the streamers get bigger.)

Is it at the zero crossing when the capacitor has had a full 8.3 ms to charge OR is it 90 degrees (4.16ms) sooner/later when AC cycle has peaked
in voltage?

For any given input current (say 60ma NST), would it be better to pick a larger capacitor size that takes a full 8.3 ms to charge then discharge it into the tank before the current reverses (at the zero crossing) 

OR would it be best to have a smaller capacitor and discharge it at the peak input voltage but potentially wasting the rest of the current available in the half cycle? (eg. step up the break rate to 240bps and fire the smaller capacitor twice.)

2. Is the timing light even accurate? The signal I'm using comes from a step down AC wall adapter. Is the secondary phase angle from this small transformer the same as the phase angle of the high voltage 15K secondary of the coil's transformer?



      
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