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Re: Remote phase adj of sync rotary gaps, tests.
Original poster: "rwall" <rwall-at-ix-dot-netcom-dot-com>
Excellent thoughts and work.
Along those lines, I have considered a 60 Hz resonant tank circuit in the
low voltage side of a noncurrent limited HV transformer. Control is by
varying the inductance or capacitance of the tank circuit. I have not done
I'm not sure, but I think your inductor (variac) and capacitor may also be
forming a tank circuit and resonant harmonics are causing the growling in
the variac. You may consider adding a low value resistor from the main to
one side of the capacitor.
Maybe you could apply your new circuit to your PT to evaluate current
----- Original Message -----
From: Tesla list <tesla-at-pupman-dot-com>
Sent: Saturday, December 09, 2000 1:37 PM
Subject: Remote phase adj of sync rotary gaps, tests.
> Original poster: FutureT-at-aol-dot-com
> Hello coilers,
> I'm building a new sync rotary gap. I was planning to rotate the motor
> in its cradle to adjust the phase, but I really prefered to use some sort
> of external phase control of the input ac to the sync motor. Now this
> problem seems to be solved.
> As we know, a variac can be used to adjust the input voltage to the
> motor, and this gives a small amount of phase adjustment, but I was
> looking for a larger range of adjustment capability.
> As a test, I connected a 50uF cap across the sync motor input, and
> then connected a 7.5A variac in series with the hot ac lead to the motor.
> The variac is arranged as an inductive rheostat. One connection is
> made to one end of the variac winding, the other connection to the
> variac wiper. (This is the same type of connection as when making
> a variac behave as a current limiter or ballast for a TC.) The variac
> is not between the motor and the cap, but is between the cap and
> the incoming ac power from the wall.
> This setup seems to work great! I obtained just about a full ninety
> degrees of phase adjustment, and the torque seems to remain
> strong. I still have to install the spinning electrodes onto the rotor,
> which will cause drag. But in any case, a larger motor could be
> used if needed and the technique will surely work well, if it isn't
> quite strong enough now. But I think it will be OK even using this
> small 1/20HP motor with this 3/8" x 6 1/2" G-10 rotor and electrodes.
> The only thing undesirable is that the variac makes a slight groaning
> noise at some spots, suggesting that some resonances may be
> occuring. I tried a larger cap, but the variac groaning got worse.
> I tried a smaller cap, but the motor loses too much torque. I don't
> think this is a real problem though... it can be lived with.
> Different motors will probably require a different sized cap and
> variac for best results, depending on the size and rating of the
> motor, the loading, etc.
> I'm using a 3600 rpm motor, so a full phase adjustment range
> is 180 degrees, but still 90 degrees is very good. Once the
> motor is rotated to give a ballpark phase adjustment, a 90 degree
> remotely controlled range should be plenty.
> There is one limitation. When the motor is started, the variac has
> to be set at minimum or near minimum inductance. This issue can
> be solved by using a relay that shorts across the variac when the
> motor is started, then drops out. Or alternatively, one can simply
> turn the variac to minimum inductance before starting the motor,
> then adjust it for the proper phase setting according to the variac
> It will be great to be able to abandon mechanical phase adjustment
> methods once this sync gap is finished.
> John Freau