Re: Synch motor Phase controller question

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

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dhmccauley-at-spacecatlighting-dot-com>

Thanks for the great tips.

I noticed awhile back (when using a small variac), that the motor would
actually stop working past a certain adjustment point.
What is the explanation behind this???

Thanks
Dan




 > Dan,
 >
 > Don't forget the variac is acting as a variable inductor, not a
 > voltage controller. At some point in the variac's range, the
 > inductance of the variac, the capacitor, motor cap and windings will
 > be matched just right to cause a 50/60Hz resonant circuit. The
 > capacitor size will determine just how high the resonance can ring
 > up. You want the resonant rise to be below 10v above the line
 > voltage. So you mix and match capacitances until the voltage rise
 > across the motor is satisfactory. I set mine pretty high (10v),
 > because my line voltage drops pretty significantly when I draw
 > 10kW :)
 >
 > I find that the rise will occur no matter what (though it may be too
 > big), if the cap is very large. If you wind the variac slowly, you
 > can stop it before it goes too high, then try a smaller cap. See
 > below.
 >
 > 1. Just hook up the circuit with a cap that "feels"  a bit too large
 > (look at what sizes John recommends on his page and go from there)
 > and voltmeter across the motor.
 >
 > 2. Begin to wind the variac slowly, watching the meter.
 >
 > 3. Watch for a resonant rise. The voltage will begin to increase as
 > you wind the variac. If the rise goes above, say, 10-12v, stop
 > winding! You don't want to damage the motor. You will find that the
 > voltage will peak at some point on the variac's range, and then begin
 > to drop off as you keep turning. Try again with a smaller cap if it
 > goes above 10v (or whatever rise you want).
 >
 > 4. If you didn't get a rise, use a bigger cap.
 > 5. Iterate until you get the right rise.
 >
 > Hope these instructions are clear.
 >
 > Cheers,
 >
 > Greg.
 >
 >
 >
 >
 >