Re: Synch motor Phase controller question

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

Original poster: "Steve White by way of Terry Fritz <twftesla-at-qwest-dot-net>" <slwhite-at-zeus.ia-dot-net>

Since the controller is a bandpass filter, if you adjust the variac too far
you are moving the center frequency of the filter significantly off of 60 Hz
and moving down the "skirts" of the filter where the voltage becomes
significantly attenuated. When the voltage falls below a certain level, the
motor will stop working.

Steve: Coiling in Iowa

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Friday, December 13, 2002 8:52 PM
Subject: Re: Synch motor Phase controller question


 > 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.
 >  >
 >  >
 >  >
 >  >
 >  >
 >
 >
 >