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Re: synchronous motor



Original poster: "resonance" <resonance@xxxxxxxxxxxx>



Some wiring diagram data for a small synchronous motor:

4 wire motors:

green and black leads connect together and go to the 120 VAC hot.
3rd lead from motor to line neutral, and 4 th lead from motor goes thru (series) a 12 uF cap and then to the line neutral.



3 wire motors:

typical for 1/20 to 1/8th HP motors:

blue lead to the 120 vac hot.

ground to motor case

white wire thru 5 uF 330 vac capacitor, then connects to line neutral.

red wire connects to line neutral.



blue motor lead to ground is one winding
red motor lead to ground is second winding       (for 3 wire motors)
white motor lead to ground is third winding


Use a variac to bring the motor on slowly for first tests --- monitor currents on each leg to be sure they don't become excessive. 1-2 Amps is typical.


Hope this helps you sort it out.

Dr. Resonance



Hi Anthony,

You might try to measure the resistance of the two winding. If both windings are the same guage and the same resistance, it might not matter which one you use for the start winding. Leaving them on all the time may harm the start capacitor. I dont think they would fight each other since one has a different phase from the other (due to the capacitor) and syncing is not an issue unless you modify the motor for sync operation. If you experiment with the windings, you may want to fire up the motor for a very short time, power down, and see if the windings are getting warm. Repeat this for progressively longer times until you are satisfied the motor is running properly. If you suspect it is not right, you may want to swap the two windings and try again.

Gerry R.


Original poster: "Anthony R. Mollner" <penny831@xxxxxxxxxxxxx>

They both seem about the same gage wire but I could run the starter one way
and than vice versa. What would happen if I left both windings on? Would
they fight each other or just not synch. up?