So recently I got my hands on an old pump motor, unfortunately the connection diagram is missing. I have already determined this is a 2 phase motor, and that in order to make it work I need a motor-run capacitor.
However I was wondering can I use any motor-run capacitor or do I need one with a specific capacitance to get the 90 degrees of phase difference? If it would be important I live in a area with 230V AC out of the wall.
Thank you, for any help/tips
ps: i have included photos of the stator;
Best Answer
Yes, you need a cap. The cap must be rated for the job. A 250VAC or better metal film cap will be needed.
The phase shift is never exactly 90 degrees but it does not have to be. The capacitance needed is roughly proportional to the size of the motor. If your cap is small you will still get starting torque but not very much. If your cap is too big, you get more starting torque but you increase no load current consumption and risk burning out the motor. Running torque does not change much with cap value.
If your load is "easy" like a fan you have a wide range of capacitance to work with. If your load is "hard" like a piston compressor you will have to get the cap right be ensuring that the motor starts under load. Under no load on the bench you could start with 10uF and take things from there.