Sourcing a Single-Phase 230 VAC Variable Speed Motor

Your motor is not designed to be speed-controlled, and the controller that you are looking for most likely does not exist. If, hypothetically, you had such a speed controller, how would you stop the motor from switching in the start winding whenever the speed dropped below the threshold for the centrifugal switch?

Most, if not all, ac speed drives of the power rating that you require are designed to work with 3-phase motors. If you need speed control you may need to change the motor to one which is designed to be speed-controlled.

thanks for the reply,

The motor in question is wired like a 3 phase motor, except the start winding has a lower resistance. Power is brought to the motor via the common terminal and the run terminal with a capacitor across the run and start winding. No potential relay necessary and the start winding gets its power from the capacitor. amperage at the start winding is quite a bit lower then at the common terminal but the circuit is always engaged while the motor is running. Like you said this might not exist. the controller would have to be able to operate on a unbalanced 3 phased circuit. Does this help any.

thanks.

John

There are a few VFDs designed for 1 phase motors, but they only work on PSC (Permanent Split Capacitor) and Shaded Pole motors. You cannot use them with split phase motors.

Can you change the motor out to PSC? If you can, respond back with where you are located (i.e. which country) and I'll dig up the manufacturers that sell them there.

Then if not PSC, can you change it to 3 phase? There are hundreds of VFDs designed to take 1 phase input power and put out 3 phase to the motor. But for that size, you will need to buy a VFD twice as large as the motor, so one rated for 60A.

Those are your only choices, you cannot do speed control on a split phase motor for the reasons posted above. In addition, the capacitors used in them tend to cause damage to the transistors in the VFD, and the high switching speed of the transistors tends to overheat the caps. So it is a race to see which one fails first.

This is an excellent reply.

I could not have given any more oinfo than what the author

JRaef has given!

Chuck Cowlagi