controlling the speed of a shaded pole motor


Thread Starter


I am doing a project on controlling the speed of a single phase shaded pole -permanent magnet- ac motor. I want to know how speed is related to the voltage applied to the motor. I dont have any algorithms and idea for this. Can anyone please help? Any site? PCB? Sample of circuit. Step by step please.

If i wont do this project, i failed this season.

Warm regards,
So far as I know, that is a synchronous motor and the speed depends on the frequency, not on the voltage. If you look in a standard motor textbook on how shaded pole motors work, you will see why.

You would need a circuit that outputs a variable AC frequency. That would probably involve a circuit that rectifies the AC to DC, and then produces an AC power output at a different (variable) frequency.

curt wuollet

You can actually achieve a degree of speed control with wound field shaded pole motors with voltage. It's very soft, (poor speed regulation) and useful mostly for fans and small blowers. I don't recall ever seeing an AC PM shaded pole motor.

In the wound motors the field poles have the shading ring. I would suppose the rotor would be PM unless they've got slip rings. And I would expect it to behave in much the same way except voltage dependence would be less as the rotor flux is constant. I would intuitively guess that you would have a knee where above a point you are in sync with the line and below that point you have some control.

My corn stove is full of voltage controlled shaded pole motors, I think they are cycle counting, but they work so I haven't thrown a scope on to see what they are doing. Might be phase controlled, but that would be a lot for a PIC.

An ordinary shaded pole motor can simply "slip" a lot when driving a fan. That's how you would get variable speed with voltage.

The original post though said nothing about a fan load (which is a special case), and he said it was for a permanent magnet style. The permanent magnet shaded pole motors have more torque than regular shaded pole motors, so I don't know if they will work well in slip mode. I haven't tried it though.

"Atlas" could of course simply *try* this and see if it works, but then of course it would need to be a fan application (about which nothing was said) and he would need a matching fan. He would also probably be better off with a regular shaded pole motor. In that case, go to a surplus store and buy a motor with fan combination so you know the motor curve is matched to the fan curve.

As for finding how to do this, well that's part of being a student. I would suggest talking to your instructor about that.