AC single phase shaded pole induction motor

The torque-speed curve of an induction motor is a function of effective rotor resistance, and also of slip. Your motor's no-load speed is very close to 3600 rpm, so the rated speed represents 17% slip. (Some high-performance induction motors would stall if loaded that much.)

Most shaded-pole induction motors that have speed controls drive window fans and furnace blowers. The ones I'm familiar with achieve two or three speed settings with a switched series inductor. Fan loads are easy to control because a fan's torque goes approximately with the square of its speed. You will find it hard to control your motor is the load's torque is independent of speed. You will need an active servo to avoid stalling below about 2000 rpm. With speed feedback, you don't need to know the torque curve very well.

If you measure the torque-speed curve at full excitation, you will find that is is small when the rotor is locked, rising as speed increases to a maximum that depends on the effective rotor resistance, then falls to zero at synchronous speed. The motor's steady state is always in the falling region. If the torque is sufficient to drive the speed to the peak of that region -- the peak available torque -- the motor stalls. Obviously, the torque of your motor peaks comfortably below 3000 rpm. maybe as low as half that.

If you use semiconductors to vary the speed, ensure that the circuit delivers DC-free drive at all speeds and loads. DC in the stator will drive it into saturation and overheat it.

Jerry

We don't yet know the application, speed range, stiffness requirement, or much else. Note that without reverse torque available, some classical servo schemes won't work very well.

jerry

Yes Yes, need more info for sure. But shaded poles not very good for Torque control. Lots of low cost DC servo controls and motors in the small size range and if he needs AC there are small single phase units.

He could also use the motor MAYBE and couple to his load with a shaft mounted particle brake and use a stra> Dennis Mchenney wrote:

Everything I can think of seems over elaborate for a 1/150th Hp motor.

Jerry

I can think of a lot of options other than shaded pole motors that would be superior -- why this particular motor? What's your application?

True enough. The big thing with the scenario as laid out by the OP, however, is that a shaded pole motor has a very low efficiency, especially one that small. You will probably find that there is almost no difference between no-load current and locked rotor current.

If all he wants to do is reduce the (available) torque, all he needs to do is reduce the voltage, and hence the air-gap flux, proportionally. The inefficiency makes the rest of the details superfluous.

If i use 3 phase ac induction motor .could suggest a method to control the torque in closed loop.

Two-phase induction motors with high enough rotor resistance to put the peak of the torque-speed curve at standstill were standard servo motors before transistors made DC drive practical. One winding has fixed excitation, with the other driven in quadrature at variable amplitude. Reversed phase provides reversed torque. There are more sophisticated techniques available now, but they may not adapt well to such low power.

If you can choose the motor, why not consider a DC motor, PM or brushless?

Jerry

I was really trying to lead you to Jerry's suggestion.

If you can monitor the motor speed you can control the torque by controlling the motor current and slip speed per Dennis's suggestion -- but if you can monitor the motor speed then you can monitor the motor position, and if you can monitor motor position then you can just use a

3-phase brushless with controlled current to much greater effect.

It would really help us help you if you could share the problem you're trying to solve, rather than tossing up motor possibilities and asking to do hard things with them. If you're worried about competition-sensitive information you don't even have to tell us that you're making a left-handed frammelhultz glitzer. You can just say something like "I need to design a motor drive that must generate up to

20 N-m, with torque controllable to +/- 0.2 N-m and speeds between 0 and 2500 RPM". Put down everything that's an issue -- price? size? is it going into existing equipment? etc. If you give us _that_ sort of information then we can help you with a solution.

And who knows, maybe your induction motor will be the right choice.