identify AC motor

[p314]

Please help to identify the type of this AC motor - photos enclosed.
It was removed from a small bathroom fan, runs on AC 240V, about 10W.
No brushes, the rotor looks remotely like squirrel cage but there is no capacitor and it always spins the same direction.

Can anyone explain its working principle - how does it start without a capacitor? How does it rotate always the same direction.

Thank you

 

[KeepItSimpleStupid]

It might be a Hysteresis synchronous motor. https://en.wikipedia.org/wiki/AC_motor The construction is similar to vintage turntable motors which had to maintain the correct speed. I'm taking really old turntables like 1950's vintage.

 

[Reloadron]

My guess is a shaded pole synchronous motor, popular in appliance fans when they look like the one pictured. A Google of "Shaded Pole Motor" will bring up several just like what you have.

Ron

 

[dr pepper]

Split phase or shaded pole.

There is another variant that has only one coil and a magnetic shunt.

 

[BobW]

I don't see any shading coils in it, which would eliminate it from being shaded pole.
I only see a single winding, so it can't be split phase.
It has the wrong kind of rotor to be either a hysteresis motor or a reluctance motor.

It would help to know what it came out of.

Edit:
It could possibly be a non-capacitor split phase type motor, if there are multiple windings brought out to a single pair of wires. The windings would be such that one of them would have a much higher inductance than the others, causing the flux that it generates to lag that of the other windings, thus giving the rotating field.

 

[crutschow]

Pictures of identical looking motors on the web describe them as shaded-pole motors.

 

[p314]

Thank you, All, for the pointers. Googling for 'shaded pole' indeed brings same looking motors. But the absence of a shading coil winding in my motor confuses the matter.

Then I found this excellent video explaining its operation and the second motor in this video is like mine. It has two hardly noticeable copper-filled gaps in the stator which serve as shading coils. If you don't look for them specially you won't spot them. There is also a good tip there how to reverse this motor.

Now it's all clear, thanks again to you fellows and to the youtube gent who kindly shot that video.

 

[RODALCO]

Brilliant video, I learned something new today how to reverse those shaded pole motors. See them often in microwave cooling fans.