Stopping a Shaded-Pole Motor

[dhwilliams]

I need to update the electronics in some machines we have sold and one of the things the existing control circuit does is to stop a 240Vac 50Hz 40W Shaded-Pole motor/gearbox at a specific position when signalled to do so (slotted optoswitch detects slot in disc on output shaft). If this was a small DC motor I would short the 2 leads but this does not work on the Shaded-Pole motor. I have found that applying 12Vdc (obviously when the 250Vac is disconnected!)stops the motor quite quickly but before I "breadboard" a circuit to remove the 250Vac then apply the 12Vdc are there any reasons why I should not do this? - Like permanently magnetising the motor, overheating the coil etc.

Thanks,
Dave

 

[motorsdirect]

Hi
I cant think of any problems you would come up against..it will only be like a crude DC injecting brake unit.
The motor should not become permanently magnetised either....I think all you need to do is to make sure that,if you leave the DC supply on for an extended length of time,that the coil doesnt get too hot..I dont think it will!!
Jeff

http://www.motors-direct.co.uk

 

[OperaHouse]

I've done this, but used a more voltage. I charged caps with enough capacity to stop the motor. You didn't mention if you would be using any timer to remove the DC after a period. If you continue to apply DC there is a chance of overheating the coil.

 

[dhwilliams]

Thanks Jeff and OperaHouse, it looks like it's now worth programming a PIC to do the timing - I hope 12V is high enough to stop the rotation in the right place because we have 12V power supplies as stock items and after being energised for an hour the coil was only slightly warm. I will probably switch the 12V off after a short time anyway as I don't think I need to "lock" the motor once it has stopped.

Dave