Questions about single-phase AC motors

Thread Starter

Benjamin3000

Joined Mar 28, 2021
8
1. How is direction changed on a "reversible" AC motor? Obviously on regular brushed DC motors, most of them can be reversed by just swapping polarity unless the motor chassis contains other stuff that is polarized. But AC doesn't have a true polarity that affects operation of the device.
2. How does one change speed in applications that require it? Light dimmers don't work very well on a ceiling fan: I never made that mistake myself, but I've heard that if your ceiling fan buzzes/hums excessively when not at full speed, that probably means somebody installed a light dimmer instead of a proper fan controller.
 

LesJones

Joined Jan 8, 2017
3,195
1 You need to give details of THE AC motor. It will most likely be an induction motor or series wound motor.

2 I have not had anything to do with ceiling fans but as far as I know the methods used are tapped winding or adding serial inductors.

Les.
 

MaxHeadRoom

Joined Jul 18, 2013
23,144
A 1ph AC induction motor is reversed by changing the relationship between the start and run winding, IOW change one from leading to lagging WRT the other.
Some (shaded pole) cannot be reversed electrically.
 

MaxHeadRoom

Joined Jul 18, 2013
23,144
Light dimmers don't work very well on a ceiling fan: I never made that mistake myself, but I've heard that if your ceiling fan buzzes/hums excessively when not at full speed, that probably means somebody installed a light dimmer instead of a proper fan controller.
There is very little difference between a light dimmer and a ceiling fan version, they are both triac based, the fan version has a inductor fitted and is about the only difference.
There is very little choice in selecting a speed controller for 1ph induction motors, as they do not control well, and can drop out of run on occasion, buzzing at low RPM is a by product.
 
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Dodgydave

Joined Jun 22, 2012
9,956
Ceiling fans are controlled by switching different capacitors in series with the run winding, reversing is done by swapping the start winding wires. Three phase motors are reversed by swapping any two phases.
 
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MaxHeadRoom

Joined Jul 18, 2013
23,144
The 1ph ceiling fans I have are either PSC, 'permanent start cap' or shaded pole and controlled with triac dimmer style control.
 

Alec_t

Joined Sep 17, 2013
12,091
Ceiling fans are controlled by switching different capacitors in series with the run winding
Proper selection of capacitor value is crucial, to avoid the cap and coil resonating at a harmonic of the mains frequency and resulting in damage-causing high voltages.
 
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