Square-wave driving of induction motors

Thread Starter

Alec_t

Joined Sep 17, 2013
11,389
Many domestic appliances running from 50/60Hz AC mains include an induction motor, e.g. a shaded-pole or squirrel-cage motor. Would such a motor work satisfactorily if driven by a square-wave source of similar frequency? Any snags?
 

Jony130

Joined Feb 17, 2009
5,176
I connected once a central heating water pump to UPS that gives square-wave.
The pump work just find except extra noise and heat.
 

crutschow

Joined Mar 14, 2008
25,108
A square-wave will drive an induction motor but the harmonics in the square-wave generate extra heat and noise as Jony noticed. So the motor could overheat if operated for long periods of time near its maximum load rating.
 

THE_RB

Joined Feb 11, 2008
5,438
Most square wave inverters are modified square wave, which have a pause between each half cycle. They will run a small induction motor good enough, it was common in the old days.
 

Thread Starter

Alec_t

Joined Sep 17, 2013
11,389
Thanks, guys. I had a feeling the square corners would end up as extra heat (assuming equal amplitudes for the sine and square waves) :).
This question was prompted by the thread
http://forum.allaboutcircuits.com/showthread.php?t=97639
I was thinking it would be easier to make a variable-frequency square-wave source than a sine-wave one, for driving a capstan motor as the OP wants.
 

alfacliff

Joined Dec 13, 2013
2,458
wwe had a problem with a crane here a while back, the motor that drives the crane on its tracks had the wires in the conduit melt together. gthe motor current was fine, but the drive put out pulses which were modulated to synthesize a sine wave, the high frequency magnetic field around the wires induced current in the steel conduit that heated it. I've heard that 400 hz power is sent through aluminum conduit because of this heaing. the motor was one that wes speced for high harmonic content, and was ok.
 
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