Square-wave driving of induction motors

Discussion in 'General Electronics Chat' started by Alec_t, May 21, 2014.

  1. Alec_t

    Thread Starter AAC Fanatic!

    Sep 17, 2013
    5,801
    1,105
    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?
     
  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
    3,957
    1,097
    I connected once a central heating water pump to UPS that gives square-wave.
    The pump work just find except extra noise and heat.
     
  3. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,553
    2,375
    You could always put a series choke in each lead to round it off a bit. ;)
    Max.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,022
    3,235
    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.
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    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.
     
  6. #12

    Expert

    Nov 30, 2010
    16,305
    6,815
    Finally! A good use for the POS I bought at Harbor Freight. :D
     
  7. shortbus

    AAC Fanatic!

    Sep 30, 2009
    4,015
    1,531
    I looked, but couldn't find, POS, on Harbor Frights web catalog. Got a SKU number for that?:rolleyes::p
     
  8. Alec_t

    Thread Starter AAC Fanatic!

    Sep 17, 2013
    5,801
    1,105
    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.
     
  9. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    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.
     
Loading...