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Dc Motor Voltage Rating

Discussion in 'Electronic Basics' started by Peter Walinsky, Aug 18, 2005.

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  1. What would happen if I had a motor that has markings saying it is a 2.25 hp
    motor, 130 volt, 18 amp and I pulsed it with a 50% duty cycle of 170 volts.
    Could it fry my motor, if yes, why? Or would the capacitance and inductance
    smooth the voltage and amperage it is getting.


    My other question was, if I rectify 120 VAC and smooth it with a capacitor,
    what will the resultand DC voltage be, assuming there is only a little
    ripple. From what I understand it would be about 120 * 1.414 = 170

    Thank you
    Pete
     
  2. Guest

    Rectified 120VAC:
    120*sqrt(2)=170VDC
     
  3. kell

    kell Guest

    If it's a DC motor you can use pulse width modulation. I tried that on
    a cordless drill and it worked. I think I used about 20 kHz.
    On an AC motor I think you would use the technique lamp dimmers use.
    It truncates part of each cycle. For a small motor, an actual lamp
    dimmer might work. Not for the motor you decribed though. Lotta
    power. Besides the high power level, the motor "dimmer" also has to
    withstand inductive spikes that you don't get with lighting. I
    remember reading a post somewhere by a guy that did use a lamp dimmer
    to control a power tool, but it was a small handheld one like a detail
    sander.
     
  4. Jasen Betts

    Jasen Betts Guest

    my dad's cheap corless drill uses PWM at a lower frequency (sounds like about
    5Khz)
    yeah for universal motors thjey do that, there are also special electronic
    controllers available controlling induction motors (like are typically used
    to power fans) the ones I saw were in australia and for 230V so chances are
    they're not what the original poster wanted... try a wholesaler.
    I've seen it done on a ceoilng fan - it was an induction moto and with the
    dimmer on 1/4 to 1/2 way it tended to get very hot...
    these ones I saw were rated at 500 watts IRC. but larger versions of the
    same concept ar available - they use them in electric trains.

    Bye.
    Jasen
     
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