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Small Motor Circuit

  1. May 21, 2007 #1

    I've been messing about with my polisher lately as those who read the other thread will know. I decided to open a more relevantly titled thread and here it is. I've acquired what I think is the circuit diagram for the motor. There is nowhere where any AC is rectified by the looks so I think it is an AC circuit. I've scanned it in anyway.


    And that's it. Can anyone throw any light on this, is it definitely AC? Also I must point out I'm new to all this and won't be in the least bit offended if someone points out that I'm in over my depth with this one and should stick to more simple stuff :redface:
  2. jcsd
  3. May 21, 2007 #2


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    Staff: Mentor

    My initial guess would be that it's a PWM speed controlled DC motor. Do I win a prize if I'm right?

    Does the motor have any markings that we/you can google?
  4. May 21, 2007 #3
    I think you should for getting so close to the mark. Thanks for that, it helps me even just to know what I'm looking at!

    I can get a photo of it if that's any use?

    I also noticed there are two toroids and some small windings in the motor circuit occuring after the circuit shown, I wonder what they do. I'll try and get some pictures.
    Last edited: May 22, 2007
  5. Jun 4, 2007 #4
    Could I full wave rectify this motor circuit if it's receiving AC at the source? And then control current through it using a variable resistor. I know this wouldn't give any torque/current feedback but would it still work?
  6. Jun 4, 2007 #5


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    Staff: Mentor

    In general you can't use a resistor to drop voltage to control speed on a motor. The power lost in the resistor takes torque away from the motor, and the motor is generally too weak to operate correctly.

    Instead, you want to deliver full power to the motor, and vary what percentage of the time that full power is delivered -- hence the PWM function.
  7. Jun 5, 2007 #6
    Understood. Thanks again, that makes perfect sense.


    Out of curiousity could one use a capacitor and other necessities as a timer to deliver square wave pulses of uniform size and seperation instead of using PWM to mimic the sine wave input with regards to pulse width?
    Last edited: Jun 6, 2007
  8. Jun 6, 2007 #7
    First in order to use a cap to make a squarewave, you would have to rectify the AC and make it DC. Secondly, a squarewave is the addition of the harmonics of a sinewave. That means that a squarewave will have alot more power than a sinewave of equal amplitude and frequency. But I believe the answer to you question is ultimately yes, but how involved do you want to get into this project?
  9. Jun 6, 2007 #8
    Not massively. I'm trying to fill out my electronics knowledge as much as anything. If PWM is easier I'd go with that, but whatever solution was found would have to be better than the bad power and torque I get out of it now.
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