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Back EMF of an electric motor.

Discussion in 'Sensors and Actuators' started by Moha99, May 8, 2012.

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  1. Moha99

    Moha99

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    Nov 18, 2011
    Hallo everyone!

    Do all electric motors produce back EMF? Because I have a small 12 volt motor I was wondering If I applied a "load" to the motor would the back EMF be reduced?
     
  2. duke37

    duke37

    5,360
    766
    Jan 9, 2011
    I think the answer must be yes but there are many, many types of motors out there.

    A motor works as a generator when it is turning, producing the back EMF. The current consumed depends on the difference between the supply voltage and the back EMF and the motor resistance.
    Applying a 'load' will slow the motor down so the back EMF will be reduced and the supply current will rise.
    It is possible to interupt the supply voltage and measure the back EMF and then supply power to bring the back EMF up to the desired value, so controlling the speed. I have done this to control the speed of a coil winder where the torque (load) can vary.
     
  3. Moha99

    Moha99

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    Nov 18, 2011
    Well thats cool.

    In general is a back EMF considered a very bad things or its normal? Motor is a generator at the same time :confused: kinda confusing to solve...
     
  4. BobK

    BobK

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    Jan 5, 2010
    Back EMF is not a good thing or a bad thing. It is what happens.

    Bob
     
  5. Moha99

    Moha99

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    Nov 18, 2011
    I meant are there any positive effects we could gain from it and any negatives that were burdened with...?
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,384
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    Jan 21, 2010
    the positive effects are

    1) that the motor consumes power that relates to load, and not simply a constant value determined by the reactance of the motor.

    2) motors can be used as generators

    3) motors work (if back emf didn't occur then neither would the reverse)

    4) laws of physics are preserved

    The negatives include:

    none that I can think of...
     
  7. Moha99

    Moha99

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    Nov 18, 2011
    Thanks Steve!
     
  8. Rleo6965

    Rleo6965

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    Jan 22, 2012
    Another positive effect of EMF.
    It can be used for Dynamic Beaking of DC motors.

    Negative.
    Don't hold those 2 wire terminals if somebody rotating the armature. You will be electrocuted.:D
     
  9. Moha99

    Moha99

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    Nov 18, 2011
    haha I won't thanks!
     
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