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What if this happened?(theoretically )

Discussion in 'General Electronics Discussion' started by Dretron, Dec 18, 2012.

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  1. Dretron


    Jun 9, 2012
    I was wondering if the magnetic field of a permanent magnet (B) became very strong.
    That the B-EMF would be higher than the inputed EMF what would happen? To the motor,electromagnets, etc...?

    In theory what would happen? I thought the input EMF would increase the current to resist the higher B-EMF?

  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    If the back EMF is higher then you have a generator, if lower, a motor.

    Back EMF can only exceed the voltage applied if the voltage applied is reduced or if some external source of power is driving the shaft.
  3. Laplace


    Apr 4, 2010
    When the generated back-EMF equals the applied EMF there would be no current flow, hence no torque produced by the motor. With no torque the motor slows down, producing less B-EMF so that more current flows. But with a stronger magnetic field the same B-EMF will be produced at a slower RPM.
  4. Dretron


    Jun 9, 2012
    Nope, say you didn't decrease the input voltage or applied a power to move the shaft, just increased the magnetic force of a magnet in a motor. That would significantly increase the B-EMF.

    And if the B-EMF was greater the motor will slow down because there is no input torque, and thus the motor would turn into a generator feeding back current to the source. But In cause a source is constantly applying voltage and current to the electromagnet and the B-EMF is greater than that input, Im imaging that the over heating would cause a major damage and something will happen but I can't imagine what exactly...
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