DC Motor Sparks

Discussion in 'General Electronics Chat' started by geratheg, May 27, 2015.

  1. geratheg

    Thread Starter Member

    Jul 11, 2014
    107
    3
    When a low voltage DC motor is running and then disconnected at its terminals and it has no fly back diode, usually I would see sparks across the wire and the motor.

    My questions are:
    1) Are these sparks the result of the DC motor being an inductive device?
    2) Are they avoided with a "flyback" diode?
    3) Are these sparks high voltage sparks (read it takes thousands of volts to break down the ions in the air?)
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    The sparks are due to the DC being generated by any P.M. DC motor that is revolving.
    The voltage is directly related to rpm and is the same polarity as the applied voltage.
    Max.
     
  3. geratheg

    Thread Starter Member

    Jul 11, 2014
    107
    3
    Would a diode prevent the sparks?
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,507
    2,367
    The back EMF or the same-polarity generated voltage is necessary to offset or oppose the applied voltage in order to reduce the otherwise excessive current at full voltage.
    Is this just a momentary effect you see or constant?
    Max.
     
  5. geratheg

    Thread Starter Member

    Jul 11, 2014
    107
    3
    Thanks for responding again.
    I read somewhere the diodes can and should sometimes be used with motors.
    Momentary effect.
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    They are often used in switching applications, not so much in linear control.
    Care has to be taken if switching bi-directional.
    Max.
     
  7. geratheg

    Thread Starter Member

    Jul 11, 2014
    107
    3
    Ok. Are they used in switching applications because of the inductance effect? Is that what causes the sparks? Would the diodes prevent the sparks?
     
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