impedance protected

Discussion in 'General Electronics Chat' started by qitara, Oct 3, 2014.

  1. qitara

    Thread Starter Member

    Jan 18, 2013
    87
    0
    Hi
    i have seen a few motors that has (impedance protected) written on it. What does that mean ?
     
  2. JDT

    Well-Known Member

    Feb 12, 2009
    658
    85
    It means that even if the rotor is stalled, the motor current will not rise enough to overheat the windings.

    This is done by having a poor magnetic coupling with the rotor. Actually a high mutual inductance. An induction motor is actually a kind of transformer with the secondary on the rotor (usually a "squirrel cage" - a shorted winding).

    Only done on small, low efficiency motors (fans, etc.).
     
  3. ScottWang

    Moderator

    Aug 23, 2012
    4,853
    767
    If the motor because any reason caused it didn't running, and the power supply still continuing then the motor will increasing the impedance to reducing the current and protecting the motor.
    What is impedance protection?
     
  4. qitara

    Thread Starter Member

    Jan 18, 2013
    87
    0
    Wouldn't a thermistor connected series with the winding do some thing similar ?
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    and add heat. ( the thermistor would reduce resistance when hot.)
    there are impedance protected transformers too, most wall warts are impedance protected instead of fused.
     
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