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Thread: Do electric motors arc?

  1. #1
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    Do electric motors arc?

    I haven't got around to studying motors yet, but i was told today that motors don't arc. I thought the brushes would arc a little, kind of like looking into a drill.

  2. #2
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    Two different motors. Motors with brushes, yes. AC induction motors, no
    If Billy Idol or John Denver is on your Ipod go and re-evaluate your life.

  3. #3
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    Single phase induction motors have internal switches that can arc.

  4. #4
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    Quote Originally Posted by ActionDave View Post
    Two different motors. Motors with brushes, yes. AC induction motors, no
    Depends on the type of induction motor.
    I agree in the case of the ubiquitous asynchronous cage induction motor.

    But there are others.
    The asynchronous wound rotor motor does have brushes and I have seen a few cases where they did arc and caused significant damage.
    And many synchronous induction motors also have slip rings which can arc.

  5. #5
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    Single phase motors like cap start or split phase motors with a starting switch also have an arc at the switch every time the motor starts.

  6. #6
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    and, did you know that those motors run on smoke, and if you let the smoke out of 'em, they don't want to run so much anymore

  7. #7
    Quote Originally Posted by Eddy Current View Post
    I haven't got around to studying motors yet, but i was told today that motors don't arc. I thought the brushes would arc a little, kind of like looking into a drill.
    Motors that run on DC without any external electronics have brushes, so they do.

    SR and BLDC type that use external electronics such as those used on computer cooling fans and HVAC electronically commutated motors don't.

    Older variable speed motors that use a wound rotor and rheostats mounted through slip rings do as well.

  8. #8
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    Quote Originally Posted by Electric-Light View Post
    Older variable speed motors that use a wound rotor and rheostats mounted through slip rings do as well.
    Slightly off topic but speed control with wound rotor motors are still alive and well.
    With modern power electronics, it's actually quite a good solution for variable speed systems particularly say, upwards of about 1MW.

  9. #9
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    So AC no DC yes? What about a pretty large motor that would run a conveyor belt line?


    I noticed a lot of the drills now are brush less would they still arc?

  10. #10
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    Quote Originally Posted by Eddy Current View Post
    So AC no DC yes? What about a pretty large motor that would run a conveyor belt line?


    I noticed a lot of the drills now are brush less would they still arc?
    Not true.

    If motor has brushes to supply current to a wound rotor it will have arcing at the brush contact points, true for both AC and DC supplied motors of this design.

    Any motor that has an internal switch that operates at a predetermined speed (like to open a starting component) will also have arcing when this switch makes or breaks contact.

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