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DC Motors

Discussion in 'Electronic Basics' started by Jon Slaughter, May 28, 2007.

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  1. Don Foreman

    Don Foreman Guest

    For permanent magnet motors:

    No-load speed is proportional to voltage.
    Torque is always proportional to current.

    Under load, the EMF that the armature sees is reduced by the IR drop
    in the armature winding and speed will then be proportional to this
    reduced EMF.

    The amount of current that the motor can draw is also related to
    speed, because a counter EMF proportional to speed is induced in the
    armature. The current is then the (applied voltage - EMF) /
    armature_resistance. So, at stall the current is V/R (V being applied
    voltage), torque is maximum (stall torque) and speed (hence EMF) is
    zero by definition.

    Maximum power is produced at 1/2 speed, because that's where the speed
    * torque product (and EMF * current product) is greatest. Some
    motors can't tolerate this much current without overheating, others
    can handle stall current indefinitely.
     
  2. Thanks guys. I'll see what happens when I get to the point of messing with
    it.

    Jon
     
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