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Electromagnetic Motors

  1. Oct 24, 2009 #1
    Hello. I'm new to this forum, and will probably be harrassing you all with questions for quite some time. My first question deals with electric motors and how they function. I am currently in a Physical Science class in my college. For whatever reason I cannot seem to get a firm grasp on how Electric motors work.

    I know they are typically made up of one permanent magnet and a electromagnet, and that the non fixed magnet is spun by the force of the fixed magnet. This is done by reversing over and over the currents within the electromagnet. I get that much (assuming that what I've posted is correct), but what I can't envision is the details in how it works. What is the relationship between the current flow and why the non fixed magnet spins? I know that a moving electric field creates a magnetic field, but I'm just confused for some reason. Can someone help me out? All help is appreciated.
  2. jcsd
  3. Oct 24, 2009 #2
    Hello Quarkie-
    There are several types of dc motors:

    PM (permanent magnet) rotor brushless dc motor
    1) The electromagnet stator is periodically switched using a Hall Effect sensor to detect rotor position.
    2) Same except the electromagnet stator current is switched by detecting the induced voltage from rotor.

    PM (permanent magnet) stator

    1) Current is supplied to armature by a commutator

    Electromagnet stator and armature
    Current is supplied to armature by a commutator. The stator and armature may be either
    1)series-comnnected or
    2)shunt connected.

    Very large dc motors have other types of connections to the armature.
    The brushless PM-rotor motors can be used at low RPM and high torque wthout damage. The dc motors with commutators can be damaged if the rotor is locked at high current.

    [Added] This list does not include stepper motors, which can provide precise RPM and positioning, but with poor torque and low RPM. The multiple stator coils are usually powered with phase-quadrature dc voltage pulses.

    Bob S
    Last edited: Oct 24, 2009
  4. Oct 24, 2009 #3
    Thank you for the post. I appreciate your answer, and you taking the time to help me, but I'm still unclear on how switching a current on a off and reversing it somehow causes the non fixed magnet to flip due to it's interaction with the other magnet when the non fixed magnet's current is reversed. Can you help shed some light on that, or is my question not clear?
  5. Oct 24, 2009 #4


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    A coil wound on an iron former will become a magnet if current is passed through it.

    This behaves just like any other magnet and it has a North pole and a South pole.

    These will attract opposite poles and repel similar poles just like a normal magnet.

    This is the fundamental way a motor operates. It is just this attraction and repulsion of opposite and identical poles.

    If two poles are attracting each other and one of them is rotating, power is applied until they are opposite each other and then it is reversed on one of them so they repel each other.
    This forces the rotating part to continue rotating in the same direction.
    Because the rotating part has some mass, this action happens very smoothly and you get continuous rotation.
  6. Oct 24, 2009 #5
    Ah....ok. Pretty straight forward when you put it like that. Thanks for the help, I don't know why I didn't get that.

    Just to be sure.....

    This motion that is produced can be used to do work and such, like spinning a fan. Is that correct? The spinning comes from the fact that the magnets share the same alignment and thus causes the non fixed magnet to spin around right? One thing I was reading was that if the electromagnet's current is cut off, then there will still be work done, as the magnetism in the other magnet will FORCE the electrons in the electro magnet to move. Is this true or am I missing something?
    Last edited: Oct 24, 2009
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