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Converting from AC to DC

  1. Feb 11, 2014 #1
    1. The problem statement, all variables and given/known data
    I just learned that in a DC motor you use a commutator to convert the AC current to DC. And in my other course I learned that you can convert AC current to DC using a rectifier circuit. If this is the case, why don't we use a rectifier circuit in a DC motor to convert the AC to DC?
  2. jcsd
  3. Feb 11, 2014 #2
    It is the other way around. In DC motors, DC is converted to AC by the commutator. Do you understand why this is done?
  4. Feb 11, 2014 #3


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    You sure about this? Can you describe in a bit more detail what you think the commutator is doing and why ?

    This isn't really homework with a 1,2 3 template, but asking for detail might help understanding the background and nature of this question.
  5. Feb 11, 2014 #4
    Oh yeah you are right, in DC motors it is the other way around. I think I get it now, you need the commutator to give AC current so that as the coil (not sure if this is the right name for the rotating object, please correct me) rotates 180 degrees, the current will flip directly to keep it rotating.

    It is because I initially saw a video on generators found here:

    In this example, could I replace the commutator with a rectifying diode circuit?
    Last edited by a moderator: Sep 25, 2014
  6. Feb 11, 2014 #5


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    Yes. Definitely. Advantageous too: less mechanical wear, less sparks etc.

    Beautiful video.
  7. Feb 11, 2014 #6
    That is not wrong in general. There is more specific terminology for electrical machines, however. From the electrical point view, a coil would be called (part of) "armature" (note there may be more than one coil in general). From the mechanical point of view, the rotating part would be called the "rotor".
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