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Generators and motors

  1. Dec 27, 2003 #1
    I just saw a demonstration of an induction motors and was wondering if its possible to build an AC or DC generator without contact brushes? The only way I can think of is if you have a permanant magnet spinning near or within a coil or wire. Is there anyway to produce a magetic field with just kinetic motion? I've searched the net and haven't found any explanation. If you have a link please include it.
  2. jcsd
  3. Dec 27, 2003 #2


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    Staff: Mentor

    Yes. Most a/c generators anyway are inductive.
  4. Dec 28, 2003 #3


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    Science Advisor

    Most motorcycle alternators have no brushes. There is a stator field coil held in place from one side, a steel rotor comprised of 2 halves with a zigzag separation cantilevered in from the other side, and pickup coils on the outside. It works the same as an automotive unit except that since it only has a bearing on one side, the field coil can come in from the other and needs not rotate. In the automotive unit, there are bearings on both sides so slip rings and brushes are needed to activate the field coil.
  5. Jan 7, 2004 #4
    Yes, and you can even convert a standard AC induction motor into an AC generator. All motors act as generators (that's why a motor uses more energy when you ask it to perform more work, and why a motor stops drawing energy if allowed to spin frictionlessly.) AC induction motors are a little weird, but since they already are generators inherently, there must be a way to use them as stand-alone generators.

    The secret: add a capacitor across the output. Then, as the rotor spins, a large AC voltage builds up and a large current exists between the motor coil and the capacitor. Spin the motor fast enough, and choose the right value of capacitor, and you'll have a 120VAC 60Hz generator.

    See: http://www.qsl.net/ns8o/Induction_Generator.html
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