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permanent magnet alternator load problem

Discussion in 'Home Power and Microgeneration' started by David Williams, Aug 6, 2007.

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  1. -> Hi all,
    -> I've made a simple permanent magnet alternator. For the sake of
    -> experimentation I've attached the rotor to a D.C . motor, and the
    -> motor to a constant voltage power supply. When I complete the circuit
    -> with my wire coils, for some reason the current draw goes up and the
    -> rpms go down on the rotor. This happens whether there is a load or no
    -> load across the coils. The coils are in no way connected(intentionally
    -> at least) to the rotor or motor. I don't know what is happening, or
    -> how to prevent it. Any help would be appreciated.

    -> Thanks,
    -> Mark

    Do you mean that you short-circuit the coils, or put just a small
    resistance across them?

    Your rotating magnet will induce a current in the coil. The direction
    of the current will be such that the magnetic field it produces
    *opposes* the changing field from your magnet. So the magnet will
    experience a "drag", slowing it down, and making the motor driving it
    take more power. The extra energy will appear as heat in the coils, and
    the load if there is one. You may not notice it immediately, but after
    a while they'll get warm.

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