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DC motor help

Discussion in 'Electronic Basics' started by James, Apr 27, 2005.

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  1. James

    James Guest

    I'd like for someone to explain how a two speed DC motor works. I have
    an idea but what I really want to know is how to increase it's speed
    if possible. Or what determines how fast the motor spins.

    This is a windshield wiper motor. The wipers on my 1980 Fiat Spider
    never did work that great when new. On the fastest speed, the wiper
    motor runs about 46 RPMS. On a "typical" car, 46 rpms would be the
    slow speed.

    The linkage is not binding, the brushes are good, it just never did
    work that great from the factory. I've got 13.7 volts at the motor,
    but I haven't tested it under load.

    Doesn't matter if the wiper motor is running disconnected from the
    linkage or if the wipers are running against a dry windshield.

    There are three brushes. One is soldered to the body so it has to be
    the ground. When power is applied to the grey wire which is connected
    one brush, the motor spins "slow". Then power is suppied to the blue
    wire connected to the other brush the motor spins faster.

    This is what I can't understand. How applying power to one brush makes
    it spin 30 RPMs and when power is applied to the other brush makes the
    motor spin 46 RPMs. Since all three brushes contact the commutator.

    I did some experimenting to see what would happen if I applied power
    to both brushes at the same time. To see if this would make the motor
    spin faster than 46 RPMs. I figured the worst that would happen would
    be I would blow a fuse. The motor actually slowed down and no fuses
    were blown.

    If I were to increase the number of windings on this armature (not
    myself but by a shop that rebuilds starters and alternators) would
    this increase the speed of the motor? There is room for more copper
    wire. Or use thicker wire.

    I'm assuming this will cause the motor to draw more amps but if that
    happens and I blow fuses, I can always wire in relays.

    Some guy rigged up a DC/DC converter and is sending 16.5 volts to his
    wiper motor and says the speed increased from 60 to 96 RPMS! But he
    won't explain where he got the parts. He says it's still in the
    testing mode. I think this would be hard on the motor after awhile.

    I just think there is an easier way to make this motor spin faster.
     
  2. Lord Garth

    Lord Garth Guest

    In universal motors, the type that has stator coils rather than permanent
    magnets,
    you can wire the stator and the armature in series and get high speed / low
    torque
    or you can wire the armature and the stator in parallel and get slower speed
    but
    higher torque.
     
  3. colin

    colin Guest

    dont forget that more turns = slower, less turns = faster, ie taking some
    turns off will make it faster.

    Colin =^.^=
     
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