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Dc motor to generate power

  1. Apr 7, 2014 #1
    I have a 1.5 hp dc motor that I am going to use water power to turn . How much power can I expect from this . It is just a summer fun project .
  2. jcsd
  3. Apr 7, 2014 #2

    The Electrician

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    The theoretical equivalence between electrical power and mechanical power is: 746 watts = 1 horsepower.

    In theory, 1.5 HP = 1119 watts.

    Taking into account various losses, etc., you probably could count on getting 700 watts. That's a fair bit of water power for a small stream, for example.
  4. Apr 8, 2014 #3
    Thanks for the info will keep you updated on how it works
  5. Apr 8, 2014 #4


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    You would need to know how the field coils of the motor will be powered first.

    If there are no field coils there will be permanent magnets and you should get output immediately.

    If the field coil connections are brought outside the motor you may be able to power them with a battery like a small motor bike battery, just as a test.

    You could drive the shaft of the motor with a variable speed electric drill and measure the output voltage.
    This would tell you if it is going to work at all.
    Mount the motor solidly to a bench or in a vice before you do this, to avoid injury.

    The output voltage will be less than the normal running voltage, but could still be quite high if it is a high voltage motor. So be careful if this is the case.

    Universal motors like the ones used in power tools are series connected and the field coil current will be zero until you connect a load to it.
    You might get some voltage out due to remanent magnetism.

    Be safe though. Wear safety glasses and keep your fingers away from anything moving.
  6. Apr 8, 2014 #5
    Thanks for the input . I was planing on using as drill to test. This motor is out of a floor polisher so it comes complete with rectifiers and all the circuitry outside of motor
  7. Apr 8, 2014 #6


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    Does your motor have any writing on it? Usually there is a metal label on it with voltage ratings etc.

    I would expect a floor polisher to have an AC induction motor in it because it would operate at constant speed.

    Can you see brushes inside the motor?
  8. Apr 8, 2014 #7


    Staff: Mentor

    If you do that, you can be certain thst you can't make more power than the drill puts out. I think most drills use 400 watts or less. To test the maximum your motor can make, you must spin it with something more powerful than the motor.
  9. Apr 8, 2014 #8


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    Depending on the motor, there is a real chance it won't produce anything at all as a generator.

    So that is why testing it at low speed with an electric drill would be a good idea. You have to start somewhere.

    You could also get full voltage out, even if you can't produce full power. Just a 60 watt lamp at the rated motor voltage would make a good load to start with.

    Electric drills are pretty universal and probably the easiest way to conduct this test.
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