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### Motor as generator

Posted: Fri Sep 11, 2015 3:27 pm
I have an old exercise bike that I would like to fool around with putting on a generator. I think I know that you can use a DC motor as a generator but I have some questions.
1. Does it have to be a permanent magnet motor?
2. As an example, if the stats on an imaginary motor says: 12v. 1amp, 700 rpm, does that mean that motor would put out 1 amp at 12 volt if driven at 700 rpm?
3. how much horsepower does it take to produce 10 watts?

### Re: Motor as generator

Posted: Fri Sep 11, 2015 5:15 pm
i have seen people use anything from permanent magnet motors to car alternators, and even some giant stepper motors.

it will take about 0.013HP to make 10 watts... feel the burn baby ! get to cranking them pedals..lol
as far a getting out what you crank out ( motor data plate ) that i am not sure of..

### Re: Motor as generator

Posted: Sat Sep 12, 2015 3:16 pm
Motors used as generators are not all that efficient, but would work especially for your purpose where efficiency doesn't matter much. Go for it!
What to do with the generated power is another concern.

### Re: Motor as generator

Posted: Sun Sep 13, 2015 10:54 pm
Sounds like the foundation for a really interesting experiment! Please share the results...

### Re: Motor as generator

Posted: Mon Sep 14, 2015 4:47 am
i have the motor out of a treadmill, the motor is rated at 2HP 120VDC
the treadmill console is shot, so i plan to repurpose the motor for something else sometime soon.
( wind mill ? )

### Re: Motor as generator

Posted: Mon Sep 14, 2015 6:04 pm
1. you should use a permanent magnet motor, you need a magnetic field and any other type of motor you would have to create that with a battery until you got going fast enough to self generate, anyway far more inefficient as you spend half your energy creating a field you get for free with a permanent magnet.
2. 12V, 700RPM and 1A does not account for torque. In your case, you probably have torque to spare, so the question is are output specs invertible to become input specs for a permanent magnet DC motor. I'm not positive but I think it would be close with some losses.
3. 0.013 HP minus losses in the bicycle mechanism. I expect 10W would be easy to generate with a modest motor.

Try it this way 1W= 1J/s and you use about 1J when you burn ~0.25 Calorie, so 10W should take 2.5 Cal out of your body and it takes about 1 minute of brisk walking to expend that energy (I couldn't find a bicycle conversion factor).