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• # HP for electrical generation?

Discussion in 'The main mechanical design forum' started by jawnn, Oct 31, 2012.

1. ### jawnnWell-Known Member

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Is it true that I will need one quarter HP plus whatever is lost into the gears to generate 1875 watts?
Or is that a matter of speed etc.
I saw a device that will spin a no load wheel fast enough to generate electricity, but I think once they put a load on it would come to a stop,
All I want to do is maintain Â¼ HP pedaling a two stage increase in speed. What wattage can I expect?
And is it true that I could get a higher output than a car generator (running at the same low rpm), with a bicycle wheel rigged as a generator with 36 magnets and coils?

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3. ### ErichWell-Known Member

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There are 746 Watts in each horsepower.
To generate 1875 Watts you need 1875/746= 2.5 horsepower.
Generators are around 90% efficient so you really need 2.5/.9= 2.78 hp.

If you can produce 1/4 hp by pedalling, you can generate .25*746*.9= 168 Watts.

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5. ### ErichWell-Known Member

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Yes. An alternator might be slightly more efficient at converting torque into electricity than a dc generator but the difference is small.

The first law of thermodynamics says energy is neither created nor destroyed but it can change forms. In a perfect world if you want 100 watts of electricity out, you have produce 100 watts of mechanical effort to spin the alternator. In the real world you have to put 110 to 120 Watts of effort in to get 100 Watts out.

6. ### jawnnWell-Known Member

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Alternator hook up?

How would I hook up an alternator like in this video?
I live off grid and need to top off my batteries on the dark days of winter, because our solar panels are not enough.
I need to push the electricity about 25ft to the batteries so what size wires do I need? Probably less than 200 watts with my quarter HP legs.

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8. ### ErichWell-Known Member

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12 gauge wire should be more than adequate.

If you buy a one-wire alternator at someplace like Summit racing, http://www.summitracing.com/

You connect a post on the alternator to the positive terminal of the battery,

Negative terminal of the battery connects to the case of the alternator.

If you want to use an alternator with an external voltage regulator, you can search the web for wiring diagrams,

They are all over.