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Power output of a simple generator

by treplag
Tags: generator, output, power, simple
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Jan9-13, 09:58 PM
P: 6
How do I convert the RPMs of a simple turbine (e. g. a windmill) into the power it generates? Let's say that I want to know if a single windmill of a certain size can power a refrigerator. Assume that I already know how long the blades have to be to produce the RPMs, and I know the energy requirements of the refrigerator. I am only looking for a basic equation of RPMs to power (watts or joules). Thank you.
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Jan10-13, 01:30 AM
I_am_learning's Avatar
P: 669
I don't know the answer, but I at least know that its not that simple.
RPM alone don't tell the full story. You could get a small baby-toy scale turbine to rotate at the same RPM as a big power turbine.
What you can get is - for a given wind speed, and for a given turbine type of certain size you can find out the mechanical power output. The mechanical to electrical conversion is often >90% efficient.
The theoretical limit to the maximum power that can be harnessed is given by
Power_max = 0.5 x Swept Area x Air Density x Win_Velocity^3
But to get anywhere near the maximum power you need to have a state-of-the art turbine design.
Jan10-13, 01:54 AM
P: 6
Hi, I_am_learning - Thanks for your input. I was afraid it might not be as simple as I had hoped. Apparently I will have to keep digging.

Jan10-13, 05:26 AM
P: 22,239
Power output of a simple generator

Power is rpm times torque divided by 5252 (English units).
Jan10-13, 09:32 AM
P: 6
Thanks, Russ!
jim hardy
Jan10-13, 12:55 PM
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Quote Quote by russ_watters View Post
Power is rpm times torque divided by 5252 (English units).
Thanks Russ !

i've been looking for an easy to remember number for that conversion, and 5252 is it .
52 twice makes me think of Tex Ritter's "Deck of Cards"

So at 5252 RPM torque and horsepower have the same number. That's right in operating band of small outboard motors i tinker with.

old jim

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