How can you calculate how much power can be generated by a motor when used as a generator (like a motor used in a wind turbine)?

Does the power depend on how fast the magnet is rotated? If so, is there a equation that lets you know given the rpm, how much power should be generated?

Also, how can I account for limiting factors such as the strength of the magnet (moving a coil around a stronger magnet should give more power than moving coil around a weaker magnet)?

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    $\begingroup$ For each type of motor/generator, there are well-known equations for the torque $T$. The power $P$ is the torque $T$ multiplied by the rotational speed $\Omega$: $P=T\Omega$. $\endgroup$ – Karlo Mar 25 '16 at 7:55
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    $\begingroup$ @MWc You should expand on that a little and make it an answer. $\endgroup$ – Chris Mueller Mar 25 '16 at 14:02

When used as a generator, a motor can generate approximately the same power that it requires for operation as a motor at rated speed and torque.

In general, the voltage produced by a generator is directly proportional to speed. Power is proportional to voltage multiplied by current. The maximum current that can be drawn from a generator is generally a fixed value that is not determined by speed. Therefore the power that can be produced by a generator is directly proportional to speed.

The effect of changing the strength of the magnetic field (field excitation) is generally to increase or decrease the voltage generated.

There are a number of factors that determine a generator's limits for safe operation. Those factors are generally similar between motor and generator operation. They need to be considered for each different type of machine, AC and DC, wound-field and permanent-magnet, induction and synchronous, plus all of the sub-categories and design variations.


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