Mike Hord wrote:
>> BUT it may be easier to simply use a fixed magnet and rotate a coil
>> past it to generate voltage.

That works in theory, but it won't be easy getting significant power that
way with a home brew design.  The rotating transformer secondary will be
easier for a do it yourself project.

> In this case, where does the power come from?

The mechanical power of the rotating shaft.  There is no free lunch.  The
magnetic forces between the coils and the magnets will push opposite the
shaft's direction when used to power the rotating circuit.  This will appear
as additional viscous drag to the motor trying to drive the shaft.  The
motor will therefore draw additional power.

Note that with a phase shift in the coil current, the arrangement would work
as a motor instead of a generator.  In this case however, the rotating
circuit would be supplying power to the coils instead of taking power from
them.


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