Monday, June 22, 2009

Re: [Electric Boats] dumb question about a fan



constancedraper wrote:
> So, I am assuming this motor was generating some amount of electricity. What would it take to capture that? Something more complicated than a diode?
>
A standard domestic fan motor is likely to be an induction motor, they
don't make good generators, there are no magnets in there, the motor has
to be supplied with power to generate the magnetic fields.
3 phase induction in larger applications can and do 'regenerate', but
they also have reasonably complex control systems as well, they don't
just hook the motor straight to a resistor (dynamic braking) or a
battery. Some of the 'brush-less' motor/controller combos being used on
our boats are capable of regeneration, the argument is over whether it's
worth the returns, not the tech. The tech works.

My electrical theory isn't up to being able to conceive how you could
get a single phase shaded pole induction motor to 'regenerate'. It
certainly won't on it's own, no magnetic fields, but I'm not clear if
you could 'excite' the system to start making electricity and self
sustaining those all important magnetic fields. Unlike a series motor
with field coils, there isn't a separate set of coils you could energise
to make the fields. Induction motors are black magic. :-) (But cheap,
simple and relatively efficient, hence popular for things like fans and
other mains powered domestic appliances that need a motor).

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