Silly question about an electric fan

[kawalekm]

If you take a regular electric window fan and stick it in the wind the blades will turn. Why is it that the fan is not producing electricity when it's turning? Is the RPM too low, or are there rectifiers that prevent electricity from going "backwards". I see a lot of sites that scrounge or even wind their own wind generator power heads, but I don't see any electric fan motors mentioned. Does anyone know the mechanics of why that is so? I'd be interested in making my own generator, but am confused as to the different array of motors that could be adapted to power generation.

[machinemaker]

most electric fan motors are "induction" motors that have have a set of coils in the stator, ( the housing) and the rotor, the part that spins is a steel core with aluminum cast around it that acts as a coil. when you apply power to the stator, it induces a current in the rotor, but there is no physical electrical connection to the rotor. This induced current is off phase to the stator, it isn't the same magnetic direction and this out of alignment of magnetic poles causes the motor to turn. So when the fan is just spinning in the wind the rotor does not have any magnetic Field or power to induce a field into the coils in the stator. But if you were to replace the rotor with a magnet(s) then you would have a generator. Have you seen the web site www.windstuffnow.com its a good site for DIY wind power.

[AlchemyAcres]

*I'd be interested in making my own generator, but am confused as to the different array of motors that could be adapted to power generation.

Permanent magnet motors are the best and probably easiest to convert to a generator.
The biggest concern if you're looking to produce power via wind, is finding a suitable low speed PM motor that'll make a good generator, without gearing or other losses.
One of the very best is the Ametek 99VDC 010300F6, but they're almost impossible to find.
Another major consideration is the fact that the shafts on most motors aren't designed to withstand the forces of a rotor.

The best bet is to build a turbine from scratch, and one of the best sources, if not the best, for that info is Hugh Piggott at Scoraig Wind, all his books have been great, but "How to build a wind turbine" is exceptional. It's the best $20 you can spend if you're interested in building turbines.

http://www.scoraigwind.com/

~Martin *:)

[kawalekm]

Thanks Kent and Martin! Those were good, informative answers.
Michael