I've been doing some thinking about wind power again...

I'd like to put a toy airplane propeller on a small DC motor as a generator. I don't expect huge wattage here, but should be enough. Since I'll be getting AC from the motor, should be no problem putting it through a transformer from a disposable camera flash, and get a couple of hundred volts. I'm looking for around 90 volts DC, to charge a very large capacitor (37,000 uf, or up to 15 in parallel). Yes, I know it'll take days or even a week or two, to get that much energy saved up.

The generator's (cheap DC motor) output will vary wildly, based on wind speed, but not sure how well such a tiny transformer meant to run off a single AA will hold up. Definitely don't want to exceed the rating of the capacitor. I have no idea how to confine the AC voltage to a safe range. Regulating the final DC charging the capacitor would be impractical. Trying to keep it cheap and simple, from salvaged parts.

 

You appear rather confused? - why would you expect to get AC from a DC motor?, I'll give you a clue - you don't!.

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In the early stages of the industrial revolution the fly-ball governor was an amazing invention from several different standpoints. It was an early example of the efficacy of closed loop feedback control, and it is an example of a nonlinear differential equation which can be linearized and solved in closed form.

In your case if you have some kind of brake that will be applied as a function of shaft rotation velocity then you can limit the speed to a range of zero to some upper limit. This should limit the output of the generator. I think the generator itself may provide enough limiting. Have you ever tried to hand crank one? It is a popular exhibit in a "hands-on" museum.

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Just for fun try putting a load on the motor, you'll need alot of wind to turn a toy airplane propeller when a load is on the motor.

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I don't get DC either... AC or pulsed DC, it'll still work with a transformer...

Confused? Mostly uneducated, but working on it, please explain the errors in my reasoning...



So, I'm kind of stuck regulating by mechanical means. Not really good for such a small scale idea. Think the propeller is about 11 inches across. I've been saving motors from everything, something will fit.

Wind... This is Florida, and hurricane season starts soon. Even if it's calm like the past few years, we still get a lot of strong thunderstorms. Anyway, I was going to use solar, but was find that building a 2 volt 1 amp panel was a little spendy. Past few days have been cloudy and windy, hence the wind power alternative. Looks like I'll be spending money regardless.

 

Have a read of this page. Part way down it has a discussion on using small DC motors as generators. The rest of the site is pretty interesting as well.

Mike.