How to use an AC 220v motor for wind gen

[Pedro Carrizo]

First post, so hello to everyone from Spain.

I want to make a small wind generator out of an AC 220v magnet motor (water pump from a washing machine). Spinning it does give AC electricity.

What would I need to used that electricity to charge 12v batteries?

I know I would need some kind of regulator, but not sure how to handle the AC to DC conversion.

Any help will be greatly appreciated. Been searching online for a while with no clear answers.

Pedro

[Rob Beckers]

Hi Pedro,

Welcome to the forums!

Well, in theory you put a 3-phase bridge rectifier on the output of your alternator, connect it to the battery bank, and bolt some blades to the driveshaft. If the stars align for you it'll actually charge, odds are though not much will happen.

Here's what needs to happen to make this work: When you bolt blades onto the driveshaft of the alternator the wind will spin them. Usually the tips of those blades will go around at about 5 - 7 times the wind speed, resulting in an RPM to the alternator. The alternator produces AC, the bridge rectifier converts it to DC. The alternator would have to spin just fast enough (starting at a reasonable wind speed, say 4 m/s) to produce enough DC to charge the batteries, around 14.5V or so for a 12V bank. As the wind picks up it will then produce more current, and so charge the batteries.

The long and short of my story is that the alternator needs to match with the blades and the battery charging Voltage. Normally that's done by design, in your case you're trying to work your way backwards.

If you know what Voltage the alternator produces per RPM you can calculate what RPM is needed to charge the batteries at a certain Voltage. From that you can calculate the blade diameter to get a tip-speed-ratio (TSR) of around 6. Make some blades, and if you're lucky it'll charge. That assumes the alternator can actually supply the needed power that goes with the blade diameter and wind speed.

Hope this gets you started!

-RoB-

[Pedro Carrizo]

Hi Rob,

Thanks so much for taking the time to reply. That's really helpful. Since I have no idea what rpm the motor is, I think I'll just get the rectifier and experiment with it an learn with the process. Then I'll think of buying a proper motor. I don't need much. 50-70w would be fine, I'm in a caravan with a 100 ah battery and two 150w solar panels.

All the best!

[Rob Beckers]

Since efficiency is of no concern it might work. The starting point is really to connect it to a rectifier, connect that to a battery, and see how fast the motor needs to spin to start charging the batteries. If you get lucky and the RPM is reasonable it could work to make a rotor for it.

-RoB-