Zero Is The New Black

2 Responses to “Can a car alternator be used for a wind generator?”

1. goober on March 20th, 2010 at 4:08 pm

   Yes, but you would need to gear up the rotation of blades to drive the alternator shaft. The alternator shaft in a car runs much faster than the blades of the wind turbine. Look at the diameter of the alternator pulley compared to crankshaft pulley and then remember that a car engine idles at about 700 rpm. So you can expect that the alternator would like to run at 1500+ RPM. It will produce some power if driven directly but it will probably not be worth the trouble.

2. Rudydoo on March 20th, 2010 at 4:09 pm

   Hey Kevin, Goober is quite right on the rotation speed. But either way, I would highly suggest against this idea. We actually tried it about 20 years ago. I did the same math Goober did, and ended up changing the pulley on the alternator to a smaller 2 inch diameter to help accomodate this. There are two problems. First, a car alternator does not have permanent magnets, it has to be, “excited,” by an external source. So anytime the wind slowed down and the turbine stopped producing, you would be draining your batteries. Virtually all commercially built turbines today have permanent magnets installed in the rotor. The other problem is the car alternator is an inherently inefficient device. It needs to be cheap, light, and last a long time in high temperature, freezing, raining and vibrational conditions. So they use an oversized cooling blade, bushings instead of bearings, and poor clearances on the rotor to add to longevity. You would need a huge turbine to make one small car alternator work.

   We ended up taking ours apart and then tried to use the alternator to produce electricity with a stationary bike. It actually worked, but you had to stand up on the pedals and pump with all your might, nobody could do it for more than about 15 seconds. This further illustrated what we already suspected, the device is too inefficient. A car engine works with several hundred horsepower, wasting an extra half horse at the cheap alternator is no problem, but a human in good shape at peak power output can only produce 1/3 hp for any extended time.

   If you really want to build your own turbine, get an electric scooter motor instead. They are cheap, small and easy to find. I will list a good source below. For your research, one HP is equal to about 750 watts. If you selected a 100 watt scooter motor, you would need at least 1/6 HP of wind energy to run it. Then you’ll have to do the rotational speed calculations again. Many websites that sell these small electric permanent mag motors will have design RPM listed, figure on being able to turn it just a bit faster than this speed to produce energy. Then all you should need is a diode between the motor and your battery so the battery won’t backfeed the motor when the wind dies down. In case you’re wondering, we are in the process of building another stationary bike with a 240 watt scooter motor right now, be a few months before it’s done. Good luck Kevin, and take care, Rudydoo

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