Battery Charging

There are several options depending upon your ultimate needs and the 400Hz 28 volt generator power rating.

1. To directly generate 120 VAC, you need a 400Hz 28 volt motor of approximately the same power rating as the 400Hz generator. Connect the 400Hz motor to a 120 VAC 60Hz generator to generate normal AC power. I personally don't see this as being something one would want to do with a windmill as you have no power when the wind isn't blowing.
2. To directly generate 12VDC to charge 12 volt deep cycle batteries, all you need is a bridge rectifier and filter composed of a large value capacitor. You would charge parallel groups of 2 batteries connected in series. This would be my personal choice, as the batteries are able to continue to provide power when there is no wind, or not enough wind.

You would need to convert everything you could, like lighting, to 12 volt. Where you must have 120VAC you would need either an inverter (converts 12VDC to 120VAC 60 Hz by electronics means and is rather expensive), or a large 12DC motor driving a 120VAC 60Hz generator. For a DC motor, look into surplus jet engine starter motors. These starter motors are what was used on the early experimental battery powered cars; one for each driven wheel. Keep in mind that anything that converts to 120AC is going to use up some of your available power from the windmill, converting it into heat which is lost. Therefore, the more you are able to use 12VDC directly, the better off you are.

Offered by Ron.

Rectifying the power to 12VDC to charge batteries sounds the most efficient to me, but from my understanding of AC motors/generators the line frequency they produce is directly related to the number of poles inside the motor (usually 2 or 4 for most 60Hz motors) and the speed at which the generator is rotated. It is a linear relationship - the faster you spin it, the higher the frequency.

Offered by Rob.