Mini Windmill

The picture is a prototype mill put up in 2011.

Made from scrap materials

Generators on hand
We have gotten our hands on 10 or so small permanent magnet brushless DC motors from an industrial ventilation system. Theese are suitable as generators since they produce three phase AC when turned. They are 90 watts each so they are only suitable for micro and small mini wind mills. They were designed to run on 280 volts, so they'll easily produce a usable voltage level, even at low RPM (rounds per minute). The challenge is to keep the current low, since the coil windings are made of relatively thin copper and as soon as you start exceeding around 1 ampere, any addtional torque seems to be lost as heat in the copper. I made a little test, and using the same chordless drill on maximum power to rotate the axle of the genrator, I managed to produce around 15 watts charging a 12V battery, whereas the genrater output exceeded 50 watts when charging a 72V battery bank. At 72V the RPM's are significantly higher and the lower current to power ratio means less heat loss in the copper for the same amount of power.

Project start: 
March, 2010