This is a PM DC motor from an 1980s vintage Vitamaster treadmill. The nameplate says its 15 amps, 90 volts, and 4800 RPM. By my calculations, if the relationship between voltage and rpm is linear, the motor would have to be going about 693 rpm before it would produce 13 volts. (I would chuck it into a drill press and test its output, but my drill press is too small.)
My questions are:
1) Is there a linear relation between voltage and rpm? If a motor goes 4000 rpm at 100 volts, will it produce about 10 volts at 400 rpm? Or does it produce more/less voltage per rpm at lower speeds?
2) Is it realistic to build a direct drive windmill at 700 rpm, or is that way too fast?
3) How nasty are chain or belt drive windmills? What are their main drawbacks? They would be less efficient and require higher start-up wind speed, but by how much? They also would probably be higher maintenance, but also by how much?
The first application for this windmill will be as a backup generator for power outages on a small island on the coast of BC, Canada. Eventually it or a later model will probably be installed as part of a full-duty alternative power system.
We've considered building a axial flux alternator for the project, but our shop capacities are limited at the moment, so we're going for the quick and simple approach for now.
Any suggestions from all you otherpower wind whizzes would be wonderful!
Thanks,
Adam
P.S. Here's a picture of the motor: