hydro generator from treadmill motor [Archive]

Sean DEpagnier

12th July 2011, 15:59

I got a treadmill motor out of a dumpster the other day. I have a prop from an outboard, and also some model airplane props which are carbon fiber. Problem is, they are designed to push water, not have water spin them. Should I try to build a prop, or could I modify some of these?

The motor is rated 120vdc 10a. I need to charge 12v batteries. I figure that if I can get 10a at 12v then it would be worthwhile. This also allows for fairly low rpm operation. My boat travels 4-6knots, so assume 5 knots of flow. The things I am wondering:

Can I just hook up a diode in series with the motor to prevent it from spinning on battery power, and allow charge, or do I need a dc/dc converter that can do peak power tracking or something?

How do I calculate the prop size/pitch needed?

How can I seal the motor to prevent water getting in? I was thinking I could hook a cable to the shaft and put the prop at the end of the cable so the motor is out of water,and the prop in the water. Even still I need to seal the motor so it doesn't die from salt water. How do you guys do waterproof bearings?

Dave Turpin

18th July 2011, 20:07

Not to be too discouraging, but I can think of several reasons this won't work.

1. If this is a sailboat, I assume something like 30 foot, then you might as well say the flow speed is something between 0 and 5 kts. At that speed, the props you have, even unloaded, would spin at like 10 rpm. This is going to be below the excitation speed for the motor, and you would produce nothing.
2. With a proper prop, there is still not going to be enough energy in the stream to extract.
3. If you did make power, it would be at much higher voltage than the batteries could take. There is no such thing as a dc-dc convertor. (unless it is a combination of an inverter, a transformer and a rectifier)

Basically you are doomed from the start. Don't go cutting holes in your sailboat to try to get a motor you found in a dumpster to work. Why not get/make a small wind turbine instead, and put it up on top of the mast?