HarveyH42

I got some airplane propellers, and went through and found which motors I had that spun fail easy and had shafts that fit with minimal modification or conversion. One is a bipolar 9V, and 2 are 12v (pretty sure) unipolar. Really clueless on how to work the diodes and phases to my best advantage. I'd be happy enough to charge 4.8 volts worth on NiMH batteries, could live with 3.6 volts, but of course more is always better. My load will be an MCU and some LEDs, nothing too heavy for the first experiment. Just want to get a feel for how much useable power I'll have. This is kind of a new direction for me, so no previous experiences. I can do a basic single phase power supply, and can probably get by with that, but I'd think I'd only by making use of maybe half of what is actually generated.

Nigel Goodwin

Why not use a normal DC motor?, self rectifying, no messing about - there are LOT'S of good reasons why steppers aren't used.

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HarveyH42

Wouldn't I need a much higher RPM to get usable power? Don't think I have any thing larger than 12VDC. I don't have a tach, but would be surprised to see 2500-3500 RPM, but it is huricane season here... Perhaps a boost converter.

Basically, I've got a box full of steppers and don't use them, only a few ideas involving steppers. This is small scale and using mostly salvaged parts. We don't get strong constant winds, usually atleast a light breeze. If I can get some useful flashing lights, might consider a much larger project.

mneary

Steppers are usually designed to offer considerable resistance against moving, even when not energized. That's probably the biggest barrier to using them effectively with low input energy.

As for rectifying them, there are some MOSFET based active rectifiers that are sometimes seen on high-efficiency switching power supplies. Later I might try to find some.

bryan1

Hiya Harvey,
Eh mate checkout the link to the backshed in my sticky as Glenn has a complete project on using a stepper motor for a small wind genny. I made one from a bipolar 5 volt 1 amp stepper and made a pvc 2 blade prop which is also shown on the project site. In a strong wind I'm seeing about 15 volts and 160mA open circuit and i've hooked it up to provide a led light path from my shed to the house.

Cheers Bryan

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HarveyH42

Thanks, will have a look. Sounds exactly like what I'm after on this project.

Hero999

In theory a stepper motor should be more efficient as there are no commutator losses, there again there will be losses in the rectifiers. You also get less noise and a smoother power supply from a stepper motor alternator with less noise so I would say stepper motors are superior to DC motors as generators.

There is nothing complicated about a stepper motor rectifier; look at a three phase rectifier and add more diodes.

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HarveyH42

I went to the site refered to in the 'sticky' (sounds dirty...), they used a full wave rectifer on each coil, tied the outputs together in parallel. They had some interesting ideas for rotor blades from PVC pipe. Also show how to use a 3 phase rectifier from a car alternator. Lots of good stuff to think about.

Hero999

Here's how I would do it.

I've even simulated it for you!

Notice how the output never drops below 52.5V even though >2.5A is being drawn and I'm only using a 470F capacitor?

The more phases the motor has the less ripple you'll get so you'll be able to get away with a smaller filter capacitor.

Attached Images

	5 phase rectifier schem.png (9.0 KB, 22 views)
	5 phase rectifier graph.png (8.0 KB, 12 views)

Attached Files

5 phase rectifier.asc (2.9 KB, 5 views)

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HarveyH42

I'll give that a try a little later. I was looking through parts for bridge rectifiers, but didn't find two of the same. I know I have more, but they must be buried some place with other seldom used parts.

bryan1

Hiya Harvey,
Eh mate all I used for the bridge recifiers was 4 standard 6 amp diodes( the ones you get for 5cents each), as a stepper wont be putting out that much current they work fine. Anyway last weekend we had gale force winds and I finally brought home the digi camera from work to take a pic for you and the genny must of spun that fast the pvc blades had disappeared only for my son to find them in the next paddock behind the house about 800 metres away. I'm now glad I didnt putup my F&P genny as planned as if I did my 2" water pipe tower would be a twisted mess. I'll need to put atleast 4 more guy wires on before it goes up. anyway when it does i'll post some pic's in my projects thread.

Cheers Bryan

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HarveyH42

I've got 3 steppers with propellers, but have done anything to mount them on a vane, or where I'm going to eventually mount them. Was going to do the fence posts, but the best ones are along the back alley and a little concerned about kids. Maybe roof mounts. Have done much lately, we are getting only light wind (it's huricane season here, and my air conditioner vent spins them faster).