Stepper or synchronous motor as generator

You might want to check on the Fischer & Paykel stepper motors they use in their washing machines ? They are easy to work on (reconfigure the coils to change output etc)

Rheilly P

the=20

Those look like nice motors, but they seem to be a bit rare in the US, = and=20 I'm not sure just how much power they can produce. From the pictures I=20 found, it looks like they have magnets on the inside edge of a large = flat=20 rotor shaped like a frisbee, and the stator is an array of about 42 = coils.

I found the following which gives a pretty good analysis of a small = stepper=20 motor used as a generator for up to 0.7 watts at 1600 RPM, and the=20 efficiency was calculated to be about 35-40%. So my somewhat larger = stepper=20 motor generating 1.33 watts at 1300 RPM is not bad.

I took apart a shaded pole blower motor and it has six poles which seem=20 rather easy to rewind if necessary, and I might try using it as a = generator.=20 But I think the shaded poles may work against efficiency. I think they = are=20 just a small section of lamination with a shorted turn to get phase = shift,=20 and I might be able to cut the shorting turn. Then I would need to drive = the=20 motor with a frequency lower than the rotational speed to make a = generator.

I also thought that I might be able to drill holes in the rotor and = insert=20 some magnets to make a generator. But the magnetic path is probably = wrong.=20 So maybe I can just replace the rotor with a non-magnetic cylinder on = which=20 I mount some magnets. I have the blower cage mounted on the motor = vertically=20 and thought it might work as a VAWT, but so far it has not turned in = light=20 wind. I may try adding some sections of thin PVC drain pipe on the = periphery=20 to catch more wind. It's mostly for a demo. I've seen all sorts of = designs=20 on youtube but I think most of them do not put out much power.

From my limited experience it seems like it takes a fair amount of = torque at=20 a pretty high RPM to generate even 10 watts. I've heard that a bicyclist =

produces something like 100-200 watts which is about 1/4 HP, and it = seems=20 like it would take a strong wind and a rather large set of fins to = produce a=20 similar amount, so the supposed 5000 watt VAWTs about the size of a = washing=20 machine tub seem unrealistic.

Thanks for the reply.

Paul=20

Forgot the link:

Paul=20

Actually, this one:

These guys have done it all. Their site's a goldmine of hippy-wind technology.

I expect that steppers would be very inefficient generators; they are designed to have a lot of copper loss, and probably have a lot of eddy current loss at decent speeds. The huge difference between input rating and available output suggests a lot of loss.

A stepper generator will be very inductive, so you'd probably get more power out of a stepper with a conjugate load match, namely add a series or parallel resonating capacitor to the circuit and optimize the resistive load. But that only works at one speed.

The windings are two or three or even 5 phase, so you'd have to deal with that too.

To measure efficiency, you'd have to measure torque as well as speed and do the math.

A PMDC motor would probably be a lot better as a small generator.

Fixed relationship:

Power = Torque * Angular Velocity (SI units)

IE. Watts = Newton.meters * 2 * PI * Revs per second.

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What do you get when you take the energy in that size of moving air, the size that can move by that structure?

have mass of air, from volume subtended by the turbine blades, and the velocity, windspeed.

This is not a 'resonant' structure, so it is not possible to get more energy than appears at the surface of the blades, right?

Hmmm...resonant structure? Wonder if there is some way to make a 'wind cave' to tap off using resonance? no moving blades just pressure waves on its internal surfaces. At least should get more power with smaller structure, right?

IIRC most windmills use induction motors which feed the mains directly. All you need is a relay to connect the windmill to the mains. You can use single phase as well.

The difficult part of a windmill is controlling the speed. You'll need at least a brake. Being able to adjust the vanes to control RPM would be a big plus.

But in practice one must add the efficiency factor, which from what I've =

found can be as low as 35%, and of course even lower if a gearbox or = belts=20 and pulleys are used to get the RPMs required. And I think the second = motor=20 I tried may be defective. I remember taking apart a Slo-syn motor and = there=20 were diodes connected to the windings. I checked the resistance on the=20 inefficient motor and it seemed reasonable (about 200 ohms). But = defective=20 diodes may only be detected at higher currents than an ohmmeter.

I'll check some of the other links and maybe learn a bit more.

There is an interesting concept called the "wind tamer", which = supposedly=20 surpasses the "Betz Limit":

But of course there is another side to this technology:

I have a speaker coming to our meeting of

I also purchased a pack of 44 slightly damaged raw solar cells for about = $40=20 from

they work quite well and put out about 1 to 1.5 watts each, but there = are=20 other factors that affect the optimistic $1/watt estimate. That may be a =

topic for another post.

Thanks,

Paul=20

I have a speaker coming to our meeting of

(sheesh - I need another cuppa coffee)

Paul=20

• A Slo-syn is NOT a "motor", it is a *transformer* where the MMF can move the rotor.

Slo-syn is a trade mark of Superior Electric for small and slow synchronous and stepper motors.

They are not synchros, which are rotatable tansformers used for transmission of angle entities.

Stepper motors are QUITE inefficient. Just crank one fast by hand, see how much effort it takes with NO load! A brush-type permanent magnet motor will be much better. Possibly a permanent magnet brushless motor can do better, as there's no brush drag.

Jon