Stepper or synchronous motor as generator

[P E Schoen]

I've been looking into the feasibility of using various types of motors as
wind-powered generators, so I thought I'd see what some motors I have will
do. I connected the motors with diodes from each pole to 10uF 400V
capacitors with a common connection, and placed the load on the (+) and (-)
legs.

Here are the results:

Superior Slo-Syn HSL063T1Y, 120 VAC, 0.4A, 50/60 Hz, 60/72 RPM

21K 269V 3.45W 300 RPM
11K 250V 5.68W 300 RPM
1K 92V 8.4W 300 RPM

Superior Slo-Syn SS50G20, 120 VAC, 0.3A, 50/60 Hz, 3.6 RPM (*20 gearhead =
72 RPM)

21K 141V 0.95W 300 RPM
11K 112V 1.14W 300 RPM
1K 23V 0.53W 300 RPM

Shinano STH-56D218, 2.1V, 1.65A, 1.8 deg/step, 1.8 ohm/phase

21K 4.24V 0.001W 300 RPM
1K 3.63V 0.013W 300 RPM
1K 14.4V 0.207W 1300 RPM
180 15.5V 1.33W 1300 RPM

I was surprised at the low power output, especially the second synchronous
motor, which is similar in size and specs to the first. I used a
battery-powered drill for the drive and speeds are approximate, but
generally the values are the maximum, as the output did not go up after a
certain lower speed was reached. The last motor actually has eight leads,
but one set is 1.8 ohms and the other set is 18 ohms, and I think they may
have been used as a speed monitor. It came out of some unknown equipment.

The first motor, which seemed most reasonable, was an almost new unit, but I
expected closer to its input rating of 48 watts. The second unit came out of
some old equipment and had a gearhead, probably 20:1, which I removed.

Do stepper motors go bad? Is there something about the circuit I used that
limits the power obtainable? I like the fact that the power of the 72 RPM
synchronous motors peak at 200-300 RPM which is reasonable for a
direct-drive windmill. 1300 RPM, not so much.

I also have some 1/4 HP DC brush motors I thought I might use, but I think
they are rated at about 8000 RPM at 12 VDC and I will definitely need a
speed multiplier with belts or gears, which will reduce efficiency.

There are also lots of DC motors on eBay such as 1-2 HP treadmill motors
which are supposed to be good for wind power. I used to have one but I may
have given it away. I'm also going to look into using a three phase
induction motor as a generator, but it needs to be driven with a three phase
source at just under the speed that is supplied on the shaft, and then using
what would be the dynamic brake as the generator load.

Thanks,

Paul

 

[P E Schoen]

"Rheilly Phoull" wrote in message

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)

Those look like nice motors, but they seem to be a bit rare in the US, and
I'm not sure just how much power they can produce. From the pictures I
found, it looks like they have magnets on the inside edge of a large flat
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
motor used as a generator for up to 0.7 watts at 1600 RPM, and the
efficiency was calculated to be about 35-40%. So my somewhat larger stepper
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
rather easy to rewind if necessary, and I might try using it as a generator.
But I think the shaded poles may work against efficiency. I think they are
just a small section of lamination with a shorted turn to get phase shift,
and I might be able to cut the shorting turn. Then I would need to drive the
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
some magnets to make a generator. But the magnetic path is probably wrong.
So maybe I can just replace the rotor with a non-magnetic cylinder on which
I mount some magnets. I have the blower cage mounted on the motor vertically
and thought it might work as a VAWT, but so far it has not turned in light
wind. I may try adding some sections of thin PVC drain pipe on the periphery
to catch more wind. It's mostly for a demo. I've seen all sorts of designs
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
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
like it would take a strong wind and a rather large set of fins to produce a
similar amount, so the supposed 5000 watt VAWTs about the size of a washing
machine tub seem unrealistic.

Thanks for the reply.

Paul

 

[P E Schoen]

Forgot the link:

http://www.solarheatengines.com/wp-content/uploads/2011/01/Current-vs-RPM..jpg

Paul

 

[P E Schoen]

Actually, this one:

http://www.solarheatengines.com/2011/01/28/generating-power-with-a-stepper-motor/

 

[Fred Abse]

From my limited experience it seems like it takes a fair amount of torque
at a pretty high RPM to generate even 10 watts.

Fixed relationship:

Power = Torque * Angular Velocity (SI units)

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

 

[Nico Coesel]

I've been looking into the feasibility of using various types of motors =
as=20
wind-powered generators, so I thought I'd see what some motors I have =
will=20

have given it away. I'm also going to look into using a three phase=20
induction motor as a generator, but it needs to be driven with a three =
phase=20
source at just under the speed that is supplied on the shaft, and then =
using=20
what would be the dynamic brake as the generator load.

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.

 

[P E Schoen]

"Fred Abse" wrote in message

Fixed relationship:

Power = Torque * Angular Velocity (SI units)

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

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
and pulleys are used to get the RPMs required. And I think the second motor
I tried may be defective. I remember taking apart a Slo-syn motor and there
were diodes connected to the windings. I checked the resistance on the
inefficient motor and it seemed reasonable (about 200 ohms). But defective
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
surpasses the "Betz Limit":
http://aristapower.com/wind/

But of course there is another side to this technology:
http://www.wind-works.org/SmallTurbines/WindtamerHypeNeedsTrimmed.html

I have a speaker coming to our meeting of www.baltimoregreenforum.com, and
he has been installing wind and solar energy systems for quite while in
Maryland, which is generally not known as an area with high wind resources
or even very much insolation. But I want to do some of my own research and
come to my own tentative conclusions before he speaks in two weeks.

I also purchased a pack of 44 slightly damaged raw solar cells for about $40
from http://mlsolar.com/Solar_Cells.html through eBay, and it seems like
they work quite well and put out about 1 to 1.5 watts each, but there are
other factors that affect the optimistic $1/watt estimate. That may be a
topic for another post.

Thanks,

Paul

 

[P E Schoen]

I have a speaker coming to our meeting of www.baltimoregreenforum.ORG

(sheesh - I need another cuppa coffee)

Paul

 

[Tauno Voipio]

* 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.