What could/should I safely expect with my stepper?

[drjeseuss]

I have a 4 phase stepper motor I'd like to use as a small wind generator to experiment with.  It's  a Superior Electric Slo-Syn M061-FD02.  The ratings listed are 5.0v 1.0A DC 200 steps per rev.  I've played with it a bit using a simple prop to spin it up while measuring output.  I'm connecting each phase pair to a bridge rectifier and connecting them in series to double volts out.  When I spun it up with no load I was seeing approx. 18-20v DC from each bridge output.  I'm not sure this is good however.  Since it's rated 5v I expected to get about 10v after the bridges were wired in series.  At the rate of volts I saw it should mean I was getting 9-10v DC per phase, almost double it's rated capacity.  Is there a safe percentage above rated while still being safe for the motor?  Or am I facing a likely burnout at this level?  If I understand the stepper configuration it should yield +5v and -5v from one phase set, which after the bridge produces a pulsing +5v only, not an additive 10v.  Is that correct?  I know once I add load it will slow the RPM's, but at such a higher voltage than expected, I'm a bit concerned of destroying the motor.  I can say the RPM's I was seeing (unsure of actual RPM, didn't measure this) seemed slower than I've seen this run as a stepper motor at the rated 5v.

[scorman]

not much ...more than just current /voltage specs!

IMHO, the basic design of a stepper is opposite what you want for a generator. By design it "cogs", since that is the way it defines it's "steps".

So even if you got it to work at some higher rpm, the built in stall at low rpm will cause you to lose most wind you want to have to get the thing going

I am currently assembling a 460v/3 phase/3 amp per leg AC PM servo motor capable of 1.5KW ...more in the line of what you should be looking for

sorry to rain on your parade

Stew Corman from sunny Endicott  

[ghurd]

I have done very bad things to steppers.  Never had one die.

Probably better off using the bridges in parallel.  In series, the phases are out of phase and the resistance is double.  Resistance is the output killer.

A load won't slow it down much.

G-

[drjeseuss]

ghurd,

  I'm curious now.  To explain my wiring a bit:  I've got 1-COM-2  and  3-COM-4.  I'm connecting 1 and 2 to the AC side of the bridge, then 3 and 4 to my other bridge.  The commons are floating (no connection).  I got the idea from this site:

http://www.reuk.co.uk/Stepper-Motor-Voltage-Doubler-Circuit.htm

The idea is to compensate for the 5v rating of the motor.  I've decided this isn't the output limit, but I still would like to stay in range to charge 12v.  If I can get 12+ in parallel, I'd like to use it instead for the heavier current anyhow, but I'd like to know more about the "double resistence" you refer to.

In reference to the cogging issue, I've seen little to no effect with my test setup.  I have since added a small bulb for load.  I notice the resistance to turn, but it seems to start in even a slight breeze.  Once the breeze becomes a few mph it spins quite nicely.  I had read of the cogging issue and was worried, but having tried it to see what the fuss was about, I'd say in my case it hasn't presented an issue thus far, and that's with a very basic 3ft diameter PVC blade.

[ghurd]

It's not how I figured you had it wired.

If you have 18-20V open, doubling the voltage isn't needed.

My luck with caps and steppers has been very poor. Even with big giant caps.

If the stepper won't reach 12V, tricks will get it to 12V, but the output is useless. Meaning about any stepper from any cheap junk printer will do better.

Steppers hit a limit to the amps into a battery. Even if the RPMs rise, the current stays the same.

Cogging with steppers has never caused me trouble.

Starting it with a bulb on it makes it start harder.  That causes drag.  It won't have that when it's connected to charge a battery, because it won't have drag until charging voltage is reached.

It was making 18-20V with a 3ft PVC blade?  Wow.  That's not bad.

What I would do:

Make a new blade about 24".  It will go a lot faster so the volts will be higher. It will start easier without a bulb attached (not easier than the 36", but it will be better for 12V battery charging)

Make a new blade about 20".  If it has trouble getting started, put the 24" back on.

Nothing is written in stone for steppers.  It is trial and error.

Don't expect 75ma into a 12V battery and you will be happy. Learn a lot too.

I wouldn't over complicate it.  I used to, but not any more.

Made this for my niece, the "K Windmill".  It's about as complex as I would go even for 12V now.

http://www.fieldlines.com/story/2006/4/25/184337/514

G-

[ruddycrazy]

For the Ozzie variant of a steppermotor wind generator go check this one out

http://www.thebackshed.com/windmill/assemblyMini1.asp

Glenn has done a great job describing how to build it from mounting to the electronics everything is there.

Cheers Bryan

[Flux]

Stepper motors are not meant to generate and only the hybrid types will do so.

You are using a by-product in its design and nothing of the ratings as a motor gives you the slightest information on how it will behave as a generator except perhaps for the resistance ( if quoted).

Volts never burns anything out, it is current that does that and the internal reactance of a typical stepper is likely to be so high that it can't be burnt out as a generator.

Only useful for toy wind power but have fun, that is the main thing. Don't be bothered about that 5v rating that is not a limit not even as a motor as they are current driven.

Flux

[wooferhound]

It may be Flea Power

but if you get enough Fleas

you will have the whole Dog

[drjeseuss]

ghurd,

  I see what you mean about a smaller blade.  I've tried both a 36" diameter, and a 24" diameter with noticable difference in RPM.  My current blades are both from 2" diameter pipe.  I've used the 0 to 25 degree rule when measuring for width.  Would I benefit from a larger diameter pipe, thus a fatter blade, or would this just increase drag again?  I'm torn, more surface, more drag. Or more surface, more energy collected.  I know with the stepper currently in use, it's my main bottleneck, but I'm trying to work up a better design before increasing the stepper to a larger gen.  Also, if the volts top out at the battery level, and the amps are also once the voltage stops climbing, it is safe to say that higher RPM is virtually pointless until I increase the gen output?

I liked your K-lite.  It's an interesting substitute for a solar path light.

Note: sorry to be so far off the main topic of this thread.  I think I might be gifted with A.D.D.  

[ghurd]

OK.  I posted (or attempted to post) something earlier but "Vista" totally sucks. Crashes every 5 minutes.

Under "I wouldn't over complicate it."

I think I said something like "Don't be discouraged" and "If it takes a lot of effort, time, money, then spend an extra day and a few extra $ to make a small quickie motor conversion to get 5 to 100X more 12V battery charging power".

I believe anything 'normal' under 30" dia needs 4" or 6" PVC.  24" seems better with 4".  It depends on who did what with what.

And I don't like the issues involved with PVC blades over 24".

"I've used the 0 to 25 degree rule when measuring for width."  

Uh, What? ("Vista" so no time to look)

I use "Zub-Woofers" measurements for PVC.  I tried changing stuff but the results were not good.  The blade plans...

http://www.fieldlines.com/story/2005/4/19/161431/811

The Volts on anything/everything top out at the battery level. (the gen can't be 50V, with a 0.7V diode drop, into a 12.6V battery)

The Amps of a stepper top out at a certain RPM level. (if it makes 100ma into a 12V battery at 1000RPM, it might only make 110ma into a 12V battery at 2500RPM)

It's not the same, but it seems you are beginning to understand that.

The bottleneck is the resistance, among the other things Mr. Flux listed.

"interesting substitute for a solar path light".

Check out Claude's stepper windmill nightlight...

http://www.fieldlines.com/story/2006/10/10/212737/59

It's your thread.  My understanding is you can take it wherever you like, because as related to the main thread, it keeps everything in one place, and the off topic stuff is related to what you want to know.

G-