I have a large DC stepper motor, is it going to be possible to use it as a wind generator?

[cutlass1972]

I put a cordless drill on it and spun it at some slower and medium rpms (not sure exactly how fast but about half what the cordless drill was capable of).

It has 4 sets of contacts and a label on the body of the motor that shows a schematic of 4 coils and lists what wire colors correspond with which coil. I put a digital multimeter on it set for ac power and read from 150-200v.

could I put all of these segments in parallel and put it through a 10-1 transformer then rectify it and feed it through my charge controller into my batteries?

 

[ghurd]

"feed it through my charge controller"

That will blow up the controller.

The 4 coils are out of phase.  Paralleling all 4 will be a short circuit, mostly.

Could probably parallel the correct 2, then the other 2, and use 2 transformers.

Test the short circuit current of a single coil.  I expect it will hit a plateau at a relatively low RPM.

The current may be almost to low to make a transformer work.

G-

[cutlass1972]

OK, I tested one coil and got 750ma on a dead short. I would think that is more than enough current to induce a current through a transformer.

So you are proposing that I put opposite pairs of coils in parallel, put the 2 pairs through a pair of 10-1 transformers, then through 2 sets of bridge rectifiers and a Capacitor as a filter, then parallel the output into my charge controller?

[ghurd]

NOT into your charge controller.

It sounds like you have a solar controller, and I expect it will blow up from too much voltage on the input.

But other than that, yes.  Mostly.

No need for a capacitor.  The battery takes care of the filtering.

Will need/want to do some experiments to determine the transformers ratio.  

I expect it would be better at maybe 5:1, but it will depend on the output curve, and the blades, and about everything else.

Not sure what the step angle is, but might have some issues with too much frequency in some transformers.  Might try to scrounge up one rated for 400Hz.

That's good output for a stepper.

G-

[cutlass1972]

I don't understand why I would not go through my charge controller? If I run it straight to my battery, is there not a chance I would overcharge the battery and boil the acid?

[cutlass1972]

Oh by the way, I am running a 12v system not a 24v. Did you still mean to only use a 1:5 ratio transformer? I would think I would want my charge voltage to be between 14v-19v for a 12v system? I would have 30v-40v with a 1:5 transformer or 15v-20v with a 1:10.

[cutlass1972]

One more tidbit here, My solar panel is only 30 watt and my charge controller is 7a, I think it can handle the solar panel and the wind turbine, if overall current was your concern.

[ghurd]

You don't understand how a typical solar controller works.

The battery gets to full voltage.  The controller opens a semiconductor.  No amps flow.  The panel goes to open voltage of 21V.

With a windmill, the battery gets to full voltage.  The controller opens a semiconductor.  No amps flow.  The windmill is unloaded, the blades go faster, increasing the open voltage even more.

The semiconductor is maybe rated for 30V.  It is trying to stop 50V? 100V?  Whatever, but it blows up.

Wind generator controllers actually regulate the battery.

The wind generator is connected directly to the battery.  

It is important for the blades to be loaded (by charging the battery) all the time.

Also, the panel is near 2A.  Without a transformer, the 4 coils are about 3A.  

If the input:output amps of the transformer can manage a lowly 1:2, then the 7A is already exceeded.

"(not sure exactly how fast but about half what the cordless drill was capable of)."

Maybe 500RPM?

Most stepper motors cog pretty bad, needing low TSR blades to get them turning in 'normal wind'.  That can make 500RPM relatively fast.

With 10:1, and 500RPM making 150V, I think it would be kind of difficult to get much output in 'normal wind'.

Stepper motors do some strange things.  It's not easy to predict how they will act in real life use.

G-

[cutlass1972]

I understand how the solar charge controller works, it bulk charges at a higher voltage until the battery reaches a certain voltage then it only allows a lesser voltage in to trickle charge or keep the battery topped off.

I see what you are saying about the wind turbine though, the less the load the less magnetic resistance the stepper motor has which means free spinning. Understood.

I guess a true wind generator charge controller would have a shunt resistor of some sort and an emergency dead short mode to stop or slow the generator drastically.

Sounds like I could stand to have a true wind generator charge controller if I want to keep from damaging my batteries.

Thanks a ton for all of your input, I really do appreciate it.

[TomW]

1972;

Read Glens post again.

We control the battery not the turbine. The turbine feeds the battery all the time at whatever it can produce. The controller watches the battery and dumps power to control the voltage on the battery. At least Ghurds controller does.

It is essential that the turbine remains loaded at all times. The battery does this. Solar controllers can either short the input or open it neither of which is what we want.

Not talking about MPPT charge controllers here like the MX60 just in case you are confusing these devices with a ghurd controller that is a completely different animal.

Tom

[ghurd]

If you don't want to jump in with a true wind generator charge controller right away,

might look into a 'ghurd controller kit'.  LOL

It's probably all you really need.

http://www.fieldlines.com/story/2007/8/24/172521/889

G-

[cutlass1972]

this is the solar charger I bought just for reference.

http://www.amazon.com/gp/product/B0006JO0XI/ref=ox_ya_oh_product

I think I understand, a wind generator charge controller has the ability to shunt to a load when the battery is full rather than simply reducing the load from the battery without shunting to a load whick would lower the magnetic load on the generator letting the turbine spin more free with less restriction.

What I need to control the power out of my wind generator is something like this with higher current handling capabilities.

http://www.shop.powerplanted.com/product.sc?productId=7&categoryId=4

[ghurd]

They say "Our charge controller will automatically disconnect your wind generator or solar array from your batteries when they are full and switch it to another load."

That's not good.

Why?  

What Watt, Volt and Ohm load will you put on it to properly load the windmill without shorting it?  It's a trick question that can't be answered.

"This controller requires a relay" is not good either.

[cutlass1972]

I thought I posted this already but I guess not.

Hey Ghurd. Is that your design / page? Will your kit handle the current my little stepper motor is going to put out? If it will do what I need it to I am going to buy one on payday!

[ghurd]

It will handle it.  Might need an extra fet.  I can't say what the kit needs until you can say what the stepper makes.

"Little stepper"?  It makes a whole lot more power than any I ever had.

G-

[cutlass1972]

it is pretty big, about 4" in diameter and 6" long with a big 1/4" thick mounting bracket on the end of it with 4 tapped holes, on on each corner. It weighs about 3lbs. It came out of a machine that was made to turn a fairly heavy weight with pretty precise control. It also shows a diagram of which leads goes to which coil on the side of the motor. I can post a pic of it tonight if that would help.

I am kinda questioning if I would be better off just trying to find a standard permanent magnet low rpm dc motor somewhere rather than try to work out stepping the voltage down on all of those phases?

After researching it I am not positive I would not have to go with 4 transformers and as you noted it may be difficult to find high frequency transformers.

[ghurd]

'a standard permanent magnet low rpm dc motor' has some pretty big value now, but it is easier.

That's a king sized stepper.

If you decide you don't want to keep going with it, feel free to shoot me an email.

Maybe we can do some horse trading.

G-

[cutlass1972]

WOO HOO! Good news, I put my stepper motor on an oscilloscope today at work and drove it with my cordless drill. I am not sure why my fluke dimm read such high voltage, I triple checked my range, I can only assume it was because the frequency was all over the place. My scope read me a perfect 28V AC. Furthermore I was able to match up all coils in phase and get 28v AC from all of them in parallel.

I wonder if my current reading was correct at 750ma on one coil shorted? If that is the case I will have one bad little +/- 3A low rpm generator here.

[ghurd]

"was able to match up all coils in phase and get 28v AC from all of them in parallel."

You mean all 4 coils paralleled together at the same time before the bridge?

I can't see how that would work.  If the coils are in phase, it wouldn't step, I think?

Try to spin it by hand connected that way, and try it with them Not connected.

See if connected is harder to turn at all.  Might see if any AC current is moving through 1 coil when in the parallel connection.

If you mean 2 seperate pairs of paralleled coils then that makes sense.

G-

[cutlass1972]

you know what, you are right. I am not sure what I was doing, maybe I had a loose connection on 2 coils or something, but I cannot get all 4 together any more. I have 2 pairs of 2 that I can connect and not get any resistance.

I guess I just have to use 2 bridge rectifiers and combine them as dc.

Is 28v peak too high to charge a 12v battery?

I did notice that it doesn't hit 28v until the stepper reaches about 1500hrz. It is pretty much dead on 12v at 1000hrz though.

I think I may have to do some gearing up to achieve the rpms I want out of my wind machine I am building. I might go with a 2:1 increase in my belt pulleys or sprockets depending on which way I go.

Any thoughts on any of this?

[cutlass1972]

I was able to run 3 12v .5a computer cooling fans (old compaq style aluminum framed fans) at pretty close to full speed with one coil of this stepper motor run through the rectifier circuit out of that old 12v power supply I was talking about a couple of replies back. I had to run the cordless drill wide open (2000 hz according to my scope) but it had all 3 fans spinning good on one coil.

 I think this little stepper motor is going to be a power house for its size!

[TomW]

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Tom

[RP]

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