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View Full Version : Stepper motor as a generator??



wiatroda
03-08-2011, 09:43 PM
Did someone try to use stepper motor as a generator?
When you connect a coils leads together it's quite hard to turn a shaft. Just wonder how good it will do as a generator eg.windmill.

Gary
03-08-2011, 10:04 PM
They do act as a generator and i have had people buy them for this, but the problem is they make a lot of noise.

Jonathan
03-08-2011, 10:07 PM
The detent torque is too high to make it useful for a wind turbine. Also what rpm do you need to get a decent voltage...I suspect it's a reasonable amount.

There's better ways - make your own with neodymium magnets and copper coils. I've made a couple for wind turbines, will post a couple of pictures in a minute.

wiatroda
03-08-2011, 10:29 PM
I think someday I'll give a try for stepper motor generator. Just for try or rather fun. I have idea stuck in back of my head to make a windmill. The only concern can be shaft thickness to cope with a rotor but tooth belt reduction and rotor on its own shaft can sort this problem out.
Gary: my neighbours got used to some weird noises blasting from my backyard and I can only hope a stepper motor generator won't over-exercise their patience :)

Jonathan
03-08-2011, 10:54 PM
If you're thinking of making a wind turbine then you might be interested in the (roughly) 1kW generator & variable pitch wind turbine I made:

(In no particular order)

4313
4314
4315
4316
4317
4318

The good thing with making the generator this way is:


It's coreless, so no cogging = low cut-in speed. Energy density/efficiency is worse, but you make up for it with big strong magnets.
Since you're winding the coils you can get the right voltage without gearing (less maintenance and SIMPLE).


My wind turbine does use a wind turbine, but not for the generator. It's to vary the pitch of the blades via a worm drive and bevel gears:

4321
4320
4319
4322

As you can see mine (along with many others) uses a hub (like a trailer wheel hub, except I made one to fit better) and tapered roller bearings. That means the rotor is mounted on six M12 rods which is plenty strong enough.

The reason I made my CNC router was to make the blades (3.1m diameter) for this wind turbine....which I've still not done as I keep changing my mind.

wiatroda
03-08-2011, 11:33 PM
Jonathan, that's one of or more likely the best DIY turbine generator I've ever seen but I'm afraid my budget couldn't handle this project and put my skills to the test :).
I honestly thought about VAWT- there are some advantages of this kind of turbine- especially in urban turbulent winds. They are slower than HAVT so they require generator to kick at lower rpm, but without messing with some kind of reduction bigger dia generator (more magnets and coils thou) of your kind from previous post would perfectly do.
What do you think about VAWT Jonathan?

Jonathan
03-08-2011, 11:47 PM
Jonathan, that's one of or more likely the best DIY turbine generator I've ever seen

Thanks.. it was my A-level project. I've not found another DIY turbine with active pitch control. I went much further than required for the A-level though. I've not done anything with it for over a year now :( ... I'm intending to test the generator with lathe on VFD as that'll be a more accurate setup than using the school Bridgeport to get readings. I machined all the parts manually... no CNC.


I honestly thought about VAWT- there are some advantages of this kind of turbine- especially in urban turbulent winds.

That's what I heard, but there's so many more sources that say they are not as good generally. How many commercial VAWT's have you seen?


They are slower than HAVT so they require generator to kick at lower rpm, but without messing with some kind of reduction bigger dia generator (more magnets and coils thou) of your kind from previous post would perfectly do.

For mine to 'kick' at lower RPM you just need to increase the number of turns on the coils since the voltage is proportional to the number of turns. Just make a test coil out of anything, spin the generator at known RPM. Then you get volts per turn per rpm ... decide what cut-in speed you want and just scale it to get the required number of turns. Then work out the biggest wire you can fit in the available space ... use multiple strands if it's too big to wind easily.


What do you think about VAWT Jonathan?

Forget it... there's just more to go wrong.

wiatroda
08-08-2011, 06:52 PM
Jonathan have a loot at this video, It nicely shows how turbulent wind is in urban area.

http://youtu.be/rLa_NY5U1nk (http://youtu.be/rLa_NY5U1nk)
Do you think HAWT is able to follow so changing wind direction ?? I doubt it.

Jonathan
08-08-2011, 10:46 PM
Jonathan have a loot at this video, It nicely shows how turbulent wind is in urban area.[/URL]

The thing is it will vary for each site, which in my opinion makes discussing in general terms not very productive.
The VAWT in that video is a drag based machine (so TSR<1), so is inherently inefficient compared to any HAWT, and better VAWTs. At a higher windspeed (which after all is what we're interested in since power is proportional to wind speed [b]cubed[b/]) the turbine with TSR>1 (i.e. VAWT or HAWT with airfoil profile blades) will generate much more power. If the wind is turbulent then I think neither of this type will be that effective since when the wind is coming from many different directions the resultant force on each 'section' of the blade will be different - so the overall torque may not be that much. So that implies that yes a drag based VAWT would work better than HAWT in turbulent wind, but still not generate much power as it wont benefit from higher windspeeds. Also in tubulant winds fatigue on the VAWT blades, which are already highly stressed compared to a HAWT, will be greater possibly leading to faliure.

I tend to agree that VAWT should be better in turbulent wind, just from common sense. I think that it's not worth considering having a wind turbine if your site is very turbulent (unless you don't need much power, say off grid). However if you've made it yourself, and therefore very cheaply then why not experiment... design the generator so you can try VA and HA with the same swept area and compare.

If the wind is that turbulent then you should just put the turbine higher, and use a HAWT. Granted planning permission is an issue, but it's clearly the best way.

[QUOTE=wiatroda;23291]Do you think HAWT is able to follow so changing wind direction ?? I doubt it.

Not one of a useful size, the moment of inertia is high and therefore cannot accelerate into the wind without a larger force from a big tail, and the gyroscopic forces would be large, so it is going to need a very strong tower to do that ... etc it's just not worth it.

Also in the video it says 'The HAWT will turn in lighter winds so it it more efficient' ... which is a bit of a dodgy statement.

wiatroda
08-08-2011, 11:11 PM
That's what I thought to build, both HA and VA and compare performance ( generator can be the the same to cut costs and make whole experiment more data accurate) .
Permission makes me hesitate to build either one of them but the idea is still in back of my head. My garden location is very turbulent place and that's why I consider VAWT more appropriate for this location. Lots of reports say vawt doesn't need tower to be so high as havt so there is less risk it will fall to neighbours' gardens :). When I have some spare time (or money) I think I'll play a bit with stepper as generator and to control load by PWM proportionally to rotor RPM. Just an another idea.
Anyway, your generator looks superb. When are you going to put it up?

Jonathan
08-08-2011, 11:17 PM
Lots of reports say vawt doesn't need tower to be so high as havt so there is less risk it will fall to neighbours' gardens :)

Lots of reports say that wind speed increases with altitude, from which you can conclude that having the turbine near the ground is less effective.


Anyway, your generator looks superb. When are you going to put it up?

Thanks, but there's still things I would improve if I made another one. No idea when as we don't have space for it (according to my Mum and Dad). I'm waiting for an opportunity to appear to mount it...