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Micro Power wind generator
By olvvlo, Section Wind Posted on Tue Feb 15, 2005 at 04:34:59 PM MST
Trying to get small amounts of electricity on a small scale at low wind speeds

I have been trying to build a 12v wind generator to do nothing more than just trickle charge a car battery.
The output needs to be just over 12v to charge although the current need only be quarter of an amp or less.
I also need it to produce this at very low RPM ideally 60 RPM as I am using a multivaned prop of about four foot diameter.

It turns well in very light winds producing a good torque and reaches a maximum of 120 RPM before it is set to tilt out the wind.
I set about building a three-phase generator with 10 coils per phase, each coil having 40 turns equalling 400 turns (26swg 0.45mm) per phase.
I have two plates rotating either side of the coils with ten ¾"x1/8" disk magnets totalling 20 magnets.

I tested the output by spinning the generator on a lath, initially I was using half inch magnets and got less than 1 volt! I then refitted the generator with ¾" inch magnets. Now I get about 2-3 volts. I increase the speed to 600 RPM at the speed I get 12 volts open circuit and 7volts under load.
I have concluded from this that I should be using thinner wire and very many more turns if I am going to achieve 12 volts at 60 RPM. It also seems it is much harder to produce small amounts of electricity on a small scale than larger rigs as everything becomes more critical and leaves less room for inefficiency!
Has anybody got any advice or suggestions as there seems to be a lack of information about generating electricity on this scale?

Micro Power wind generator | 19 comments (19 topical)

Re: Micro Power wind generator (3.00 / 0) (#1)
by iFred on Tue Feb 15, 2005 at 09:58:59 AM MST

Yes you can! Look for small DC motors and use smaller faster blades. I don't why you want 60 rpm's? thats pretty slow for just about anything. If you want slow RPM's like that your going to need a rotor that is like 15 to 18 inchs or a gear or belt drive system. But for the power level (milliamps) that you need I would start playing with small toy type dc motors and a higher preformance type blade, the blade need only be like a foot or two in diameter or so but be higher rpm and balanced. The only problem I forsee is the bearings in the motor, which are not designed to handle the stress. however, if you could somehow gear a motor; so the gears and shaft and rotors take the stresses rather then direct drive to the dc motor then you could make it last much longer and not worry about the bearings in the motor. Those DC motors put out anywhere from .250 to .750 ma power or so.. the larger ones put out a bit more.

my two cents worth.

>> all energy used to produce this comment or post came from solar and wind energy! It works!

Re: Micro Power wind generator (3.00 / 0) (#2)
by ghurd on Tue Feb 15, 2005 at 10:09:41 AM MST

Nice to see I'm not the only one!

Are the magnets neo? There is no substitute for good magnets.
And they seem a little small or thin. Maybe neos and double the thickness?

I was working on something similar. It needed 1800 turns per phase for 150rpm cut in(if I remember right). The magnets were neos, and a little smaller.

I went to a 1/30 HP conversion. It works! Wired a little different I think it could get 12v at 80rpm, but surely less than 0.050a (extremely high coil resistance). A better magnet rotor should get the cut in a little lower.
The conversion was a lot easier, faster, and cheaper. Doing things (that worked) was about 4 hours, new motor and magnets were $7.

The blades cover some pretty good area. Maybe try gearing it up for a faster gennerator speed?

Maybe a little conversion like mine fastened above or below what you have there, and a little fan belt from the conversion around you magnet rotor (like a pulley)?
Or the same thing with bike chain and sprockets?

G-
Ghurd.info

Re: Micro Power wind generator (3.00 / 0) (#3)
by olvvlo on Tue Feb 15, 2005 at 10:28:52 AM MST

Thanks but I have gone down the path of using small electric DC motors, as you say they do need to be spun reasonably fast but would indeed do the job. However I need to use the present design as having cloth sales keeps it ghostly silence and hence meets the approval of the neighbours. Previous to this I have used dual rotor designs and have also have arrangements involving gears however both produce a lot of noise and need fast wind speeds.
You do have a point about the diameter of the generator, I guess if I made this significantly larger the magnets would pass the coils much faster and also allow me to increase the number of winds per coil.
Yes the magnets are Nero but perhaps a little small. I do wonder whether increasing the number of turns on the coil is also important.

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#4)
by ghurd on Tue Feb 15, 2005 at 10:54:20 AM MST

I didn't mean a DC motor. I just put magnets in an AC induction motor. Same as a Maytag conversion, only a lot smaller. Lots of pre-wired turns, add 1 wire and 4 magnets, and away it goes.
G-
Ghurd.info
[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#5)
by Flux on Tue Feb 15, 2005 at 11:03:23 AM MST

Your magnets are very small and you are right that you have to increase the number of turns.

To be realistic I think you need to use 16 poles ( 32 magnets ) of that size.

I would do it in a single layer winding with 12 coils with those round magnets.

I think you could get your cut in at 60 rpm and manage about 1 amp at 120.

If you can live with less output then you may get away with 12 poles ( 24 magnets) and 9 coils.

It is perfectly possible to produce a silent machine with a better propeller with a tip speed ratio of 4 that would let you use a lot higher speed, but it is perfectly possible with your sailwing rotor.

Would be much easier to start with some decent magnets such as 2 x 1 x 1/2".

Flux

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#7)
by olvvlo on Tue Feb 15, 2005 at 12:31:21 PM MST

Sounds like good advice, if I increase the diameter and have as you suggest a single layer of coils there should be room for 16 poles and 12 coils.
I wonder what gauge wire should then be, I guess it wants to be fairly fine as if it is to large the resistance will drop and the current increase as far as I understand. This would surely then increase the drag and at low rpm such as this, may stall the mill.
You suggest I use larger magnets 2 x 1 1/2" difficult to know quite how to pitch all these variables.

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#8)
by Flux on Tue Feb 15, 2005 at 01:28:28 PM MST

Stall is not going to be a problem with that rotor and speed, use the thickest wire that you can get in with the turns you need. Your limitation is going to be to get enough speed and the lower the resistance the better.

As you already have a lot of those magnets I would use more of them rather than start again with the bigger ones.

If you are prepared to experiment I think you might be able to use what you already have if you make a 20 pole single rotor, either with 15 coil single layer or with a 20 pole version of your existing winding.

The normal problem is to find good enough core material but in your case with very low frequency and high starting torque, thin mild steel strip or even annealed crate banding strip may be good enough. With the thin magnets, eliminating one mechanical gap will give you a lot more winding space, you need to keep your stator thin.

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#10)
by olvvlo on Tue Feb 15, 2005 at 02:06:47 PM MST

Great, have you any advice on the approximate number of turns as Ghurd above mentioned 1800 turns per phase. Making my 400 seem completely inadequate?
Not sure what you mean by core material, are you suggesting I fill the area inside the coils with metal? And if so would this not generate a huge cogging effect?

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#6)
by electrondady1 on Tue Feb 15, 2005 at 12:08:23 PM MST

love your geni. reminisent of the anchient creten , truly elegant. i'm going with a vertical axis design. it must also produce at 60-150 rpm. i was thinking 3 large dia. mag disks. lots of poles(16) two stators lots of coils . maybe two phase. i think when your pushing the envelope with low rotational speeds you've got to concentrate on coil/mag. shape to get the most out of it . check out windstuff ed's . ijust got back from the machine shop 1 hr. ago with my parts. gonna start right now! good luck!

Re: Micro Power wind generator (3.00 / 0) (#9)
by iFred on Tue Feb 15, 2005 at 01:48:47 PM MST

I have found that if you double the magnets up you will increase the strenght 1/4 and thus the output. Also, if you make the core thinner and increase the flux, you get more power as well. Make a core with say #26 wire which can handle 3amps without problem, you could go with #28 or 30 and limit to no more then 1 amp or less. increase core size slightly to about say 6-8 inchs, decrease the thickness of the core and increase the magnetic field strenght.

Setup a small work station to test a single coil and two rotors with the magnets attached to get a fix on rpm vs output, this is the way I do it. once I know the output of a single turn and 10 turns, i can caluclate the exact output of the machine at any given rpm and the number of turns and coils needed.

here are some basics
http://www.internetfred.com/generate/generate.html

Good Luck!

>> all energy used to produce this comment or post came from solar and wind energy! It works!

Re: Micro Power wind generator (3.00 / 0) (#11)
by olvvlo on Tue Feb 15, 2005 at 02:15:50 PM MST

Re: Micro Power wind generator (3.00 / 0) (#12)
by olvvlo on Tue Feb 15, 2005 at 02:19:00 PM MST

Just seen you post, very good point about doubling magnets up.
I think I will stick to #26 wire as I already have a few hundred metres left, and having 3 amps gives a little security.
and yes it does make sense to set up a workstation, I should have done first time round and will certainly do before I set anything in resin this time.

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#13)
by olvvlo on Tue Feb 15, 2005 at 02:21:50 PM MST

Just followed you link, thanks looks like there is loads of information there.

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#14)
by iFred on Tue Feb 15, 2005 at 02:36:27 PM MST

I think if you can get the flux way up there, reduce the thickness and douple the mags, then do a work station test you might find you require less turns, to many turns will increase the resistance thus kill the output. I would estimate with around 150-200 or less turns per coil or less. The key is to get the cutin voltage at 60 rpm or so. means you got to play a bit. if your good with electronics you could build maybe a pulser circuit as others have suggested for low wind conditions, might help as well for charging. best to ask on this..

>> all energy used to produce this comment or post came from solar and wind energy! It works!

Re: Micro Power wind generator (3.00 / 0) (#15)
by olvvlo on Tue Feb 15, 2005 at 02:50:48 PM MST

Hum, when you reckon on 150-200 turns how many coils have you in mind?
And a pulser circuit? Sounds interesting. Do have any info on these circuits or leeds?

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#16)
by Flux on Tue Feb 15, 2005 at 03:14:43 PM MST

Advice is coming in so thick and fast that even I am confused by this lot.

With 16 poles dual rotor using those magnets I think you will need about 800 turns per phase with a gap between magnets of 1/4" but if you loose a lot of winding space you will need more.

When I mentioned core I was talking about the backing laminates with a single rotor arrangement with only one magnet set. This is for an unslotted backing laminate, you could do better if you are prepared to make slots but then I think silicon iron would be needed even in this case.

You may do some good with bits of lamination in the holes of the coils on a dual rotor but you are in unknown territory and it may have problems.

When Ifred mentions core he seems to be meaning the stator but I may have misunderstood. In his reference it seems to be used both ways.

I certainly agree that you need to experiment rather than cast anything at this stage.

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#17)
by iFred on Tue Feb 15, 2005 at 04:26:23 PM MST

do a search on this site "pulser" or capulser, theres lots of info.

>> all energy used to produce this comment or post came from solar and wind energy! It works!
[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#19)
by olvvlo on Tue Feb 15, 2005 at 05:16:25 PM MST

yep, looks like a whole new area to explore for me and perhaps very relevant thanks

[ Parent ]

Re: Micro Power wind generator (3.00 / 0) (#18)
by olvvlo on Tue Feb 15, 2005 at 05:14:02 PM MST

Thanks to everybody who have contributed to this post so far and I will look again tomorrow to see whether there are further developments.
I have become increasingly intrigue by the concept of micropower and I hope there will be more posts on this topic. As there is a huge amount of emphasis upon generation of electricity at relatively high wind speeds but in your average year most people experience seemingly few days with adequate wind.
If we were to concentrate on low wind speeds then perhaps the accumulation will equal a net result much greater, in a similar way that solar panel's operate. Continuous accumulation of energy perhaps being more useful than short bursts of high energy!

Micro Power wind generator | 19 comments (19 topical)

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