My second windmill after the HD wind generator

[mrkooo]

After I finished my first wind gennerator made with HD magntes http://www.fieldlines.com/story/2005/9/24/152446/359  It works fine and was good for a test, now I want to build a bigger one. My problem was the neo magnets, it is very hard to find them here in Peru, a friend send me 24  2"x1"x0.25" from US and this is what I have done with them.

3 phases 9 coils estator. Each coil have 75 turns of #14 wire, 1 ohm per coil.




12" disc, testing a sigle coil




This is just like Otherpower design, SKF hub with ball bearings from a farm machine.




The stator came out with 2 cracks, but no problems yet with them.




Generator assembled







The genny is located at ta top of the building where a live







I´m using an old 70amp car batery, 500W 12V to 220V inverter.




The Shunt regulator

I have the impresion that the blades are to small for the generator, I´m using the sames 1m blades that I used for the HD magnets windmill. With the HD genny they turn at +400rpm, now the fastes is 170rpm.

Volts 12V

Cut in speed  120rmp

max rpm       170 rmp

wind speed    20 Km/h (+-13mph)

Amp at 170rpm  8amp

I thinking to built a 1.3m blades, I think that when the genny star charging there is a lot of resistance that the blades can`t handle.

What do you think about this.

Thank you for all your help

Francisco

[willib]

cool urban wind generation.

i like that.

More blade  root might help , also try charging at 24V it will raise the cutin but give you more speed and power , overall

[Flux]

Nice job.

120 rpm cut in is far too slow for a 2M diameter prop. If you can find another battery try it into 24v as willib suggested, I think it will come to life at 24v.

If you can get at the star point you could connect it delta or Jerry rig ( rectify each phase separately). Even so at 12v I think you will need to open the air gap.

Flux

[electrondady1]

nice job mr.koo!

[richhagen]

At first I thought your blades were stalling badly, and they probably are a bit, but when I looked at the available power compared with the output power you reported, it looked better than I would have expected given the small blade size for that alternator and the low rpm reported.  (providing I didn't misread something or make a math error)

At 20Km/hr air speed, for a 1 meter diameter blade there would be about 344 watts of kinetic energy in the air passing it, so if you are harvesting 8 amps at around 12 volts, you are getting 96 watts of it, or just under 28% of it, which isn't that bad considering your blades appear like they should be in a stall condition because of the low tip speed ratio they are operating at.  Still, you could potentially achieve a higher or similar efficiency for a larger swept area, thus generating significantly more power.  While your blades can't go faster because they can't harvest more power, they are still generating reasonable lift based upon the efficiency.  That surprises me given the low RPM.  I would have expected the efficiency to go much lower.  

If the numbers provided are correct, I don't think that just going to 24 volts with the same blades will help a whole lot, as while the rpm will go up, and possibly the efficiency, I don't see it going up by more than 6% to 35% overall(about a 21% increase in output power) and I doubt it would go up that much.  There is only so much power in the wind.  

You have the thinner magnets than the standard designs usually built here, and the stator is about the same thickness.  Still I would think that longer blades, such as 5 foot and fewer turns of wire in the stator, would enable you to utilize your 12V system, and generate much greater output.  With larger blades optimized for a lower wind speed you will have to adjust the furling to ensure that the stator doesn't over heat in high winds.      

On a good note, the view looks lovely, and I am happy to see that you can mount the turbine on your building.  Here, I only mount tiny ones that do not attract too much attention.  I don't even know how one would go about getting a permit to mount a large turbine on a rooftop here.  Rich

[mrkooo]

Thank you all for your comments, very good and interesting analisis Richhagen. Before I go to the bigger blades, I will try a bigger airgap and see what happend. If the blades are stalling badly with a bigger airgap the blades will make it better and have more output from the genny, thats what I understand. If nothing happen and the output still the same, that means that there isn´t more energy in the wind to harvest and I need bigger blades.

About the roof, fortunly no neighbourght have claim about the mill on the roof, when I told them that I`m using it to lighting my apartment and saving money, all of them want a wingenerator too. Here in Peru we dont have a law yet about RE, also I belive that I`m the only one in the country that have a windgenny in the roof. It gets the atention of everyone that see the genny and get very curios about it.

I will post what happend increasing the airgap.

Thanks

Francisco

[willib]

Rich i dont see where your getting such a high figure for the available power from the blades.

i see 134 Watts available from a 1m radius blade ( 2m dia)at 20km/h, so he is getting 72 percent of the available power.

they are real nice blades btw, what kind of wood is that?

i agree that opening the gap will help as flux also sugested ..if  Francisco doesnt want to go for 24 volts ?

[richhagen]

72% would beat the Betz limit.  I am using 1/2 times the mass times the square of the velocity for the kinetic energy of the air passing the blades, and a density of air of 1.28 kg per cubic meter.

The air passing the blades each second would be the equivelant volume to the swept area time the distance the air travels in one second.

20 kilometers per hour = 20000 meters per hour, and dividing by 3600 seconds per hour yields 5.56 meters per second.  

The area, since the blades are one meter, is pi times one meter times one meter, or 3.1415 square meters.  

The volume of air passing the blades is then 3.1415 square meters multiplied by 5.56 meters, or roughly 17.45 cubic meters.  

The mass of this air would then be 17.45 cubic meters times 1.28 kg per cubic meter, or 22.34kg of air.

The kinetic energy in the air moving past the blades would then be 1/2 times 22.34Kg times 5.56 meters per second times 5.56 meters per second, or about 345 watts.  I think I had 344 watts above, but I didn't round until the end.  

That is how I came up with the efficiency I listed above.  I am not sure how you arrived at the 72% figure.  I suspect we are looking at the problem differently.  If one was to figure that about 40% of the total energy is the maximum that one could obtain and use that for a basis, then the 28 or 29% would be near 72% of that.  Rich Hagen

 

[willib]

Holy crap Rich, i was just going by the program i listed earlier..

the warlock blade calculator, or the Alton's blade calculator , they both list the power output of the blades at a certain wind speed .

they both come out about the same warlock's is 117 Watts and altons is 112 Watts

[Flux]

I think you are looking at things differently.

The total power in the wind, given by 1/2 rho x Ax V^3, can not be obtained as the wind would stop and pile up in front of the mill.

The generally accepted maximum that you can expect is the Betz value of 59.3% of this, when the wind velocity is reduced to 1/3.

Some regard this figure as 100% of available power. I find it much less confusing to think in terms of power coefficient, where the momentum value is 1, the Betz limit is .593 and realistic prop output is about .35, when you take alternator efficiency into consideration you are generally at .2 or less.

A 2m dia prop at 12.5 mph produces about 110W at a Cp of .3      

flux                                                              

[Flux]

Yes, increase the gap a fair amount to raise the speed.

You will still have a winding with too much resistance and you will not see the same improvement as into 24v or with a change of connection but it should be worthwhile.

Flux

[mrkooo]

I would like to change to 24V, but my inverter is 12V and I think there is no way to use it with a 24V system.

Francisco

[Flux]

I assumed that you were stuck with 12v because of the inverter, that is why I suggested trying it at 24 v to see the improvement.

As wound at present your stator is better matched to 24v. You will get an improvement with a wider air gap but the stator resistance is going to prevent you obtaining the best results. You may choose to live with it or produce a stator for 12v or try to re-connect the present one.

By using too low a cut in speed you have too many turns of wire that is too thin for 12v. Using a bigger prop will force more out of it but you will have to satisfy yourself that it will not over heat.

I am inclined to think that your thin magnets will prevent you using a prop much larger than 2M, but you may be able to increase it a bit to about 2.4M if you get the winding matched to the prop.

If you could get at the connections you could connect your stator in 2 sections with half the turns and feed 2 rectifiers in parallel to match it better to 12v.

Flux

[Bruce S]

mrkooo;

 Very nicely done. Since this unit has been up and running how are the 2 stress cracks doing?

Are those the beautiful Andes in the background?

One idea of looking for magnets for your next project; start looking for broken or thrown away laptops or laptop HDs. These HDs are much easier to harvest the magnets than the bigger cousins that everyone else is looking for. And they are just as powerful and you can stack them.

you could also hook up the "mill" to a 24v battery setup and merely keep the inverter connected to 12v.

 Will act the same as having multiple taps on a battery bank for different voltages for different needs.

great pics too!!

Cheers

Bruce S

 

[mrkooo]

I increased the airgap in 1cm, now the blades are running faster and the sound of it them are a lot difference, no stalling anymore. Today was a windy day, before changing the airgap the ampmeter mark 8amp peak, after increasing the airgap 8amp continously, 12 amp peak and a increably one only peak of 18amp in a  hight momentary wind. Much better after changing the airgap. I need a anemometer ASSAP.

I want to know how much I can get from this genny, so I will make a new stator, it could be 40 turns two hands #14 wire.

The cracks are going well, at the begining the stator blend a little but not big deal, centering it again into the two rotors solve the problem.

Francisco

[electrondady1]

congratulations mr.koo that's good power!

[Flux]

Well done.

I agree about making a new stator to get the best out of it. The 2 in hand wires will make it a lot more efficient and will keep the temperature down.

You will soon having it peaking at over 25A.

Flux