wire size for 12V wind turbine

[fabieville]

I am building a 12V wind turbine from scratch but I am kinda confused as to what gauge wire to use and how many turns of the wire that each coil should receive based upon my expectations. I live in a low wind area so I seldomly see wind speeds pass 15mph. I want my wind turbine to produce at least a 100watts in low wind speed of above 10mphs. So please tell me what gauge wire I should use and how many turns does each coil should recieve. I am using 24 round microwave magnets that i salvage so that means there will be 12 magnets on each steel disc plate. I am planning to use either 6 or 9 coils for the stator. Please comment.

[SparWeb]

I'm probably not the best person to answer, but you've waited too long so far.

My suggestion is to start with some experimentation.  Your microwave magnets are not as strong nor as consistent as the neodymium mag's that are preferred.  At least your expectations are realistic enough for what you have.  That is not a lot of wind.  It will take a fairly large set of blades to capture a useful amount of energy.

At this point, you seem to have settled on the ratio of 12 poles to 9 coils, which is standard for a 3-phase alternator.  Considering the size of the magnets (about 3 inches/7.5cm right?) the diameter of the alternator will be quite large, so you should expect it to be heavy.  This is working against your low-wind site, too.

Since you're right at the beginning, I suggest that you find Hugh Piggott's book Wind Power Workshop and read it through.  It will ground you in the science of the turbines so that you can experiment with them with more focused attention. 

[Flux]

I am not sure how realistic this is so I am a bit reluctant to comment.

To produce 100w in a 10mph wind you are really looking at something like a 10ft prop. If you mean 10mph average wind speed then that is very different.

Ferrite magnets are weak compared with neos and the small ferrites used in microwaves are not very impressive, The hole and the limited thickness means that you will struggle to get anywhere near what you want with only 12 of them. If you had 48 and could stack them on each pole you would have a better chance.

It will be large and heavy and you will have to use a lot of thin wire to get your cut in speed. i suspect you will be able to load a 10ft machine at 10mph but my concern is that you will not be able to load it when you get higher wind ( not often perhaps but it will happen). If you can devise some method of preventing the blades from overspeeding in these high winds then all will be well. I am not certain that you will be able to furl it safely unless you can make a very light tail if you stick to the conventional scheme. Short circuit braking is out of the question so it's furling, air brakes , mechanical brakes or a tail that can be pulled at right angles to the wind.

If it is for fun give it a try, if it is a serious attempt to get power that you need then I sometimes question the wisdom of using whats available rather than investing a small sum in suitable materials. Neos equivalent to those magnets would cost very little and unless you can get the wire for nothing then I suspect your overall cost will be higher using the free magnets and the performance will be very compromised.

If it is a fun project then I would suggest you go for something rather smaller for those magnets, perhaps with a 6ft prop, it will be more realistic but you will not reach your 100W at 10mph. it would give you a lot of experience and would give you a much better idea of the wind you have available and also get you some useful power whilst you collect bits for a bigger and better machine.

Without a lot more details of your magnets I can't give much idea of the coils. I suggest you use steel rotors such that you have similar sized gaps to the magnet diameter and use 9 coils and not make them too thick, perhaps 1/4". You will most likely be looking at test coils with over 100 turns even with a fairly fast 6ft prop.The resistance will be quite high.

For a 6ft machine you should be able to get enough protection from simple furling and in a low wind area even if it got out of control a well constructed wooden prop would frighten you but it would hold together.

Flux

[artv]

Hi Fabieville,....I'm currently working with the same magnets,but only a single rotor.I'm just using the wire out of the transformers from the microwave.I couldn't get hardly any voltage with ring shape magnets (probably my poor workmanship though).I found by stacking them the flux became more concentrated  because the outer row of magnets are rectangles, centerd over the ring below but you have to use a steel spacer over the ring to make the rectangle stick,the center of the hole is opposite polarity of the mag face. I don't know what the steel does but it works.I made an aluminum cap to go over my stacks, screwed down to the mag backer, only the faces of the rectangles were exposed,but when I spun it up my magnets managed to get out from under the cap, went flying everywhere.So just a word of caution if you do go stacked make sure they are well secured,those magnets will come out of there like bullets,I'm just lucky none hit me. Lots of thin wire in the transformers, 2 ,3, 4 in hand makes various types of guage........good luck.........artv

[XOKE]

Hi fabieville,
I have a friend that build 2 wind generators with this kind of magnets, one with 12 magnets and 9 coils and another with 16 magnets and 12 coils, they are both for 24 volts system; the first can get 350 watts and the second  more than 1kw.
Their machine has a 12 foot rotor.
The smaller have magnets in pairs (48 totals) and the second 3 magnets stick together (96 totals).
The wire he use on the first it was 1, 5 mm and on the second 1,7mm.
I'm building one too, with 12 magnets and 9 coils, the magnets are in pairs, with the experience of my friend put another magnet we double the voltage, so I have a total of 48 magnets.

I'm waiting for the metal disks and bearing, to put all together, I have 12v system.
I intend to build an 8 foot and can get about 350 watts.

Regards

Xoke