14 inch rotors which magnets?

[StingrayCrazy]

Hello, I'm building my first wind turbine (12' downwind) and looking for advice. I currently have 32-N50 (2" x 1/2" discs) for 16 per 14" rotor going with a 12 coil stator giving good spacing between the magnets --- Or should I go with 24-N50 (3" x 1/2" discs) crammed close together on the 14" rotors and a 9 coil stator? I'm searching the board but having trouble finding out which way is better for a low average wind speed unit... The alternator will be 48V feeding my Xantrex SW4048D power panel. Thanks in advance!

Frank

Took the ["] out of the title which would have prevented replies. AKA "50 character limit bug". TW

[wpowokal]

My money is on the first one because of flux leakage, space for coils & cancelation.

allan down under

[Flux]

How are you going to control it, not my problem fortunately.

Flux

[wpowokal]

He He good point I missed that!

I realy believe PPL supply insuficient information in ignorance of the subject most of the time, hard for me to tell the difference most of the time though.

allan

[StingrayCrazy]

The mill is going to be connected directly to the batteries. I have a small Allen-Bradley PLC to handle the dump control to a DC water heater.

[wpowokal]

http://www.fieldlines.com/story/2004/8/14/10223/3082

[Janne]

I think what Flux wonders is how are you going to prevent it overspeeding? With downwind design you can't use the normal furling scene, and pitch control or tilt-up furling are the only options that come into my mind.

[StingrayCrazy]

I want to model my turbine from one made by Ed Lenz, (Windstuffnow) I really like this design and it's simplicity. I will try 3 6' blades and maybe later go to 5 if I don't get the low speed performance I'm looking for.

[StingrayCrazy]

Sorry about that Flux, I didn't understand your question.

[Flux]

It's ok, you seem to have thought about it. That is one of the very few ways to control a down wind turbine other than pitch control.

I am not sure if you are meaning blades 6ft long or 6ft diameter. 12 ft would reasonably suit your magnets, but with a 6ft prop you would haver far too much magnet for sensible use of materials. Twelve ft may be quite bold for that system of control but it might be ok.

Flux

[StingrayCrazy]

Flux, yes that would be 12' diameter blades.

So if I go with the 32 2" X 1/2" N50 discs for better separation of the magnets and coils, wound with two strands of #15 wire in hand x 75 turns, would that be a good fit for the blade diameter? And what cut in speed do you think I would have?

Thanks Frank

[StingrayCrazy]

Turns of wire       

volts    55    Open voltage

poles    16    total magnets

rps    1    revolutions per second (rpm/60)

tesla    0.55     gauss / 10000

area    0.002026326    sq in x .000645 of 1 magnet

coils    12   

# turns    129   

in star    74   

I stumbled across Ed's formula for calculating turns on coils while searching and ran my info. I'm not sure on the gauss but I think that the lower number would be a safe bet. I'm planning on using these Applied Magnet fiberglass low wind speed blades (Below) to test the unit. I'm going to make 2 hubs one for 3 and the other for 5 blades. The hubs will add about one foot to the diameter of the blades putting the turbine at 11.5' I'm looking for an early cut in without stalling the turbine. Any suggestions'?