coil problem on 20' 24V machine

[mosseman]

Hey

I'm building a 20' 24V machine:

• Turbine 20' (5 meter)3 blades
  
• Dual rotor
  
• 20 magnets per rotor (3" x 1-1/2" x 3/4")
  
• 3phase - 5 coils per phase
  
  

So, i'm doing same machine as this : http://www.otherpower.com/20page1.html

But i want to get 24V output not 48V

So, what should i do diffirent?

I think only coils have to be diffirent?

What kind of coils i have to do if i want cut-in to be 60-70rpm?

Any ideas?

Thanks!

Tero from Finland - Moventas OY www.moventas.com - Windturbine gears manufactorer

Here's my first 10' machine : http://koti.mbnet.fi/teroala/  

[finnsawyer]

Wind the coils two in hand.  There is a question, of course, whether one can wind the wires as tightly two in hand as one can with a single wire.  If you end up with a fewer less turns your cut-in rpm will increase.  Oh!  I'm assuming the coils are made of turns of single wire.  May not be the case.

[Flux]

In theory you use half the number of turns of twice cross sectional area wire.

In real life I suspect you are going to struggle as the wire is probably just about as thick as you will get away with. You could keep the same size wire and use twice as many wires in hand. It's not going to be fun dealing with that section of copper.

Flux

[tecker]

Bring a neutral out of the 3rd coil in each phase so you have a center tap on each phase.

[Janne]

Hi mosseman!

Nice to see other finns build wind turbines too I've also just completed a 10' machine very similar to yours.. where are you located if I may ask?

anyways sorry for off topic post..

t. Janne

[mosseman]

I live in Jyväskylä city, but that windmill is in Ruovesi.

How's your 10' is going?

[mosseman]

Okey

I think that 24v is maybe too litle voltage becouse highwinds can brobably make 200 - 250A peaks, so the stator may burnout and leads should be thick and expensive.

i guess 48v is only way to manage such currents sensibly?

[Lumberjack]

If my quick read is right the original is wired in star... Use the same coils but wired in delta instead.

[mosseman]

Sorry, i don't understand. What should i do with those center taps?

[mosseman]

Interesting option. What will happend to cut-in speed?

[mosseman]

Turbine is 6,1 meter not 5 as i wrote first...

[scloyd]

I see wind gen folks deal with the same issues I did on induction generators and phase converters.  What your respondent is referring to is that if the 3-phase line to line voltage is 48 Volts then the line to line voltage between the centertaps is 24 Volts and you can draw twice the current provided you do your design in Delta.  If you design in wye you would need balance caps on the 48 Volt leads and you just don't want to try to optimize a mess like that.

[tecker]

Yes you would have 24 volt taps to parallel with tha 48 volt winding method .

[Flux]

Assuming you start with star giving a cut in of 48v, delta will give you 48/1.73 or 27.7v.

Your cut in in delta will be at slightly lower speed, but near enough and this may help to compensate for extra line and rectifier drop.

I didn't suggest this easy option because this type of alternator performs fairly badly in delta with rectifier loads. You may be happy with it and if you are then this is a simple option. The circulating harmonic currents will slightly delay start up but I still think on a big machine it will start in winds below which it will produce power so that is no issue. In low winds the efficiency will be lower and you will need more wind for the same output but again you may not even see the difference.

Whatever you do at 24v you will struggle to get a decent efficiency at such high power.

Normally I would advise against using delta but in this case it would let you try the 24v option and if you didn't get on with it then you could simply reconnect to star and change to 48v with the same winding.

Flux

[Janne]

Hi!

My turbine is located in Heinola. It's been doing quite ok so far, though it's not still running on it's own. You can find some pictures and story of it in my other posts.

What kind of tower are you planning on your bigger mill?