need some help

[maxoutput]

hi,

this is my first wind gen.and have some questions before i start ordering some parts

I want to start small so here goes.....the rotor in my pics. is 7" with 1"x1/4 round

mags. The disc that i am looking at are 8" should i make a new drawing with say    1 1/2 mags. to fit the 8". Because it might not be to easy to cut off 1" and still be real round...lol. What i am looking for is a 12 volt gen. to charge a 8D battery

so i can run my 2400 watt inverter from. I would like to try to keep the blades size

3'-5'. Some test coils that i tried were from some old phone wire (.065) that i was able to get 55-70 turns to fit in the stator. So i was thinking of maybe #16 wire with 80 turns? I dont know what the cut-in speed or output would be. Also i was wondering, has anyone tried to make a stator with coils made of different wire size to get good low and hi speed output?

[windstuffnow]

   To find the approximate prop speed at various tip speed ratio's here is a quickie formula...

Windspeed x 88 / ( diameter x 3.14 ) x TSR = rpm

So lets say your 5 ft prop will be designed to run at a tip speed of 4 and you want to find the rpm at around 7 mph, which might be the cut in speed of the alternator....

7 x 88 / ( 5 x 3.14) x 4 = 157 rpm

At a tsr of 6 it would be

7 x 88 / ( 5 x 3.14) x 6 = 235 rpm

You'd want your cut in speed to occur at around 157 rpm with a TSR of 4 or at 235 with a TSR of 6.  It might be easier to use the higher rpm when winding the stator using small magnets.   It will take a considerable amount of turns to get 12 volts at cut in.   So, the formula I use for the alternator is...

NARBP*2 = voltage

where...

N = total number of turns per phase

A = area of 1 magnet ( in sq meters -  sq inches x .000645 )

R = revolutions per second ( rpm / 60 )

B = magnetic flux in Tesla ( gauss / 10000 )

P = number of poles ( only count one disc on a dual rotor )

B is the only one that is usually difficult to measure unless you have a gauss meter.   If your using neodymium and you keep the air gap to around .625 to .75 then the Tesla penitration would be about 0.5 .   This is measured from an N35 grade neo.  

So if we change the formula around to find the number of turns it would look like this...

N = voltage / ( A x R x B x P x 2 )

Your using 1 inch diameter magnets to the area is .7854 sq inch ( 1^2 x .7854 ) then we change it to sq meters... .7854 x .000645 = .000506 sq meters.  

R will be the higher rpm of 235 or 235/60 = 3.91 revolutions per second

B we'll use the 0.5

P your showing 12 poles

So...

N = 12volts / ( .000506 x 3.91 x .5 x 12 x 2 ) = 505 turns of wire to make 12 volts at 235 rpm

Now you have 3 coils in series per phase so you can divide the total number of turns by 3 to get turns per coil  505 / 3 = 168 per coil

If your going to wire it in star you can divide the turns per coil by 1.732 ( 168/1.732 = 97 turns per coil wired in star.   If you made a single phase or 3 phase wired in delta then you would have to use the 168 turns per coil to get the voltage you needed at that speed.

Hope that helps

.

[maxoutput]

thanks for the reply ed,

  so what you are telling me is that i need 97 turns. would rounding it off to 100

be ok. going to try 3 phase star.  

  I cant seem to come up with the 505 turns  that you did for 12 volts @ 235 rpms.  I dont know why?

  wonder if i should try to make this 48 volts because of the low wind speed here

  (4-10)mph avg.

 Also, if you look at my pics. there is a prop that i was going to try to use.

 Its only 28" but i was thinking,,,,,,maybe try to make the hub which is 3/16 steel , one of the rotors with 12 neos. 1 x 1/2 round mags on a 8" diam. circle moulded into it with a 1/2" stator thickness.

Iam ready for the steel disc. that we talked about befour, and will send you an e-mail on what i need.

                                   thanks for you help

                                          charles

p.s.  how do you post a pic. with a reply?