Hello,
There is a copy of an e-mail i've receive from ed from windstuff website. Couldbe usefull for you.
Cinosh07
The following formula will get you in the ball park for how many turns of wire you'll need...
Voltage= NARBP*2
where:
N= number of turns
A= area of 1 magnet in square meters ( the triangle neo's are .001525 )
R= revolutions per second ( rpm/60 )
B= flux passing the coils in Tesla's ( gauss / 10000 )
P= total number of poles
To find number of turns:
Voltage / ( P * R * B * A)/2 = Number of turns
B is confusing because not every one has a Magnetometer ( gaussmeter) so I'll give you what I've come up with while working with different versions:
On a dual rotor system, not exceeding an air gap of .75" between the magnets you'll see 0.5Tesla through the coils
A simple coil over laminant will get around 0.4 Tesla throught the coils
And a slotted silicon laminant with an air gap of .030 between the magnet and stator will see slightly over 1 Tesla through the coils with these magnets.
As an example my 8 inch dual rotor shown on my site, using 0.5T in the formula to find the amount of turns per coil would go like this...j
Number of turns = 14volts / ( 12poles * 3.33rps * 0.5 Tesla * .001525 area) / 2 = 229 turns
There are 36 coils in that arrangement total and each phase has 12 coils.... 229/12 = 19 turns per coil
Since its wired in star you can divide the 19 by 1.732 which equals 11 turns per coil
If you were using a 9 coil arrangement ( 3 coils in series per phase) then 229/3/1.732 = 44 turns per coil
That should get you in the ball park for designing an alternator that will work with the blade you want. You want to use the largest size wire you can fit into the space allowed for maximum power. Its best to keep the resistance in the wire as low as possible to achieve maximum output.
As far as the relationship of coils per magnets... On a single phase machine you would have 1 pole per 1 coil ( so if you have 12 magnets you would have 12 coils for single phase ). The normal 3 phase is 4 magnets per 3 coils. So you can have 8 magnets and 6 coils or 12 magnets and 9 coils... the magnets are always added in multiples of 4 and coils are added in multiples of 3. Another way is 2 poles per 3 coils where 8 poles would have 12 coils or 12 poles would have 18 coils. And finally you can overlap the coils using a single phase arrangement with 3 phases where each pole would have 3 coils so with 8 poles you would have 24 coils and 12 poles you would have 36 coils. The 4pole/3 coil arrangement is the most popular because of its simplicity and the coils are laid out in a single layer.
Hope this helps
Have Fun
Ed
www.windstuffnow.com/main