## Axial Flux Wind Turbine

24 pole, 3 phase alternator. 18 coils of #20 wire 80 turns each, 6 coils in each phase connected in series, then wired 3 phases in star config. Put out lethal voltages at a very low rpm. Using N45 2" x 1" x 1/2" Neo Mags, two discs of 24 each attracting each other through coils. I need to know what the number of turns would be for #13 wire, same configuration for charging batteries.

Hello all, I have put together a 24 pole dual rotor axial flux alternator with a distributed winding, the middle phase is always producing less voltage can some one suggest why?

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Umm the power output of the generator is governed by Faraday's Law of Induction. The current it each of the loops of wire is induced to counteract the change in the magnetic field change when the magnets are moving over it going from North to South. The magnetic field strength drops off in strength with the cube of the distance so it's important to get the coils close to the magnets. I'm still trying to figure out how the amperage works. My best guess is that as long as you keep the generator turning at the same speed you can pass any amount of amperage through the thing. So the more amps you pull the harder it is for the generator to turn at that RPM. Of course increased amperage will result in your coils heating up, as the copper wire has a resistance that is correlated to the diameter and length.

V=-N*A*(2*pi*RPM/60)*B

where V=voltage, N=turns per loop, A=area (magnet or wire loop?), B=magnetic field strength in tesla

B=u/4*pi*2*U/d^3

where B=magnetic strength, u=permeability constant, d = distance from center of dipole (center of magnet), U=magnetic moment

Also it's important how you wire your coils. Of course with the 3 phase setup you are able to put the 3 phases which are 30 degrees out of phase of each other through a rectifier and produce a steady DC current; as the summation of the three waves results in a line. So assuming you have 9 coils you can have 3 sets either in parallel or in a series. If you put them in a series you can produce hire voltage at lower RPMS. Although apparently putting them parallel has benefits at higher RPMS.

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I'm thinking of trying to make my generator with 2 stators and 3 rotors. Thus allowing the average distance each of the coils to be closer to the magnets. I still have not run the calculations to see what benefit this would product. I'm hoping to lower the number of coils needed. I'm trying for 24 volts at 300 RPM, well actaully I would want what 28 volts so I could then charge two 12 volt batteries in series. Apparently due to lenz's law you need 14 volts to charge a 12 volt battery. I haven't had the chance to look into this.

Oh I had another thought. If all the magnets had their poles facing the same direction rather than alternating (alternating current) the generator would produce direct current rather than alternating. However, this would surely reduce the power output.

I ran an excel to calculate what can be expected from a 3phase PMA.

Since I cannot attach a file here is the sheet.

The basic formula I used is: V=#phase*n*A*B/t

I will be happy to hear comments, and also send the excel if someone wants to review it

number of poles 24

magnet placement angle (degrees) 15

#Phase PHASE 3

n coils per phase 6

n per coil 21

N per phase 126

A cm^2 11

A A m^2 0.0011

B (Gauss) 13200

B B (Tesla) 1.32

RPM (for 2*pi rotation) 120

time to rotate 15 degrees (sec) 0.020833333

"since the coil enters the N pole and S pole simultaneously

we probably need to consider the time it takes to rotate 7.5 degrees"

t time to rotate 7.5 degrees (sec) 0.010416667

V V per phase 17.563392

V star 52.690176

V delta 17.563392

resistivity Ohm-cm 0.00000167

wire cross section cm^2 0.01227

single loop length cm 14.4

single coil resistance Ohm 0.041157946

The RMS voltage (Root Mean Square) is the average effective voltage of a sine

wave. An example of how this RMS value is applied.

Say you have a toaster oven, an oddball, the Mfr. rated input is 100 volts DC.

Your source of power is AC. An alternator The Oven is resistance circuit only.

If you dial up a hundred volts with readout from a scope P to Peak the Oven

will barely heat up. The answer is, multiply DC volts by 1.41 = 141 volts AC.

Your multimeter or any RMS AC meter will be reading 141 volts but will show

the effective DC equivalent of 100 volts.

Peak to peak voltage of 100 is equal to 100 * .707 =70.7 RMS.

The 240 volt service to your home is actually 338 volts. P-P.

A more involved explanation on the link below.

http://www.tonmeister.ca/main/textbook/node82.html

25 = 2.3v ac

40 = 3.9v ac

63 = 6.2v ac

100 = 9.5 v ac

125 = 12.56 v ac

160 = 15.10 v ac

200 = 19.10 v ac

250 = 24.90 v ac

315 = 30.50 v ac

400 = 37.50 v ac

500 = 49.50 v ac

630 = 59.20 v ac

800 = 74.00 v ac

These measurements were taken across 2 leads of the 3 phase output and it was wired in a star configuration.

I stumbled on to this bit of info, could be a good way to lower the cut in speed

also lots of good stuff here.

http://www.thebackshed.com/Windmill/FORUM1/forum_posts.asp?TID=1138&PN=3

"one volt of electrical pressure is created when 100, 000,000 magnetic lines of force are cut per second."

as an example, If your dual magnet system produces 150 thousand lines and your magnets pass

the coil in 1/100 second. This is 100 X 150000 =15 million lines per turn. you would need 6.6 turns per volt.to achieve the 100,000000 required when 2 more coils are series wired to this calculation the number of force lines cut per second is tripled, coil turns would have to be reduced accordingly. If you do not know the field strength of the magnets then perhaps the MFR. could supply it for you. again good luck

with your project.

. How many volts with a load on it?

.

. Theoretically, the size of the wire is not important - use the same number of turns. Lots of info on the Intertubes about winding coils. (Delete "generator" for more hits on general coil winding.)

. Or just use a transformer. If you can build that generator, you can roll your own xformer. Google is your friend.