How long is a piece of string?
What voltage, what prop diameter, what wind speed, what air gap between magnets.
Is your proposed speed cut in or working speed at 300W output.
I take it you are doing an overlapped coil 3 phase design with 12 coils and 8 magnets.
All I can offer you at this stage is a formula to calculate the number of turns for the cut in.
If you are star connected your ac line voltage will be battery volts divided by 1.4
For a 12v battery you will need about 8.6v ac at cut in speed.
If you can establish the flux per pole ( flux density x pole area) then you can use this formula
V =4.4 x ( flux per pole) x frequency x N where N is the total number of turns per phase ( 4 coils in your case).
Frequency you can determine once you set a cut in speed. The flux density will depend on the air gap between magnets and unless you can measure it you will have to guess. You can reasonably expect 600mT in a 1/2" gap with those magnets.
Having found your number of turns you will need to calculate the size of wire that will fit, then work out its resistance and see at what speed you reach your 300W .
To make a decent working machine you also need to establish that your chosen prop can supply about 600W at your 300W working speed. If the wind sped is way off what you want then try again with a larger ( slower ) or smaller ( faster ) prop.
Flux
