magnet to coil thickness ratio?

[wgatenson04]

I am in the early stages of building a 3 phase wind genni.  I have the rotor already constructed, it is an axial-flux 24" 40mag rotor.  Each mag is a N40 neo 2"x3/4" and 1/4" thick.  The rotor steel is also 1/4" thick.  So I was going to use 30 coils, wired in wye.  Shooting for 200-300 RPM.  Either using 16, or 18 AWG wire.  I was wondering if there is some sort of ratio for the thickness of the mags to the thickness of the coils that you are supposed to use?

[DanB]

I think there is somewhat of a ratio that makes best use of wire and magnets (most economical).  But it depends quite a lot on the design of the machine.  Is this a single rotor machine with laminates, or is it a dual rotor machine without them?

If its a dual rotor machine, then the strength of the stator is one factor - it  has to be thick enough to be rigid and flat, probably at least 1/2".  So then the coils can be 1/2" thick.

What voltage is this machine for?  

[Flux]

1/4"  seems very thin for a 24" magnet rotor. It's more than adequate magnetically but I am not sure you will be able get a close air gap without it warping, there is a lot of force on it.

I agree with Dan that your stator thickness will be limited by mechanical considerations in this case.

For a dual rotor the optimum air gap is about 1.5 times magnet thickness but you will probably not have a stator that is rigid enough at 3/8". For a single rotor it works out about 2/3 magnet thickness but the laminated backing can support the stator in this case.

With Neo the demagnetising line is linear and you can alter the air gap quite a lot and still work well.  If you go for a very small gap you tend to loose out as the physical air gaps take up a lot of your winding area and the loss of winding space tends to more than offset the gain in flux.

Your thin magnets are better suited to a single rotor at this diameter.

Flux

[picmacmillan]

just a short comment that may help you......i used # 18 awg with 200 turns....it had 1 ohm of resistance per coil.....which is alot.so i had to go three phase like you are suggesting...if you do use # 18 don't do like i did and think bigger is better..just maybe i can save you some headaches..take care.pickster