Question about coil shape

[ezee]

I've seen different examples of coil shapes:

Some v shaped:

Some square/oval:

any advantages/disadvantages to either?  Are there any other "tricks" one should know about coil shape and its effect on performance?

(my question references dual rotor axial only, if that helps)

[willib]

Yes i personally have had good results by making the hole in the coil smaller than the magnet dia.

in fact i make it the distance between mags on all my three phase machines.

[ezee]

interesting...you use round magnets?  Most of the designs I have seen here use bar or wedge mags.

What shape do you use for your round magnet units?

[willib]

This has some good shots of the stator on the minigenII

http://www.fieldlines.com/story/2007/1/21/25816/5826

[willib]

And here is the output figures that i got using a excercize bike to power it.

http://www.fieldlines.com/story/2007/3/28/0485/82530

[ezee]

Thanks for those links....but Im still wondering, is there any benefit to the different shapes?

[RP]

Here are some of the factors that go into making a generator with wire and moving magnets.

You want the magnet path to be perpendicular to the wire

You want to avoid cancellation by ensuring that the two "legs" of the coil never see the same magnet pole at the same time

You want to maximize voltage by ensuring that the two legs DO see opposite poles at the same time (one leg seeing a north pole while the other sees a south)

You want as many turns as needed to achieve the desired voltage/rpm.

You want the thickest wire you can fit to minimize resistance.

You want the thickness of the stator (for air core axials) to be as thin as possible to have maximum flux between the rotors.

When you add these to the various shapes of available magnets, you end up with a variety of coil shapes each with its own set of compromises.

Hope this helps

[willib]

the way i see it , it depends on the magnets

if you have round mags , use round coils

if ya got rectangular mags , use rectangular-ish coils or triangular-ish coils

the object to me ,is to not leave too much empty space, which is why i wound the coils with a small hole.

that accomplished two things for me , it let me get 79 turns of 0.045"dia wire in a very thin coil/stator , and the stator resistance was also resonably low.

[alancorey]

Wire that isn't perpendicular to the magnet path doesn't generate anything, it only wastes wire and adds resistance.  That's part of the reason for triangular and trapezoidal coils.

  Alan