Formulas and calculators > Coil winding
Coil shape for axial flux generator
michal:
Hello everyone,
I'm in the process of making an axial flux generator for my VAWT , but find it difficult to digest all the information available on various websites. I'd like to know what is the best shape of coils, depending on the configuration of magnets.
The information I found on different forums is sometimes confusing and since I'm not an expert I hope someone here will help me to get my head around it.
I understand that for a single disc configuration (like the one below for example) the coil should be big enough, so that the coil legs pass over two magnets and cut thru the flux lines.
Plan view
Section
My problem is that I want an axial flux generator with two discs of magnets, yet found information on some website that the coil shape should be the same for this case also.
As the direction of magnetic field would be different on two sides of coil, would the the generated currents not cancel each other?
With the mainly vertical direction of magnetic flux (depending on magnet strength, gap size, etc…) wouldn't I be better to have the coil shaped similar to the shape of magnet?
Please let me know what you think about the best configuration.
Many thanks in advance… :)
electrondady1:
hello michal,
i build verticals as well as they are best suited to my circumstances .
your showing a 3 phase configuration.
3 coils for every 4 mags
and describing a dual rotor axial flux alternator.
i would suggest that you could make the centre hole of the coil the same size or slightly smaller than the magnet and let the shoulders of the coils touch each other .
michal:
Thank you for quick reply,
And regarding the shape of the magnets - what would you recommend?
For single rotor I understand the advantage of wedge/rectangular shape, but for double rotor design, would the circular shape be a good idea ?
(I wonder if the coil would be exposed to more uniform magnetic field ---> round magnet= round coil???)
Any opinion?
Flux:
I don't think there is an answer to your question. For axials the most logical starting point is with trapezoidal magnets and coils but if you choose to use other shape magnets then logic goes out the window.
For a high efficiency conventionally loaded alternator your rectangular magnets would probably work best with the trapezoidal coils. but for direct battery charging, the circuit resistance has a lot to do with how much you can get out of the thing and changing to rectangular coils would reduce resistance way below the long turns of that trapezoidal coil.
If you are rectifying for direct battery charging then there is little doubt that coils roughly the shape of the magnets is the way to go, so rectangular coils for rectangular magnets and round coils for disc magnets. Even here resistance is a big factor and you may be better off squashing round coils to ellipses. Any turn smaller than the magnet will not link all the flux and won't contribute full voltage, but it will contribute very little resistance and you usually get an overall gain.
How you load the thing has a big influence on how it behaves and use of material and how much you can get out without frying is what you are really optimising for direct battery charging, efficiency has to suffer to get a match to the blades. If you load conventionally with resistors or with a mppt inverter then efficiency can be a factor and it changes a lot of the requirements.
Flux
electrondady1:
if the magnet is round, then the centre hole would be round, and so the coil will also be round.
if the mag is rectangular as you have shown in your illustration then the centre should be the same shape .
it will become more rounded as you add turns.
your coil jig will dictate the maximum size the coil can be.
in an ideal circumstance all magnets would be wedge shaped and the legs of the coil would be parallel to a radius
in the case of a 9 coil stator the coils would form a segment 360/9=40 degrees
i kind of posted before i realized flux had answered he is the authority
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