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Axial flux turbine MK 2
karlb:
It has been a while since I last posted with my first turbine build here.
To cut a long story short, it only produced about 9v at 20w - not enough voltage to charge a battery.
So I geared it up 3:1 with a bike chain. You can see in the video in my sig that I get about 19v turning it by hand after the gearing up.
The problem is that the bike chain introduces too much friction and the blades only turn in a high wind and even then quite slowly. There are also problems with the chain falling off occasionally.
I have a bit more time on my hands again and am planning a rebuild.
The way I see it there were two problems: not enough blade and not enough magnet.
I plan to double the blade size and double the magnets.
I'm also going to go with direct drive this time so that less energy is lost to friction, and to keep the whole build simpler (can't be bothered with problems with the chain falling off any more). My idea is that if I get enough poles in the first place, and build my alternator properly then I won't have to deal with the whole hassle of gearing.
Last machine was dual rotor 8 magnets per rotor with 6 coils.
Planning to make this 16 magnets per rotor with 12 coils.
Magnet size is 10mmx10mmx20mm
Can anyone on here calculate the expected power from an alternator, given number of magnets and magnet size?
Heres a quick sketch, rotor on top and stator on bottom with coils shaded in.
I've gone for magnet spacing of half a magnet width here. So 5mm between each magnet on the inner edges. Could anyone let me know what spacing is optimal?
Is it best to wind the coils around a rectangular form the same shape as the magnets, or wind it around a wedge shape with one end the same width as the magnet and the other end slightly wider? With the first way the coils only touch eachother on the inner most corners, but with the second they touch along the entire length so I'm thinking this will be better?
Also can anyone recommend me a wire size? I'm trying to get a voltage of about 19v to charge 12v batteries. I know from my previous build that the voltage varies massively with different wire sizes so it would be good to get it right first time. Course I will make a test jig to test one coil and estimate from that but are there any rough calculations I can do before hand?
Thanks
Mary B:
What kind of magnets?
karlb:
Neodymium grade N35 :)
electrondady1:
i have no computer animation skills.
i use tracing paper to draw out coil configurations .
use a thumb tack to centre it over a mag layout drawing . you can rotate it and check how the coils and mags interact.
it can be surprising.
i recently went with wedge shaped coils with the coil legs running parallel on a radius . it seemed to give a bit more time that the two coil legs were over the mags.
some builders are shrinking the width of the centre hole to slightly less than a magnet width. giving a bit more room for a few more turns.
karlb:
Thanks for the advice.
Will use wedge shaped coils. My thinking was that the edges of two adjacent coils are meant to be under the same pole as the magnets turn, so it would make sense for their whole length to be touching.
In regard to the centre hole, I can see that shrinking it to slightly less than a magnet width would get you more turns, and I've even thought about doing this myself. Can anyone else confirm the theory on this?
Also what's the optimum gap between two magnets on the rotor? I've assumed half a magnet, but can anyone else confirm?
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