trying to match coils and blades to very low winds

[windwatcher]

hello

this is my first post. hello to everyone.

hoping for some design help with my axial flux turbine

have one 13 inch disc with 24 2x 1/2x 1/2 n-42 neo magnets

already set in resin.

laminates- cut strips and coiled for return flux.

have not purchased magnet wire yet.

plans are 18 coils 3 phase 6 coils to a phase wired star

test coil of 50 turns awg 18 2 in hand gave me 1 vols at 130 rpm.

star formula minus rectifiers equals 12.8 volts at 130 rpm (i think)

i have very low winds with lots of trees here in east texas 6 to 10 mph

thinking of 11 foot 3 blade prop with tsr of 6.5

with furling for storms that do come through

will this work and if it does when to furl.

suggestions please,runaway blades, stator burnout, other things

i am ignorant about,always watching for wind

thanks and like this site,                        windwatcher

[Flux]

For a low wind area I wouldn't have chosen that construction, but never mind you are stuck with it now. I expect the laminated return path will loose a lot of your output below about 8mph.

You don't say whether your test coil is in the air gap between the magnets and laminated core or whether you have tried with just the single magnet rotor so it is impossible to help much.

For that construction I suggest you keep the air gap between magnets and stator core to no more than 3/8" and keep your coils below 5/16" thick to give a working gap.

I wouldn't have wound that with 18 coils, I  would have used 36 with overlapped coils as you can bend the ends down over the core, but for a first attempt you are probably right to stick to 18 coil single layer for simplicity.

Come back with a test coil figure with the core in place and a suitable air gap then we can have another look.

I don't think you have anywhere enough magnet to effectively hold an 11ft prop down in high winds but as you are in a very low wind area and with a significant core loss you are probably right to use a large prop. You will have to satisfy yourself that you can make it furl really early otherwise you will be in trouble in the first high wind. If you can do that satisfactorily I think you will be ok.

Flux

[Flux]

Your second post seems to have vanished, probably they are trying to make you keep it in one place.

My reply also vanished, but maybe it doesn't matter. I have had a quick look at your figures and at present it doesn't look promising. Is there any chance of trying again with a much thinner coil. Probably you can still use 2 in hand #18 and see if you can get 25 turns in with a coil about 3/8 thick or less and preferably with an air gap under 1/2". Your flux density is dreadfully low at present and I suspect half is wasted in leakage. The small gap should reduce the leakage to a more reasonable figure. Could you let me know the wire length for the new coil ( length of each strand, to avoid confusion)

Flux

[windwatcher]

new test coil, must go with 18 coil setup, put plywood up flush with laminate and can not bend the ends down.  

coil- 44 turns 3/8 inch thick, awg 18 2 in hand, each strand 28 feet long, gave me 1.1 volt at 130 rpm. 3 phase star minus rectifier equal 14.3 volts at 130 rpm.

gap- 7/16 between laminate and magnet.

magnet- 24 n-42 neo magnets *2x 1/2x 1/2 inch*small mags

blade- 3 blade prop 11 foot tsr 6.5

i could wind thinner coil with less turns if need to.

thanks windwatcher

[Flux]

Thanks.

The flux is still coming out very low, maybe that is a snag with the very thin magnets, the 1/8" round the outside is never very effective so perhaps you only have a width of about 1/4" working effectively.

There is probably little to gain with a smaller air gap.

That winding will give you a resistance of just over an ohm and that is high for 12v.

You can use your 11ft prop and it will be very good in low winds but you will need to keep the maximum current below about 15A. There will be little effective load in higher winds so you will need to be really careful with furling. As long as you can solve that then it should do what you want.

For a reasonable wind area I would suggest a match to no bigger than 8ft prop with cut in speed increased to about 180 rpm, but the 8ft prop will give you very little below 8mph

Flux

[windwatcher]

hey flux.thank you so much for your time and patience