Coil wire exposed width

[Bosman]

Hi

To recap I am using Dan's 10'plans with locally available substitutes. Main variation currently the mags which are 50x20x5 mm instead of 50x24x12 as suggested.

This means thinner mag and some 4mm per magnet less in mag face width. I therefore gain some area on the rotor disc between the mags (since they are 20mm wide each and not the 24mm actually suggested). To try and compensate I need to keep the airgap as small as possible and to now get the 44 (double #14s) windings (44 is more than standard Dan suggestion, but calculated via formulas from this page to compensate for smaller mags) and keep the stator width down is my challenge. If I now make the coil winder spacer thinner, I can keep the stator thinner, but that would imply more layers and thus wider exposed coil areas. (I know I gain in resistance but think the smaller airgap may be worth it?)

If I keep the coil center gap to the 20mm mag width for my coils(9/12 config) they will be 24mm of wire on either side of the coil's open center. This will be a very snug fit but it should fit just! Main question: is it ok for the coils' exposed wire areas to be 24mm wide each side of the hole while the mags are only 20 wide as long as I keep the center gap equal to the mag diameter?

Thanks as always!

[Flux]

No chance of halving( or worse) the magnet material and keeping it capable of loading a 10ft machine.

You may be in with a chance if you double up on the magnets but even then you would be pushing your luck with magnets 10mm thick and with reduced area. That design doesn't have much excess magnet in the first place.

I haven't checked any figures but your present magnet set up will probably let you build a 6 or possibly 7ft machine, with higher cut in speed.

You will need to reduce the distance between your magnet rotors very significantly to get away with 44 turns at the same cut in speed and there is no way that you will get 2 in hand #14 in there. Even if you could you will have a fair increase in resistance going to 44 turns.

Flux

[Bosman]

Thanks for the advice Flux. Sad but logical. In the formulae I used .35 as a magnet value but that was just a guess as we have no way of knowing that right now.

So to get practical; for my existing magnet setup would you suggest still going 37 windings or should I asume half magnet half output and not wind 2 in hand?

Or should I wind them as big as I can fit in the space, test on a bench and then armed with that info then decide which blades to use?

[Flux]

With half magnet thickness you need to halve the stator thickness to keep the same flux density. You also have a smaller magnet area so if you keep the flux density the same your total flux will be lower.

If you kept the original 36 turns you ought to have enough room to wind with a single #14 wire. With the reduced total flux your cut in will be higher but that is just what you need for the smaller prop.

I have had a quick play around and I think I would try for a stator 8mm thick. If you are very careful you should manage to get it wound with single #14. If you keep the disc diameter the same you can reduce the width of the hole in your coils down to 20mm and that will gain you some winding space.

I think you will end up with a winding suitable for a 7ft prop with cut in in the 200rpm region and it should manage a peak output of 350 to 400W.

Flux

[Bosman]

You are a star Flux! That would work for me. I will still build the alternator and do some bench checks to finalise before making the blades but I am comfortable with what I hear thanks.

If ever you come to South Africa I will not only be proud to go show you the result of our efforts, but will surely buy you a couple of beers!