work in progress: a 10 footer

[dinges]

Have started this weekend on the first parts for a 10ft windgenny of the axial flux type. It's going to be a fairly standard one, 24V. Coils have just been wound. 67-70 turns each. 9 coils, 2x12 magnets. Wire diameter 1.50 mm (AWG??). Magnets will be the usual 2"x1"x.5" NdFeB, N40. It was originally meant to be wired in star for 24V. Yet, in delta, it should provide 14V (24/1.7) at cut-in; which would make it useable too for a 12V system (with limit in power, due to max. current through the coils); only half the power of a 24V system, but still, it gives another option. The stator will be built so that each phase has 2 wires to the outside (brass bolts) so as to provide external delta/star switch capability.

Here are the coils (9 and 2 spare ones), the coil winder and, in the background, my very first mini-axial flux genny. The coils of the 10footer are almost the size of this genny

Question: the wire is 1.5mm (1.588mm including lacquer). How much current do you expect to safely put through this? In transformers, I calculate with 4A/mm^2, which is very conservative. I'd dare go to 8A/mm^2 for gennies. Yet, when I look at the power that a 10footer of the Dans produces during furling, 700-1000W, this could mean 20-30A/mm^2. Seems like way too much to be safe, yet their gennies seem to handle it pretty well.

fixed it up best i could

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What happened? One picture disappeared, and lettertype seems to have changed?!

Here's the original pic:

[Flux]

I am surprised that you can only get 1.5mm wire in with 70 turns. It will be interesting to see what cut in speed you get, I think you must be aiming for a fairly thin stator.

Transformers generally are not run very hot and they are run at full rating continuously.

Wind machines spend only a small part of the time at nominal rating and that combined with the direct wind cooling will allow you to push the current density in the wire to higher values than you would use in a conventional transformer.

Don't kid yourself, these machines run hot at those maximum ratings that some push them to. Probably at the top end of class H, but only for fairly short periods.

I suspect they have a limited life, but if you use wire other than polyurethane ( self fluxing) it dies slowly at these temperatures and if you get a few years from a stator it keeps most people happy.

I have no experience of how long they last, I have never run one at this temperature for any length of time. I changed to boost converters years ago and you can halve the number of turns and work with 1/4 the resistance for the same power out.

Flux

[dinges]

Flux,

Yes, the coils are fairly thin, 10mm. I had asked about this before, initially I wanted to go to 8mm but on your advice (you said to go to 12mm) I went to 10mm. They're thin. And I may have to increase airgap between the magnets. On the other hand, it's not that much work to build a new stator, should it be necessary.

As far as pushing machines to their limits goes; I'm much more conservative myself. When I build it would have to last & work for an eternity, without too much care & fuss. So overbuilt design and conservative ratings are the way for me.

Thanks for the reply.