Greeting, where do the Eddy Currents form?
Flux explained it pretty well. From a practical standpoint, there's limits to how big the wire is you can wind with, how fast you drag the flux over the copper mass in the coils and how big your poles are in a air core generator. It's like dragging a big neo across a piece of aluminum. If you move it over the aluminum very slow you won't feel any "drag" and no heat is generated due to an opposing magnetic field in the aluminum. Drag it across it fast and now you get drag and heat.
In these generators, 2,000 rpm is way too fast with 13 AWG wire. Anything below 1,000 rpm is fine with the 2 x 1 x .5 N42 neos used here.
I built one delta 12 volt generator using AWG 12 and that also worked fine at 800 rpm. Using the same AWG 12 wire in wye with number of turns divided by 1.732 for the star connection end up with a stator that ran just sizzling hot. I attributed this to the fact that with the coil groups connected in series there must be a "buildup" of resistance to current flow caused by the eddy current that generates a lot heat. With the delta connection the problem went away, as you have basically two coil groups feeding one "leg" in parallel, reducing the total length of the copper that the total current has to pass thru.
Modified post to add a note: The wye stator was wound two-in hand, the delta was wound with a single strand of 12 AWG.
These neo magnets are too powerful for geared generators, in all reality. It takes a careful balance of components to get the desired results. A wound field with a laminated steel core stator would be ideal and that's one of the projects I'm working on at present.
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Chris