Thanks for the comments.

Yes, high current is an issue I'm very concerned with, especially with plastic brush holders (I've seen plastic brush holders melted in motors). That's one reason I went with 2 brushes for each side of the circuit. It would be easy enough to make it 3 or 4 per side if need be, or just find higher capacity brushes like you suggest.

I have a 24 volt system and don't expect this generator to put out much over 20 or 30 amps, about 10 - 15 amps per brush. Still might be too much, I don't know, but I should find out soon.