You started well in your introduction and I thought Hugh gave you a fairly precise answer and the offer of help.

From your reply you seem to have completely misunderstood the whole thing and my comment was just to make you think.

Although Hugh said that he may not come back, he did and I hope you can follow the explanation. If we could use less magnets for larger blades and keep everything else we should all be on a winner.

You can always get any cut in speed you want with any quantity of magnets, but cut in doesn't really determine blade size, it works the other way. Blade size decides your expected power level and you need a cut in to match the blades. You also need to be able to safely handle the output of those blades in the useful wind speeds.

It would be safer to accept the higher cut in speed with smaller blades and you could still see the same power out as with the original alternator, but in higher winds.

Hugh points out that you can reduce the cut in speed to match the original 10ft blades in low winds and if you are in a poor wind area it has some merit and I have sometimes suggested this to people. The big snag is that with the slower winding you reduce the maximum power capability of the alternator and you also reach it in fairly low winds.

For this to work satisfactorily you need to be able to furl the thing in quite modest winds. From comments I have seen here over a period I am not sure that many people can achieve this reliably so I have been reluctant to continue this advice.

I see you are using Volvo parts and see you mention struts, I hope you are intending to furl this and not copy Dan's early faith and hope approach.

As long as you understand the full implications of the problems of using the 10ft blades and can solve the furling issue then you can get two 10ft machines for the cost of magnets normally used for one and the energy capture on most days in a low Wind area will be significantly better.

If you are in a higher wind area or have never built any form of furling machine before then I would strongly advise you to go for the smaller prop and accept the higher cut in. Your total energy capture will not be much greater with two machines than the original planned bigger one, perhaps a little better but you don't have all your eggs in one basket.

Not sure that the 1/8" thick flux return disc is thick enough magnetically or mechanically I would not use less than 1/4".

You can use slightly lighter cables for each mill but with the two mills I can't see any hope of gain there. Similarly I see no gain with the charge controller.