Typically the flux density in the gap of the original dual rotor would be in the region of 600mT. If you remove one rotor then the average flux linking the same stator will be something like 300mT and you will measure about half volts. The flux close to the magnets will be nearly that of the dual rotor but that at the far side of the stator will be very low indeed and the far half of the stator will contribute more resistance than volts. For a single rotor you would probably be better starting with a thinner stator, but the flux distribution will be poor.

If you replace the second magnet rotor with a spinning disc then there will be far more incentive for the flux to cross the air gap and not fringe between magnets on the same disc. Obviously you can't hope to have as high a flux density as with the dual magnet rotor unless you reduce the air gap and that will reduce your winding space ( impossible in this case with a bought in stator). I would expect the average flux density in the same gap as the dual rotor to be about 450mT. When you consider that output power is roughly proportional to the square of the flux then it is obvious that the second disc gives a substantial improvement over a single rotor with no return path.

The big question with starting with a stator intended for another purpose is whether you can somehow get a good match with your prop at a standard voltage.

With single rotor I think you will be forced to use the 24v stator at 12v and accept quite a low power out and it will not take a very big prop.

With the spinning disc I would expect the thing to still work at 24v but with a smaller faster prop bringing the volts back up with the lower flux.

If you are prepared to accept a faster prop with a bit more noise then I suspect you could get away with 8ft at tsr7. The stator will handle the same maximum current of the original 10ft machine, so your peak power will not drop but you will need more wind to get it. An 8ft prop will do far better in light winds than the size of prop needed to get it running at 12v without the spinning disc. At 12v your peak power is reduced to half for the same stator heating so you loose out all ways.

I agree when you say people don't know how to match their props to their generators. Hugh Piggot's Windpower Workshop talks about it... but even after reading it... I didn't quite understand exactly what he was getting at. I guess it just takes some experience and experimentation to understand what he and other do it yourself wind guys are talking about.

Switching the blades to a smaller diameter isn't a huge deal, it's another $40 and will probably be worth it, if what you guys are saying is correct. I'm just wondering if circular magnets will make a huge difference or the smaller prop will be all I need.

Also, if I do switch out my blades, will my furling system still work for the smaller diameter turbine... I based it on the ratios of the 9.5 foot turbine, so it will be too big but does that necessarily mean it won't work....