so i rewound my 5kw generator. 10hp Tecumseh engine. we have another generator, 9hp Briggs but same company, Generac. its windings read 0.26 ohms for 120v, .53 ohms for 240v. i think its is wound with the same size wire for each half of the winding. mine isn't.
Stock winding consisted of 3.2 pounds of copper. Wound two in hand of 16 awg to make the 120v 30 amp rated coil, and two in hand of 17 awg to make the other 120v 20 amp rated coil.
I rewound it with 15 gauge wire, 24x10 turn coils. pitched across 10 slots. this required about 500 feet of copper. connected in wye for nominal 240 volts at the knee of the saturation curve. it produces a nice sine wave connected in wye, but there is significant third harmonic content at the wye center point. most likely this is because the rotor is electrically 90 degrees wide, rather than the usual 150 degrees. in fact it could be made into a 4 pole machine, by bolting on two more arc shaped segments.
so here's the thing.. the stock winding had a 64 turn coil wound with 20 gauge wire to feed power to the rotor. no regulation. just saturation. it was positioned at 90 degrees to the 120/240v winding. the 64 turn coil was full pitch, spanning 12 slots.
i must have messed up a little bit on the calculations because i'm getting 280volts out at 62 hz, rather than 240. i can get 240vac with just 20 volts ac headed to the rotor. the stock 64 turn coil would have produced about 64 volts open circuit, i think.
anyhow the extra voltage is good because i'm intending to use a boost converter to charge 32, 12v batteries in series from it, then run a vfd off that to get 120/240 3p. http://i.imgur.com/B6nFrb2.jpg
anyhow, there are other options as well. the generator prior to the rewind, was consuming 0.56mL second of gasoline at idle, works out to 19kw waste heat i believe, very similar consumption with our other generator, the 9hp briggs.
i will have to measure the idle gas consumption again and see how it is with the rotor disconnected.