It’s a single-stator with 3-phase star connected windings this time. The ferrite magnets (16 of them at 50 x 50 mm) are crammed close together. This reduces the moment of inertia and also allows short turns on the coils which reduces overall resistance. Chris could have put a lot more copper into the stator but actually the loading to max out the Classic is only 30 amps (at 100 volts) so he decided that it was efficient enough already.
The big advantage of the Classic controller is that it allow the alternator to work at variable voltage while charging a battery at relatively constant ’24 volts’. By programming the Classic, Chris can keep the tip speed ratio at 6 over a wide range of windspeeds. At the same time the alternator voltage rises in stronger winds, reducing the current in the coils which makes the alternator more efficient. It’s a win/win situation with an MPPT controller (so long as it doesn’t blow up 🙂 ).
The stator ended up 10.5 mm thick wound with 45 turns of 13 AWG wire. It produces 119.1 volts @ 1,000 rpm with an 18.5 mm air gap. The voltage is about 80% of what I would normally see with a larger hole in the coils, and more widely spaced magnets, but the compact style of construction has potential for much reduced resistance.
Resistance of the star-connected stator is .55 ohm. Losses at 30 amps should therefore be around 500 watts for a 3 kW output. That’s a hot stator but safe with good cooling. I calculate the power dissipation on the surface of the coils to be around 0.5 watts/sqcm (6W/sqinch).
Gear ratio is .4 to 1 (or 2.5 times up-ratio) so it can produce battery voltage at about 100 rpm on the blades – nice for low windspeed cut-in.
here is a video of the turbine mechanical stuff part assembled
The whole story is here.