[serialk11r]

The issue with PM generators (especially in gasoline engines) is that the amount of power available increases with rpm, but vehicles need the same amount of electrical power at idle. As the vehicle is moving and the engine is running many times higher than idle speed, the PM generator is running at very low load, and that's where PM motors/generators are not efficient.

I don't really understand magnetic hysteresis very well but I know eddy current losses (which dominate at higher speed) can be cut drastically if you spend more money making thinner laminations for the rotor. Money is hard to come by though :P

Basically, this is not stuff you can do in your garage. The most DIY-able way I can think of where you mostly work with hardware off the shelf is cycle a normal alternator between 0 field current and maximum voltage, charging a bigger lithium ion battery through a step down converter, and using a larger pulley on the alternator to reduce its speed.

I think you could probably raise the alternator efficiency 20% (relative) by doing this, while losing 10% charging the battery, so you'd still be ahead.