winglit, sorry but I can't see your idea working, automotive alternators are all 3 phase machines and you'll get bugger all out of them if only using 2 of the 3 stator windings - I've tried! Further more they need to be running at several thousand rpm to give a decent output, and this would give a frequency way over 400Hz. You would still need to use the rectifier and regulator to control the voltage even if taking the AC direct from the windings.