I would like to build a battery charger for my boat really cheap but talented (20-30A and regulated). My boat is in an area that things have a tendency to disappear. A $50 20A battery charger seems to mysteriously levitate and float away and I want to leave it there and not worry about it. I'm thinking a full bridge rectifier directly out of an existing GFI recepticle into a pwm controller driving a 400v 30A power FET that I have a few lying around. I was thinking of using a 555, but I think that I should use a frequency of about 1M Hz. Maybe the vco of a 4046? I have looked through the forum and not found anything quite up to snuff. Any suggestions?