The battery charger pictured here is a real beast. It will dump 60 amps into a 12 volt battery bank that is low, and will taper down to about 10 amps charging current as the batteries fill. Total cost, $20!
The basis of this charger is dead 1000 watt inverter from Heart. A lightning strike fried the electronics in this unit, but the transformer was intact. The owner elected to replace it with a new model, and we picked it up for $20. The inverter case made a handy case for the charger, too, because of the handles. The whole unit weighs over 50 pounds.
At the time, we did not have a large enough bridge rectifier available, so we built one out of 9 car alternator doides connected in parallel to a heat sink. The bridge gets hot in use, but the diode bus bar is a peice of unistrut that's massive enough to dissipate the heat produced.
Close up of home built diode bridge
home built diode bridge--note the insulated standoffs so the diodes don't ground to the case.
Here is the wiring diagram for the charger. Buying a bridge rectifier big enough to handle 70 amps would simplify construction...the home built diode bridge was the most complicated part of the project. Check our products page, we sometimes have large bridge rectifiers for sale.
Here is the circuit schematic for the charger conversion: