If I understand the process requirements, I think you would want a constant current power supply, like used on a DC stick welder. A constant voltage power supply, like used on a MIG welder might not work. The only problem I see with using a welder is that the open current voltage is anywhere from 40 to 80 volts and I am not sure if this high voltage would cause problems or not.
Have you considered a heavy duty battery charger? Another option might be to use an electric motor to drive an alternator for DC power.
