Why not just get a used tossed away converter - soooo many of the folks here just toss them in the trash because they require a few parts to repair. The parts typically cost less than $5.00 total and maybe 30 minutes of my time to repair most are as good or even better then new when operational - higher quality parts makes a difference.
I currently use a 75amp w/ remote pendant WFCO that easily (simply press a button when needed) gets me 14.7 Volts at 70 plus amps, or 13.6 or 13.2 Volts (for as long as needed) cost me <$20.00 total for the unit.
