I always use 12 volts when doing the calcs. A battery puts out more than that when charged and a charging system puts out even more voltage than the battery (it has to or it couldn't charge the battery). By using 12 volts rather than battery or charging voltage it means that the amperage draw is higher for the same wattage, and that automatically makes cable size choices erred on the safe side.
I have a marine spec VSR (BEP Marine) backed up by a marine battery combining switch. I do not expect to have a problem with the VSR, but if I do I can use the marine combiner switch as a manual back-up. Having used the simpler continuous duty solenoid in the past I do prefer the idea of the primary battery getting fully charged first before the solenoid brings the secondary battery into the charging circuit.
Last edited by ntsqd; 11-22-2010 at 04:47 PM.
I used to swerve around my hallucinations, now I drive right through them.