Forum Discussion
pnichols
Feb 14, 2020Explorer II
kohldad wrote:Our small motorhome on the Ford E450 chassis has the V10 in it. When drycamping and the coach batteries get low, I bring them up a bit by idling the V10 for awhile. It's fed off the main 55 gallon tank and it idles very quiet. It's 130 amp alternator dumps way more current into the batteries initially, when they're quite low, than the motorhome's built-in charger can. Doing this shortens overall charge time quite a bit for when using the motorhome's generator or a portable generator to finish up the charging. While doing this V10 idling, we can also use the main cab heating and air conditioning systems to also heat/cool the entire coach area.
You would do better by adding in a battery-to-battery charger. This way the coach battery will see a higher charge rate during the entire idling time. I'm adding one not for while idling, but to maximize the charge rate during my short move days where normal running wouldn't have a chance at a full charge.
When my two 115AH Group 31 AGM deep cycle batteries (230 amps total) get run down to around 50% SOC - and I then use my idling V10 for 1 to 1/2 hours to supply an initial boost charge (of 14.XX volts) into them - the ammeter I've installed shows this process as initially pumping up to 80 amps from the 130 amp Ford alternator into the coach batteries and then tapering down to around 25-30 amps at the end of the 1 to 1/2 hours of V10 idling. I'm not sure that a B-to-B charger between the engine battery and the two coach batteries could do any better than this.
My motorhome of course has it's engine alternator much closer to the coach batteries than what a tow vehicle's alternator would be to a trailer's or 5th wheel's battery bank. Our motorhome also is using 8 guage cabling between the engine alternator and the coach batteries ... hence the high current that is able to flow from the alternator to the coach batteries due to only a small voltage drop between the alternator and the batteries.
Actually, a truck camper could also use the above approach for initial high current boost charging of it's camper batteries.
When drycamping, I can finish the coach battery charging by running the built-in Onan generator or our portable Honda generator for several hours after the initial engine alternator boost charge.
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