House battery charging issue

pianotuna wrote:
Hi Bill,

Charging from the alternator is mostly just a trickle charge.

It is possible to add an external diode to the alternator and then some serious charging is possible.

Now a days DC to DC converters are an excellent, if some what expensive, way to get excellent results.

Whether it's a trickle charge or not depends on the way the motorhome is wired up, and how well done it is. On mine, it's far more than just a trickle charge, and I think it's probably typical of not a few class C's. There is a heavy (2 gauge or so, I think) wire between the chassis battery and the hose batteries, and a continuous-duty solenoid to connect the two together when the engine is running or the emergency start switch on the dash is pressed. I've happened to see 20+ A charge even when the house battery isn't extremely low, and would not be the least surprised if it's higher at times as the ammeter isn't really visible from the driver's seat.

Diode-based isolators tend to have poorer charging performance due to the voltage drop across the diode. Systems installed with smaller wires also tend to perform less well due to the voltage drop in the wire. In ones with a solenoid of some sort (or a BIRD, which is a solenoid plus some fancy control electronics), the house battery charging won't work if the solenoid isn't functioning properly, and they are somewhat prone to wearing out--perhaps because they're often somewhat underspecified, and sometimes more or less exposed to the elements.

For a trailer, charging from the tow vehicle is indeed more like a trickle charge in the majority of cases, and especially via the standard 7 pin trailer connector; but motorhomes are different.