Originally Posted by 73shark
I agree re: running off batteries but wouldn't it take quite a bit of capacity to power 2.5 KW plus a much larger inverter?
Forget I said anything. After giving the matter more thought, the 12vDC Mercedes rooftop a/c in place of the 120vAC Airstream-installed a/c brings with it more problems than it solves.
Either unit would require hooking up to shore power or firing up the generator to run the a/c. But with a 120vAC a/c unit, when you're on shore power the inverter/charger is in charge mode, not invert mode. The a/c doesn't drain the batteries at all. When the generator is running to power the a/c, the inverter is in invert mode, but it's inverting the generator output, not battery output.
With a 12vDC a/c unit, it's different. When on generator power, the a/c would be running off direct generator output without going through the inverter. So far, so good. But running on shore power, the a/c unit would be drawing off the batteries, and you would need a larger inverter/charger to keep up with the demand without depleting your house batteries, and the amount of current flowing through the batteries would be problematic.
Running on battery power alone, the 12vDC a/c unit would kill the batteries in no time, kind of like the tank heaters that can kill them stony dead in four hours or less.
Guess it really is better to use the Mercedes 12vDC rooftop a/c as a supplement to the 120vAC a/c unit, not as a replacement.