by **EricZ** » Fri Jul 20, 2012 2:47 am

Skater is correct that running the A/C off of batteries for any significant length of time is not realistic.

It is, however, possible to run the A/C from batteries for short periods. I've installed three 100 Ah (amp-hour) AGM batteries under the couch in my B190 (note that ONLY sealed batteries, such as AGMs, should go inside the living space), for a total battery bank capacity of 300 Ah. I have a 2000-watt Xantrex PROsine 2.0 inverter with 4500 watt surge capability. (The A/C draws well over 2000 watts on start-up, so that surge capability is important. For example, I can't reliably run the A/C on a 2000 watt Honda EU2000i generator.)

Using this setup, I've run the A/C for about 30 minutes on batteries without problems. I saw battery current as high as 160 amps for short periods, but mostly it was between around 20amps (when the compressor was off) and 75 amps (when the compressor was on). I thus estimate that I could go as long as 2 hours without draining my battery bank past the halfway point (more than that dramatically reduces their life span). I'll be able to better estimate when I install an Ah meter (I have a Bogart Trimetric, just haven't wired it up yet).

But Skater is right, this would be completely impractical for all-night use.

As for power calculations, again, follow Skater's email: Amps*Volts=Watts. I recommend converting everything to Watts, as they're a consistent measure of power, regardless of voltage.

1 Amp at 120volts = 120 watts. 10 Amps at 12 volts = 120 watts

(But with inverter inefficiencies, it turns out that to get 120 watts I'm actually drawing more like 11-12 Amps.)

You also mention an inverter, Jonny. Airstream 190s (at least all the ones I've encountered) came from the factory with a CONVERTER (something that converts 120 volts to 12 volts to run the 12-volt accessories and charge the house battery), but not an INVERTER (something that converts 12 volts to 120 volts). Inverters can be installed, but they're not cheap. An upgraded converter might be about $200-$300. A nice inverter might be $1000-$2000. (Note that the stock converters are pretty bad. Also note that some inverters also include converter functionality.)