Thor Forums

[Beau388]

If you are running the coach A/C and the residential refrigerator on the inverter at the same time, there is not enough output from the coach's engine alternator to charge the batteries. It works this way - the engine alternator is rated at 175 amps @ 3,000 rpm and above, but that rating assumes the alternator is at 80 F degrees. The actual max output of the alternator at 130 F degrees is 100 watts. The engine needs 19 amps to run the computer and fire the injectors. The A/C consumes 26 amps on blower speed 2 and 38 amps with the blower on 4. The frig consumes 6 watts @120 volts or 55 amps @13 volts. Inverter is about 80% efficient at low wattages so figure 70 amps @ 13 volts. Total needed is 115 amps, thus the frig is running down the batteries at 15 amps per hour of driving. Now the frig doesn't run all the time so it is not quite that bad, but remember there are other loads in the coach. The electrical system prioritizes the alternator output so the chassis battery has to be fully charged before the systems starts to charge the house batteries.