3813MS - 12v lost off shore power

[Ram Montana High Country]

Got a friend full timing in his 3813MS. When he unplugged shore power at last campsite, all his 12v shut down. I asked him to start checking 12v power with meter. His new AGM Batteries he said were measuring 13.2 volts, pos to neg terminals??? The battery disconnect was rotated on and off and is in the position where the key will not come out (should be on). Converter must be working if 12v works on shore power. No generator installed. Could this be a transfer switch?

Any thoughts?

And to make matters worse, they hit hit a post on a turn starting at basement door and stopping just before dump hookup. Now looking for a metal fabricator in Albuquerque to get metal shaped and installed.

[Carl n Susan]

This does sound strange. I see he has a 3813MS. Is this the model with a residential refer? If yes, does the inverter work without shore power connected?

The 13.2V at the battery is unusual AFAIK. Without out shore power and the converter, a battery normally is at 12.6 or so fully charged. If the converter is working under shore power, the battery will read 13.4 or more (depending on charge level). You do have to let the battery sit for 30 minutes after removing shore power to let it settle down to the 12V level. 13.2V sounds like the converter was just turned off before the measurement. Which supports the converter is operable theory.

The wiring for the 12V side is pretty simple. Disconnect shore power and have a cup of coffee, or adult beverage, to let the battery equalize. Starting at the battery + side, it goes to the two 50 amp self-resetting circuit breakers (red plastic cover on the back wall). Check for 12V on both sides of the breakers. Power then goes to the On/Off switch in the convenience center. Check the switch for 12V power on both side. The wiring then goes to the converter. There should be 12V at the connection posts.

With the shore power connected there should be 13.4 or more voltage at the converter connection posts. As new batteries were mentioned, check the "Reverse Polarity" fuses on the converter to see if the have blown. It doesn't take long (< 1 second) to blow these if someone hooked the batteries up backwards.

Somewhere along this path you should find the problem.

[Ram Montana High Country]

Yes to Resi fridge. He’s checking the inverter now. Batteries were installed four stops ago. This doesn’t eliminate converter fuses.
More in put later.

[BB_TX]

Carl has given you very good troubleshooting info. Since he has voltage at the batteries, it is a matter of then checking for voltage point by point from the batteries to the converter and/or fuse panel to see where the voltage is lost.

If they reversed the polarity when installing the new batteries it would blow the reverse polarity fuse.

No transfer switch in the 12 vdc power circuit.

[Ram Montana High Country]

Turns out inverter breaker was tripped , hydraulic breaker bad and inverter off with gfi tripped also. All is well now.