120V AC and 12V DC systems ARE already separate.
Turn the 120V AC Circuit Breaker for converter OFF or unplug it if not wired to a CB) and 12V DC system is strictly on battery supply...which will then need an alternative source of charging
Replace Converter and then you have best of both worlds
Working Charger for battery/DC System Power source when connected to 120V AC and
Battery to supply DC System when NOT connected to 120V AC
120V AC System:
A/C Unit, microwave, TV, Fridge/Water Heater electric elements, wall outlets, Converter
12V DC System:
A/C Unit T-stat---Furnace, water pump, Lights, Fridge/Water heater Propane controls, fans, etc
