12-volt DC – A recreational vehicle’s low voltage, direct current system, powered by either one or more batteries or, when the RV is connected to electrical hookups or a generator, an inverter. Direct current means that the electrical current flows in one direction in the circuit, from negative to positive. 12-volt DC powers components in the RV such as lights, water pump, LP gas furnace fan, generator starter, fans, tank level indicators, and DC powered entertainment equipment. DC power is also required for controls and propane ignition for the camper furnace, hot water heater, refrigerator and stove. 12-volt DC outlets are often provided to power other devices.
A towable RV, such as a travel trailer, fifth-wheel trailer, or tent trailer, will have one 12-volt DC system. A motorhome will have two, the coach system for the living quarters of the RV, and the 12-volt chassis system, which powers the vehicle electrical requirements. Each system has it’s own battery or batteries. Multiple circuits may be provided in the DC systems, with each circuit protected by fuses or DC breakers.
When a motorhome’s engine is running, both systems’ batteries are being charged. There are usually little or no other interconnections between the two systems. Exceptions might include a battery boost switch for additional power for starting the engine if the engine battery is depleted or a radio power switch to power the vehicle’s radio from the coach system when the motorhome engine is off.
A number of devices powered by 12-volt DC can drain the coach battery when the unit is not in regular use. Examples include: entertainment system or radio clocks, a light left on, a TV antenna booster, or propane gas detector.