Many persons using campers for recreation find themselves drawn to remote camping away from any power grid, sometimes called boondocking. To fully enjoy this autonomy it is necessary to have on board a comprehensive, fully operational and well-protected 12 volt electrical system. This 12-volt installation will comprise dedicated outlets, usually of the round type found in regular autos and used for cigar lighters, along with lights and a wide variety of appliances. When designing such a system, or planning the upgrade of a pre-existing system, a number of primary considerations have to be addressed before details can be thought out.
Decide how many coach batteries will be required. The coach battery must be of the deep cycle type, which is very different to the battery which starts the engine. So long as the coach battery is kept charged, all the 12-volt appliances and accessories will work without connection to shore power. A bank of batteries will last longer than a single battery. To increase amp hour capacity, connect a battery bank in parallel. To increase the voltage capacity, connect a battery bank in series. Always install a master battery disconnect switch.
Draft a wiring diagram of all the circuits and appliances necessary for the installation to meet all your needs. Direct current (DC), as supplied by the coach battery, operates by allowing current to pass in one direction through an appliance. It flows from positive to negative and actuates the appliance as it passes through. Thus all circuits must start with a fused connection to the deep cycle battery, and end with a connection to ground.
Consider fitting a monitor panel; a useful centralised hub of gauges and dials which inform the user of battery charge as well as ancillary camper information such as the fullness of propane and holding tanks.
Calculate what size inverter will be required. Your camper may have as standard a number of 120-volt appliances such as a microwave, a water heater and a television-based entertainment system. You may have equipped the camper with 120-volt accessories that are common in a home such as a can opener, a coffee percolator or a hair dryer. In a 12-volt camper these items must all be run from an inverter, but it is not a power-economic use of the battery's resources.
Plan to install an umbilical cord to connect the camper to shore power. An shore connection is a valuable addition to the 12-volt wiring. Equip the cord with a 30-amp TT-30P plug (for convenient connection to campground disconnect boxes) at one end, and a breaker panel at the other. The breaker panel should have a 30-amp master breaker and smaller breakers serving branch circuits, sometimes called spurs. As in a regular home, any 120-volt outlets which might be exposed to water, such as those in the galley and bathroom and any exterior fitments must be protected by Ground Fault Circuit Interrupter (GFCI) sockets.
Choose a converter to be installed near the breaker panel. A converter does the opposite of an inverter, transforming 120-volt current to 12-volt for running 12-volt appliances and circuits such as lights, the water pump, slide-out motors and the fan in the furnace (even if it's fuelled by propane), all from a non-battery source. It is also an important part of the 12 volt system because it allows automatic charging of the coach battery when shore power is connected.
Design a 12-volt fuse board to operate in tandem with the 120-volt breaker panel. Always keep spare fuses on hand. It is conventional to locate both the breaker panel and the fuse board close to where the shore power umbilical cord enters the camper.
Decide if a solar power system is a viable way of recharging the coach battery. A system comprises a photovoltaic panel mounted on a panel sustainer kit, which supplies power to a charge regulator and then to the battery. Although effectively a source of free energy, the panels are fragile, the installation is expensive, and when parked the camper must be oriented so as to be in direct sunlight.