How to Do RV Electrical Workby Don Bowman
A recreational vehicle's electrical system is divided into two separate voltages. It has 12-volt DC that runs the lights, radio and the refrigerator and 120-volt AC that operates all appliances in the volt range as well as the air conditioner. The 12-volt system incorporates the vehicle's battery and alternator and a separate battery located on the side of the RV. When the vehicle is running, the alternator is operating all the 12-volt accessories throughout the vehicle in conjunction to charging the auxiliary battery on the side of the vehicle. When the vehicle is shut down, a solenoid under the hood cuts the vehicle's main battery out of the line so the accessories cannot run the battery down. The auxiliary battery takes over. There is a state of charge indicator usually around the door or by the refrigerator.
The vehicle picks up the 120-volt AC from either the generator or an outside source through a plug in. Most RVs use a 5,000-watt generator which delivers power from the generator to a motherboard and then to the outlets, air conditioning and appliances. The motherboard is the key to all the electrical work for the most part. It can be accessed close to the floor--usually in the kitchen area. It will have all the circuit breakers and fuses as well as indicators for auxiliary battery condition. There will also be LEDs indicating whether it is allowing a charge to go to the auxiliary battery when the generator is engaged. The generator can also charge the battery.
The refrigerator can also be operated on 12-volt DC if desired. This is only desired if the propane is getting low. This can be changed on the bottom of the refrigerator by taking the baseboard off. When the baseboard is removed, the switch (that allows different modes to be selected) is accessible. There are no 12-volt outlets on the vehicle in the form of wall outlets. They are in the form of a plug in like a cigarette lighter located at various places throughout the vehicle. The vehicle interior lights are strictly 12-volt DC.
In operation, the vehicle starts and, at this time, power from the alternator is supplied to actuate a solenoid under the hood and allow power to go to the auxiliary battery to charge it. There is a charge indicator in the motherboard. When the battery is fully charged with no drain from appliances, it shuts the power off to the solenoid under the hood and cancels the charging. All appliances are running off the auxiliary battery at this time. When the generator is started, the motherboard cancels the engine charging and begins charging the auxiliary battery by itself while still supplying 120 volts to the air conditioning and the wall outlets. When the vehicle is parked and the generator is no longer needed (in lieu of an external source of 120 vac), the motherboard kicks out the breaker for the generator and directs the incoming 120 volts through the wall outlets. It converts the 120 vac to 12 vdc to charge the battery and operate all the 12-volt accessories. A good piece of advice is to have a voltmeter and a carbon pile in the motor home to check the auxiliary battery. This battery must always be maintained in good condition to lessen any chance of electrical problems. First of all, if the battery is putting out 12 volts but has a bad cell, it cannot be charged fully and will wear down quickly. It will cause the alternator to charge much harder while the vehicle is running, and it is a good likelihood that it will cause a premature alternator failure. Not only that, but it puts undue stress on the motherboard, which is expensive and the heart of the whole system.