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RV Basics: 12-Volt DC Systems
Jan Kuderna

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All RVs have two separate electrical systems, 12-volt direct current (DC) and 120-volt alternating current (AC).

The 12-volt system powers all the essential appliances that are needed to camp without campground hookups. Coupled with rechargeable batteries, this is what allows RVers to camp away from cities and towns and experience the beauty of nature with all the comforts of home. This freedom from the electrical grid is what draws many people to RVing.

The 12-volt system has its own fuses, receptacles, wiring and power source. Automotive fuses are often used to protect the 12-volt circuits. The fuses are usually located behind a metal panel, close to where the power cord enters the RV. Be sure to carry spare fuses of the correct size and rating (these are indicated by the color of the fuse and a number on the end).

Receptacles for the 12-volt system are usually the round cigarette-lighter type found in automobiles. Televisions and other appliances that run on 12 volts are available for RVs.
The power source for the 12-volt system is the battery. Batteries store electrical current and appliances use current. RV batteries are called deep-cycle batteries because they are built to be discharged deeply and recharged many, many times without damaging the battery. (The ins and outs of batteries will be covered in detail in another article.)

RVers who camp without hookups (boondock) have to be aware of how much battery power they use. To prevent permanent damage to the battery, RV batteries should only be discharged from 50 percent to 80 percent of their capacity.
The basics of RV life—light, water, heat, fans and motors, refrigeration, entertainment, and safety—are provided by the 12-volt system. The battery provides power for:
Learn all about 12 volt systems at RVbookstore.com.
·Water pump
·Furnace fan
·Kitchen fan
·Bathroom fan
·Slide-out motor
·Refrigerator circuit board
·Stereo and CD player
·TV (only a 12-volt model)
·LP gas detector
·Inverter (not all RVs have one)

Lights: RV light bulbs are either the small, round automotive type or fluorescent tubes that operate on 12 volts. If a lot of lights are on at one time, they can use quite a lot of battery power.

Water: The water pump brings water from the fresh water tank on demand and uses small amounts of current.

Heat and Fans: The furnace burns propane gas, but the furnace fan and the thermostat need 12 volts to operate. Furnace fans use quite a bit of current and can quickly deplete a battery on a cold night. Kitchen and bathroom fans are typically run for shorter periods of time.

Slide-outs: After boondocking for several days, the battery may be too weak to move the slide-out. Starting the engine of the motorhome or tow vehicle will provide power for the slide-out motor.

Refrigeration: The refrigerator circuit board takes a very small amount of current from the battery. Most refrigerators run on propane or 120-volt AC electricity, but some can operate on 12-volts.

Entertainment: Electronic devices, such as radios and black and white TVs, use small amounts of electricity. Color TVs use more. Most RVs have a TV antenna amplifier that uses very little electricity and boosts the TV signal coming from the antenna.

LP Gas Detector: A very important safety device, the LP (liquid propane) gas detector uses very little current. It could save your life and prevent a fire.

Phantom Loads
Appliances that draw small amounts of current but run 24 hours a day can deplete a battery in just a few days. Many RVers are unaware of phantom loads until they leave their RV for a few days and return to find a dead battery. Sources of phantom loads are illuminated switches, clocks, gas detectors, stereo memory, motion activated lights and the circuit boards in refrigerators and thermostats.

What Is an Inverter?
An inverter takes 12-volt DC electricity and increases it to 120-volt AC electricity. Motorhomes and large 5th wheel trailers that are equipped with a generator usually come with an inverter. Travel trailers and smaller 5th wheels usually don’t. An inverter makes it possible to operate standard household appliances, like microwave ovens and electric coffeemakers, when the RV is not plugged into a campground receptacle.

There is a high cost for this increased power an inverter provides. To increase 12 volts to 120 volts, the voltage is increased by a factor of 10. The cost for that increase is paid in current. For example, running a microwave oven takes 10 times as much current from a 12-volt battery, going through an inverter, than it would if the current came from 120-volt shore power.

Running 120-volt appliances from a 12-volt battery can be a big drain on the battery. RVers who boondock with all the comforts of home need two or more batteries and a generator or solar battery charging system.

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