Welcome to the Smith Auto Repair & Electric R.V. Electrical page. The purpose of this page is not to give detailed information on how to troubleshoot a specific electrical problem, rather we will cover how the different systems work and interact to make up the complete electrical system of an RV. Having an understanding of these systems will allow you, as an owner of an RV to make an intelligent decision on whether to try and repair the system yourself or seek professional help. Many of the systems in an RV interact and one system can affect the performance of another. The information below is based on a dual battery system, where one battery is used for engine start and the other is used for coach accessories. Many more elaborate systems are available, but let’s keep it simply for now. It is our hope at Smith Auto Electric that this information will be helpful in maintaining and trouble-shooting your RV electrical system. Proper maintenance of your RV electrical will help make your travel adventures more enjoyable. Have a safe trip.
Understanding DC Battery Systems
Most RV’s contain a minimum of two batteries. It is important from the outset that you understand the differences between these batteries and do not interchange them. Many RV’s have a large engine to power the heavy weight that an RV is required to haul, including pulling an extra vehicle or trailer. To assure that the engine will start quickly under all conditions, you should install the largest battery that the compartment will handle. Use only a premium automotive battery here that is rated at 800 to 1000 Cold Cranking Amps (CCA).
DC power for the coach requires an entirely different type of battery. This battery does not need to give a burst of energy, but rather must be designed to give its power in smaller quantities over a longer period of time. It must be able to be discharged and charged over its life many times. Commonly called a deep cycle battery, it is usually rated in Reserve Capacity or Ampere Hours (AH). Each person has different needs in power consumption and you must gear your battery to work efficiently with your needs. If you only go out in the wilderness occasionally (dry camp), then a coach battery with a 50 AH rating will work fine for your needs. However, you may stay out for extended periods and require several hundred AH’s to get by. This may mean you will need more than one battery connected in parallel to accomplish this. Weigh these considerations carefully before making your battery purchase.
DC Battery Charging, Engine and Coach
Let’s talk about recharging the battery system while you’re traveling. An
important point is that the batteries must be isolated from one another. If you decide to connect the two batteries together without some way of isolating them, you must use large battery cable or you may overheat the wiring when the engine starter tries to pull current from the coach battery during starting. You also run the danger of running both batteries too low to start the engine while you are parked. This could be a serious problem if you are dry camping miles from no where. Some RV’s have a dual battery switch that allows you to connect the batteries together. Don’t leave this switch in the dual position, unless you are sure it is control by the ignition switch! The better of these systems use a time delay to allow the engine battery charge to stabilize before closing the circuit to the coach battery via a solenoid.Battery Isolator The best systems use a Dual Battery Isolator to solve this problem. The isolator allows each battery to be charged by the engine alternator, but does not allow a drain from one battery to the other. This is important if you are dry camping. Some RV’s will also have a solenoid with a momentary switch in the event that you need to start your generator on a low RV battery or boast your engine battery during starting. I would only rely on this in emergencies, thus avoiding current surges between the two batteries, one of which may be fully charged and the other low. If possible, it is better to start your engine and let the alternator charge the system a little first. It is also a good idea to have a circuit breaker installed in the circuit between the isolator and the RV battery to avoid overworking the alternator and wiring. Now you understand how the engine alternator keeps both batteries maintained, but what happens when you stop driving and start camping? We will cover this next.
Converter and Fuse Panel
Virtually all RV’s use a battery converter to allow the 12 volt accessories to be run by 120 volts AC when plugged in to shore power or when the generator is running. This saves battery power for when you need it. The converter also recharges the coach battery. Many of the newer converters are able to charge the battery at the rated output of the converter. This is a real advantage if you use the generator to charge your battery when you are dry camping. Many of the older converters only trickle charge the battery at 3 or 4 amps. This could take a long time and lots of generator fuel.
In addition to the above features the converter is also connected into the 12 volt distribution panel so that it supplies power to 12 volt accessories when it is on, or allows the battery to supply power when not plugged in. The distribution panel usually consist of a row of fuses marked for each circuit it runs. All DC power to the coach should come off of this panel. This is important! The converter does not charge the engine battery, since a properly wired RV will not have any coach accessories coming off of the engine battery. It is also important that as part of your routine maintenance that you check for drains on both batteries. This should be measured in milliamperes and will alert you to possible problems that may arise from something being left on. Many dead battery problems have been traced to a light in the closet that is on. For this reason some RV’s use a disconnect solenoid to power down the coach when it is not in use. You now have a basic understanding of how everything is connected and interacts on the DC side of the coach, now how about AC accessories?
AC Power Distribution
In many RV’s, AC power works very similar to your house power with one very important difference. Most RV’s have more than one AC power source. Normally you would have a shore power cord to connect to outside power and many have there own Generator. One important point to remember is that AC power sources must never be connected together! In a modern RV, all incoming power goes through a transfer switch, which is a device that keeps the different incoming AC power sources separated even though you may be plugged into shore power and the generator is running. You can only use one AC power source at a time. The transfer switch is normally installed ahead of the circuit breaker panel and due to the mechanical nature of it, should be suspect when no power problems occur at the breaker panel.
If you add additional AC power sources to your RV, such as a battery inverter, you must make sure that it also has a transfer switch or you will need to install an additional one. Again, all AC power sources must be protected from each other! An exception to this is a small inverter that has its own receptacle outlet and lets you plug an appliance (VCR etc.) directly into it. This unit is not connected into the breaker panel. Once the power gets to the breaker panel it is routed to the various AC devices normally with Romex style wire, with various junction boxes and switches. If you have AC problems the first place to check is your AC power cord. This cord takes a lot of abuse and if it shows signs of heat (melted plastic) or is loose at the plug-in connection, than this should be replaced. Also carefully examine any adapters you may have. I hope this gives you a better idea of how the AC power is distributed in an RV.
Many RV’s enjoy the luxury of having their own AC generator. This allows you to enjoy many AC appliances such as air conditioning while dry camping and also recharges your coach battery through the converter. Some important things to remember about generator operation are:
1. Check the oil and air filter often and service regularly.
2. Have the AC Voltage and Hertz checked for proper setting.
3. Remember the generator runs out of fuel when the tank is below 1/4.
4. Do not use the generator compartment as a storage area, keep it clean.
5. Have the exhaust system checked often for any for cracks or leaks.
6. Maintain a service log by date and hour meter reading.
Item 5 is very important. The generator is often run while parked and unless the exhaust gases can get out from under the coach, they may rise into the inside of the coach and they are lethal. Do not take a chance on this. Have any problems taken care of. Consider having your generator tuned up and inspected by a professional each season before you get underway. A mis-adjusted generator can cause severe problems with delicate electrical accessories. With a little care, a generator will give years of reliable service.