RV Electrical – The Basics
Here at Wild Mountain RV, the RV electrical system seems to be the area that causes the most confusion. There are many components to an RV electrical system, and I plan to write a blog post for each one down the road, but for now I wanted to give a high-level explanation to answer the question: How Does the RV Electrical System Work?
There are 2 electrical systems in most RVs. RVs are unique in that these 2 systems are isolated and integrated at the same time. The 2 main electrical systems running all RVs are a 12-volt system and a 110-volt system. In a nutshell, the 12-volt system runs off the RV 12-volt battery bank, and the 110-volt system runs off the shore cord when plugged into an outside electrical service or generator.
12-volt system.
Almost all RVs have a 12-volt electrical system – measured in VDC (Volts of Direct Current). Basically all the lights, fans, and circuit boards of your appliances run off 12 volt power. As well as the water pump, radio, lp/co detector, slideouts, electric jacks, power awnings, and some tvs.
The 12-volt system has a battery bank that supplies power. This battery bank can consist of 1 battery (a single 12-volt battery), 2 batteries (2 x 6-volt batteries, or 2 x 12-volt batteries), or more – the largest we have seen to date was a motorhome with 16 x 6-volt batteries.
Batteries deplete as they are being used, and most RV systems need 12 volt or more to function properly. For example, a 12-volt battery’s voltage will measure about 13.4 volts when fully charged, and 12 volts when it reaches about half charged. When below 12 volts, the loads (lights, appliances, etc.), may still function but sometimes not properly or with weakened output.
Battery banks are usually charged in 3 ways:
Plugging in your RV. The RVs charging system is enabled when the RV is plugged in and will charge the batteries automatically. All modern RV charging systems use ‘smart charging’. This means that it will regulate how much charge to put into the battery bank to that they don’t charge too fast, or over charge; either can lead to damage to the battery.
Using a generator. For most RV users this is the same as plugging in as they still physically plug their RV into the power source using the shore cord, but many motorhomes have ‘on board’ generators. Once these generators are started they charge the batteries while running.
Solar. This is becoming more and more common for those who like to camp off grid, or those who don’t have the time or capability to charge their batteries when the RV is stored. Many people think that solar supplies power directly to the system. This is not the case; solar recharges the battery bank that supplies power to the system.
What about while driving you ask? It is true that RV batteries will charge from the vehicle’s electrical system, but this charge is very minimal and the driving time is often shorter than required. Do not count on this for proper charging of your battery bank.
110-volt system
Most modern RV have a 110-volt system – measured in VAC or just AC (Volts of Alternating Current). The 110-volt system powers items in your RV that the 12-volt system cannot – the air conditioner, microwave, tvs, all the outlets, and your converter.
This power can be supplied in 3 ways:
Shore cord – plug in your shore cord to a 110-volt power source – an outlet or external generator. The power requirements will be determined by the type of power system your RV has, but normally it will be 15 amp, 30 amp, or 50 amp service. 15 amp is usually only found on older and small RV’s (some tent trailers or vans) which require very little power. 50 amp is found on large pull trailers and 5th wheels and most Class A motorhomes. 30 amp is the most common RV electrical configuration. Even though RVs should be plugged into the proper power supply, all of these can be plugged into a regular 15/20 amp plug using an adaptor. For 30 and 50 amp systems, this is usually only done to ensure the batteries are being charged, and caution should be used when trying to operate any heavy draw appliances (a/c or microwave), or using multiple power loads at once. Ideally if the power draw is too great, a breaker will trip, but if that failsafe is not in place or not working, damage to the electrical system may occur as well as the risk of fire.
An onboard generator. RVs with an onboard generator need only to start it up and their 110 system will be supplied with power.
Inverter. An inverter is a power supply that draws 12-volt power from the battery bank and steps it up to 110-volt power in order to supply power to the 110 system. This topic will require an entirely separate blog post as there is so much to unpack here. For now, just know that most inverters do not supply the same level of power as a shore plug, and because it is drawing so much power from your battery bank to create 110-volt power, your batteries will deplete very quickly. For these reasons, inverters are often used only for brief periods and/or for specific temporary uses.
The Converter. People often use the terms Converter and Inverter interchangeably. Although they often look similar, and they both change the power from one type to another, they in fact do opposite jobs. A Converter converts power from 110-volt into 12-volt. An Inverter turns 12-volt power into 110-volt. The converter on an RV serves 2 purposes (and often consists of 2 different sections to perform these functions):
Convert the 110-volt power to 12-volt power in order to directly supply power to the 12-volt system. This is why most of your 12-volt power system will function properly when plugged in even if you don’t have a battery connected.
Powers the battery charging system which regulates the battery bank charging (as explained earlier). If your 12-volt system is working when plugged in but the battery bank is not charging, then the charging section of your converter needs replacing. Most types of converters can have just the charging section swapped out, but some need the entire converter replaced.
Trailer exterior power – lights and brakes. The exterior power system operates on its own as an independent electrical system. The trailer taillights, clearance lights, and brakes all operate from 12-volt power supplied from the tow vehicle through the plug (most often a 7-way plug). The tow vehicle will send power through the wires of the 7-way that will operate your lights and your brakes. The only exception to this is the emergency breakaway switch (the cable that you attach to your vehicle when towing. This switch is powered by your RV battery when engaged. In the case the trailer separates from the tow vehicle, the cable will engage the breakaway switch that will supply full braking power from your RV battery to your trailer brakes. This is why it is necessary to always have a battery connected when towing.
Repairs. As a repair shop, electrical problems are the ones we have the hardest time trying to estimate cost for repairs. As you can understand, diagnosing an electrical problem can take a few minutes or many hours. Newer trailers and larger motorhomes also have much more complicated electrical systems than can increase this diagnostic time. When we have electrical problems to diagnose, we pre-arrange the amount of time the customer is willing to spend and do not go over without further approval.
This is a summary of how the electrical system in an RV works. If you have further questions, please feel free to contact us via email at info@wildmountainrv.ca or call us 403-286-3535.