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How Does the RV Electrical System Work?

How Does the RV Electrical System Work?

Posted by Eric Johnson on Sep 10th 2015

I get asked a lot of questions about electricity in RVs, and while my background is not as an electrician, I have gained knowledge of the RV systems through trial and error (Luckily not too much error). Electricity and RV’s are a bit complicated. The main reason it can be a bit difficult to follow is because unlike a regular house that only has AC power, the RV runs AC and DC components. Just to confirm the terms here, AC means alternating current (2 way current) and DC means direct current (One Way Current). AC comes from the power lines and DC comes from batteries. So just look over this diagram and it will all come clear:

RV Electrical System

Kidding of course, but what in the world is going on in this diagram? I see power coming in, and then I see batteries providing power. Then I see all of these funny little convertor and invertor boxes. Understand this, different components in a RV are designed to run on different types of power, either 120 volts AC or 12 volts DC. Since the origin of the power is AC, assuming you are plugged into shore power, then you need to convert that 120 volts of AC power to 12 volts of DC in order for those DC components to work.

Running your RV Power System While on Shore Power

So when the 120 volt AC power comes in from the pedestal, it hits a transfer switch, and from here some of that power just flows right on through the circuit breaker and to the components in the RV that require 120 volts of AC power. This is why you have breakers and fuses in your RV, the breakers handle the AC and the fuses handle the DC. Generally the items that run on AC power are your luxury items like TV, air conditioner, microwave, and wall outlets. The items that run on DC power are things that do not typically draw too much power like lights, water pump, heater blower, refrigerator (not residential style, that would be AC power). So we powered the AC items with the 120 volt AC power coming in from the pedestal, and now we need to power our 12 volt DC items with that same 120 volt AC power. This is where you will need a convertor. Your RV has one of these and it is likely installed in one of your underneath bays. The 120 volt AC power goes through the transfer switch to the convertor and comes out as 12 volt DC power, we will just call it magic. From here the DC power heads to the batteries and keeps them charged. From the battery, that DC power goes through a fuse panel, and then to the DC components that need power. Here is another chart that is a bit easier to follow than the one above:

RV Electrical System

The batteries in your RV will stay nice and full because of the power coming from the AC convertor. As you see in the diagram above, the batteries are also charged by the engines alternator while the engine is running.

Running your RV Electrical System Without Shore Power

Now you may find yourself using your RV without outside power, referred to as dry camping. Well this fouls everything up that I just wrote about how RV systems work. If you do not have 120 volts coming from an outside source, then what happens to the batteries and the AC dependent components in your RV? Well nothing changes with the DC components, those items still get their power from the batteries, but without the AC power coming in, the batteries are not getting charged.

So this leaves the AC items in your RV without power, because if batteries are now the only source of power, and we know that batteries only produce DC current, then the AC items will not run, right? Yes, that it correct, but luckily there is another magic box that turns DC power, back to AC power, and this is called an invertor. So to review, a convertor changes AC to DC, and an invertor changes DC to AC. There are boxes that can do both functions of converting and inverting, and newer RVs may have these in them. Once the DC battery power is converted to 120 volt AC power then it goes through the AC breaker panel and then on to the AC dependent components. Inverting power from DC to AC takes a good amount of battery power to make this conversion, and therefore deep cycle batteries are recommended to withstand the punishment. Obviously without a source to continue to charge your batteries, your life cycle at your current location will not be long. If you are on battery power only, be sure to conserve energy in every way you can.

On a side note, a good way to conserve some energy is to convert your RV to LED lights. LED lights use much less power than standard bulbs and therefore your batteries will last longer.

Other Sources to charge your batteries

Charging your RV Batteries with Solar PanelsBecause many RVers like to be “off the grid”, there must be creative ways to charges the batteries without shore power. There certainly is - solar panels are very popular for RVers. All you need is a nice sunny day and the solar panels will work to keep your batteries charged. Whether or not the solar panels can keep up with your power consumption is dependent on your level of power consumption versus the extent of your solar power system.

A lot of RVers use generators. Having a generator is the equivalent of being hooked up to shore power from the RV electrical stand point, but much noisier. This is a solution for a many RVers, but is not the cheapest option as you have to keep them filled with gas. If you get a big enough generator then you could run all of the AC and DC components of your RV.

You can also keep your batteries charged with wind power, but this is not very practical and not many RVers resort to this. As a last resort you can always start your RV and charge the batteries with the alternator from your engine, but I would not use this as a normal source of power as it will reduce the life of your alternator since you would likely only do this if the batteries are low. The alternator works harder and hotter to charge a low battery versus maintaining a full battery,

Protecting Your RV Electrical System

I tried to write this in a way I would understand it when I was starting off so I hope this is helpful to those that did not know this, and I hope it was not to boring for those electrical experts out there. I think it is good for everyone that RVs to have a base knowledge of their electrical system. What is most important is that you protect all of these vital components. 12 Volt DC components can be a bit finicky and ensuring that proper voltage is supplied to your RV is top priority. The simplest way to do this is to get an Electrical Management System. While this sounds complicated, it really isn’t. Technology has come a long way and these units are mostly plug and play. There are a lot of choices out there and we believe the best system is the Surge Guard Total Electrical Protection System. These units will continuously monitor the power supply coming into your RV and if it detects a variance outside of the tolerances then it will shut the power down. If you do not have one of these devices in place then you are playing a risky game with your RV. Without the device, a power spike or even low voltage from old worn out park pedestals can do damage to your electrical system. I get emails all the time of RVers telling me how their Surge Guard systems saved their RV. Unfortunately I get emails of those not using these systems, and they are telling me about damage they took on as a result. Check out our full line of Surge Guard Electrical Protection Systems and if you need any assistance picking one out then just email us at or call us at 866-324-7915.