Wednesday, June 22, 2011

RV Power for Dummies

If you know much of anything about electricity, this article is not for you. You already know all this!
For the beginner, this will seem like a lot of info, but I've tried to keep it simple. Just read it over a couple of times and hopefully it will help you to begin to understand the electrical power in your RV.

Before I go any further, one note . . . If you are ordering a new Lazy Daze, I think one of the most important options you can pay for is to get as many 12-volt (Direct Current or DC) and 110 volts (Alternating Current or AC) outlets as they will give you. It's been my experience that they're never where you want them, so I like having them everywhere! We got all they would allow, and still had to put more in!

110 volt power is what you have in a regular house. It comes from the power poles that feed your home. You access it via through those familiar 3-prong plugs.

12 volts is what is supplied to your RV from your battery bank. In your RV, if you're sitting out in the middle of nowhere, you're running off of 12-volt power supplied by your batteries. Think of the plugs that go into a cigarette lighter. That is a 12-volt outlet.

The 12-volt plugs cab dash are powered by the cab battery located under the hood. The house batteries, which power the lights, etc. in the living quarters of the motor home are located somewhere in the body of the motor home.

One short note about house batteries. They come in two types, flooded cell and sealed (AGM or gel cell). If you have flooded cell batteries you must maintain them by checking that they have enough distilled water in them. If your batteries don't have enough water, they will die a premature death. There are many ways to water your batteries but that's another subject. Just remember that this is a crucial step in preserving your power. KEEP YOUR BATTERIES WATERED!!!
Tech Note: A Profill system is commonly used to keep the batteries topped off.

If you have replaced your flooded cell batteries with AGMs or gel cell, they are sealed and never need water. There are many advantages to sealed batteries, but they are considerably more expensive than flooded cells. Since most RVs come with flooded cell batteries, that's what I'm going to talk about here. [In 2010, AGM batteries became standard in Lazy Daze]

So here you are, out in the desert, relying on your batteries for power. You can only use lights and appliances that are 12 volt; nothing that uses a 3 prong plug (ac) will work.

If you want to use regular 110 volt items (DVD players, some TVs, charge your computer, etc.) you need an inverter.

An inverter takes 12-volt power from your batteries and changes it into 110 volts. Inverters come in several models, portable and hard wired. A small portable inverter plugs into a 12-volt outlet and contains regular 3-prong house plugs.

Different inverters can handle different amounts of power, so before you buy one, you need to do a bit of research. We opted for a hard wired full house inverter, so with the flick of a switch, all the 110 volt outlets in Cholula Red are "live". When we don't need this feature, we simply turn it off. Tech Note: A 400 watt inverter is more than adequate for charging computers, phones, a DVD and other low power requirement devices. If you want to power something like a hair dryer, you will need a 2000 watt hard wired inverter. The price difference between a portable 400 watt and hard wired 2000 watt inverter approaches $2,000. Also the 12-volt outlets will supply, at best, 10 amps, less the more removed they are from the batteries. Short story, anything that needs more than about 5 amps will need a hard wired inverter connected directly to the batteries.

Charging the Batteries

Depending on how much power you consume dictates when you will need to charge your batteries. This can be done in one of four ways.

First, anytime you are plugged into shore power, the batteries are being charged by the converter/charger unit.

Second is the option of solar power. Solar is a great boon to RVers and we love having it on Cholula Red. We have four panels, giving us lots of power for the batteries, assuming we have the sun to power them. That said, solar is somewhat expensive, and not for everyone. While we often have hook ups, we have found that solar gives us the opportunity to camp at places with no power for extended periods of time. I look at solar as an addition that opens up options. It does a great job of charging the batteries, but since it's an option rather than a standard item, I'm only mentioning it here for informational purposes. Tech Note: The power from the solar controller is fed directly to the batteries, bypassing the converter/charger.

Third, you can run your cab engine. This will charge your batteries via the engines alternator, and it's fairly efficient. HOWEVER, it's noisy, it pollutes and it uses a good amount of gasoline, so it's really not the best option. Tech Note: The batteries are charged by the alternator controlled by the engine's voltage regulator. Not ideal as the chassis and house batteries are probably at different charge levels.

Fourth, if you have a generator, you can charge your batteries with it. It also uses gasoline, but not as much as running the engine (.6 gallons per hour under a low load), But, there's a catch to charging the batteries via the generator. In order for your generator to charge your batteries, it has to use a device called a charger. And chargers come in various models.
Most RVs come with a single-stage charger as part of the built in converter. It takes the power made by the generator and it stores it the batteries. But here's where it gets tricky. Your batteries are sensitive, and they can only go to 100% charged. If you continue to charge them, they will start to “boil”. [The water appears to boil, but it’s actually hydrogen bubbles you see.] When they “boil”, your batteries will lose water.


Tech Note: The charging ability of factory supplied converters varies. If you have the original converter, the charging will be very slow in all coaches manufactured before November 2001; that's when LD started installing the more modern 7345 converter. The earlier model 6345 converters charge at an incredibly slow rate so don't attempt to charge your batteries by running the generator.

So here's where you might want to consider a smart multi-stage charger. Not only does it charge your batteries, but it communicates with them. It knows when the batteries are low and need a lot of charge and it pumps the power in at a fast rate. When it reads that your batteries are getting close to full, it backs off to a lower rate of charge. And when it reads that your batteries are near to completely full, it goes in to a trickle charge mode. Three stage "smart" chargers are a real boon to RVers and I think a necessary upgrade for many users.

Now I want to talk a bit more about the power in your batteries. Now that you understand that the power comes from your batteries to your appliances, the question comes up, how do you know just how much power is left in your batteries?

The answer is simple. You need a battery monitor.


Short story here …When we first got Cholula Red, I was truly clueless about RV power. I understood that I didn't understand, and I wanted to learn. But when people would try to explain to me about power, they would start talking amps, volts and watts, and honestly, my eyes would just glaze over.

But, I did know that I was using a lot of power and I wanted to know where I stood. After all, we were running lights, watching television, playing DVDs, charging phones, computers, you get the idea. I wanted to know when my batteries were getting low, and I was completely clueless about how to find that out. Several people had told me that I could get this information from my solar controller (the device that monitors/controls the power from your solar panels to your battery). The catch was this - it would only give an accurate reading when there was no power going into or coming out of the batteries. And when would that be? Yep, I would find myself getting up in the middle of the night, turning on my flashlight and sneaking up to the display, trying to figure out how much power was left in the batteries. [Tech Note: Equating a voltage reading to the amount the batteries are discharged is up to 25% off.]

Now, with the push of a button the monitor tells me that I have exactly 83% left in my batteries (or whatever the percentage is at any given time). For me, managing the power in the RV became pretty simple after I got the battery monitor. If you don't want to have to learn all the math, it's the easiest way to manage your power.

Tech Note: Battery manufacturers warn that discharging below 50% will shorten the life cycle of the battery. Most users consider 65% the low threshold.]

by Kate Klein