(This post is part of a series. If you’re new to my blog or this is the first you’ve seen of this series, you might look at the introduction first.)
I had planned to cover all the house systems (water, waste, gas, and electric) in one post, but as I got to writing about the electrical system I realized it would need its own post. The rest will be covered in the next installment.
Twelve Volt Basics
All RVs have a 12 volt DC electrical system. This powers interior and exterior lighting and a pump for the fresh water system, as well as exhaust fans and the blower of a forced-air furnace. Most newer rigs have smoke, propane, and carbon monoxide detectors, all running on 12 volts, and ignition and control electronics for the propane-fired combustion appliances.
More About Batteries
The 12 volts is supplied from a deep cycle storage battery. This is similar to a car battery, except that it is designed for deeper discharge at low current. A starting battery, in contrast, is designed to deliver short bursts of high current. Another reason not to use the engine starting battery to power the house loads is to avoid becoming stranded in the event of running the battery down while camping.
The house battery is charged by the RV or tow vehicle’s engine alternator while driving. There is also a “converter” which converts 120 volt AC to 12 volts DC, while connected to electric hookups, powering 12-volt loads without discharging the battery. The converter usually incorporates a charger as well. Photovoltaic solar panels can be added to generate power whenever there’s sunshine. With a decent sized battery bank and solar system, combined with mindful conservation habits, it is possible to go almost indefinitely without connecting to shore power or running an internal combustion engine.
What I’ve Got
What do I have? I’ve got 500 amp-hours (6000 watt-hours) of rated house battery capacity. In practice, a storage battery should not be discharged past 50% capacity or the life of the battery is severely impacted, so that leaves me with 3000 watt-hours to use. I have a 500 watt solar system, so an average six hours of insolation on a sunny day gives me, not incidentally, 3000 watt-hours of daily charging ability. Take a look at your latest electric bill. Do the math and determine what your daily kilowatt-hour usage is. Could you live on 3 KWH per day? I can, at least when I don’t need air conditioning.
Household Power To Go
What about all the common electrical conveniences and necessities that run on regular 120-volt AC power? Most RVs have a 120-volt electrical system with standard receptacles. The power comes in through what amounts to a big thick glorified extension cord which you plug in when you stop at a campground or RV park offering hookups. But what about in the middle of nowhere? There are two options: inverters and generators.
Inverters change 12-volt DC battery power into 120-volt AC household power. They are available in numerous sizes from 100 watts, suitable for operating laptops, electronics, and small appliances through multi-kilowatt units able to power almost anything. Many RVers find that 300-500 watts is enough to power their TV, DVD, computer, and kitchen gadgets with power to spare. If you want to be able to power a microwave oven from your battery bank, you’ll want at least a 1000 watt inverter, though some folks will just run a generator for that. I have a 3000 watt (there’s that number again!) inverter that will allow me to operate anything I own, limited only by the capacity of my battery bank.
A generator can deliver all the power you might want or need, as long as you have fuel for it. Most motorhomes have a generator as standard or optional equipment, while trailers usually don’t. Trailer owners often carry a portable generator. In addition to powering standard 120-volt loads, the generator can also, via the converter/charger, power 12-volt devices as well as charge the house battery during a cloudy spell or for folks who have no photovoltaic system.
Twelve Volt Native
An alternative to using an inverter or generator is to find 12-volt appliances. You’d be surprised at all the different things that come in 12-volt versions, and not just electronics. I’ve seen blenders, coffeemakers, hair dryers, and even microwave ovens designed to operate directly from 12 volts DC. My recommendation, however, is for large or heating appliances that only get used occasionally for short intervals, stick with standard 120 volt versions. Most of the 12-volt kitchen appliances I’ve seen offer very disappointing performance. Electronics, lighting, and ventilation, however, are good places to look for 12-volt options.
Generator vs. Solar
There seems to be two kinds of RVers at any boondocking gathering. There are the folks who have an adequate solar system and are careful about their usage. They do this to avoid having to run a noisy, smelly generator any more than absolutely necessary. They might have to succumb to generator usage either to recharge batteries after a string of cloudy days, or perhaps for a few minutes occasionally to operate a high-current appliance (microwave or coffeemaker, for example) if they have only a small inverter. They enjoy the peace and quiet and community with nature. The other group enjoys their creature comforts and either have undersized (if any) solar systems or can’t concern themselves with energy frugality. These are the ones who fire up their gensets at the crack of dawn and run ’em until noon, and then fire them up again around dusk and don’t shut ’em down until long after dark. I’ve seen some campgrounds and events where they actually segregate campers based on generator usage. For the record, count me in the first camp. I prefer not to use a generator if at all possible.
Bucket Of Juice
Most people are used to having a virtually unlimited supply of electricity. Sure, you might try to conserve a bit to save money or help the environment. But you know that as long as you pay your electric bill, you aren’t going to run out of electricity unexpectedly. Not so when you’re off-grid. Your battery bank is like a bucket of electricity. It holds a finite amount of energy. Every time you turn on the light, listen to the radio, grind some coffee, or read my blog, you’re taking electricity out of the bucket. When the sun is shining, the generator is running, or you’re connected to shore power, you’re putting electricity back into the bucket. There are some pretty fancy instruments made that can measure the amount of energy going into and out of a battery bank and give the user a reasonably accurate indication of where they stand – much like the gas gauge on your car lets you know how far you can go before you need to fill up.
I don’t have such a fancy system. I have very simple voltage and current metering, which keep me advised of the overall health of the system, and I rely on my experience with the system and familiarity with all of my devices and how much power they use to keep track of things. While off-grid, I am very conservative with my usage. I don’t leave things on when I’m not using them. I use only the lights I need, turn off or sleep the computer when not using it. I ration my TV and internet usage as well as my broadcast radio listening. If I’m not inside, then everything is shut off. Remember that 3 KWH figure I cited earlier? That’s not a goal – that’s a very real limit on my daily consumption.
Are we there yet?
Whew! This ended up being much longer than I expected, but there’s plenty of room in the comments if there’s something I left out, you didn’t understand, or would like more info about.