Few things in life are as frustrating as needing the furnace to kick on in the middle of the night because it’s freezing out, and discovering that your batteries are out of juice and won’t power your heat. Turns out that while the furnace may produce heat via propane, the blower fan still uses good old-fashioned 12 volts of power to turn on and circulate that heat. Today we’re going to cover a few basic ideas on electricity, amp requirements, and how to estimate how much power you need on an average camping day.
While RVing, you will never have access to an unlimited supply of electricity, like you do (in a way) at home. Batteries run out, generators need power to keep generating, and campsites won’t let you use theirs forever. Once you fully realize that on any given day there is a limited amount of power to work with, and that when it’s gone, it takes time or effort to get more, rationing becomes easier.
Amps = Watts divided by Voltage (A = W / V). This will come in handy to calculate how many amps you are drawing, or using, at any given time.
Your RV most likely has two separate electrical power systems. One uses 12 volts, which runs off your battery just like a car, and one is a 120-volt system, like you have at home, that is fed from your generator or a campsite electrical hookup.
The 12-volt system powers your furnace, refrigerator, most of the interior lights, your water heater start-up, water pump, CO2 detector, and more.
The 120-volt system powers smaller things you use more often, like your TV, kitchen appliances, and other electrical devices.
RV batteries can consist of a single 12-volt battery or multiple batteries wired together in a parallel circuit (meaning, they all produce power at the same time). A popular option is to harness two 6-volt batteries together, which gives 12 volts of power but usually provides a much longer battery life. While it is true that two batteries need more room than one, a lot of folks prefer the extended battery life over the minimal space lost.
Let’s switch from volts to amps. Most RVs come with either a 30 amp cord (3 prongs) or a 50 amp cord (4 prongs). Learn which amp capacity you have, and find out what the next campsite will have as a hookup. Some campgrounds only offer 30 amps, at which point a good $20 adapter will allow your 50-amp RV to play nice and get along. Just remember, that adapting thing only works one way–you can’t pull your 30-amp RV up to a 50-amp hookup and expect to get power. Don’t forget to probe that campsite power with a polarity tester to make sure their power supply is what it should be. A faulty hookup will ruin your weekend.
What if you are away from a campsite or a steady source of hookup juice? Keep in mind, some campgrounds don’t allow generators to run, so quite often it will all fall on the shoulders of your batteries. Different items in your RV will use different amounts of power, and especially if your RV has a 30-amp system, you can’t run too many things at once. Anyone who’s ever lived in an older building with outdated wiring knows what we mean, and no doubt they fondly remember hunting down the circuit box after tripping a breaker switch. The same idea applies here: draw too much power, and your system won’t be able to support it. Ideally, a breaker would trip, but it’s always possible something could be damaged.
Usual suspects for greedy power usage: heat, A/C, running those heavy slides, most kitchen appliances, and smaller items like curling irons or hair dryers. This is where learning to estimate how much power or amps your RV needs per day will come in handy, and prevent the scenarios you can probably imagine.
Basic math is your friend, regardless of how you may have viewed it in high school. Most battery manufacturers recommend using only half of the battery capacity you have on hand for extra battery life (which we like), so if you have a battery with 100 amp hours, you should plan on having 50 amp hours to use. That’s not a lot when you think about it.
But first, it’s time to play detective and find out how many amps those plugged-in culprits draw on an average day. Don’t worry, it’s not that bad; just a few numbers to work through. Remember the A = W / V equation from earlier? Piece of cake–most appliances, light bulbs, and other electrical items will usually have their watts and voltage rating right on the back, or on the package. Watts divided by volts will give you the amps needed for an hour of use.
Let’s say your water pump draws around 5 amps per hour as an average, and you have the shower running maybe a half hour a day; that’s 2.5 amps per day for your water pump. If you have LED lights, give thanks, because those bulbs only draw maybe .20 amps per hour, where something like a roof A/C might drain 12-13 amps over the same amount of time. The microwave is even worse.
Don’t forget though, your DC-AC inverter swipes about half the power that goes through it, because it’s greedy and selfish, so that 5 amps for the water pump now becomes 10 amps needed. So we double all amp requirement estimates for anything fed from an inverter (anything that runs on 110 volts), which when you’re not hooked up to external power is a fair amount. This means plugging in that coffeemaker or charging your phone is now twice as costly.
Total everything up, and you can see how your battery can empty itself mighty quickly. A day’s amp hour total might range anywhere from 50 for a smaller hybrid or travel trailer on up to a gazillion if you’re in a massive fifth wheel or Class A motorhome with a thousand people using a thousand things. Here is where you start to weigh your options, and maybe reduce or eliminate some electrical usage if possible.
At this point, if there isn’t enough battery to go around, most RV enthusiasts will look at upgrading and/or adding more batteries to their system. Consult a pro before doing so, as they can guide you through electrical requirements and how it all ties together.
Another option is solar power. A decent solar array on a sunny day can add a lot of recharging time to your batteries, which saves having to run the generator, and if you’re in a compact rig and living efficiently, you could go for quite some time that way. Until, mind you, a cloudy day rolls around.
Lest we forget, stay on top of your maintenance. Regular looks at all your various systems and connections (especially before any trips) will often reveal a molehill before it grows into a mountain, so to speak. Make sure your connections look solid, with no obvious wear or damage, and everything is corrosion-free.
Have any tips or stories of your own? How do you manage your RV power usage? Feel free to let us know in the comments below!