How Much Battery Does Your Inverter Eat?

We posted an earlier blog entry on the wonders of using shower power provided through the media of an inverter. An inverter is a device that changes battery power into something more edible to devices like power tools, computers, televisions, and such.

Like everything else in life, there's no such thing as a free lunch, and if you use your microwave to heat yours, there is a certain and fearful toll to be taken. The more "shore power" your device uses, a LOT more battery power will be consumed. Let's take our "Nuke me some lunch!" scenario.

Let's say your RV microwave oven uses 1,000 watts (check out the data plate on the back of whatever device you're using) to operate. To heat up a couple of plates of last night's leftovers, let's say you'll be operating the microwave for 5 minutes. How much battery power will you "eat" for lunch?

The formula is quick and easy: Battery amp-hours consumed is this: (AC Watts/12) x 1.2 x time of use (in hours). Our microwave operates at 1000 watts, divided by 12 equals 83.3 times 1.2 (the inverter isn't completely efficient, so this factor allows for inefficiency). That equals 100. We multiply this against the usage time, 5 minutes divide by 60 gives us the "hours of use" of .083. The total amp-hours consumed in reheating lunch equals 8.3.

That may not sound like a whole lot, but if you were charging your battery with a 100 watt solar panel, it would take over an hour of strong, full sunlight to "pay" for heating up your lunch. That doesn't even take into account battery charging inefficiencies. This is one of the reasons you'll see serious boondockers running a rooftop full of solar panels.

So before you start firing up the inverter, run some quick calculations and see if you can 'pay the inverter piper.'

Power Inverters--Take Shore Power With You

In our traveling tool box, battery powered portable tools have a favored place. What would you do without that drill? But when time comes to recharge that drill, where you gonna find power in the boonies? If you have a generator, yes, you could fire it up for a few hours to recharge your favorite Makita, but that's a lot of waste and noise. Here's where an inverter can help.

An inverter converts 12-volt RV battery power into "shore power," that many other shore power-loving devices can work with. We'll keep this entry simple and expand into more detail in the future. For small power applications, say your blender and battery charger applications for portable power tools, a small, "plug it in the cigarette lighter" inverter is ideal.

Where do you find such a beast? RVers spend a lot of time on the road, and there's always a truck stop close at hand. "Trucker stores," have plenty of inverters for sale, and the price is usually fairly competitive. You can also find scads of them on e-Bay.

How much inverter do you need? Read the manufacturer's plate on the device you want to power up. Usually battery operated tools need very little juice to operate. Since inverters are rated in "watts" for power output, match or exceed the number of watts required by the device. Mind you, when you get into larger loads, your cigarette lighter socket won't be able to put out enough juice to keep up with the inverter--and a blown fuse or even worse could result. NEVER exceed the rating of your "power plug." Yes, you can hard wire an inverter to your system for increased capacity, but that's a subject we'll take up later.

Always turn off your inverter when not in use--even when not actively "inverting" power, they do use a small amount of "standby current."