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Monday, June 25, 2007

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.'


  1. Just how easy do u think it would be for me or anyone else for that matter, to pull out our microwave ovens, stoves or tv's so we can check the wattage? While the formula is easy to use, getting to the starting wattage is somewhat of a task that many of us find unappealing and therefore will not take the time to do.

  2. Russ and Tiña De MarisJuly 13, 2007 at 7:43 AM

    Good point, Hiberian. A much easier way to get the information would be go drag out that stack of user manuals. That same information should be available in print. RD

  3. If you can not use a tester or have one, go to Wal-Mart and ask the nice person to find it for you. It really is easy to look on unit Lable Plate and read what you need to know. Gordonbear

  4. Lilikoi Jungle CottageOctober 26, 2007 at 4:38 PM

    Hiberian, people who don't do the footwork are the people that don't get the job done.

  5. Personally I think this is a useful article and equation. If you have a camper/ caravan that runs items off an inverter, how can you be simple enough to not know how much you're using? If finding a wattage rating is too 'unappealing, use the internet. I assume that someone of 'hiberian's' lazy disposition would find a flat battery even less appealing. I sure won't be jump starting you!