Inverter shopping? Here’s a handy primer on inverters


By Russ and Tiña De Maris
Considering the RV boondocking lifestyle? You’ve probably already been mulling over solar panels and bigger battery banks. That’s great for your low-voltage needs – lights, fans, all that typically 12-volt stuff. But today’s RVer generally won’t be satisfied with “just” 12-volt power. There are plenty of uses for “shore power,” and if you truly want to take advantage of your solar system, an inverter is a requirement.

New to the game? An inverter is a device that takes your 12-volt DC power – the kind that’s stored up in your RV “house” batteries – and converts it to power that can be used for items normally “plugged into” wall outlets: TV sets, corded power tools, microwave ovens, vacuum cleaners and, for some of us, CPAP machines.

Inverters come in a variety of sizes, from small ones that plug into a lighter socket and may kick out enough shore power to operate a laptop computer, to much larger ones that could theoretically operate your RV air conditioner. We say “theoretically” as you’d have to have a large enough bank of batteries to support the huge load – and a hugely substantial solar panel array.

Top: Pure sine wave. Bottom: Modified sine wave. Credit: MrLejinad on wikimedia commons.

Aside from sizing, another major consideration when choosing an inverter is the power output form: pure sine wave or modified sine wave. The former “looks” like the stuff that your power company sends to your sticks-and-bricks house: smooth curves, easily digestible. Modified sine waves don’t have that nice, smooth shape. The picture above tells the story. Somebody once described the difference as driving down the road with nice round tires (pure sine wave) versus tires that were square (modified sine wave). Which would you prefer?

Where the “rubber meets the road” for inverters is the final consumer – the shore power device being fed by the inverter. Some things don’t give a hoot if the road is bumpy: your vacuum cleaner will still suck and an electric fan may run fine, although you may notice it buzzing. But other shore power consumers may run hot, inefficiently or just not at all when fed modified sine wave power. Here’s a list of things that generally REQUIRE pure sine wave power:

Microwave ovens
Laser printers
Variable speed tools
Many cordless tool battery chargers
Some TVs
CPAP machines with humidifiers
Medical equipment
Sensitive electronics

With that in mind, why would anyone install a modified sine wave inverter? It’s that old thing: money. For example, we recently did our own inverter shopping. We needed an inverter that would provide 2,000 watts. Modified sine wave inverters in that range cost anywhere from $130 to $200. Pure sine wave inverters were definitely more, starting at about $250 and easily hitting $400. In the end, we considered all that we needed to run from the inverter and bought a pure sine wave unit. Don’t let the price difference frighten you off – just a few years ago the price difference between the two types was even steeper; the cost of the “better” technology has actually come down.

Keep in mind, while you may be able to make some equipment operate on modified sine wave power, it may not operate nearly as efficiently, and may run hotter. In the end, what you “save” in buying the lower-cost modified sine wave unit may be more than made up in the decreased lifespan of equipment that you operate with it.

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2 months ago

A note about CPAP machines. Most (if not all) CPAP manufacturers make a DC power cord/converter for their machines. You may have to go to the manufactures website to find it. Most CPAP suppliers don’t carry it because Medicare won’t pay for it. If (like me) you don’t want the inverter running all night this is a good alternative.

3 months ago

We started our fulltime adventure 11 years ago with a 2500 watt modified sine inverter in our 34ft 5th wheel that came with it new. At that time I had no clue about the difference between modified & pure sine. After several years of some problems with some of our equipment & the inverter itself, I had educated myself on the difference & upgraded to a 3000 watt pure sine inverter. What a difference. Everything runs so much better now. It was well worth the extra cost. If you’re in a larger rv with a wide variety of electric & electronic equipment, don’t even think about getting a modified sine inverter. It will cost you a lot more in money & headaches in the long run, than just biting the bullet & getting a pure sine up front.

3 months ago

In my power control center there is a place to turn off or on the inverter. Should it be on always ?

1 year ago

We suffered from “dirty” power at our residence for 17 years so we used battery backups to power our PC and sensitive electronics. Recently I was fortunate to be able to get several discarded large capacity battery backup units from a company that went out of business. I replaced the batteries and then placed them in the RV. Not only do they “clean up “ the inverted seine wave power but they give us additional battery time.
I don’t know how it would compare cost wise if you had to buy them new though.

chris p hemstead
1 year ago

If you run high-wattage appliances, you may want to consider a 24, 36 or 48v inverter. 12v installations require huge, cumbersome wiring and can heat up while pumping out that large amperage. Your 12v needs can be met using a DC-DC converter. Works for me, as I run a/c now and then from my Lithium battery @ 48v.

Greg Illes
1 year ago

Russ, the other thing that I’ve found in a few anecdotal cases was that the pure-sine inverters had a higher quiescent current than the modified sine. For example, my Cobra 2500 uses about 1A of quiescent current, while my nephew’s Xantrex pure-sine uses over 3A. This can make quite a difference if you run your inverter for long periods of time (like a CPAP application).

FWIW, my microwave doesn’t seem to care about the chunky sine wave, running for years now.

Tommy Molnar
1 year ago
Reply to  Greg Illes

I too have been running a Cobra 2500 watt inverter – for years. It’s not fancy but it seems to serve our travel trailer just fine. It runs our Dish box all day (we use it for the music). We charge all our ‘rechargeables’ (cell phones, cameras, drone, drill battery, laptop, everything) and have had zero issues. Once or twice a year we may use the ‘nuker’ (microwave). And wifey’s hair dryer works fine.

Bob P
3 months ago
Reply to  Tommy Molnar

As was said in the article computerized equipment can be very sensitive to modified sine wave inverters. I used a modified sine wave 2000 watt inverter in the semis I drove, I used it each morning to make my coffee, I heated up my breakfast in a microwave with a turn the dial timer, no digital display, and ran a small portable tv without computer controls. Everything worked great, but I wouldn’t think of using it with computer chip equipment as it could cause very expensive repairs or replacement. I’m to old to live dangerously any more.