Choosing an inverter for your RV

An inverter is a device that converts 12v D/C electricity (aka your batteries) into 110v A/C.  A/C, or Alternating Current, is used to run things like your microwave, tv, DVD player, coffee grinder, etc (assuming you don’t have 12v versions of these items). Since we know that we want to do a fair amount of boondocking, we knew that we needed to install an inverter in our coach instead of running the generator.

About electricity

There are three basic units that you should know when talking about electricity.  Watts (P), Volts (V), and Amps (I).  Ohm’s Law is the main formula that you will need when working out your electrical needs.  Ohm’s law can be expressed as I=\frac{P}{V}.  Using Ohm’s Law, we can calculate any value as long as we know the other two.

I=\frac{P}{V}
amps = watts divided by volts

P=V\times A
watts = volts times amps

V=\frac{P}{A}
volts = watts divided by amps

Types of inverters

There are three primary classes of inverters to choose from; square wave, modified sine wave, and pure sine wave.  They get their names from the way the output wave looks on an oscilloscope. Each of these have distinct characteristics that should be taken into consideration when choosing an inverter.

Square Wave
The simplest inverter is a square wave.  They will run the most basic of power tools but anything else will probably not run correctly.  Very few inverters, especially those designed for RV use, will be square wave.  Don’t bother with this type of inverter.

Modified Sine Wave
The next type of inverter is the modified sine wave.  This type can also be referred to as a modified square wave inverter.  Most devices will work with this type of inverter however; many will function with less power or efficiency.  Some devices like modern electronics, bread makers, certain coffee makers may not even function at all.  These inverters will be slightly cost-effective but only if you have devices that will function properly with them.  You will want to consider your needs carefully before jumping into a Modified Sine Wave inverter.  While you can save a few bucks, you could find yourself with devices that aren’t working properly.

Pure Sine Wave
This type of inverter produces the same electricity as what is provided by the utility company to your home.  As a result most of your modern electronics are designed to work with sine wave electricity.  These inverters will be a bit more expensive but you can be guaranteed that all of your devices will work.  In short; you’ll want a “Pure Sine” inverter if you’re running any kind of modern technology such as laptops, tablets, phones, and even some of the more modern appliances.

Output Power

The next thing to consider is how big of an inverter do you need.  Our microwave alone will pull close to 1500 watts by itself so a 1500 inverter would be too small for the scenario of watching a movie and making popcorn at the same time.  It could also be too small for running a hair dryer while running an electric griddle.  You get the idea.  You will need to take a look at the devices you use and total up the wattage to determine what size inverter you need.  I would also recommend adding 10-20% for growth and stop at 3000 watts.  I am of the opinion that anything larger than 3000 watts just isn’t practical in an RV except in the most specific of cases.

You could certainly get an inverter larger than 3000 watts but remember you will need the battery capacity to run such a beast.  A maxed out 3000 watt inverter will pull roughly 234 amps from the batteries  (3000 watts / 12.8 volts = 234.375 amps).  This is important because (a) you need to have enough battery capacity and (b) the wiring needs to be able to support this high of a draw.  Too light of a wire and it is possible to actually melt the wiring at high amperages.  See my post about Sizing battery and inverter cables.

Inverter Brands

There are several brands of inverters to choose from.    The most popular seem to be: Go Power!, Magnum, Outback, Xantrex.  They are all good brands and seem to be highly regarded in the RV community.  You may want to consider things like warranty, customer service, and country of origin as well as price.

What we chose

We decided on the Go Power! (GP-SW3000).  We didn’t need a combination inverter/charger.  For an inverter-only model, Go Power! seemed to offer the best bang for the buck for us.

References:
http://gpelectric.com/
http://www.xantrex.com/
http://magnumenergy.com/
http://www.outbackpower.com/
https://en.wikipedia.org/wiki/Ohm%27s_law
http://www.solar-electric.com/inverter-basics-selection.html
http://engineering.electrical-equipment.org/forum/general-discussion/types-of-inverters

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