Inverter Installation

An inverter has become a necessity for us, especially since replacing our refrigerator with a compressor model that only runs on 110V AC. I installed our first inverter in 2007 and have learned a lot about them both before and since that initial installation.

What Inverter Should I Buy?

Wattage and Physical Size

There are several choices to make when choosing an inverter. First you need to decide what capacity you need from your inverter. They make nice inverters with outputs ranging from 300 watts up to a whopping 3000 watts. Keep in mind that the larger the inverter capacity, the bigger the inverter is going to be physically. You need to mount that inverter somewhere, preferably somewhere very close to your RV house battery or batteries. The inverter also generates heat, since the inverting process is not 100% efficient (a good inverter can be over 90% efficient), so the place you mount the inverter needs to have ventilation and needs to stay clean and dry. The shorter the cables between your inverter and your batteries, the better. Once you get above a 2000 watt inverter, you will probably need 4 / 0 (pronounced "four - ought") gage cabling, which is about 3/4 inch in diameter. The inverter manuals will tell you what gauge cabling you need, depending on the length of the cable run you need to make. If you just want an inverter to power small electronics, then 300 to 600 watts should be sufficient. If you want to run your compressor refrigerator like I do, then 1000 watts will work. A microwave will need at least 2000 watts (2500 would be better for some microwaves). A good rule of thumb is to add up all the peak watts of the electrical appliances that you envision using at the same time, then double that. Also remember that many appliances (refrigerators, microwaves, etc.) have a higher starting current, then will rapidly taper down to their running current. Your inverter needs to be able to handle those higher starting currents. I decided to mount our inverter under the passenger-side second row seat, since that space was available and was only about 5 feet from the forward battery. That space could also be ventilated. Any inverter I buy must fit inside that space.

Pure Sine Wave

I would also recommend that you buy an inverter that puts out pure sine waves, which is the same shape of alternating current that your home electrical system uses. The cheap inverters just output relatively square waves of alternating current. Many devices don't work as efficiently with this shape of current and may have problems running. The pure sine wave inverters may cost more, but will be more efficient.

No-Load Current Draw

Another important consideration in inverter selection is the no-load current draw. This is the amount of current that the inverter uses when it is just idling - turned on, but not powering anything. This number is extremely important because a higher no-load current draw will cause more battery power to be wasted inside the inverter rather than powering your equipment. If you are trying to conserve your battery power, this can be critical. I ended up replacing a 1000 watt inverter that had a no-load draw of 1.7 amps with a 1000 watt inverter that only drew 0.6 amps when idling. This made a big difference in my battery run time. You often have to download and peruse the inverter's user manual to find out it's no-load current draw. Most companies don't advertise this number unless it's quite good.

Combined with Battery Charger

Many of the higher end large-capacity inverters have very good battery charging circuits built in. If you need a battery charger, this can be a nice space saver. If you already have a good battery charger in your RV, then this will not be needed. The Parallax 7300 converter / charger that originally came with my Roadtrek was not particularly good, so I welcomed the built-in high quality charger that my first inverter contained. When that inverter stopped working, my next inverter did not contain a battery charger, so I had to install a nice stand-alone charger, which I physically placed right next to the inverter, making for an easy installation battery cable-wise.

A large inverter installation turned into quite a learning experience for me. After extensive research, I'm still no expert, but know considerably more than when I started out. Hopefully I can share some of what I learned on these pages. Overall, the initial project took me twice as long as I envisioned (about 2 weeks of working on it every day, sometimes all day long). The project seemed to turn into a series of mini-problems, each of which required a solution before I could continue on. I enjoy problem solving as well as working with my hands, so in the end I found this project very rewarding. Do not attempt this installation unless you are familiar with both 12V and 120V electrical systems. An incorrect installation could be deadly to yourself or your loved ones. When in doubt, seek expert help.