RV Inverter Install: Four Different DIY Methods to Get off the Grid

Hopefully you’ve read my previous post “How to choose the Best RV Inverter” which means you did your research, estimated your power requirements, and finally came to a decision.

You ordered your inverter and today, it arrived! You’re now ready begin your DoItYourselfRV inverter install.

rv-inverter-install-1

If you went with a small inverter (around 75 watts), then it can be plugged into a cigarette lighter outlet.

Anything larger will need to be wired directly to your batteries.

In order to reduce the voltage loss, you need to install the inverter as close to your batteries as possible.

The inverter manual will probably suggest a wire size. Use the recommended size or larger. Remember that the bigger the wire the smaller the gauge number.

Whatever you do, you want to limit the voltage drop as much as possible.

You should make every effort to keep the loss below 0.075 volt.  The table below gives the voltage drop per foot of wire for various sized inverters. This is important to consider for your RV inverter install. For other inverter sizes, the drop will be proportional.

How Long Wires Can Drop Your Inverter’s Voltage

As an example, using the table below assume that you will be installing a 2000 watt inverter (Scroll top to bottom and find 2000 watts).

It will be connected to the batteries with 5 feet of #4 AWG cable (scroll right to left from the 2000 watt load till you find the 4 column).

The voltage loss will be .0420 x 5 (length of wire between battery and RV inverter) = .210 volts.

This means that if your batteries are charged up to 13 volts, the inverter will only be seeing 12.79 volts (13 Volts - .210 of loss). It might seem to work, but you won’t like the results.

It would be much better to go to a #00 AWG cable, which will have a total of .066 volt loss, well under the recommended .075 volt loss threshold.

The best approach is simply to use the largest size that will fit in the inverter’s terminals.

RV Inverter Install: Voltage Loss Per Foot of Wire

Wire gauge (AWG)
#0000
#000
#00
#0
#2
#4
#6
#8
For 100 Watt Load0.00040.00050.00070.00080.00130.00210.00330.0052
For 500 Watt Load0.00210.00560.00330.00410.00650.0110.01650.026
For 1000 Watt Load0.00410.00510.00650.00810.0130.0210.0330.052
For 1500 Watt Load0.00620.00830.00980.01220.01950.03150.04950.078
For 2000 Watt Load0.00820.01020.01320.01620.0260.0420.0660.104
For 3000 Watt Load0.01230.01530.01950.02430.0390.0630.0660.156

If you have trouble finding suitable wire for your RV inverter install, automotive battery cable or jumper cables are readily available in 4, 6, and 8 AWG (American Wire Gauge).

Welding cable comes in larger sizes, but is expensive as many times you have to buy a whole spool. If there is a supplier near you, see if they will sell the short lengths that you need instead. You might get lucky at your local welding shop.

Wiring the Inverter

The AC (Connecting the inverter to the RV electrical system) side of the RV inverter install can get more complicated. But in any case, you need to ensure that you don’t have either shore power or generator power connected to the output of the inverter.

There are several possible ways to wire your inverter. Whichever option you select, you can do the wiring with standard 14 AWG, household type nonmetallic cable.

However you do it, you absolutely must ensure that you do not have your converter turned on when the inverter is on. The problem with having both on at once, is that you are pulling current out of your batteries with the inverter, while pushing current back into them with the converter.

Since neither the inverter nor the converter are 100% efficient, each trip that current makes around the loop will waste some power as heat. You will very quickly run down the batteries until the inverter shuts off for low voltage. That will happen even if no load is connected to the inverter.

RV Inverter Installation Method 1.

rv-inverter-install-AC-distribution

The most elegant (and of course, most expensive) solution is to connect the RV inverter directly to RV’s AC distribution boxthrough a transfer switch (keep in mind the type of switch used varies based on the power of the RV inverter and if you have a generator). The switch will automatically select shore power if it is available, and inverter power if it is not. If you go this route, you still have to avoid powering the converter from the inverter. The most common method for achieving this is to use a split distribution panel, with the converter on the part of the panel that is not connected to the inverter. If that seems like a more complex RV inverter install than you want to try, read on for how to use a relay.

RV Inverter Installation Method 2.

rv-inverter-install-extension-cord

At the other extreme, you can run an extension cord from the inverter to whatever device you want to power at the moment. My first inverter installation worked that way. It gets the job done, but we very soon got tired of plugging and unplugging different devices into the extension. Though a simple RV inverter install, it left me tripping over the cord on a regular basis.

RV Inverter Installation Method 3.

rv-inverter-install-electrical-outlet

Slightly less crude, is to connect one or more dedicated outlets to the inverter. You can either install new outlets or disconnect existing outlets from the distribution box. The difficulty in accomplishing this type of installation will depend on where the outlets are located, and how hard it is to get wire to them. This RV inverter install method means having some outlets that don’t function when you are on shore power  which could lead to some frustration.

RV Inverter Installation Method 4.

rv-inverter-install-30-amp

A good compromise is to install a 30 amp receptacleon the outside of your RV and then connect it to the output of the RV  inverter. When you want inverter power, you just unplug the RV from shore power and plug it into the new 30 amp receptacle. With one modification, this is how my current RV is set up.

You recall that the converter and inverter should never both be on at the same time? No problem. I just flipped the circuit breaker for the converter before turning on the inverter. That is, until the time I forgot to flip it, and went to bed. I got up in a hurry when the low battery alarm on the smoke detector started beeping at me.

The reality is it should have been idiot proof. The solution is to get a relay (an electrically operated switch) with a 120 VAC coil and normally closed (n.c.) contacts that are rated at least 10 amp, DC. The figure below shows how to wire it. Connect the relay coil to the inverter output. Then disconnect the hot supply line from the converter and reconnect it through the n.c. relay contacts. Now, when the inverter is turned on or off, the relay automatically switches the converter off or on.

rv-inverter-install-wiring

It will be most convenient to mount the relay on or close to the converter. Because the relay coil draws only a very small amount of current, you can use 18 AWG (lamp cord), or cut up a heavy duty outdoor extension cord if it needs physical protection. If your relay has any additional contacts, just ignore them.

RV Inverter Install – The Remote Switch

If you bought a remote switch for your inverter, you will need to connect it. They are usually connected with a standard telephone cable. If you need a cable longer than the one that came with the switch, it may have too much resistance to work. If your longer cable doesn’t work, you will have to substitute a cable with heavier gauge wire. Buy some 4 conductor, 18 AWG cable. Cut about 1 foot off of each end of the supplied phone cable and splice in your new wire.

For reference you can see a video regarding a RV inverter install in a Keystone Cougar 276RLSWE Fifth wheel RV Trailer.

Now with any luck, you should have your RV inverter install completed:

1.  You have made sure that you won’t be destroying it by feeding shore power into it.

2. You are sure that your converter will never be powered from your inverter.

3. Congratulations. Turn it on, hit the road, and go get off the grid!

Gary Brinck

Gary Brinck, aka “RVRoamer”, is a well-known participant on major RVing sites and email lists. He serves on the staff at two RV websites and operates the Internet By Data Card Yahoo Group for folks who use cellular modems and hotspots to access the internet. He lives in the Ocala, Florida, area with wife of 48 years, Nancy, and together they travel several months a year in their 2004 American Tradition coach. Their journeys have covered much of the USA, including Alaska, and western Canada. They have also worked as workampers for 7 summers, at RV parks from Maine to Washington. Gary took an early retirement from IBM in 1993, after a 28 year career in computer systems design and software development. Early retirement gave him plenty of time to get deeply involved in RVing and the internet, and he soon put his skills and technical training to work to become an expert on RVs and to help others solve their RVing problems. Contact: Gary (at) RVForum.net