Hopefully you have 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 are now ready begin your do-it-yourself RV inverter install.
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 which is very important to consider for your RV inverter install. For other inverter sizes, the drop will be proportional.
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 which is 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)
|For 100 Watt Load||0.0004||0.0005||0.0007||0.0008||0.0013||0.0021||0.0033||0.0052|
|For 500 Watt Load||0.0021||0.0056||0.0033||0.0041||0.0065||0.011||0.0165||0.026|
|For 1000 Watt Load||0.0041||0.0051||0.0065||0.0081||0.013||0.021||0.033||0.052|
|For 1500 Watt Load||0.0062||0.0083||0.0098||0.0122||0.0195||0.0315||0.0495||0.078|
|For 2000 Watt Load||0.0082||0.0102||0.0132||0.0162||0.026||0.042||0.066||0.104|
|For 3000 Watt Load||0.0123||0.0153||0.0195||0.0243||0.039||0.063||0.066||0.156|
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.
The AC (Connecting the inverter to the RV electrical system) side of the RV inverter install can get more complicated. For starters, you need to ensure that you do not have either shore power or generator power connected to the output of the inverter. Otherwise, you will destroy it. There are several possible ways to accomplish this. 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.