Learn how these electrical devices work, and why RVers might benefit from having one on board.
By Mark Quasius, F333630
November-December 2025
An inverter is a handy device to have in a recreational vehicle. It can operate 120-volt electrical components when no shore power is available, and when you either don’t have or don’t want to run an auxiliary generator. But there are limitations as to how much an inverter can power. The size of the inverter and the capacity of the battery bank come into play. Inverters won’t run an entire RV with multiple air conditioners and heated tile floors, but they are perfect for operating a microwave oven for a few minutes or for powering up the entertainment center to watch a movie.
Let’s look at what an inverter is, how it “makes” 120-volt electricity, and practical applications.
The Xantrex PROwatt SW 2000 inverter is one example of a small inverter that can power appliances in an RV.
INVERTER BASICS
An inverter doesn’t make electricity. It takes 12-volt-DC battery power and turns it into 120-volt-AC power. For practical purposes, think of it as doing the opposite of a converter or battery charger, which converts 120-volt-AC power to 12-volt-DC power in order to charge batteries and operate the RV’s 12-volt accessories, such as lights, water pumps, and fans. An inverter’s work happens electronically, so no exhaust fumes or noise results, which is great for quiet time at campgrounds. Using an inverter also saves the fuel required for generator operation.
As noted, inverters do have their limits. Because inverters use battery power to create AC output, they do not work well — or sometimes at all — for high-current loads, such as air conditioners, water heaters, or anything with a sizable electric heating element. The drain on the batteries would quickly deplete the battery bank’s charge level, and in some instances, the inverter may not work at all. For this reason, inverters are typically used for short-term heavy loads, such as a microwave oven, or for smaller loads that may run for a longer duration, such as entertainment systems.
Inverter-equipped RVs generally have larger battery banks to provide plenty of inverter runtime. Eventually, the battery bank must be recharged. This can be accomplished by running the generator for a few hours at a convenient time, or while driving if you own a motorhome. This also can be accomplished via solar panels or arrays.
Inverters connect to the RV battery bank via wires that are sized to handle the electrical draw, and they must be properly fused. For small inverters used to provide the minimal power needed to operate a TV, for instance, wires as small as #10 gauge may be sufficient. A heavier wire gauge is needed as the wattage rating of the inverter increases, and also as the distance between the inverter and the battery bank increases. Correct cable sizing info for any inverter can be found in the manufacturer’s instructions for that unit and should be observed to operate the inverter safely. Ideally, the inverter should be placed as close to the batteries as practical to minimize the voltage drop that occurs. The power output from small inverters can be hardwired to a remote electrical receptacle in the RV, or a receptacle may be mounted in the inverter itself.
Larger units tend to be designed as a combination inverter/charger capable of performing two functions. These devices supply 120-volt-AC power from the batteries when required, but they also serve as a converter to recharge the batteries and to supply power to 12-volt accessories when shore power is present or the generator is running. If an inverter/charger is installed, a converter is no longer needed.
The Magnum MS2812 inverter/charger boosts performance by combining inverter output with shore power for greater assist capacity.
The output from an inverter/charger generally feeds into a breaker subpanel to power multiple branch circuits. These units also have an input connection for 120-volt-AC power. When AC power is present at this input, it simply passes through the inverter’s internal transfer switch to the output circuits. At the same time, some of the incoming AC power recharges the batteries. When incoming AC power is no longer present, the inverter draws power from the batteries, changes it to 120-volt-AC power, and sends it to the inverter’s output circuits. Many inverter/chargers also can equalize wet-cell batteries to remove sulfation from the battery plates and restore them to full capacity.
WAVEFORMS
All AC electrical components operate from a sine wave power source. Sine waves are created through electromagnetic induction within a generator. But an inverter has no moving parts, so it must create its output electronically. The power from RV inverters generally is in one of two forms: modified sine wave or true (pure) sine wave.
Historically, the first inverters created square waves that were very inefficient. Next came inverters that created modified sine waves, which became the preferred option. They worked well for powering simple resistive loads such as toasters, lights, and heating elements, but electrical components in an RV were fairly basic at that time. As technology advanced, more high-tech electronics were incorporated in everything from refrigerators to entertainment systems to NiCad battery chargers, which may not function properly with modified sine wave inverters and could even be damaged. To satisfy the needs of these high-tech devices, true or pure sine wave inverters were created to mimic the power provided by true AC power found on the utility grid. Today, true sine wave inverters are available at reasonable prices, and most inverter/chargers in modern RVs are true sine wave devices.
BATTERY REQUIREMENTS
An inverter cannot create energy, but as noted, it transforms 12-volt-DC battery power to 120-volt-AC power used for the majority of our electronic devices. To run a large number of accessories, or to operate them for longer periods, necessitates a fairly large battery bank. To draw 10 amps of 120-volt power for one hour requires 1,200 watts of power, which is equivalent to 100 amp-hours at 12 volts from the batteries. Inverters are not 100 percent efficient, so check the efficiency rating on the inverter to verify its true output. For example, if the inverter has a 90 percent efficiency rating, approximately 10 amp-hours will be needed from the batteries.
To avoid drastically shortening the lifespan of wet-cell and AGM battery banks, they should never be drawn down below 50 percent. Therefore, a 220-amp-hour battery bank would be needed to power that load for one hour — about the rating for one pair of 6-volt batteries. After running that load for one hour, the battery bank will be depleted and must be recharged.
Recent advances in lithium battery technology have allowed these batteries to use most of their capacity, so the 50 percent rule for wet-cell and AGM batteries won’t apply to them. Check with the manufacturer, though, because not all batteries are created the same.
RV manufacturers typically supply inverter-equipped RVs with four to eight batteries. A typical bank of four 6-volt golf-cart-style batteries provides 440 amp-hours at 12 volts. Using the 50 percent rule, this gives you 220 amp-hours to work with. Adding more batteries increases the potential runtime and also results in higher battery voltage readings when in use.
When considering how much energy you are pulling from a battery, you need to account for not only the amount but the duration. A 3,000-watt inverter that pulls 3,000 watts for 5 minutes (250 Wh) will put less strain on the batteries than a 2,000-watt inverter running at half capacity for an hour (1,000 Wh)
One example of a low-power, long-duration load is what would be required for an evening of television or DVD viewing on an entertainment system. An example of a high-current, short-duration load would be a microwave oven operating for a few minutes. Either of these loads lends itself perfectly to inverter use. Installing residential refrigerators in RVs has become popular, but they are widely misunderstood, since their power consumption isn’t as large as one may think. These refrigerators consume medium power, and thanks to their efficiency, actual runtime is minimal, so using inverter power may be possible assuming that the battery bank is properly sized.
INSTALLING OR UPGRADING AN INVERTER
First, a reminder: If the following procedures are outside your comfort zone, or if you do not possess the appropriate skills, have a qualified RV service technician or electrician do the work.
An existing modified sine wave inverter can be upgraded to a true sine wave inverter of similar size or one with a larger output capacity. A larger inverter requires more battery current to achieve higher output levels, so it might be necessary to replace the inverter battery cables with heavier-gauge cables. Consult the inverter’s owners manual for the specified size. If you keep the same size inverter, the existing cables should be sufficient, but verify that by checking the manual.
Also check the size of the fuse that should be installed in the battery cable at the positive terminal of the battery to protect the inverter and DC cables in case of a short circuit or fire. The AC circuits should be able to remain the same unless a fairly small inverter is replaced with one that has a much larger output. In that case, it’s best to treat it as a new installation.
A high-capacity fuse assembly, shown installed in the inverter’s battery cable, feed provides critical overcurrent protection, helping to safeguard the system and prevent potential electrical damage.
Upgrading an inverter generally means replacing the inverter’s remote display panel with a new one. You may be able to use the existing communications cable from the inverter to the control panel, but in most cases, a new network communications cable will be needed. Again, consulting the owners manual or calling the manufacturer should give you specifics as to what is needed.
A high-capacity fuse assembly.
To add an inverter to an RV that doesn’t have one, you’ll need to do some research and planning. First, decide where to mount the inverter. An inverter generates heat, so it should be installed in a large basement area or in a smaller, vented compartment that is dry. Placing the inverter close to the batteries helps to reduce the voltage drop that will occur when you attempt to pass large amounts of current through the battery cables. However, never place the inverter in the same compartment as wet-cell batteries, as heat from the inverter could ignite explosive battery gases. Also note that locating the inverter farther from the batteries may require a battery cable with a higher capacity.
The Victron Energy MultiPlus-II inverter/charger
Once the inverter mounting location and cable requirements have been established, plan how to connect the AC devices to the inverter. A small inverter may be used to power a television and a few entertainment system accessories, such as a DVD player and satellite receiver. If the inverter has a built-in receptacle, simply locate the unit close to the entertainment system, making certain to run adequate DC wiring to the batteries. A 450-watt inverter may only require #8 or #6 wiring, depending on the length of the cable run. If the inverter has a fused hardwired output, you should place it in a basement area close to the batteries to minimize the voltage drop and then run longer AC wiring to a receptacle near the entertainment system. Some inverters do not have pass-through AC power, so you must unplug devices from their normal outlet and plug them into the inverter. Inverters that do have pass-through power, such as the Xantrex Freedom X, can be located anywhere in the AC line and controlled via a remote display panel.
The Victron Energy MultiPlus-II inverter/charger combined with the BMV-702 battery monitor will both charge and draw energy from the batteries while helping you keep track of the amp-hours used and the state of battery charge.
Larger inverter/chargers can power many circuits. Generally, the main breaker panel feeds such inverter-chargers with 120-volt power, which is used as bypass power and to charge the batteries when generator or shore power is present. The inverter/charger’s output goes to a subpanel; circuits fed by the inverter (such as a microwave oven, various receptacles, and a residential refrigerator) are connected to the subpanel. If you plan to install an inverter in an RV that doesn’t have one, you’ll probably need to add a subpanel. In some cases, though, it’s possible to replace the main breaker panel with a combination breaker panel/subpanel in one box.
An inverter can perform only as long as it has adequate battery power available. Unless you simply add a small inverter to power an entertainment system, extra battery capacity most likely will be needed. The size of the battery bank depends on the expected load and how long it will run. Once you have determined the number of batteries needed, make sure the RV has enough physical space for them. Wet-cell batteries release hydrogen, so they must be located in a vented area. AGM batteries are more expensive but do not release significant amounts of hydrogen. Many inverters can handle lithium batteries, but check with the manufacturers regarding compatibility.
INVERTER OPTIONS
The Xanbus System Control Panel provides diagnostics and full control of Xantrex Freedom SW inverter/chargers.
The most common option is a remote display panel to control the inverter’s functions and setup parameters. Without a remote-control panel, most of the inverter’s features cannot be accessed. The panel connects to the inverter via a communications data cable, most likely a four-conductor, twisted pair cable or a category 6 (cat 6) cable similar to that used in a computer network. Often, other accessories can be controlled from this same panel. Magnum Energy’s Battery Monitor Kit displays state-of-charge information pertaining to the battery bank.
Automatic generator start (AGS) modules can be used to monitor the battery voltage so that when voltage drops below a set level, the generator automatically starts. AGS also can be used to start the generator should shore power fail while the air conditioner thermostat is calling for cooling, which is an invaluable feature for people who leave their pets unattended in an RV. Some remote display panels are now equipped with Bluetooth wireless networking, which lets users view key system information on a smartphone or tablet when in close enough proximity. Some even include Wi-Fi capability so you can monitor the system wherever you are.
Automatic generator start (AGS) modules, which automatically activate a generator, are available from a variety of manufacturers, including Magnum Energy.
Today’s RVs often have a multi-plex communications system, which allows numerous accessories — including lighting, HVAC systems, water systems, and power window shades — to be controlled by a whole-coach display. That panel generally can be used to control the inverter and the generator as well.
Most RV manufacturers rely on name-brand inverters that RV service centers are familiar with. Xantrex, Magnum-Dimensions, and Victron are three that come to mind, but several other quality brands are also available. Xantrex has been producing inverters since the original Freedom 458 and is well established in the RV industry. Dimensions inverters were merged into the Magnum line when its parent company, Sensata Technologies, acquired Magnum Energy in 2014. Magnum inverters were among the best and very popular when they were made in the United States, but after the Sensata purchase, manufacturing moved offshore, and the popular Magnum inverter line eventually was discontinued and no longer available in 2024. Many RV manufacturers switched to either Xantrex or the high-end Victron inverter line. As of April 2025, Sensata sold the Magnum-Dimensions line to DMX-Power. DMX-Power plans to return manufacturing to the U.S. and intends to have product available sometime in 2025; so, fans of the Magnum line will once again have access to service, parts, and new inverters.
BENEFITS
Inverters are the perfect solution when other power sources are not available or desirable. They reduce the need to run the generator for small tasks and provide a quiet, emission-free power supply for light loads over a long duration or for heavy loads during a short time. It’s just one more option RV owners have to make RVing more enjoyable.
Resources
AIMS
aimscorp.net
DMX-Power
(formerly Magnum Energy)
magnum-dimensions.com
Go Power!
gopowersolar.com
Samlex America
samlexamerica.com
Victron Energy
victronenergy.com
Xantrex
xantrex.com