Add up the watts of everything you will run at the same time, allow for the biggest starting surge on top of that, then check the battery can supply the current. That total, not the longest appliance list, sets the inverter size.
What Size Inverter Does Your RV Need? Watts, Surge and the Battery Behind It
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At a glance
- Size by what runs at once: add the running watts, then leave headroom for the biggest start-up surge.
- The battery sets the limit: Renogy's 2,000 W inverter draws up to 166.6 A from a 12 V bank, while one 100 Ah lithium battery is rated 100 A continuous.
- Air conditioning is the hard case: a 13,500 BTU roof unit rated 1,340 W needs roughly 112 A from 12 V, so it takes a large bank and a large inverter.
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Our picks
- Xantrex Freedom XC 2000 inverter charger: 2,000 W continuous with a transfer switch; Xantrex wants 100 Ah or more behind it
- Renogy 2000W pure sine wave inverter (P2): draws up to 166.6 A at 12 V and charges nothing, so plan a separate charging source
- Victron MultiPlus-II 12/3000/120 inverter charger: PowerAssist tops up a weak supply; Victron lists a 400 to 1,200 Ah bank behind it
What an inverter does
An inverter turns the 12 V DC in your batteries into 120 V AC for the outlets, so a microwave or a residential-style refrigerator runs with no hookup. Jayco's 2027 towable owner's manual warns that the power button on its factory unit does not disconnect DC power from the inverter.
The power converter does the opposite job, turning 120 V shore power into 12 V DC to charge the batteries. A plain inverter charges nothing: Renogy's pure sine wave inverter manual says its model only drains the battery, so you need a separate charging source.
What size inverter do you need?
Plan against the inverter's continuous rating, not its surge rating. The Xantrex Freedom XC 2000 is rated 2,000 W continuous with 4,000 W of surge, and its overload alarm starts at about 2,100 W.
| Item | Watts | What the figure is |
|---|---|---|
| Furrion FMAM11AA microwave | 1,500 W | Max rated input (1,000 W cooking output) |
| Greystone 0.9 cu. ft. RV microwave | 1,350 W | Input (900 W output) |
| Hamilton Beach 2-Way FlexBrew | 1,050 W | Electrical rating at 120 V |
| Remington D3190NA hair dryer | 1,875 W | Rated max power |
| ResMed AirSense 11 CPAP | 56 W typical, 73 W peak | Power consumption, 65 W supply |
| Furrion Chill 13,500 BTU roof AC | 1,340 W | Power watts, cooling |
Sources include the Furrion microwave manual, the ResMed AirSense 11 user guide and the Furrion Chill manual.
Then leave headroom for starts. Xantrex puts motor starts at two to six times running current, worst for compressors, and Go Power says start power can reach twice rated power. Makers differ, so size above the running total.
Tip: A microwave's advertised wattage is cooking power. Go Power says it consumes 40% to 100% more, so read the rating sticker on the back of the oven for the real draw.
Pure sine wave or modified sine wave?
Pure sine wave is the safe choice for an RV, because modified sine wave can upset sensitive gear.
Go Power's modified sine wave manual says not to power medical devices or computers from that type. It also warns that some fluorescent lamps may not work properly, and that a TV full of static or buzzing speakers means an incompatible device.
For a CPAP, go by the machine's maker. Jayco says its factory inverter is not intended for any medical device and tells owners to check the CPAP manual first. Philips recommends an inverter of 150 W or greater for the DreamStation Go. ResMed's AirSense 11 guide does not mention inverters, so no waveform requirement can be claimed for it.
How long will your battery run it?
The battery, more often than the inverter, sets the limit. Watts divided by volts gives the battery current: 2,000 W at 12 V is about 167 A (calculated), and Renogy prints 166.6 A for its own 2,000 W model. One 100 Ah lithium battery from Battle Born or Renogy is rated 100 A continuous, so it cannot feed that inverter at full output.
For run time, Renogy multiplies watts by hours for watt-hours, then divides by 12 V for amp-hours. A 1,500 W microwave for 6 minutes is 150 Wh, or 12.5 Ah out of the bank (calculated). Renogy adds a 1.25 allowance for inverter losses.
How much of the bank that uses depends on the battery chemistry. Battle Born rates its 100 Ah lithium at 100% usable. Lifeline recommends using no more than 50% of an AGM on average, so a 100 Ah AGM gives about 50 Ah. Bigger inverters want bigger banks: Xantrex recommends 100 Ah or more behind a Freedom XC, and Victron 400 to 1,200 Ah behind the MultiPlus-II 12/3000/120.
Tip: Battle Born says current limits add up when batteries are wired in parallel, so more batteries means more current for the inverter. It also requires a Current Surge Limiter with inverters rated 3,500 W or higher.
An inverter also draws power with nothing plugged in: under 24 W for Renogy's 2,000 W unit, 13 W for Victron's MultiPlus-II. Switch it off when you are not using it.
Cables and fuses: no single answer
Use your own inverter's cable and fuse table, because makers disagree even within the same 2,000 W, 12 V class. Starts pull far more than the running current: Xantrex warns the Freedom XC can draw surges of up to 400 A from the battery, and undersized wiring can seem fine until a microwave starts.
| Inverter | DC cable | Fuse |
|---|---|---|
| Xantrex Freedom XC 2000 | No. 2/0 AWG, under 5 ft one way | 250 A DC maximum |
| Go Power SSW-2000-12 | 2/0 AWG, up to 10 ft per cable | 300 A Class T |
| Renogy RNG-INVT-2000-12V-P2 | 1/0 AWG supplied, 3 ft | 250 A battery fuse |
Sources: the Xantrex Freedom XC guide, the Go Power SSW manual and the Renogy manual linked above. All of them put the fuse or breaker in the positive cable as close to the battery as possible, and Renogy and Xantrex say not to mount the inverter in the battery compartment.
Inverter chargers and transfer switches
An inverter charger lets the RV switch between shore power and battery by itself: it charges and inverts in one box with a built-in transfer switch. The Freedom XC switches in under 20 milliseconds, and Victron's MultiPlus-II adds PowerAssist, which tops up a weak shore or generator supply from the battery during short peaks.
A plain inverter has no transfer switch. Victron and Go Power warn never to put the inverter and another AC source on the same wiring, and Go Power recommends an automatic transfer switch where more than one source feeds the circuits.
Wiring an inverter into the RV's 120 V panel is not a DIY job. Go Power and Xantrex recommend a certified technician or licensed electrician, and Victron says only a qualified electrical engineer may install the MultiPlus-II. Hire one.
Can an inverter run the air conditioner?
Only with a large inverter and a large battery bank, and the start is the hard part. Furrion rates the 13,500 BTU Chill at 1,340 W while cooling, about 112 A from a 12 V bank (calculated) before inverter losses. Dometic prints amps for its Brisk II 13,500: 12.4 A at the compressor plus 2.5 A at the fan on 115 V. That is roughly 1,710 W running (calculated).
Dometic lists 68 A locked rotor for that compressor, and Xantrex says an inverter may shut down on overload trying to start such a motor even when its running draw is within limits. Micro-Air, which sells a soft starter claiming up to a 75% cut in start current, says a roof AC on batteries needs enough high-wattage solar panels, a robust battery bank, preferably lithium, and a powerful inverter.
Tip: Switch the inverter on first, then turn loads on one at a time, as Xantrex advises, so it never has to supply every start at once. Renogy agrees: do not power up the inverter with loads already on.
Common questions
What does the inverter do on an RV?
It runs your 120 V outlets from the 12 V batteries when there is no hookup, which may be what keeps a residential-style refrigerator running. It does not charge the batteries; that is the converter's job.
How big of an inverter do I need for my RV?
Big enough for everything you will run at the same time, judged on its continuous rating, with headroom for the biggest start. Then size the battery to match: a 2,000 W inverter at full output needs more current than one 100 Ah lithium battery is rated to deliver.
Do I need a pure sine wave inverter for my RV?
If you run a CPAP, computers or a residential refrigerator, pure sine wave is the safer choice. For a CPAP, check the machine maker's own guidance first.
Can an inverter run my RV air conditioner?
Only with a large battery bank. Victron lists a 400 to 1,200 Ah battery bank behind its 12 V 3,000 VA inverter charger, and the compressor start needs headroom on top of that.