Use the power inverter collection after completing your load list. Compare verified continuous output, starting capability, input voltage and battery requirements before choosing a model.

1. Separate Watts From Watt-Hours

Watts describe the rate of power use. Watt-hours describe energy consumed over time. The inverter must support the power demand, while the battery must provide enough usable energy for the operating period.

A 100W appliance running for three hours uses 300Wh of AC energy before inverter losses are included. A larger inverter does not reduce that appliance’s energy requirement or add storage to the battery bank.

2. Make an Appliance Input-Power List

List only the AC equipment you intend to operate from the inverter. Appliances already supplied directly from the DC system should not be counted as inverter AC loads, although their battery use still belongs in your overall energy budget.

Use the appliance input rating, manufacturer information or appropriate measurements. A microwave’s advertised cooking output is not its AC electrical input. Likewise, a power supply’s maximum label rating is not necessarily its normal consumption.

• Record running watts and VA where available.
• Identify startup requirements and the time they last.
• Record hours of use and any duty cycle.
• Mark which appliances will run together.
• Include loads that remain on unnoticed, such as networking equipment.

3. Calculate the Simultaneous Running Load

Add the running input power of equipment that may operate at the same time. Do not total every appliance in the RV unless your actual plan is to run all of them together.

Where VA and watts are both specified, ensure neither limit is exceeded. Do not apply a fixed conversion between them unless the relevant power factor and load conditions are known.

4. Evaluate Starting Events Separately

Now consider a hypothetical compressor appliance that runs at 100W but requires a total of 700W while starting. If the previous 130W of equipment stays on, the temporary starting demand is 830W.

Starting total: 700W + 130W = 830W. Do not add the compressor’s 100W running value again if the 700W starting figure already represents its complete startup demand.

The inverter must support the duration of that event as well as its magnitude. If several appliances can start together, assess their combined event or use a verified load-management plan. A generic percentage margin is not a substitute for startup information.

5. Check Continuous Output at the Expected Temperature

Use the rating that applies to the compartment temperature and operating conditions. Some inverter models deliver less continuous power as ambient temperature rises.

Also distinguish model numbers and VA classes from continuous watts. The manufacturer’s datasheet for the exact hardware version should control the comparison. Do not buy around an unexplained number in a title.

6. Estimate Daily AC Energy Use

Multiply each appliance’s running input by its operating time. For cycling appliances, use a defensible duty-cycle estimate based on actual conditions or measurements.

7. Include Conversion Losses and Inverter Overhead

For a simplified estimate, assume 90% load-conversion efficiency and separately allow 5W of inverter overhead for eight enabled hours.

Battery energy estimate = 800 ÷ 0.90 + (5 × 8) ≈ 929Wh.

This illustrative accounting assumes the 90% conversion figure excludes the separately added overhead. If your measured efficiency already includes operating overhead, do not add it twice. Actual efficiency changes with load, and economy-mode operation may affect the result.

8. Compare With Usable Battery Energy

As another hypothetical example, a battery bank rated at 12.8V and 100Ah represents about 1280Wh of nominal energy. If the manufacturer permits an 80% usable allocation for the intended conditions, that planning allowance is 1024Wh.

The estimated 929Wh inverter demand leaves only about 95Wh within that allowance, before other DC loads or additional reserve. That is a narrow energy margin, not a recommendation for this battery size.

Use your battery manufacturer’s actual recommendations. Temperature, age, discharge rate and system cutoff can change available energy. A permitted discharge percentage must not be assumed for every chemistry or model.

9. Verify Battery Current and BMS Limits

Enough watt-hours do not guarantee sufficient discharge current. A simplified DC estimate is AC load divided by actual DC voltage and conversion efficiency.

At an assumed 12V and 90% efficiency, a 1000W AC load would require approximately 1000 ÷ (12 × 0.90) = 92.6A, before separately modeled overhead.

This is not a cable or fuse specification. Current can rise as battery voltage falls. Review continuous and short-term battery limits, BMS behavior, voltage drop and all power-path component ratings with the installer.

10. Match the Product to the Completed Worksheet

Shortlist models only after the running load, startup event, energy budget and DC capability are understood. For example, the Victron Phoenix Inverter 12/1200, 120V VE.Direct NEMA GFCI can be researched by its exact part number; its name alone is not a sizing recommendation for the examples above.

Compare the available inverter specifications and include installation costs. Fixed-circuit supply, source transfer and protection require a suitable design, not simply a larger inverter.

Frequently Asked Questions

Will a 2000W inverter run my entire RV?

Not necessarily. Add the actual simultaneous loads and starting requirements, then check the battery system and distribution design. An output number alone does not establish whole-RV capability.

Does a 30A shore-power connection determine inverter size?

No. Shore-service capacity and your selected battery-powered loads are different planning questions.

Can I extend runtime by installing a larger inverter?

No. Increase usable energy, reduce consumption or adjust operating time. A larger inverter may also have different idle consumption.