Van Inverter Sizing: Pure Sine, Modified Sine, and How to Get It Right
Most van builders get inverter sizing wrong in one of two directions. They buy too small and find the inverter trips under load. Or they buy too large and drain the battery bank faster than the solar system can recover. Van inverter sizing starts with knowing the inverter's role, which appliances run simultaneously, and the output type they need. Getting this right before the build saves money and prevents rewiring.
What a Van Inverter Does
An inverter converts 12V DC battery power into 120V AC power. That conversion is what allows standard household appliances to run inside a van operating off battery. Laptops, coffee machines, microwaves, and phone chargers all require it.
The inverter does not generate or store power. It draws from the battery bank and converts what is there. All three charging sources (solar, shore power, and alternator) replenish the bank. It is sized for the appliances it runs, not for battery capacity.
Pure Sine vs Modified Sine Wave Inverters
The waveform type is the most important inverter decision after size. Pure sine wave inverters produce smooth, grid-quality AC power. Modified sine wave inverters produce a stepped approximation that is cheaper but incompatible with some devices.
| Feature | Pure sine wave | Modified sine wave |
|---|---|---|
| Output quality | Smooth, grid-equivalent | Stepped approximation |
| Compatible appliances | All AC appliances | Basic resistive loads only |
| Sensitive electronics | Safe | Can damage or cause failure |
| Noise | Quiet | Can cause hum in audio equipment |
| Cost | Higher | Lower |
Battery chemistry and inverters interact directly. LiFePO4 batteries with an inverter/charger function require pure sine wave output.
For most van builds, pure sine wave is the right choice. Modified sine wave is only appropriate for very basic applications with no sensitive electronics.
How to Size a Van Inverter
Van inverter sizing follows a straightforward process. List every appliance you expect to run at the same time. Add their running wattages. Then check surge wattage for any appliance with a motor or compressor.
Understanding surge vs running watts is essential. Running wattage is what an appliance draws while operating. Surge wattage is the higher peak it draws for one to three seconds at startup. Surge wattage for appliances like microwaves and compressor fridges can be two to three times the running wattage.
Once the total running wattage is calculated, add 20 percent headroom. This protects the inverter from running at its limit and gives room for appliance variation.
| Appliance | Running watts |
|---|---|
| Laptop | 90W |
| Coffee machine | 900W |
| Phone charger | 20W |
| LED lighting | 30W |
| Total | 1,040W |
Add 20 percent. 1,040 × 1.2 = 1,248W. A 1,500W inverter suits this load. A 2,000W inverter gives additional headroom for growth.
Remote work builds often add a monitor (50–80W) and additional USB loads. These are modest additions, but coffee machines and induction cooktops dominate the sizing calculation.
Common Inverter Sizes and What They Can Power
| Inverter size | Typical applications |
|---|---|
| 300W | Charging electronics, small fans |
| 600W | Small appliances, lighting |
| 1,000W | Coffee machine, laptop and phone charging |
| 1,500W | Most daily van life loads without cooking |
| 2,000W | Standard camper van setup, microwave |
| 3,000W | High-draw appliances, multiple loads |
2,000W inverter use cases cover the vast majority of van life needs. Air conditioning is the exception and typically requires 3,000W or more alongside a large lithium battery bank.
Van inverter sizing should match realistic peak use, not theoretical maximum.
Common Van Inverter Sizing Mistakes
Sizing only for one appliance. Buyers often size around a microwave without accounting for everything else running simultaneously.
Ignoring surge wattage. An inverter rated for 1,000W running may only handle 1,500W surge. A coffee machine or fridge can trip it at startup.
Mismatching the battery bank. A 2,000W inverter at full load draws roughly 167A from a 12V battery. An undersized battery bank cannot sustain that draw.
Buying modified sine wave to save money. The savings disappear when sensitive electronics fail.
Undersized wiring. A 2,000W inverter at 12V draws over 160A. The cable between inverter and battery must be rated for that current and fused within 30cm of the battery terminal.
Inverter connection inspection is part of maintaining a safe van electrical system.
When Professional Installation Makes Sense
Van inverter sizing is one decision inside a larger electrical system. The inverter must match the battery bank chemistry, the solar charge controller capacity, and the wiring gauge. A mismatch in any of these components affects the others.
Professionally designed builds specify the inverter alongside every other electrical component before a single cable is run. Retrofitting an undersized or mismatched inverter is one of the most avoidable van electrical rework jobs.
Mango Vans designs and builds custom Sprinter, Transit, and ProMaster conversions out of South Florida. Electrical systems are specified as complete, integrated designs. See the completed builds gallery to see how inverters are integrated into full builds.
Frequently Asked Questions
What size inverter do I need for a camper van?
For most van life builds without air conditioning, a 2,000W pure sine wave inverter covers daily needs. List simultaneous appliances, add running watts, then add 20 percent headroom.
Is a pure sine wave inverter worth the extra cost?
Yes, for most builds. Pure sine wave inverters work with all AC appliances and run sensitive electronics safely.
Can a modified sine wave inverter damage electronics?
Yes. Laptops, variable-speed motors, audio gear, and some fridges can malfunction on modified sine wave power. The cost saving is rarely worth the risk.
How do I calculate the right inverter size?
List every appliance you will run simultaneously. Add running watts. Check surge watts for anything with a motor. Add 20 percent. That figure is your minimum inverter size.
What is the difference between continuous and surge power?
Continuous power is what the inverter sustains indefinitely. Surge power is the higher peak it handles for a few seconds at startup. Both ratings appear on inverter spec sheets.
Can I run a microwave from a van inverter?
Yes. Most microwaves draw 1,000 to 1,200 running watts. A 2,000W inverter with a sufficient lithium battery bank handles a standard microwave.
How does battery size affect inverter performance?
A 2,000W inverter at 12V draws roughly 167A. The battery bank must sustain that draw. Undersized batteries limit practical output regardless of inverter rating.
Should I choose a 1,000W or 2,000W inverter?
A 1,000W suits electronics and charging. A 2,000W handles a coffee machine, microwave, and multiple devices simultaneously. The 2,000W is the practical standard for most van builds.
Can I upgrade my van inverter later?
Yes, but battery cables and fusing may need upgrading too. Planning for a larger inverter from the start is more cost-effective than retrofitting.
Why should a camper van electrical system be professionally designed?
A professional design matches the inverter, battery bank, charge controller, and wiring as a system. Mismatches are the most common cause of van electrical problems after the build.
