Pure Sine vs Modified Sine Inverter: Which Do You Need for a Van?
When you're choosing an inverter for a van or RV, the pure sine wave vs. modified sine wave question comes up almost immediately. Here's the honest answer: buy a pure sine wave inverter. The reasons why — and what modified sine actually means in practice — are worth understanding.
For inverter sizing and installation, see the inverters & 120V power guide and what size inverter do I need?.
What the waveforms actually are
Utility power (the power from your wall outlet at home) is a smooth sine wave — voltage that rises and falls in a clean, mathematically perfect curve at 60Hz. This is what most electronics are designed around.
A pure sine wave inverter reproduces this — its output is electronically synthesized to match grid power closely enough that virtually any appliance works correctly.
A modified sine wave inverter produces a stepped approximation — a blocky, square-ish wave that rises and falls in steps rather than a smooth curve. It delivers power at the right voltage and frequency, but the waveform contains harmonics (extra frequencies) that can cause problems.
What goes wrong with modified sine wave
Sensitive electronics: Switching power supplies (in laptops, phone chargers, LED drivers) may run hot, charge inefficiently, or fail prematurely on modified sine wave power.
CPAP machines: Most modern CPAPs require pure sine wave. Running a CPAP on modified sine can cause audible humming, inaccurate pressure delivery, and in some cases machine damage or voided warranty. Always use pure sine for a CPAP — see best power station for CPAP.
AC motors: Induction motors (blenders, fans, some power tools) run hotter and less efficiently on modified sine. In worst cases, they can burn out.
Audio equipment: The harmonics in a modified sine wave create an audible 60Hz or 120Hz buzz through speakers and amplifiers.
Appliances with digital displays or timers: Microwaves, coffee makers with digital clocks, anything with a control board — these may behave erratically or fail.
Appliance warranties: Many manufacturers void warranties if the appliance is run on modified sine wave power.
Don't run a CPAP on modified sine
CPAP manufacturers specifically state that their machines should only be used with pure sine wave power. Audible humming, incorrect pressure delivery, and machine damage are all documented. Use pure sine or a power station with a built-in pure sine inverter.
What works fine on modified sine
- Simple incandescent or halogen bulbs (rare in van builds today)
- Basic resistive heating elements
- Simple single-speed power tools (no speed control)
- Older, simple battery chargers
The reality for a modern van build: almost nothing you'd actually want to plug in falls into this "fine" category. You'll have a laptop, a phone, probably a CPAP, likely LED lighting from an inverter — all of which prefer or require pure sine wave.
The price difference is smaller than you think
Modified sine wave inverters are cheaper — a 1,000W modified sine unit might be $60–$80 vs. $150–$250 for a pure sine equivalent. That sounds significant until you factor in:
- The cost of an appliance that fails prematurely
- The efficiency penalty (appliances draw more power on modified sine, draining your battery faster)
- The CPAP compatibility issue
- The laptop or charger that gets cooked
For a van build that represents thousands of dollars in time and materials, saving $80 on the inverter by going modified sine is a false economy.
Pure sine inverter recommendations
For most van and RV builds:
- Renogy 1000W Pure Sine Inverter (~$120) — reliable and well-supported, good for light to moderate loads
- Renogy 2000W Pure Sine Inverter (~$200) — for anything that includes occasional high-draw loads (coffee maker, hair dryer)
- Victron Phoenix 12/1200 (~$350) — premium build quality, connects to VictronConnect for monitoring, excellent for Victron-integrated builds; see Victron Phoenix review
- Victron MultiPlus 12/1600 (~$500–$600) — if you want an inverter/charger combo for shore power integration
For full inverter sizing guidance and installation: how to size an inverter for a van or RV and how to wire an inverter.