Pure sine wave vs. modified sine wave: which do you need?
Short answer
For home backup, choose pure sine wave. A pure sine wave inverter produces power shaped like the electricity from a wall outlet, so everything runs normally. Modified sine wave is cheaper but can make motors run hot and noisy, cause buzzing, and make some medical devices, chargers and appliances misbehave or fail to work.
What the difference is
Household AC power alternates smoothly up and down in a curve called a sine wave. An inverter has to create that curve from a battery's DC power.
- Pure sine wave inverters recreate the smooth curve closely.
- Modified sine wave inverters approximate it with a stepped, blocky shape. It is simpler and cheaper to make, but it is not the same as grid power.
What can go wrong with modified sine wave
| Appliance | Pure sine wave | Modified sine wave |
|---|---|---|
| Refrigerators, freezers, pumps | Normal | Motors may run hotter, noisier and less efficiently |
| CPAP and other medical devices | Normal | Some may not work properly; check with the manufacturer |
| Laptops and phone chargers | Normal | Usually work, sometimes with buzzing or extra heat |
| Microwaves | Normal | Often run with less power and more noise |
| Simple heaters and incandescent bulbs | Normal | Usually fine |
| Devices with timers or digital clocks | Normal | Clocks may run fast or slow |
How to check what you have
Look for "pure sine wave" on the spec sheet or the label. Almost all current portable power stations from established brands use pure sine wave inverters. Modified sine wave is more common on cheap plug-in car inverters and some budget generators.
What about generators?
Generators have a related issue called harmonic distortion. Inverter generators produce clean power similar to pure sine wave. Conventional open-frame generators can produce rougher power that sensitive electronics do not like. See inverter vs. conventional generators.
Medical devices: if you rely on a CPAP, oxygen concentrator or other device, use a pure sine wave source and confirm compatibility with your equipment supplier.
Frequently asked questions
Do I need a pure sine wave inverter for a refrigerator?
It is strongly recommended. A fridge compressor can run on modified sine wave, but it may run hotter and noisier, which can shorten its life.
Can a CPAP run on a modified sine wave inverter?
Some can, but many manufacturers recommend pure sine wave. Use pure sine wave or the machine's DC power cord to be safe.
Are all portable power stations pure sine wave?
Most current models from established brands are, but check the specs. Very cheap units and car inverters are more likely to be modified sine wave.
Sources and method
Runtime figures assume 85% of battery capacity reaches AC appliances and typical US appliance ratings. See exactly how we calculate. Found a mistake? Tell us and we will fix it.