Wall power in a home is a smooth sine wave. A power station’s inverter has to build that waveform from its battery’s direct current. A pure sine wave inverter reproduces it closely. A modified sine wave inverter approximates it with a few flat steps, which is cheaper to build.
Which devices care
On a modified sine wave:
- Motors (fans, pumps, fridges, some power tools) usually run, but less efficiently, hotter and often noisier.
- Devices with a transformer inside can overheat if they were built with little margin.
- Audio gear may hum.
- Simple resistive loads (incandescent bulbs, heating elements) and most switch-mode power supplies (laptop and phone chargers, most computers and TVs) generally work fine.
Medical devices such as CPAP machines should only be run on what their maker approves, which in practice means a pure sine wave.
What the stations here use
Nearly every power station sold now has a pure sine wave inverter. Of the 121 ranked here, 2 use a modified sine wave: the Westinghouse iGen400s and Duracell M250. Both are small, low-output units.
Where a maker doesn’t state the waveform, we leave it blank instead of assuming.
Sources
- Wikipedia, Power inverter: how modified sine wave output affects motors, transformer-based devices, resistive loads and switch-mode power supplies.
- Waveforms: each product’s manufacturer specifications, linked from its page.