What is a pure sine wave inverter?
It is an inverter that makes a sine wave like the power from an electrical outlet.
One engineering analysis puts pure sine wave inverters in the range of 3% total harmonic distortion (THD). One maker's manual we hold describes its pure sine wave as voltage that rises and falls in a smooth fashion with very low harmonic distortion, and lists a THD under 3%.
What is a modified sine wave inverter?
It is an inverter whose wave is closer to a square wave than a sine wave. Engineers describe it as basically square waves with some pauses (dead spots) between the positive and negative halves.
The wave is timed so its RMS (root-mean-square) voltage matches a sine wave's: a nominal 115 or 120 V. But its peak voltage is different from a sine wave's, and one engineering article notes that this can cause trouble for devices that depend on the peak.
How much distortion does each kind have?
One engineering analysis gives distortion as total harmonic distortion (THD). It found that even the best-tuned modified sine wave has a THD of 23.8%, against about 3% for pure sine wave inverters.
Which devices can have trouble on a modified sine wave?
Engineering sources name these groups:
- Motors. One engineering article says the extra harmonics can cause trouble in motors.
- Sensitive equipment, such as medical monitors, in one engineering report.
- Devices that depend on the peak voltage, since a modified wave's peak differs from a sine wave's.
One engineering article says inverter datasheets frequently caution that certain devices may not work on a modified sine wave. One engineering report lists laser printers, laptop computers, power tools, digital clocks and medical equipment as devices a modified sine wave may cause damage to.
One engineering article says pure sine wave inverters are typically used where clean power is needed, such as medical and instrument uses.
Is a modified sine wave inverter cheaper?
Yes. Modified sine wave inverters cost less than pure sine wave inverters; one engineering report calls them much cheaper.
Pure sine wave vs modified sine wave, side by side.
| Pure sine wave | Modified sine wave | |
|---|---|---|
| Shape | Sine wave, like outlet power | Closer to a square wave, with pauses |
| Distortion (THD) | In the range of 3% | 23.8% at best, in one analysis |
| Where it matters | Typically used where clean power is needed, such as medical and instrument uses | Its distortion can cause trouble in motors and sensitive equipment |
| Cost | Higher | Lower |
How do you check which kind an inverter or power station makes?
Look for the output waveform in its manual or spec sheet. Some also list a THD figure.
Our inverter product pages show the output waveform when the maker states it.
Which inverters does Solar Gear Scout track, and what waveform do they make?
The table below is live: it is filled in each time this page loads. It lists inverters whose maker states the output waveform first, then best-value inverters whose maker does not. A waveform is shown only when the maker's own document states it.
| Inverter | Output waveform (maker-stated) | Continuous output | Best current price | Value |
|---|---|---|---|---|
| Renogy 3000W 12V Pure Sine Wave Inverter | Pure sine wave | 3,000 W | $414.99 | 7.23 W/$ |
| Renogy 3000W 12V Pure Sine Wave Inverter with UPS Transfer Switch | Pure sine wave | 3,000 W | $461.99 | 6.49 W/$ |
| Renogy 1000W 12V Pure Sine Wave Inverter | Pure sine wave | 1,000 W | $175.99 | 5.68 W/$ |
| Renogy 2000W 12V Pure Sine Wave Inverter with UPS Transfer Switch and Built-in Bluetooth | Pure sine wave | 2,000 W | $364.99 | 5.48 W/$ |
| Renogy 3500W 48V Solar Inverter Charger | Pure sine wave | 3,500 W | $769.99 | 4.55 W/$ |
| Renogy 1000W 12V Pure Sine Wave Inverter with UPS Transfer Switch | Pure sine wave | 1,000 W | $269.99 | 3.70 W/$ |
| MidNite Solar Little Rosie MNLR4548RE Inverter/Charger | Pure sine wave | 4,500 W | $1,709.36 | 2.63 W/$ |
| EG4 Electronics FlexBOSS21 Hybrid Inverter | not stated | 16,000 W | $4,435.59 | 3.61 W/$ |
| EG4 Electronics 6000XP Off-Grid Inverter | not stated | 6,000 W | $1,898.27 | 3.16 W/$ |
| EG4 Electronics 12kPV Hybrid Inverter | not stated | 8,000 W | $3,036.50 | 2.63 W/$ |
You can browse every tracked inverter on the inverters page.
A sine wave checklist.
- Find the output waveform on the manual or spec sheet.
- Look for a THD figure on the same sheet.
- Motors and sensitive equipment, such as medical monitors, are the uses the sources flag for a modified sine wave.
Related tools and pages.
- What size inverter do I need?
- Off-grid or hybrid inverter: which do you need?
- How to size a portable power station
- Inverters
- Power stations
Sine wave inverter FAQ.
What is a pure sine wave inverter?
An inverter that makes a sine wave like the power from a wall outlet. One engineering analysis puts pure sine wave inverters in the range of 3% distortion (THD).
What is the difference between pure sine wave and modified sine wave?
The shape. A pure sine wave matches the power from a wall outlet. A modified sine wave is closer to a square wave, with pauses, and in one engineering analysis carries far more distortion.
Can a modified sine wave cause trouble for electronics?
Engineering sources say it can, in motors and sensitive equipment. One engineering report lists laser printers, laptop computers, power tools, digital clocks and medical equipment as devices a modified sine wave may cause damage to.
Is a modified sine wave inverter cheaper?
Modified sine wave inverters cost less than pure sine wave inverters; one engineering report calls them much cheaper.
The general statements on this page rest on two engineering sources, each quoted in our facts file: J. H. Hahn's analysis of modified sine-wave inverters in Power Electronics Technology (2006), and a Worcester Polytechnic Institute engineering report on pure sine wave inverters (2007). The statements about one maker's inverters come from that maker's own manual, read and checked by Solar Gear Scout. Solar Gear Scout has not tested any inverter.
The inverter facts in the live table are filled in from Solar Gear Scout's data each time the page loads.