What is the difference between Modified Sine Wave and Pure Sine Wave?

Posted on 8/7/2017 by Justin G.

Inverter Question: “What is the difference between a pure sine wave and a modified sine wave inverter?”

Pure Sine or “Normal Sine, Sine, Pure Sine, PSW, True Sine“ is the smooth sine wave as seen in the picture above. In the simplest of explanations, it is the cleanest and best type of sine wave due to its smooth oscillation waveform. Pure sine is the type of sine wave that comes from your AC (wall) outlets in your house and allows all electronic devices to operate smooth, clean, and efficiently.


Modified Sine or “Square, Modified, Simulated, MSW” is a manufactured type of sine wave that is less expensive to produce. Able to operate with most electronic devices, it is an affordable and adaptable alternative to the Pure Sine Wave Inverter.

Getting Technical
Pure Sine Wave (PSW) is the best because the voltage rises and falls smoothly and changes polarity instantly when the voltage crosses 0V (zero volts). This does not cause excessive heat build-up or add stress to electronic devices as it is a smooth and consistent change.
On the other hand, Modified Sine Wave (MSW) is more like a light switch with abrupt voltage rise and falls (as seen in the waveform) with long periods of rest at 0V. This abrupt change causes some devices to simply not work, create electrical noise, and can cause failure in sensitive electronic devices.

So what does that mean for me?
Ideally, the pure sine wave (PSW) is the best solution to your power needs; it allows all electronic devices to operate as intended. The downside of a PSW inverter is the cost to manufacture it; the price can be 2-4 times the amount of a Modified Sine Wave Inverter.
Modified Sine Wave Inverters (MSW) are inexpensive to produce and provide the same amount of power (in watts) as the PSW Inverters do. Unfortunately, the square sine wave produced is not compatible with some sensitive electronic devices such as rheostats (dimmer switches, variable speed devices), built-in clocks, heaters, CFL & HID lights, some power tool battery chargers, sewing machines with variable speed controls, copy machines, and laser printers.

Which is my best choice?
If you are in need of an inverter that is going to power sensitive electronics such as: medical devices, computers, anything with a dimmer/variable speed, heater/heating coil, or just needs clean power; buy the pure sine inverter… you can’t go wrong with that choice.
On the other hand, if you need temporary power while tail-gating, camping, road-trips or to charge your laptop/two-way radios, power fans, run a blender, power a microwave, etc., the modified sine wave inverter is smart and affordable choice.

The Take-a-way
Modified Sine Wave inverters sound scary, right? In reality, MSW inverters are not scary, dangerous, etc., they just need to be used appropriately. I have used a MSW inverter for most of my life during camping, road-trips, RVing and the like…and have never experienced any problems with them. MSW Inverters are perfect for 90% of applications for the average user; you must realize their limitations and use them accordingly. Want to err on the side of caution(?)... buy a Pure Sine Wave Inverter and you cannot go wrong!

Take a look at our Pure Sine Wave Inverters and our Modified Sine Wave Inverter models


More reading on Inverters and How-to power them:

• Understanding Inverters and How-to Select the one that is right for you

• Generator vs. Inverter: How do they stack up?

• Bring Some of Home’s Amenities With You camping

• Powering Household Appliances in your Car

• How to Connect a Large or Small Inverter to a Battery

• Customer Question: I need wall (AC) power while camping!

Share this Article: