Pure vs. Modified Sine Wave Inverters -puresunnergy.com

True Sine Wave or Modified Sine Wave?

Because the AC electricity from the electric grid is in the form of sine wave, the inverters we use aim to produce a current that is as close to sine wave as possible.  While modified sine wave inverters present an inexpensive alternative, there is no comparison to the clean, undistorted sine wave provided by pure sine wave inverters. 
Pure Sine Wave Inverter

A pure sine wave inverter, also known as a true sine wave inverter, produces a clean, undistorted electrical output.  Depending on the manufacturer of the product, pure sine inverters have a perfect sine wave output that's in phase with the AC grid of the utility company.  Because of the sinusoidal form, pure sine wave inverters, like the Cotek SK3000-148, are used for grid-tie solar systems and work for virtually any AC load.

PSI2000N Series pure sine wave inverter

PSI2000N Series pure sine wave inverter
Because they produce no harmonic distortions in the frequency, pure sine wave inverters allow any electronic device to function well without overheating or creating an irritating "buzz" sound.  Though pure sine wave inverters are undoubtedly the best and most versatile kind of inverter, they are more expensive than modified sine wave inverters.

Pure sine wave inverters are necessary for highly sensitive products such as digital clocks, audio equipment, and video-game consoles.  As a general rule of thumb, if you're powering any electronics, you'll probably want to stick with a pure sine wave inverter. 

Modified Sine Wave Inverters

The cheaper alternative to a pure sine wave inverter is a modified sine wave inverter.  A modified sine inverter converts DC electricity to a non-sinusoidal AC wave that is "modified," or distorted.   When an inverter produces modified sine wave, the voltage output (represented in the Y axis of the image) essentially jumps from zero volts to positive, where it plateaus and drops back to zero, to negative voltage, and then back to zero again. This is signified in the image by the squared edges seen in the modified sine wave, which is contrasted by the smooth oscillation of a voltage that is produced by a pure sine wave inverter.  The modified sine wave is a stepped waveform that is designed to mimic a true sine wave.  Because it is not a clean form of energy, modified sine wave does generate a certain kind of interference called harmonic distortion (though not as much as a square wave).
Modified sine wave inverters can work for the majority of low-end appliances, but take caution when using them for your electronic devices.  Because these inverters do not produce a clean output, a "buzz" often accompanies modified sine wave inverters.  Highly sensitive electronic products that were intended operate with a clean AC waveform will certainly overheat when connected to a modified sine wave inverter.  Since modified sine wave inverters are less efficient than pure sine wave inverters, the excess energy produces heat that can be detrimental to some devices.  The impure energy produced by modified sine wave inverters can curtail the longevity of many appliances, and utterly destroy some electronics that were originally designed for clean AC.
Though it would be wise to choose a pure sine wave inverter for a television, video-game console, or audio equipment (so they don't overheat), a modified sine wave inverter is suitable for most rugged, low-end products.  At such a low cost, it makes financial sense to use a modified sine wave inverter if your equipment can handle it.
If your goal is merely to power some lights and a refrigerator, a modified sine wave inverter will surely satisfy your needs.  If there's even a chance that you will be powering sensitive electronics with your inverter, opting for a pure sine wave inverter is highly recommended.  Don't stress over what is compatible- with pure sine wave inverters: there is no hassle, no interference, no noise, and a longer lifetime for your appliances.
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