When shopping for an inverter online, many folks ask about the practical differences between "modified square wave" inverters and those advertised as "sine wave" or "pure sine wave" inverters.

Below we have some pictures of inverter output waveforms displayed on an oscilloscope. These pictures demonstrate the differences that are found in the sine waves of less expensive inverters in comparison to sine wave models form.


Signal from an inexpensive, portable modified sine wave Inverter


Cabin sized modified sine wave inverter  Low wattage sine wave inverter


Low wattage sine wave inverter


Residential home scale pure sine wave inverter

With regard to functionality, all of the inverters will run most loads just fine. The modified sine wave models may have some unexpected side effects as a trade off stemming from their generally lower cost.

Modified sine wave inverters may:

• Run resistive loads just fine
• Run motors hot and consume 30% more energy from your batteries
• Create a buzz or whine from motors
• Create interference with tv and radio reception
• Disrupt timers or digital clocks
• Disrupt washing machine controls based on timers
• Damage battery chargers or batteries, especially for rechargeable power tools
• Damage high end stereo equipment
• Void warranty coverage on many appliances, electronic equipment, or computers

Pure sine wave inverters, on the other hand, with generally meet or exceed the quality of electricity supplied from the power company. The peak voltage, and RMS voltage of these waveforms from inverters will generally match that of the grid or come very close. The quality of the sine wave output for pure sine wave inverters, will generally ensure the proper operation of all types of AC loads.