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Differences Between Pure Sine Wave And Modified Sine Wave

Updated: Jul 7, 2020

Most inverters in the Nigerian market are described as ‘pure sine wave inverter’. For those who have little or no technical knowledge of the science of inverters, but who need to know, the questions often are: On what basis are inverters classified as ‘pure sine wave’? What are the alternatives to pure sine wave inverters? What makes them a better choice for appliances than the alternatives? Et cetera.

A power inverter or inverter is an electronic appliance that converts DC (direct current) electricity from sources such as batteries or solar cells to AC (alternate current) electricity for use in appliances. As their names imply, they produce electric voltage in either direct or ‘alternating’ ways. In other words, alternating current describes the flow of charge that changes direction periodically and direct current describes the flow of charge that does not change direction but flows in one direction, mostly a straight line.

Their output waveforms are shown below.

DC output waveform
DC output waveform

AC output waveform.
AC output waveform.

Either of the two can be ‘modified’ or ‘rectified’ depending on the needs and nature of the appliances that use them.


Sometimes, the output voltage may require additional smoothing and adjustment to produce a uniform steady voltage. The DC output waveform can be modified in two ways, full-wave or half-wave as shown below.

The AC can be rectified or modified in these two ways, square or triangle.


Modified Sine Wave (Modified Square Wave or Step Wave) inverters have an output waveform in an approximate or modified form of a pure sine waveform. A square wave inverter will run simple things like tools with universal motors with no problem – but not much else. Since producing a modified sine wave is a much simpler process than creating a pure sine, modified sine wave inverters are less expensive than pure sine wave inverters, but they are generally considered less effective, less complex and generally disadvantageous.

Disadvantages of Modified Sine Wave Inverters

Power Surge

The major disadvantage of the modified sine wave inverter is that peak voltages usually varies with the voltage of the battery. Although it is cheap, without the regulation of the power supply, the modified sine wave inverter can cause electronic devices to behave erratically because of power surges.

Power Wastages and Reduced Efficiency

The use and waste of power is another disadvantage. The modifying circuit that is used to adjust the output waveform will inevitably use up some power and create loses during the conversion process. For instance, if the inverter is 80% efficient, expectedly some 20% of the power is lost during the conversion process further reducing the net output and efficiency of the inverter. The power is mostly lost in the form of heat.

Appliances like refrigerators, microwaves, and compressors that use AC motors will not run as efficiently on a modified sine wave as they would on a pure sine wave. Some may not work at all on modified sine wave.

Some fluorescent lights will not operate quite as bright. Also, appliances with electronic timers and/or digital clocks will often not operate correctly. Because the modified sine wave is noisier and rougher than a pure sine wave, clocks and timers may run faster or not work at all.

Buzzing and Beeping Sound in Appliances

Due to the rectification process and unwanted interference, appliances that use modified sine wave usually make a continuous and annoying static, beeping or buzzing sound.

Possible Damage to Appliance

Most appliances run on pure sine wave thus, when a modified sine wave is forced on them, they run the risk of damage.

Excess Heat

In some cases, running an AC motor on a modified sine wave may lead to a buildup of excess waste heat that could damage the appliance.

Unwanted Interference

Some devices suffer from unwanted interference from a modified sine wave inverter. For instance, a radio powered by a modified sine wave inverter, may pick up interference from the modified sine wave, which could make it difficult to listen to.


A pure sine wave inverter is an inverter that gives charge in the pure unmodified sine waveform as described above. Though they are relatively costlier than square wave inverters, pure sine wave inverters are generally preferred to modified sine wave inverters and regarded as more advantageous in the inverter world.

Advantages of Pure Sine Wave Inverters

  • The major advantage of a pure sine wave inverter is that all appliances which are sold on the market are designed for a pure sine wave. Using a pure sine wave inverter guarantees that the appliances will work to its full specifications and achieve optimal efficiency.

  • Appliances run faster, quieter and cooler.

  • Pure sine wave output voltage waveform is as clean as, and perhaps even better than, utility-supplied or grid electricity.

  • Reduced or absence of noise in appliances.

  • Some appliances, particularly microwaves and variable speed motors, will not produce full output if they do not use sine wave power.

  • Other appliances, particularly medical equipment may not function at all unless you use a pure sine wave inverter.

  • They produce a much higher equivalent wattage compared to a modified sine wave power inverter.

  • There is a greater range and variety of appliances that can be powered by pure sine wave inverter. They can power any AC appliance without risk of damage.


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