Articles: Pure vs Modified Sine Wave Inverter

An inverter, is an electrical power converter that changes direct current (DC) to alternating current (AC), the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits.

Solid-state inverters have no moving parts and are used in a wide range of applications, from small switching power supplies in computers, to large electric utility high-voltage direct current applications that transport bulk power.

Inverters are commonly used to supply AC power from DC sources such as solar panels or batteries. There are generally 2 main types of power inverters, Pure(True) Sine Wave or Modified Sine Wave Inverters.

For the selection of inverters, how do we classify and distinguish them?

We can classify and distinguish the AC Output Waveforms by whether they are Pure Sine Wave or Modified Sine Wave.

Modified Sine Wave

Modified Sine Wave (Modified Square Wave or Step Wave) inverters approximate a pure sine waveform.
Are designed to satisfy the efficiency requirements of most devices while being less expensive than pure sine waveform inverters.

Disadvantages of Modified Sine Wave Inverters

Power Surge

The major disadvantage when using the modified sine wave inverter is the fact 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 waver inverter can cause electronic devices to behave erratically because of power surges.

Waste of Power

The use and waste of power is another disadvantage. Any equipment which is used to convert power from direct current to alternating current loses power during the conversion process. This means that if the inverter is 80 percent efficient, 20 percent of the power is lost during the conversion process. The power is lost in the form of heat. This leads to the inverter not being able to convert power at optimal level. The inverter also requires some power to run it and as the size of the modified sine inverter increases, so does its inefficiency.


Advantages of Pure Sine Wave Inverters over Modified Sine Wave Inverters

1. Output voltage wave form is pure sine wave with very low harmonic distortion and clean power like utility-supplied electricity.
2. Inductive loads like microwave ovens and motors run faster, quieter and cooler.
3. Reduces audible and electrical noise in fans, fluorescent lights, audio amplifiers, TV, Game consoles, Fax, and answering machines.
4. Prevents crashes in computers, weird print out, and glitches and noise in monitors.

Reliably powers the following devices that will normally not work with modified sine wave inverters:

  • Laser printers, photocopiers, magneto-optical hard drives
  • Certain laptop computers (you should check with your manufacturer)
  • Some fluorescent lights with electronic ballasts
  • Power tools employing “solid state” power or variable speed control
  • Some battery chargers for cordless tools
  • Some new furnaces and pellet stoves with microprocessor control
  • Digital clocks with radios
  • Sewing machines with speed/microprocessor control
  • X-10 home automation system
  • Medical equipment such as oxygen concentrators

The Benefits of using a Pure Sine Wave Inverter

1. All equipment currently on the market is designed for use with sine waves.
2. Some appliances, particularly microwaves and variable speed motors, will not produce full output if they do not use sine wave power.
3. Other devices, particularly medical equipment may not function at all unless you use a pure sine wave inverter.
4. A TRUE Sine Wave produces a much higher equivalent wattage compared to a modified sine wave power inverter. It is somehow believed that the more you will be using this type of inverter, the greater the variety of electrical devices and appliances you will be powering.

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