Conversion of a MODIFIED sine wave inverter into a PURE Sine Wave Inverter - PART 1

Hi Guys,

In this series of posts, I will guide you through the steps I have taken to modify and convert a Modified Sine Wave Inverter to a Pure Sine Wave Inverter.

Considering the cheap price of the modified sine wave inverters, one may wonder if it is possible to convert an a modified sine wave inverter into a pure sine wave inverter.
The answer is YES! (With a little bit of work, indeed).

The inverter I have used to carry out the conversion is a 3000W (5000W peak) Modified Sine Wave Inverter of brand ELIMINATOR (bought at Canadian Tire for around 200 $ CAD on sale).

Below is a picture of the box holding the beast.

The selling price of the modified sine wave inverters are typically much lower than the pure sine wave inverters. In fact the modified sine wave inverters are typically sold for half the price of the pure sine wave inverters.

However pure sine wave inverters do offer some very interesting advantages over the modified sine wave ones.

The sketch below depicts the difference in the wave form of a Modified Sine Wave versus a Pure Sine Wave.

Here are a few issues with modified sine wave inverters:

• Loads using dimmers will most likely not function correctly
• High harmonic content in current and voltage will provides interference to radios and TVs
• High harmonic content will make AC motors and compressors overhead (fridge, ventilation, fans, compressors, power tools, etc.)
• Although the RMS voltage may remain within an acceptable range depending on load drawn on inverter, the Peak voltage may vary considerably depending on current drawn from inverter and this may cause malfunction of devices using switching power supplies (some computers, TVs, etc.)
• High harmonic content will stress filtering components of devices which are using switching power supplies (computers, TV, cell phone chargers, etc.)

However, the pure sine wave inverter will be mimicking almost perfectly the grid voltage wave shape. Therefore, provided that adequate filtering is being provided, all issues stated above disappear.