Inverted Thinking

Many boaters ask what the technical difference is between the more expensive Pure Sine Wave inverters and the basic Modified or Quasi Sine Wave inverters.

Of course, many know that a lot of the fussier mains powered domestic equipment on boats needs pure sine wave and won't run properly on MSW/QSW inverters.

However, few know why...

These are the waveforms that I captured from my two inverters.

This one is the output from the Mastervolt pure sine wave inverter on Willawaw:

This one is the output from a Maplins cheapy modified sine wave inverter that I use in the car sometimes:

Even without any electronics expertise, you can see that they are very different and the distorted (almost squared) waveform of the MSW inverter is a compromise between a reduced technical complexity, which allows it to meet the price target and its ability to supply many, although not all, mains appliances.

The pure sine wave from the Mastervolt is an emulation of the mains that you get from your household socket. It is achieved with a lot more circuitry, which results in the increased cost.

Most devices with motors or microprocessors, digital clocks, etc struggle with the outputs of MSW/QSW inverters.

As is usual with electronics, you get what you pay for.

If you don't want to spend all that money on a pure sine wave inverter, then the answer is to run as many appliances as possible from 12 or 24VDC and then just use a small Maplins type MSW inverter to charge your phone, camera, etc.