Pure Sine Wave vs Modified Inversion

[AnchorageGuy]

unbusted, if going the modified route we have had very good success with the ProMariner units. I think most manufacturers now offer both . The top end are Victron and Mastervolt. WG

[GeoPowers]

I went pure sine. Main reasons: not a lot of price difference (at least for the Magnums I had narrowed it down to), PSW are less prone to annoying humming through electronics than MSW, and wanted to avoid having to upgrade later if/when our usage changes.

[David M]

Its unfortunate the manufacturers use the misleading term "modified sine wave". It was never a sine wave to begin with. The basic waveform is actually DC current that cycles between negative and positive at 60 Hz. Additionally the corners of the wave are electronically lopped off to make it a little closer to a sine wave.

This is the actual shape from one modified square wave inverter as seen on an oscilloscope. If you know electronics, you know this is an absolute garbage wave form. I don't think one could honestly call it AC.


Explanation of the differences...


In my opinion a modified square wave is very dirty power and should be avoided if you have that option. The reason is that not all devices can run, or run at full power, when powered by a modified square wave. A modified square wave can also introduce noise into audio devices.

I used to have such an inverter onboard untill large true sinewave inverters became available. The old square wave inverter caused a few wall power converters to go up in smoke. And as you know, "Once you let the smoke out, there's no putting it back in to fix it."

[btrayfors]

Agree with David 100%.

Here are a couple of screen shots from an oscilloscope showing: (1) the "modified sine wave" from an older marine inverter/charger (Heart 1200W model); and (2) the mains power from my shop. These were taken minutes apart.





Comparing the Heart shot with David's example, you can see that the Heart's voltage rises very quickly to it's maximum, stays there briefly, then drops back to zero and below. The only thing which makes this "modified" from a square wave is the pulse width.

I used this Heart inverter/charger on my boat for over 10 years. It did a decent job with many 120VAC appliances and devices, including motor-driven tools, but there were some devices which just wouldn't work at all. I don't doubt that it also did some damage to certain devices which wasn't immediately visible.

Ultimately, I went with the Victron MultiPlus inverter/charger which is pure sine wave, providing current which looks exactly like shorepower (but better regulated!).

Bill

[s/v Jedi]

To the OP: Victron is the absolute top but if you just want a good inverter, I can recommend Sinergex. I have a couple of those and they are pure sine and very reliable... and not too expensive (not cheap either of course).
The 600W version I have was even sold by mastervolt (in their color and with their name on it... but it was the Sinergex inverter).

cheers,
Nick.