Pure Sine Wave vs. Modified Sine Wave

[Karl Welhart]

Ok, I am thinking about replacing my Xantrex Prosine 2.0 with a Magnum unit.  What is the difference between a pure sine wave unit and a modified sine wave unit.  

Do I really need a pure sine wave inverter?

[Bill Jourdain]

Delicate electroincs such as LED TV sets, computers, etc, perform much better with pure sine wave.

Here is a short article on this:

http://www.xantrex.com/documents/Tech-Doctor/Universal/Tech1-Universal.pdf

[David T. Richelderfer]

Having a degree in math I certainly understand the graphical, or mathematical, difference between pure and modified sine waves.  But not knowing anything about electricity, except that it hurts to get shocked, I don't know the functional difference.  Why is pure sine wave power more efficient?  Why is pure sine wave power easier on motors and other devices?  It's all a mystery to me.  Has it all to do with the "abruptness" of the power change, as evidenced by the modified sine wave... versus the "smoothness" of the power change, as evidenced by the pure sine wave... in the alternation of the power from high to low, and low to high?

[Dick Simonis]

Functionally, I've run MSW inverters for years.  First on our boats and more lately on our Beaver.  I've never had any problems except that you can sometimes notice things running a bit slower, or, like the microwave cooking a bit longer.  On the other hand, I have always avoided using high demand appliances on the inverter simply due to the huge amount of battery power it takes to make that happen.

When we got the new Magnum installed last week, we went PSW but I have yet to use it much so we'll see it it was worth it.  I suspect the PSW will work better but the MSW worked fine.

Regardless, be sure to shop around, there are some real good prices available.

[Edward Buker]

The issue is that all the 120V electrical devices that are made in the world assume that you will be powering them with a pure 60 cycle sine wave. You will not know if any given device or motor will tollerate a modified sine wave until you use it. Most devices handle it well, but you rely on the original circuit designer of the unit and whatever the circuit design approach was that they used and tolerances that they assumed. Either pure or modified sine wave will probably work, but pure sine wave will always work.

Later Ed

[Steve Huber]

Dave,
This might help explain why equipment with motors run much better with pure sine wave. Actually anything that relies on magnets or inductive coils will work better as they see a smooth voltage transition rather than the abrupt changes seen with a modified sine wave inverter output.
http://rimstar.org/renewnrg/sp_pure_true_modified_sine.htm
Steve

[David T. Richelderfer]

Thanks guys fo the explanations.  In the end, it seems pertinent to explain this pure versus modified as it relates to my golf swing.  When I stay with my pure swing - slower backswing, stopping without a loop at the top, then accelerate smoothly through impact with an inside to outside head movemnt - my scores are always better.  But, man o' man, when I use that modified swing, then be ready to pay out to the other guys.

[Dick Simonis]

Thanks guys fo the explanations.  In the end, it seems pertinent to explain this pure versus modified as it relates to my golf swing.  When I stay with my pure swing - slower backswing, stopping without a loop at the top, then accelerate smoothly through impact with an inside to outside head movemnt - my scores are always better.  But, man o' man, when I use that modified swing, then be ready to pay out to the other guys.

Interesting analogy.  Now that I have a PSW inverter my golf swing will also become pure....that is good news.

[Joel Weiss]

What was not mentioned in the preceding discussion is that many devices rectify (convert) AC current to DC either in external power bricks or internally. If you think about it, in global commerce a device that rectifies to DC can essentially be sold around the world with shape of the power plug often being the only thing that changes from country to country.

Such devices are more likely to be able to run off of a MSW inverter although this is not guaranteed. The reason that Samsung refrigerators have become so popular as residential retrofits in RVs is that Samsung has stated (in writing) that its products can operate with MSW inverters because the current is rectified before use.

If my Xantrex were to fail I would definitely replace it with a PSW inverter, but until then I don't find the MSW to be a serious disadvantage.

[John Maguire]

I might also point out that many VFD's or Variable Frequency Drives can have DC bused right in and they will output 60Hz TSW (many you can even adjust the sine wave in 2Hz increments)..they could also be put inline with more sensitive devices on the ac output of a MSW...again I don't believe anything is full proof but its a very real possiblity....I have purchased them on eBay for as little $40.00 for amperage capable of easily drving a TV at 120v.