Rich Grise wrote:
On Wed, 21 Dec 2005 14:09:10 -0500, Steve Spence wrote:


wrote:

George Ghio wrote:



Tell us why anyone would modify a sine wave.


It's called "engineering," George.

Nick


Really... Wouldn't they rather modify a square wave to approximate a
sine wave? What would be the point of modifying a sine wave, when a sine
wave (or close approximation) is the required result?


I hope you're not serious here.

They don't make a sine wave and modify it, they make a rectangular
wave and call it a "modified sine wave" because it passes enough tests
for harmonics and crap that it will run most stuff, and they can get
away with it. ;-)

Anybody wanna do an FFT of various duty-cycle waveforms, and give us real
THD information, and how that relates to power factor, and etc, and etc,
and etc?

The one inverter I've ever had my hands on the guts of made a waveform
like this:

---- ---- ----
| | | | | |
- - - - - -
| | | | | etc.
- ---- ----

And the regulator was just based on an ordinary rectifier - they didn't
care about RMS, or it was scaled to get "close enough".

But I do wonder, what does the harmonic content really do when you vary
the duty cycle?

Some years ago, in the USAF, I saw some pulses on a spectrum analyzer,
and they had some really pretty envelopes. :-)

Thanks,
Rich


That's my point. There are modified square wave inverters (marketed as
Modified Sine Wave), and there are "Sine Wave" inverters, which are
really MSW's with such fine steps that finicky equipment can't tell the
difference. There are a few folks on this group trying to justify the
"Modified Sine Wave" sales moniker but there is no logic to it. Folks
who should know better, but can't find it easy to "agree" with george
even for a moment. It even kills me to do it, but hey, he has a point
for once.


--
Steve Spence
Dir., Green Trust, http://www.green-trust.org
Contributing Editor, http://www.off-grid.net
http://www.rebelwolf.com/essn.html