Maker Pro
Maker Pro

"modified" sine wave inverters ?

Anyone have any idea just "how modified" the waveform is on these
inexpensive inverters. Certainly if you look for True Sine Wave
Inverters, there is a huge price difference.
Are MSW just square wave, maybe with a big capacitor to round off the
edges?
Regards,
Don
 
M

mike

Jan 1, 1970
0
Anyone have any idea just "how modified" the waveform is on these
inexpensive inverters. Certainly if you look for True Sine Wave
Inverters, there is a huge price difference.
Are MSW just square wave, maybe with a big capacitor to round off the
edges?
Regards,
Don

Think of a square wave with a flat spot (zero volts) at each transition.
The peak voltage is scaled to be approximately peak of sine wave.
Pulse width is adjsted to make the RMS value approximately the RMS
of a sine wave. This often works.
I have some equipment, TEK scope, that uses a series capacitor to limit
the input
based on a sine wave. If I try to run it from a MSW inverter, it blows
the fulse.
mike

--
Return address is VALID but some sites block emails
with links. Delete this sig when replying.
..
Wanted, PCMCIA SCSI Card for HP m820 CDRW.
FS 500MHz Tek DSOscilloscope TDS540 Make Offer
Wanted 12" LCD for Compaq Armada 7770MT.
Bunch of stuff For Sale and Wanted at the link below.
MAKE THE OBVIOUS CHANGES TO THE LINK
ht<removethis>tp://www.geocities.com/SiliconValley/Monitor/4710/
 
J

Joel Kolstad

Jan 1, 1970
0
Anyone have any idea just "how modified" the waveform is on these
inexpensive inverters. Certainly if you look for True Sine Wave
Inverters, there is a huge price difference.
Are MSW just square wave, maybe with a big capacitor to round off the
edges?

No, modified square wave is 120 degrees +V, 60 degrees 0V, 120 degrees -V, 60
degrees 0V, and repeat. The magnitude of the voltage is something like 177V,
I believe.

The benefit of this method over a a regular square wave is that it eliminates
(or, in practice, noticeably attenuates) the third harmonic relative to a
simple square wave. This produces less losses (and hence heating) in
transformer operated equipment.

---Joel Kolstad
 
A

Andy

Jan 1, 1970
0
Andy writes:

Another advantage is that a diode peak rectifier will
output the same DC peak as a sine wave, which is an
advantage for simple power supplies that are lightly loaded.

Also the DC heating value is the same as a sine wave,
into a resistive load, which is good for hot filaments and
things....

So the modified sine wave has the same peak and the
same DC heating value as a true sine wave. I think, a
very good idea.

The old style square wave 50/50 inverters can not
provide these simulataneously, and the power supplies of
some equipments did not work the same as with a true
sine wave...

Andy
 
P

Pooh Bear

Jan 1, 1970
0
Joel said:
No, modified square wave is 120 degrees +V, 60 degrees 0V, 120 degrees -V, 60
degrees 0V, and repeat. The magnitude of the voltage is something like 177V,
I believe.

Not in my country it wouldn't be, nor most of the world actually !

Graham
 
If you did the Fourier transform, you'd find that the three-level
waveform had no third harmonic content, and a much lower fifth harmonic
content than a simple square wave.
Higher harmonics are reduced progressively less with rising harmonic
number, but the amplitude of the highner harmonics in a square wave
already goes down in proportion to the harmonic number.

It is a neat trick. "Magic sine" pulse width modulation, as popularised
by Don Lancaster, has to work a lot harder but can get rid of more of
the lower harmonics.
 
J

Joel Kolstad

Jan 1, 1970
0
Pooh Bear said:
Not in my country it wouldn't be, nor most of the world actually !

Well, you know what they say... at least here in the US, we can find where the
cables are routed just by plugging in a space heater and feeling the walls.
:)
 
Anyone have any idea just "how modified" the waveform is on these
inexpensive inverters.

I have the "modified" inverter and a sine wave inverter, too.

"Modified sine wave" is a marketing term. The more accurate term, used
less frequently is "modified square wave". "Effective sine wave", while
not used, has meaning, and the "modified" type inverters have the same
peak to peak voltage and RMS voltage as the sine wave they are used to
replace. What they do *not* have is the same *spectrum*. They have
harmonics, while pure sine power has only the one spike in the
spectrum.

It helps to have both types and test all loads with each type to see if
the "modified" type induces unacceptable heating, or perhaps unsteady
operation in the connected device. Even a sine wave inverter will not
drive the most sensitive loads. But they will drive almost any load.

It makes sense to drive small loads, when possible with a modified type
inverter, as they are substantially more efficient with small loads.
Larger loads that can use either inverter are best driven with the
least expennsive inverter. My inverters are rated in idle current and
full load current. The pure sine wave inverter draws about four times
the idle current that the modified type draws. At the same larger load,
their consumption is almost the same, but you already mentioned the
price....

A true sine wave inverter would be like a class C amplifier, or even
class A. Very ineffienct, but high quality power. It's said this has
been done with high power car audio amps. I cannot confirm it.

I am experimenting with self-excited induction generators, a heavy,
medium efficiency source of extremely pure sine wave power, when
adapted to a particular load. Search "SEIG" for these
mechanical-to-electrical "converters".

Yours,

Doug Goncz
Replikon Research
Falls Church, VA 22044-0394
DGoncz at aol dot com email
 
I said:
Search "SEIG" for these
mechanical-to-electrical "converters".

Sorry. SEIG is an acronym and also the word associated with the Nazi
"Heil".

Search "self-excited induction generator OR generators" in Google,
Google Groups, Google Scholar, or your favorite search engine to get
the best results.

Doug
 
K

kell

Jan 1, 1970
0
Sorry. SEIG is an acronym and also the word associated with the Nazi
"Heil".

Search "self-excited induction generator OR generators" in Google,
Google Groups, Google Scholar, or your favorite search engine to get
the best results.

The common German word you're thinking of means "victory" and is
spelled Sieg, not Seig.
 
R

Rich Grise

Jan 1, 1970
0
Anyone have any idea just "how modified" the waveform is on these
inexpensive inverters. Certainly if you look for True Sine Wave
Inverters, there is a huge price difference.
Are MSW just square wave, maybe with a big capacitor to round off the
edges?

It's a "rectangular wave". Something like this:

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

I once had occasion to work with a line of brute-force inverters -
these guys were awesome, for the day - 2400VA in a box about the
size of "a breadbox" - now that I think about it, about the volume
of a "desktop" computer. (don't most people put them on the floor
these days?) A little thicker and squattier than the box that computers
come in these days - and one whole side of the box was extruded anodized
aluminum heatsink. The idiot that designed it had TWO - count 'em, TWO -
mongo transformers with their secondaries _IN SERIES_ so that during the
"dead spots" (the segments at zero volts in the diagram) the two
transformers were actually bucking each other (yes, I know the joke
potential there, for jokes, please prepend "OT:" thanks) and the output
was regulated by changing the relative phase of, essentially, two whole
inverters. They were awesome. There's something to be said about the
visceral feeling you get while watching ~100 amps coming off a bank of 24V
lead-acid batteries running several desk lamps, a bench grinder, and a
hand drill simultaneously, and no fires. ;-)

Of course, the product died an unceremonious death. Nobody
could afford the damn things, and they weighed close to 75 lbs.
(~35 kg) apiece.

But they _were_ fun to work on! They had about a dozen TO-3 transistors,
(per each!) and in the scrap pile I saw a few boards that had failed
catastrophically - all of those TO-3 transistors (in the example
"oops!" boards) had little craters in the case, where the die had
vaporized. =:-O

Cheers!
Rich
 
W

Winfield Hill

Jan 1, 1970
0
[email protected] wrote...
WTF? Sure, incredibly precise sequences of carefully chosen bits can
emulate a sinewave Class D, but if even one solder joint isn't right,
the whole thing won't work.

I'm talking about a *reliable* generator that won't fail when it takes
a bullet.

Solder joints? Reliability? Doug, Doug. We're talking about some
lookup tables in a microprocessor, not solder joints. Once those
are designed and typed in, they never change. No solder joints, or
unreliable connections would affect a magic sinewave, or other PWM
technique, preferentially over more simple approaches, once they're
embedded inside the microprocessor code. Bullets? Bring them on.
 
Winfield said:
[email protected] wrote...

Solder joints? Reliability? Doug, Doug. We're talking about some
lookup tables in a microprocessor, not solder joints. Once those
are designed and typed in, they never change. No solder joints, or
unreliable connections would affect a magic sinewave, or other PWM
technique, preferentially over more simple approaches, once they're
embedded inside the microprocessor code. Bullets? Bring them on.

No way. uP code depends on the existence of a uP, and it's hard to
harden such. If you pry a bullet out of a motor/generator, there's a
reasonable chance you can improvise a repair. If you pry a bullet of a
uP case, there's almost no chance of getting it to run again using a
Swiss Army knife, tape, and a bit of wire.

Sure, you can harden computers. Motor/generators are inherently hard to
begin with. It's a power source, fer heck's sake! It's got to be the
*last* thing to fail. Everything depends on the source. Live are at
stake.

Doug
 
Top