What REALLY requires a pure sine inverter?

rin67630

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Pure sine inverters are expensive, but for which usage are they REALLY required?

Some will say: for powering sensitive electronics...
Did you really consider what mainly happens in >95% of today's electronics?
The AC input signal is rectified to DC before going to a DC-DC converter.
So it makes exactly NO difference if they get a pure sine or a modified sine.

Pure sine inverters are not only more expensive, they have a much higher quiescent current (no load loss) and a lower efficiency.

For which usages did you really experience that a pure sine inverter is absolutely required?
 

rin67630

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One type of device that really do not like modified sine inverters are the 433MHz remote radio controlled plugs.
Not because of the interference, but because they have a capacitive voltage dropper. which will overload on getting square input.
 

wholybee

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It really depends on the construction of the power supply. Active PFC power supplies which are becoming common are particularly problematic. If I plug my laptop power supply into a modified sine wave inverter, it works, but makes a loud high pitched noise, and quickly gets very hot. I have not run it except for a minute or two, but I expect it would quickly fail. My old Mac computer did not work at all with modified sine wave.
 

Ampster

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Why bother with anything other than sinewave? If one wants to save money eliminate AC and go with DC. Edison wasn't completly wrong about DC?
 

Lt.Dan

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I dont know a whole lot, but I know somehow my parents have burned out a half-dozen coffee makers using their Magnum Modified Sine inverter in their motorhome.

Now, I can't prove the inverter caused the damage, but if it looks like a duck and quacks like a duck...
 

Boondock Saint

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Some will say: for powering sensitive electronics... YES I 100% SAY THAT
Did you really consider what mainly happens in >95% of today's electronics? YES I'VE SPENT MORE THAN 40 YEARS ON IT
The AC input signal is rectified to DC before going to a DC-DC converter.
So it makes exactly NO difference if they get a pure sine or a modified sine.
Your statement is an over-simplification. When you rectify pure AC you get a DC pulse that is almost contiguous and the use of capacitors help to mitigate the pulsing of the voltage and current at the frequency expected without clipping, jitter, higher total harmonic distortion and blank-outs. (Blanking is a dead time between the rise and fall of two consecutive wave forms where there is no rise, no fall, just nothing. You can still have 60hz with blanking, but you'll still get straight line dead time.)

A modified wave inverter uses less post processing from the digital signal creating the "wave form" and therefore draws less power at idle, and runs cooler, seemingly more efficient. It's cheaper to mass produce. However it most often has the high total harmonic distortion, clipping, jitter and especially blanking between the waves forms.

A pure sine wave inverter uses more power at idle and much more post processing of the digital pulses in order to deliver the smooth and clean AC wave form.

Circuit designers use calculations based off of a pure sine wave in the rectification and filtering in a power supply. Assuming the 120v or 240v line voltages are clean and purely sinusoidal the psu are specked around the minimum parts and space to provide the various voltages required to operate the TV, VCR, DVR, laptop etc. There is no need to employ additional rectification, filtering, ground plane and capacitance etc. Often there is more than one output voltage of the psu in a device, there may be several. A typical PC psu uses 3.3v, 5v with higher current and 12v. Is anyone willing to fry their PC or HAM equipment in order to save money on a chintzy inverter?

Which is better quality - a class D amplifier or a class A amplifier? Class A is less efficient and runs hotter by design in order to produce the cleaner sound with much lower THD.

The effects passed on by modified wave form inverters can cause noise, digital interference and additional heat in electronic devices.

Board design is more complicated than your trip to Radio Shack to buy a simple rectifier in your overly simple statement.
 

Primal1

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It so happens today is my first day running a PSW inverter in my off grid shop and home. I replaced a Krieger 1100w MSW with a Victron 1000w PSW.

First thing we noticed was the dorm fridge was quieter and the back was warm to the touch. When powered. by the MSW the back of the refrigerator was always too hot to touch.

The bench top sander and dremel were snappier and more responsive, my wife noted her drill seemed smoother. All the tools ran MUCH cooler.

The laptop usally hums from the power brick and it becomes quite hot, well, today there was no noise from the power block and it was barely warm.

Just what we noticed after 2 years of the MSW daily use vs today on a PSW.
 

rin67630

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Why bother with anything other than sinewave? If one wants to save money eliminate AC and go with DC. Edison wasn't completly wrong about DC?
It is not about money but -read me again- efficiency and quiescent current.
 

rin67630

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When you rectify pure AC you get a DC pulse that is almost contiguous and the use of capacitors help to mitigate the pulsing of the voltage and current at the frequency expected without clipping, jitter, higher total harmonic distortion and blank-outs...
ROTFL!
When you rectify a pure sine AC Signal, followed by capacitors, you get tremendous current pulses having nothing common with a sine again. It clips all the time on the peak of the sine waves blanking out in between..
1620793299572.pngThe higher the smoothing capacitors, the bigger and shorter the current pulses.
Tell me about harmonic distortion and jitter...
ROTFL.
Often there is more than one output voltage of the psu in a device, there may be several. A typical PC psu uses 3.3v, 5v with higher current and 12v.
Even more: every current CPU runs on different -variable- voltages ranking from 1.1V to 3.3V and a few outputs are 5V. 12V is a relic of the 80's you won't find it any more.
... and how do you believe these various voltages are realized?
Do you think there is an old transformer with different voltage outputs like at Edisons' time?
🤣
The computer PSU has a DC rectifier, followed by a main isolated high frequency DC-DC converter, followed by separate buck converters, one for each voltage. The CPU has its own programmable DC-DC converter.
So once the primary input voltage is rectified, everything behind is 100% the same.
 
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rin67630

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eliminate AC and go with DC.
That's very true.
Most contemporary PSUs will work better if fed with DC, since they will get already rectified current.
There is only one BIG caveat: Switching >100V DC is not trivial, you get tremendous sparks.
AC or modified sine has 0V times in between that erases the spark.
 

rin67630

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I dont know a whole lot, but I know somehow my parents have burned out a half-dozen coffee makers using their Magnum Modified Sine inverter in their motorhome.
That is well possible on coffee makers with electronic timers (fed by a capacitive voltage dropper cf. my post #2).
It really depends on the construction of the power supply. Active PFC power supplies which are becoming common are particularly problematic.
Active power supplies which are now quasi 100 of all PSUs are particularly well suited to be fed with modified sine.
 

Bud Martin

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Did you test the Power supply with Active PFC fed by modified sine wave to see what the result is? Does it still maintain PFC of close to 1?
 

rin67630

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Did you test the Power supply with Active PFC fed by modified sine wave to see what the result is? Does it still maintain PFC of close to 1?
Of course! It it more than happy with modified sine wave.
I forward the question to wholybee
If I plug my laptop power supply into a modified sine wave inverter, it works, but makes a loud high pitched noise, and quickly gets very hot. I have not run it except for a minute or two, but I expect it would quickly fail. My old Mac computer did not work at all with modified sine wave.
Did you REALLY do that or do you just BELIEVE it would get hot?
 

rin67630

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Additional remark:
Also asynchronous motors with a capacitor to build up the 90° phase do not run well on mod sine.
 

MurphyGuy

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Modified sine inverters are very hard on electronics, even if they don't damage them, they are likely shortening the life expectancy of any device connected to them.

Instead of asking what needs a true sine inverter, a better question is "what is modified sine good for?", and the answer to that is pretty simple.. Resistive loads do well.

Old fashioned incandescent light bulbs, toasters and other heating devices.. all run well with modified sine inverters. Very small motors like what you find in a wood stove fan, desktop fan, fish tank pumps, etc, also seem to do fine on modified sine.

Everything else = not so much.

Almost everything will run on modified sine, but those items won't be happy.
 

Bud Martin

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Of course! It it more than happy with modified sine wave.
I forward the question to wholybee

Did you REALLY do that or do you just BELIEVE it would get hot?
So per your test, it still maintains PFC of close to 1?
 

rin67630

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Modified sine inverters are very hard on electronics, even if they don't damage them, they are likely shortening the life expectancy of any device connected to them.
Do you just BELIEVE that or have you got a concrete experience?
Everything that internally directly rectify AC to DC before converting to required voltages (almost everything today) runs well (better) with modified sine.
Old stuff with traditional transformers not that well.
 

Bud Martin

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There is nothing like a PFC with a rectifying-smoothing power supply. You get current pulses, not a nice current sine with a defined Phi.
What do you mean by "There is nothing like a PFC "? The active PFC also boost the DC output Voltage. That topology used in many power supplies these day, I.E. TV and PC power supplies.
But then again, are you still getting PFC of close to 1 or not since you made the test?
Here is the example of the PFC topology:
 
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