Are Pure Sine Wave inverters really necessary?

Thread Starter

Lumenosity

Joined Mar 1, 2017
515
At another forum is a very interesting thread. A person who presents himself / herself as very knowledgeable in electronics stated that in approximately 95% of cases with modern electronics, Modified sine wave Inverters are all you need and that Pure Sine Wave inverters are mostly a gimmick and unnecessary.

Specifically this.......

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.
Since I don't know about this I'm wondering what the consensus among experts here would be?
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
515
True answer: depends.
That person is 95% correct.
Thanks Mr.Chips.

What's odd is that somehow I seem to manage to get nearly 100% of that 5% of things that "need' a PSW inverter.
I had nothing but trouble running my fridge on a MSW inverter. Maybe the newest ones are different?
I use an inverter in my vehicle and it seems everything I use on a MSW inverter just runs louder, hotter or not as good if it works at all. In other words, my personal real life experience seems to disagree with this.

Has there been a trend in consumer electronics to provide all the mechanisms necessary internally to provide clean power to their circuit boards and reduce dependence on "clean PSW" power from utilities? Appliances are being made better? I find that hard to believe. If anything it seems corners are being cut more than ever to produce things as cheaply as humanly possible. I'm really confused about all this.

Also, if that's the case, why does it matter if utilities supply such clean power?

Couldn't they save billions by just providing much cheaper MSW power? Is this to say that they are spending billions more annually just for 5% of devices? If so, it seems Green Energy could be unnecessary if all devices were simply made to utilize MSW power, allowing utilities to cut costs and only generate MSW AC, shifting the cost (and liabilities) of producing PSW AC to manufacturers.
 
Last edited:

nsaspook

Joined Aug 27, 2009
8,382
If there is a requirement for a quality inverter that I need to trust for power during a emergency I always buy Pure Sine Wave inverters. A big factor is not the quality or suitability of the power signal (but that is a important factor) it delivers to X equipment, it's the quality of inverter build. I've found that most Modified sine wave Inverters are rock-bottom, under built, over-rated pieces of electronic junk.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
515
If there is a requirement for a quality inverter that I need to trust for power during a emergency I always buy Pure Sine Wave inverters. A big factor is not the quality or suitability of the power signal (but that is a important factor) it delivers to X equipment, it's the quality of inverter build. I've found that most Modified sine wave Inverters are rock-bottom, under built, over-rated pieces of electronic junk.
Interesting.
But, they "could" build good quality MSW inverters if the market demanded it right?
 

nsaspook

Joined Aug 27, 2009
8,382
Interesting.
But, they "could" build good quality MSW inverters if the market demanded it right?
Sure, but the retail market for MSW is usually on the lowest possible cost end. If you need AC power to run a space heater resistance coil who cares about the waveform as long as the unit runs 7/24 but if you need good frequency control, accurate voltage regulation and low harmonic content for reactive AC driven devices, it should matter.
 
Last edited:

LowQCab

Joined Nov 6, 2012
517
There is no such thing as a "Perfect" Sine-Wave, except maybe on paper or in theory.
There will always be deviations.
How large those deviations are, and at what frequency those deviations occur
is what makes the difference.

A "Pure" Sine-Wave Inverter has very small, very high frequency, deviations,
which are quite often completely Filtered-Out of the Output-Voltage.

"Modified" Sine-wave inverters are very crude devices, with substantial
deviations from a Pure-Sine-Wave, and generally at much lower frequencies,
which are virtually impossible to Filter-Out of the Output-Voltage.

Certain types of equipment are not seriously affected by "Noise" on the Power-Supply,
but other types of equipment may not even function with heavy-noise,
or may over-heat, or suffer from any number of other weird reactions to noise.
.
.
.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
515
There is no such thing as a "Perfect" Sine-Wave, except maybe on paper or in theory.
There will always be deviations.
How large those deviations are, and at what frequency those deviations occur
is what makes the difference.

A "Pure" Sine-Wave Inverter has very small, very high frequency, deviations,
which are quite often completely Filtered-Out of the Output-Voltage.

"Modified" Sine-wave inverters are very crude devices, with substantial
deviations from a Pure-Sine-Wave, and generally at much lower frequencies,
which are virtually impossible to Filter-Out of the Output-Voltage.

Certain types of equipment are not seriously affected by "Noise" on the Power-Supply,
but other types of equipment may not even function with heavy-noise,
or may over-heat, or suffer from any number of other weird reactions to noise.
.
.
.
Thanks for that.
So far, I have two "experts" who say that 95% of the time your concerns (and mine) are baseless...in essence.
They may be correct. I still don't know why any items are made that need PSW power if all devices "could" be made to run happily on MSW which is much cheaper to produce so said.
 

Ian0

Joined Aug 7, 2020
2,193
If there is a requirement for a quality inverter that I need to trust for power during a emergency I always buy Pure Sine Wave inverters. A big factor is not the quality or suitability of the power signal (but that is a important factor) it delivers to X equipment, it's the quality of inverter build. I've found that most Modified sine wave Inverters are rock-bottom, under built, over-rated pieces of electronic junk.
Inverters for emergency power must have less than 5% distortion (EN 50171), unless it can be proven that they are compatible with the load. As no-one knows what the load might be, and no-one who sells a mains product needs to state that it will run on anything other than a sine-wave, it is impossible to prove.
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
515
Inverters for emergency power must have less than 5% distortion (EN 50171), unless it can be proven that they are compatible with the load. As no-one knows what the load might be, and no-one who sells a mains product needs to state that it will run on anything other than a sine-wave, it is impossible to prove.
If 95% of devices will run equally as well from a MSW inverter as they will a PSU, then why "must" they meet EN 50171?

Is it an outdated standard?
 

Ian0

Joined Aug 7, 2020
2,193
If 95% of devices will run equally as well from a MSW inverter as they will a PSU, then why "must" they meet EN 50171?

Is it an outdated standard?
Because emergency power must power everything that was previously connected to the mains before the mains failed.
95% of devices allegedly run equally well from a MSW inverter, but 0% of devices are required to run from a MSW inverter.
Imagine that the electricity supply to an operating theatre failed, and the lights continued to work but the anaesthetic equipment and heart rate monitors didn't.
Also, I bet you can't give me the standard for a "modified sine wave".
 

Thread Starter

Lumenosity

Joined Mar 1, 2017
515
Because emergency power must power everything that was previously connected to the mains before the mains failed.
95% of devices allegedly run equally well from a MSW inverter, but 0% of devices are required to run from a MSW inverter.
Imagine that the electricity supply to an operating theatre failed, and the lights continued to work but the anaesthetic equipment and heart rate monitors didn't.
Also, I bet you can't give me the standard for a "modified sine wave".
I'm not arguing with you.

I was told that very few devices require clean power. Specifically that 95% do not. I find that amazing.

My question in your case would be, "If manufacturers are responsible for implementing circuitry intheir devices to rectify power to meet the needs of those devices, why wouldn't hospitals (your example) be required to have devices in their facilities (along with backup generators) that would rectify incoming Ac power to meet their needs inside their facility? That would allow utilities to save billions annually by reducing the cost of producing AC power altogether. The hope being we would all realize those savings (probably not in reality)

Why not require those institutions that need that clean power to clean it up themselves and let those who don't use the dirty power?

My question revolves around my personal difficulty understanding (or believing what 2 experts have stated), which is that 95% of devices do not need PSW power, basically.
 

LowQCab

Joined Nov 6, 2012
517
Everything Commercial is designed to fit into a certain "Price-Range".
If everything was designed like the Engineers would prefer it,
then YOU couldn't afford to buy it.

An interesting short story ..........
The Dad of a friend of mine used to work as a Television Design Engineer.
( back in the Vacuum-Tube days )
He said, after the Engineering Team put their stamp of approval on a new design,
the new design went to the next department where individual parts would actually be
cut out of the Circuitry one by one, until the TV stopped working.
Then they would put the last part back in place,
and look for other components that could be removed.
Every part was removed that was not absolutely required for the TV to sorta-kinda-function.

This is still common practice today.
.
.
.
 

Ian0

Joined Aug 7, 2020
2,193
95% is an interesting statistic. I also read that 45% of all generated electricity is consumed by motors, and you can bet that whilst a few of them are run via variable frequency drives, but the vast majority are induction motors connected straight to the mains, just like the one in your fridge, that runs noisily and hot when running on a modified sinewave.

Sounds to me like a vast number of that 95% are sub-5W devices plugged into the wall, and that they are only using quite a small amount of the world's electricity.

"Also, I bet you can't give me the standard for a "modified sine wave"."
"I'm not arguing with you."
Apologies - Rhetorical question - if the world's manufacturers had to guarantee that their products would run off a modified sinewave, the first thing they'd need to know is precisely what constitutes a modified sinewave!
 

nsaspook

Joined Aug 27, 2009
8,382
I'm not arguing with you.

I was told that very few devices require clean power. Specifically that 95% do not. I find that amazing.

My question in your case would be, "If manufacturers are responsible for implementing circuitry intheir devices to rectify power to meet the needs of those devices, why wouldn't hospitals (your example) be required to have devices in their facilities (along with backup generators) that would rectify incoming Ac power to meet their needs inside their facility? That would allow utilities to save billions annually by reducing the cost of producing AC power altogether. The hope being we would all realize those savings (probably not in reality)

Why not require those institutions that need that clean power to clean it up themselves and let those who don't use the dirty power?

My question revolves around my personal difficulty understanding (or believing what 2 experts have stated), which is that 95% of devices do not need PSW power, basically.
The percentage is a meaningless number, IMO designed to confuse the issues because we have no idea what's in that group. The 95% could be most of the $1 wall-warts and light bulbs in the world with the 5% being everything else.
 

Ian0

Joined Aug 7, 2020
2,193
Everything Commercial is designed to fit into a certain "Price-Range".
If everything was designed like the Engineers would prefer it,
then YOU couldn't afford to buy it.

An interesting short story ..........
The Dad of a friend of mine used to work as a Television Design Engineer.
( back in the Vacuum-Tube days )
He said, after the Engineering Team put their stamp of approval on a new design,
the new design went to the next department where individual parts would actually be
cut out of the Circuitry one by one, until the TV stopped working.
Then they would put the last part back in place,
and look for other components that could be removed.
Every part was removed that was not absolutely required for the TV to sorta-kinda-function.

This is still common practice today.
.
.
.
My boss used to do that to my designs, but without the "put the last part back in place" stage. Then we'd put it into production, and have to retrofit that "last part" during testing.
 

Ian0

Joined Aug 7, 2020
2,193
An interesting comment about the design of inverters:
At the bottom end of the price range, most inverters have a DC-to-DC converter running at 50kHz or so, followed by either an H-bridge, which produces either the modified-sinewave by a simple switching process or the true sinewave via PWM. The true sinewave needs filtering before it gets to the mains socket, to remove the high frequency PWM. The only real difference is the cost of the filter.
At the other end of the price range - the professional products - the transformer operates at line frequency, and uses its leakage inductance as the filter, so there is no extra cost in making a pure sinewave. In fact, because of the high harmonic content of the modified sinewave, it works better with a pure sinewave, so there is little advantage in outputting a modified sinewave.
The drive circuit is more complicated, but that stuff is cheap. The magnetics, power devices and heatsinks are where the money is.
 

MisterBill2

Joined Jan 23, 2018
8,749
I run power tools off of the noisypoer from the non-sine-wave inverter and the work wellThat is a disk grinder, a skillsaw, and a hammer drill motor. And the vehicle battery never goes dead because the engine run and recharges it. True sine waves are needed for audio equipment and some radio equipment.
It is a case of having the correct tool for the job. A hammer is seldom the right tool when you need a screw driver.
 

crutschow

Joined Mar 14, 2008
27,194
why does it matter if utilities supply such clean power?

Couldn't they save billions by just providing much cheaper MSW power?
MSW power is generated by electronic converters.
Utilities don't generate the waveform with electronic circuits, they use AC generators, which can be readily designed to output a low distortion (pure) sinewave without any significant additional cost.

Induction motors don't like MSW power with significant distortion, since the distortion (higher frequency harmonics) generate high frequency currents in the windings that provide no power to the output shaft.
 
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