UPS output waveform

'Negativity' is no different than 'positivity' when discussing numerical realities. Either it has a defined number / definition - or it is subjective 'mumbo jumbo'. 'Modified sine wave' is a marketing term in color glossies. Those who deal unemotionally with reality instead use numeric specifications. Nothing emotional about that reality. Irrelevant is what color glossies say. If the manufacturer does not make that claim in numeric specs, then he is not liable when a function is missing.

Most important number to this discussion is THD. High THD percentages create the buzzing that James Sweet's test would detect. High THD is why some so called 'modified sine wave' outputs can be harmful to electric motors. Will all 'modified sine wave' outputs be harmful? Without numbers, then no one can say with certainty.

So you tell me. What THD constitutes a sine wave and what THD constitutes a 'modified' sine wave? This same marketing game is played even with bread. Whereas 'whole wheat bread' must meet a government standard; 'wheat bread' can be white bread colored by molasses.

'Modified s> Boy, I'm detecting a lot of negativity there ! I thought that most of the

Excessive loads (ie laser printer) may be harmful to a lesser designed UPSes. Repeated large loads may degrade UPS batteries that typically have a woefully short life expectancy. Just some reasons why a laser printer should not be powered by a computer grade UPS. Another reason to not power the laser printer would be a modified sine wave output.

James Sweet demonstrated the problem when he posted:

Why does the transformer buzz? Harmonics - higher frequencies - cause buzzing, heating, and other adverse effects to electro-magnetic devices such as transformers and motors. Computer grade UPS means an electric output so dirty as to only be for devices more robust - less affected by those harmonics - such as computers. 'Dirty' electricity from some UPSes may be harmful to small electric motors and to power strip protectors; but is perfectly acceptable for more robust appliances such as computers.

Harmonics from a 'modified sine wave' can be harmful to electric motors in some laser printers. Just another reason why a laser printer should not be powered by a UPS when in battery backup mode.

Does that output > This doesn't have anything to do with the type of output coming from

Listen, friend. I don't have a problem with the validity of anything you say here, just the context. Of course the numbers are important *if* you want to do a statistical analysis of the waveform, or to start doing valid comparisons between degrees of pseudo sine wave, and the real thing.

In the case of this thread however, the OP asked a *simple* question that required only a *simple* answer, which is what he had been getting up until your first post.

In order to describe what a saw is, there is no need to start going into teeth per inch figures and tooth set angles. To describe what a car is, there's no need to start discussing spark plug gaps and valve clearances, that's all I'm saying, and that you seem to be going to a great deal of effort to completely miss this point.

Arfa

(snip)

One last entry into this thread.

The modified sine wave tries to accomplish two things by using a three state output. They want both the RMS voltage correct and the peak voltage correct. Since the peak for a 120 V AC sine wave is 120 x sgrt(2) = ~169 V they output pulses of that peak voltage with a width appropriate to generating a RMS value of 120 V. It looks more like a series of positive and negative pulses rather than a square wave. The waveform has only three states. 0V,

+169V, and -169V. Intermediate steps are rarely used. If a pure square wave was used, you can not have the peak and RMS values simultaneously correct.

Signing off, David

One more here. You don't need digital to create a modified sine wave. One way, is to create a 60 Hz square wave, then filter it. depending on the filtration, you get various looking sine wave types. It does require getting into the linear region creating heat in the Mosfets. It may also be possible to use ppassive filtration from the Mosfet switching, increasing efficiency.

greg

You really need an oscilloscope to see what the waveform is from your unit.

The good quality UPS's have a sinewave, that is very fine stepped. The very high end UPS's which are very costly have a nearly distortion free sinewave. If you want to pay out the dollars, you can have a UPS with less than 1% distortion.

The low end converters and UPS's have what they call a modified sine wave. Their waveform is about 3 steps in each side of the cycle. If you use a device that uses a transformer on it, the transformer may make a buzzing noise, and possible run a bit on the hot side. This type of low end device is good to run device that uses a switching power supply, or to run some lighting.

Very good article about power converters:

Waveform to show what a low end modified sinewave looks like compared to a fine stepped sinewave:

High end modified sinewave compared to a very good quality sinewave:

Jerry G. ======

is

you get

filtration from the

There are some pretty beefy mosfets around now so generating a half decent sine wave should be a doddle. I would use a microcontroller and an d/a convert driving a power amplifier stage into mosfet outputs. parallelling the mosfets will allow plenty of power output.

Marra wrote in news: snipped-for-privacy@e65g2000hsc.googlegroups.com:

Efficiency would be more important than fidelity.

"How long will the battery will drive a particular load?" would be the first question I would want answered.

The 'particular load' would determine how good the sine wave would need to be.

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Review the first Arfa Daily post:

IOW he looked on a scope, saw one output describes as a 'modified sine wave', then assumed all 'modified sine waves' are same. Arfa Daily failed to even grasp the 'whole wheat bread' example.

Modified sine wave can be most anything as long as there is a sine wave inside that waveform. Even this UPS that is two 200 volts square waves (no intermediate steps) is listed by specifications as a 'modified sine wave'.

So what is the output of that UPS? With only the phrase "modified sine wave", then no one knows. As James Sweet noted, the problem is not making a sine wave. The problem is amplifying it. Using filters to convert a square wave into a sine wave (at that frequency and amperage) would be even more expensive. That cost also should have been obvious to that poster.

Since computers are so robust, then most UPSes simply output 'dirtiest' electricity when in battery backup mode. Dirtier means it may even harm small electric motors. Without numerical specs from the UPS - such as THD - then no one can answer with certainty. Worse is the quoted post from Arfa Daily that is misleading. Then is followed by his emotional outburst - and no numbers.

Power on surge current from a laser printer is only one of many reasons why UPS manufacturers quietly recommend no laser printers and no power strip protectors on their output. This UPS that claims to be a 'modified sine wave' is two 200 volt square waves (no intermediate step) with a spike of up to 270 volts between those square waves. This 'modified sine wave' would probably create noise and heating as described by James Sweet's large transformer experiment. It may also be harmful to some small electric motors. It is called a computer grade power UPS because it is intended for devices far more robust - such as computers.

'Modified sine wave' is a subjective description for color glossies

- for the technically naive. The phrase provides little useful information. Answers based in reality start with numbers from manufacturer's specifications.

What UPS outputs sine waves sufficient to power a laser printer? How many $thousands did it cost?

You can slag me off all you like - although I would point out that I was perfectly civil to you.

You are still missing the point though. I said then, and I still say now, that I am not disputing anything you say. I was just trying to keep it simple. Of course the term "modified sine wave" is just manufacturers' glossy fodder, but what would you have them call it instead ? " Dirty Crap Bipolar Output " perhaps ? " Harmonic-y Garbage that Computers Don't Mind " maybe ?

They have come up with a phrase which is fairly innoccuous, and neither particularly helpful nor particularly misleading in its descriptive nature. It's meaning is pretty much 'accepted' in that it means that the device has an output which is bipolar, and is constructed from a small number of voltage steps - maybe as few as one per 'half cycle', but often two or even three steps. An appreciation of the numbers is not required to understand that concept. If you are going to start speccing one for a particular job, then the numbers might become important, but in general, even then, you could probably rely on what the manufacturers said it was suitable for powering.

So rather than wasting your energy having a pop at me, I suggest that your time might be better spent getting your own issues under control. " Emotional outburst " ? We have a phrase here that goes " Pot calls the kettle black ... " Rather apt in your case, I would venture ? End.

Arfa

In article , Arfa Daily writes

That's usual for w_tom, as will be confirmed if you do an advanced google groups search on w snipped-for-privacy@usa.net. He's only interested in furthering his own agenda, and any attempts to counteract his nonsense result in personal attacks, hysterics and outright lies.

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