What kind of UPS do Europeans use? My modified sq wave UPS + PFC'ed load = CRASH !

| An example of power factor corrected PSU: |

Do you have any schematics or design theory?

| The passive PFC on a power supply like the one linked above is the same | type as the one in my ballast. Since computer power supplies in the US | typically don't have a PFC, we're fine, but how do Europeans get their | PFC equipped computers to get along with their UPS? I searched "PFC | UPS" on Google and looks like I'm not the first one to have issues with | a UPS interecting badly with a PFC power supply.

I would have thought that a proper power factor corrected load would be indistinguishable from a linear resistive load. Maybe what they are talking about is just the phase angle, rather than harmonics? Maybe this kind of PFC is actually making harmonics worse?

| My UPS shares the transformer between inverter operation and charging. | It's a steel core transformer with center tapped secondary. When | operating on battery, the center tap on secondary is tied to one of the | battery terminals and the MOSFETs switch the other terminals back and | forth between the two taps on the sides. A relatively common design.

And that's not producing any backfeed?

I don't know about that specific power supply, but this is the general schematic of a passive power factor correction that goes in the input stage of a switch mode power supply or a ballast:

Look at figure 2 on page 2.

This L-C type circuit is tuned to work with sine wave of specific frequency.

All ballast meant for commercial use have power factor correction of some sort so that it will get at least PF >0.95 most likely because there's some regulations mandating it.

Residential application ballast doesn't have any form of front end circuit to correct PFC and they don't have a problem with my UPS. Apparently the extremely high harmonic content modified squarewave doesn't play nicely with L-C circuit tuned to work with sinewave.

The inductors are actually quite large. Despite the weight, it's the preferred choice for many electronic ballasts, because it's the cheapest design and works quite well.

That's the goal, but there's still harmonics. Again the L-C circuit is designed to limit the current rise so that it doesn't abruptly rise while the voltage sweeps in sinewave. Since in modified squarewave, voltage goes from zero to full almost instantaneously, i'm sure the situation is very different.

This is what modified squarewave looks like:

though the sales likes to call that modified sinewave, it's not.

The only reason it's called modified is because there's a slight pause before polarity is reversed.

This might qualify as modified sinewave though:

Not sure, I haven't put the effort to reverse engineer the UPS any further.

Because a computer power supply is so resilient, then these plug-in UPSes don't normally affect the computer. However that modified sine wave is a threat to other less robust appliances such as small electric motors. UPS manufacturer quietly note that even a plug-in surge protector on the output of that UPS can cause serious problems when UPS is in battery backup mode. The fluorescent ballast as a load would only complicate the operation of that UPS in battery backup mode.

You have also demonstrated that UPS connects computer directly to AC mains when not in battery backup mode which is why problems only exist in battery backup mode.

PFC is not an issue. Different appliances will place different loads at different frequencies (harm> I have an APC UPS that puts out modified squarewave (the

You're missing the point entirely. I was not talking about potential damage to the computer.

An electronic fluorescent ballast has the same front end as a switch mode poewr supply. The front end is made of rectifier and smoothing capacitors.

P ower factor corrected ballasts and power supplies simply have an inductor and a capacitor upstream of the rectifier input.

Yes, the passive PFC is an issue with my UPS. Not because things smoke, but the reactor/capacitor PFC circuit adversely reacts with the UPS causing it to crash(power cuts out immediately) which defeats the purpose of having an UNinterruptable power supply.

I know for fact it is the PFC front end that's causing the problem. When I bypass the PFC by putting a rectifier and a capacitor before the ballast (which makes the passive PFC a spectator since inductance only responds to A/C), UPS doesn't crash. This is a good way to determine the cause, but it's not a practical real life solution.

My point apparently was not obvious. Because computers are so resilient, then these plug-in UPSes "do it on the cheap"; output dirty, crappy electricity when in battery backup mode. I was not talking about a UPS damaging computers. I demonstrated why plug-in UPSes output very dirty power - power that may be destructive to some small electric motors. Because computers are so resilient and would not be harmed by that "dirty" UPS electricity.

What is the frequency response of that PFC circuitry - if it really is a PFC circuit. Is circuit the EMI filter that is required by EU (and other) regulations? Then, does that filter impedance increase or decrease with higher frequency? These line interfaces vary in design so that only you can tell us what that circuit really is. But a line interface circuit must include a line filter. Does the line filter design cause lower impedance (short out) those higher frequency components? If so, then that is the answer of why a line filter (or PFC circuit) caused UPS problems.

A UPS with high THD (too much power in higher frequency harmonics) would see a short circuit in that filter.

Again, most plug-in UPSes are built as cheaply as possible. So cheap because computers are so resilient; are not adversely affected by poor quality UPS power when in battery backup mode. If you can even find one, try a UPS with a Total Harmonic Distortion of less than 5%. Good luck in that search. Most plug-in UPSes tend to be on the order of 20 to

30% THD which is why there is so much power in harmonics and why your ballast circuit (its line filter) would have problems with that UPS.

Part of the problem f> w_tom wrote:

Isn't it sad that the UPS that's giving me a headache is one of the smaller APC SMART UPS? This isn't supposed to be like the $29.99 junk.

I don't know the frequency response. The series reactor extends the current rise time of the typical rectified load and it is tuned to give a PF of >0.95 when used with a constant load on 60Hz 120V line.

The EU regulation now requires PFC on computer power supplies. EMI filter was most likely mandated long before that.

See the PDF file in my previous post. It shows you how the typical PFC is setup. I don't have any specific information on the actual components in ballast.

hmm mine says 28% total harmonics, 21% single harmonic.

Example UPS output is a modified sine wave. Output under light load is two 200 volt 'very sharp' square waves with a

270 volt spike between those square waves. That is called a 120 VAC modified sine wave. That would create hell with most everything but a computer.

Why do replacement batteries cost almost as much as the entire UPS? Plug-in UPSes for computers are made a cheaply as possible because computers are so resilient and because consumers so often 'wish' those UPSes do things they really cannot do. Look at what is called a modified since wave in the example UPS. Two 200 volt square waves. People have even claimed that could not be true because it said 'sine wave' on the box. Manufacturer did not lie. Manufacturer simply demonstrated propaganda. A square wave is nothing more than lots of different sine waves simultaneously. The only person who was lying was the consumer who wanted to believe something different.

Find, if you can, a UPS with low THD. Clearly you have the typically worst THD I have seen in UPSes.

It sounds like you may have a passive PFC circuit which is really little more than a filter. A filter that also provides EMI protection. There are many ways to meet PFC requirements

- both active and passive. Incidentally, I believe the EU has since weakened its PFC requirements.

The typical plug-in UPS is good for protecting data from blackout and extreme brownouts. It is why they are so cheap and why they are dangerous to small motors and power strip surge protectors. And yet still many will even insist that UPS also provides hardware protection to 'sensitive' computers. You have now seen the numbers AND have experienced what those numbers mean - "28% total harmonics,

21% s> Isn't it sad that the UPS that's giving me a headache is one

It's the same type waveform as a typical 12V-110V travel inverter.

Not on mine.

Battery is about 1/4 to 1/6 the retail price of the UPS.

Actually it's more like 150V. The peak is lower than the sinusoidal peak of 120V.

Which would be the sinewave Smart UPS. So going back original question. Do Europeans buy sinewave UPS just so it would be compatible with their PFC computer power supplies? They're VERY expensive.

APC advertises their Smart UPS as for Network Computers and Servers....

Let me explain something about sine wave ouput converters.

First the input to the chopping transistors is a DC. This is now chopped up and you have a square wave .

NOw to get a sine wave output, (Other than useing a bunch of choppers and makeing a stepped wave which costs even more) You must have an LC filter on the output . Generally this is a parrellel resonent filter that reduces higher order harmonics.

Now you have a square wave coming out of the chopper and a sine wave output. For this to be, there must be a series element of some kind to absorb the difference between the square wave output of the choper and the sine wave output.

Generally an inductor is used to perform this function, being relitively losseless. But the fact is that the Inductor to absorb the volt seconds and to carry the DC generally winds up being about half the size of the output transformer. There is no getting around this. The inductor or some series element must be there to act as a voltage absorber between the sine wave output and the square wave.

Now there is another way to acomplish this function. The Inductor can be put in series between the input voltage and the center tap of the output transformer so the voltage upon the switching transistors is a partial sine wave. There are some draw backs to this. The voltage on the transistors will now be higher.

But there is another advantage. The output transformer can now become part of the LC filter. But there is a problem with this. If the sine wave is to have less than about 5% harmonic distortion the current in the output side of the transformer must be about 5 times the load current or it must have a Q of about 5. But if the output transformer was not part of the tuned circuit, the ouput filter inductor would still have to carry about 5 times load current and have a Q of about 5. So there is little added weight with the much bigger output transformer.

Now to get the harmonic distortion down below about 3% you generally need a series LC fiter across the output. But in general this is quite small. The use of the inductor ahead of the transformer gives you a lot of advantages if you want short circuit protection. By using a tapped inductor, you can arrange to have 0 volts out at other than 0 pulse width. This reduces the pulse width range that the converter has to work over between full output voltage and 0 volts into a short circuit.

Such converters were built for the military by a company called Electrosolids some years ago.

For more information on these types of converters see my series on Magnetics and Converters.

In article , AC/DCdude17 writes

I run an APC SmartUPS 600 and a PC with a Fortron/Source power supply with passive PFC without any problems. Just a data point.

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Mike Toml>>Since computer power supplies in the US

Hello,

You have a nicer UPS than I do. I did some data digging on APC site and found that:

The your UPS has a SINEWAVE inverter.

Your APC SmartUPS 600VA:

$FILE/0600-9.pdf On page 38, it says "on battery waveshape: sinewave" Frequency tolerance on your unit is +/- 0.1 Hz

Your UPS is no longer made and APC actually recommends my UPS as a direct replacement (SmartUPS 620VA) (

) which is a seriously economized version. It doesn't have all the bells and whistle (i.e. sensitivity adjustment) and the output waveform is MODIFIED SQUAREWAVE!!! AAARGH!!!

Manual for SmartUPS 620VA

$FILE/D7041-1E.pdf "On battery waveshape: Stepped sinewave" This isn't one of the better stepped sinewave that kinda goes up and down like a stairway. It's a "modified squarewave" that goes from zero to full at once which I verified on my oscilloscope.

I think this model puts the SmartUPS name to shame. I personally feel this unit should have been put on BackUPS line.

I believe you having a sinewave and me having a modified squarewave unit is a good explanation for the discrepancy in our result.

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Mike Toml >> Since computer power supplies in the US typically don't have a PFC, >>we're fine, but how do Europeans get their PFC equipped computers to >>get along with their UPS? >

Hello,

You have a nicer UPS than I do. I did some data digging on APC site and found that:

Your UPS has a SINEWAVE inverter.

Your APC SmartUPS 600VA:

$FILE/0600-9.pdf On page 38, it says "on battery waveshape: sinewave" Frequency tolerance on your unit is ± 0.1 Hz

Your UPS is no longer made and APC actually recommends my UPS as a direct replacement (SmartUPS 620VA) (

) which is a seriously economized version. It doesn't have all the bells and whistle (i.e. sensitivity adjustment) and the output waveform is MODIFIED SQUAREWAVE!!! AAARGH!!!

Manual for SmartUPS 620VA

$FILE/D7041-1E.pdf "On battery waveshape: Stepped sinewave" This isn't one of the better stepped sinewave that kinda goes up and down like a stairway. It's a "modified squarewave" that goes from zero to full at once which I verified on my oscilloscope.

I think this model puts the SmartUPS name to shame. I personally feel this unit should have been put on BackUPS line.

I believe you having a sinewave and me having a modified squarewave unit is a good explanation for the discrepancy in our result.

In article , AC/DCdude17 writes

Thank you. Handy to know.

and thanks for that. Grabbed for future reference (I bought the unit secondhand, hence no manual, and replaced the batteries.)

Possibly. I don't have enough direct experience to comment.