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

Discussion in 'Electronic Basics' started by AC/DCdude17, Jul 8, 2004.

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  1. AC/DCdude17

    AC/DCdude17 Guest

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    I have an APC UPS that puts out modified squarewave (the marketing
    people calls it modified sinewave) when on battery. I connected a
    fluorescent fixture with an electronic ballast containing passive L-C
    power factor correction. The UPS crashed and shut down as soon as it
    switched over to battery. The UPS doesn't have issues with residential
    electronic ballast such as CFLs which doesn't have a PFC circuit. It
    must not be getting along with the PFC. UPS is rated at 600VA. Light
    only takes 100VA.

    Electronic ballasts have the identical rectififier+capacitor front end
    as switchmode power supplies used in computers. Like electronic
    ballasts, computer power supplies are available with PFC. They're rare
    in the US, but EU legislations mandated power factor corrected power
    supplies on new computers.

    An example of power factor corrected PSU:
    http://www.savastore.com/products/product.asp?catalog_name=Savastore&product_id=10262447&pid=44

    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.

    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.
     
  2. Guest

    | An example of power factor corrected PSU:
    | http://www.savastore.com/products/product.asp?catalog_name=Savastore&product_id=10262447&pid=44

    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?
     
  3. AC/DCdude17

    AC/DCdude17 Guest

    X-No-Archive: Yes

    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:

    http://www.irf.com/technical-info/designtp/temp004.pdf

    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:

    http://www.fords-mtm.com/electric images/waveforma.jpg
    even 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:
    http://www.wojack.net/Our Solar System/MODIFIED_SINE_WAVE.GIF


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

    w_tom Guest

    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 (harmonics)
    regardless of PFC circuits. That 'so called' sine wave output
    is really power at many frequencies (harmonics). No problem
    to computers. But a serious problem to small electric motors
    and some other loads such as your fluorescent lamp. UPS
    manufacturers don't like the public informed that a typical
    plug-in UPS outputs some of its dirtiest electricity when in
    battery backup mode. Such information tends to undermine
    myths that promote more UPS sales such as the resiliency of
    computers.
     
  5. AC/DCdude17

    AC/DCdude17 Guest

    X-No-Archive: Yes

    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.
     
  6. w_tom

    w_tom Guest

    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 finding that UPS - many manufacturers
    fear to inform consumers since many UPSes are purchased on
    mythical recommendations. Complete set of numerical
    specifications for UPSes are difficult to locate.
     
  7. AC/DCdude17

    AC/DCdude17 Guest

    X-No-Archive: Yes

    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.
     
  8. w_tom

    w_tom Guest

    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% single harmonic". This is how we learn by obtaining both
    the theory (specifications) and experimental evidence (your
    ballast connect to that UPS).
     
  9. AC/DCdude17

    AC/DCdude17 Guest

    X-No-Archive: Yes

    It's the same type waveform as a typical 12V-110V travel inverter.
    Not on mine.
    http://www.controlcable.com/details/item.asp?id=35511018|AP112|

    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....
     
  10. bushbadee

    bushbadee Guest

    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.
     
  11. 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.
     
  12. AC/DCdude17

    AC/DCdude17 Guest

    X-No-Archive: Yes


    Mike Tomlinson wrote:

    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:
    http://sturgeon.apcc.com/techref.nsf/partnum/990-0600A/$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) (
    http://www.apc.com/support/tech_refs.cfm ) 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

    http://sturgeon.apcc.com/techref.nsf/partnum/990-7041/$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.
     
  13. AC/DCdude17

    AC/DCdude17 Guest

    X-No-Archive: Yes


    Mike Tomlinson wrote:


    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:
    http://sturgeon.apcc.com/techref.nsf/partnum/990-0600A/$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) (
    http://www.apc.com/support/tech_refs.cfm ) 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

    http://sturgeon.apcc.com/techref.nsf/partnum/990-7041/$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.
     
  14. 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.
     
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