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Questions about APC UPS units

Discussion in 'Laptops' started by Charlie Hoffpauir, Jan 4, 2009.

  1. I have two APC UPS units (BK 650 MC) that I used for backup on my
    computer until they "quit working", ie they failed to power the
    computer when the line power went out. When the first one failed, I
    just bought the second one since replacement batteries were so costly.

    But after a time when the second one failed similarly, I went to a
    higher power rated unit.

    Then I decided to try to recover one or both of the old units for
    powering other devces (we have a lot of power outages). so I bought a
    new battery and installed it, then found that the unit only supplied
    about 85v AC when the power went out. This made me question whether I
    had a problem other than a bad battery.

    So the questions are:

    1 Is there any adjustment that I can make to increase the output
    voltage when on battery backup?

    2 If not, is 85 VAC typical, and

    3 Will a low voltage harm devices that I have connected to the UPS?

    Typically, I have the units backing up my computer and a DirecTV
    Digital Video Recorder.
    Charlie Hoffpauir, Jan 4, 2009
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  2. Charlie Hoffpauir

    BillW50 Guest

    In Charlie Hoffpauir typed on Sun, 04 Jan 2009 10:48:56 -0600:
    What are you using to check the AC voltage? As UPS normally doesn't put out
    true sinewave output and the reading on a multimeter may not read it
    accurately. Plus a lot of devices won't even turn on if they only get 85VAC.
    But if it is true, those that will run may make up for the loss of voltage
    by drawing more current. Which can be a problem for some designs. I may
    check my Powmax UPS with a multimeter later just to see what mine reads. If
    I do, I'll post the results.

    2 Gateway MX6124 - Windows XP SP2
    3 Asus EEE PC 701G4 ~ 2GB RAM ~ 16GB-SDHC
    2 Asus EEE PC 702G8 ~ 1GB RAM ~ 16GB-SDHC
    Windows XP SP2 ~ Xandros Linux - Puppy - Ubuntu
    BillW50, Jan 4, 2009
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  3. Bill,

    Thanks for your comments.

    I used a cheap digital multimeter (several years old, but I think I
    paid about $15 for it)

    What should I use, and do I get a "better" reading if it (the UPS) is
    powering a small load, or if it has nothing plugged in. I think I
    have a very old analog VOM around here somewhere, if I find it (and it
    still works) I'll try measuring the output with it.
    Charlie Hoffpauir, Jan 4, 2009
  4. Charlie Hoffpauir

    BillW50 Guest

    In Charlie Hoffpauir typed on Sun, 04 Jan 2009 12:17:14 -0600:
    Well virtually all mutimeters takes an average and converts it to DC to read
    it. And for AC, it is adjusted to read AC @ 50-60 Hertz sinewave. UPS are
    not really sinewaves. So that could throw the meter reading off.

    I did go downstairs to grab a cheap Radio Shack pocket multimeter and
    unplugged my UPS from the power outlet (which kicks my UPS on and this
    laptop without a battery kept running) and my meter read 110VAC. So maybe
    you do have a problem going on there. :(

    2 Gateway MX6124 - Windows XP SP2
    3 Asus EEE PC 701G4 ~ 2GB RAM ~ 16GB-SDHC
    2 Asus EEE PC 702G8 ~ 1GB RAM ~ 16GB-SDHC
    Windows XP SP2 ~ Xandros Linux - Puppy - Ubuntu
    BillW50, Jan 4, 2009
  5. Charlie Hoffpauir

    westom1 Guest

    The multimeter is probably correct. However confirm those numbers
    with an incandescent bulb. Power that bulb with the UPS connected to
    AC utility power. Then watch that bulb intensity when UPS power plug
    is disconnected. If the UPS is outputting insufficient AC voltage in
    battery backup mode, then an incandescent bulb will significantly
    decrease intensity when that UPS switches to battery.
    westom1, Jan 4, 2009
  6. Charlie Hoffpauir

    BillW50 Guest

    In typed on Sun, 4 Jan 2009 14:27:00 -0800 (PST):
    I totally agree! And I was going to suggest this same thing. Although
    westom1 beat me to it. :)

    2 Gateway MX6124 - Windows XP SP2
    3 Asus EEE PC 701G4 ~ 2GB RAM ~ 16GB-SDHC
    2 Asus EEE PC 702G8 ~ 1GB RAM ~ 16GB-SDHC
    Windows XP SP2 ~ Xandros Linux - Puppy - Ubuntu
    BillW50, Jan 4, 2009
  7. OK.... I tried that, and the bulb definitely dims a bit. Not a "lot"
    but it definitely is "noticable". So does this mean that I shouldn't
    try the UPS with a computer load? Or in other words, do I risk
    damaging the computer when I unplug the line power from the UPS? BTW,
    I do have two of these UPS units, both with new batteries, but not
    batteries bought from APC. Their batteries were about the same price
    as the same rated battery available locally, but the shipping cost for
    a pair from them was about $40!. I guess it's possible that the
    battieries are defective, but the multimeter reads 12+ VDC after the
    battery is charged, and the charger disconnected.
    Charlie Hoffpauir, Jan 5, 2009
  8. Charlie Hoffpauir

    BillW50 Guest

    In Charlie Hoffpauir typed on Sun, 04 Jan 2009 20:45:44 -0600:
    Not good.
    This is very questionable. What I mean is most of the time you should be
    okay, but sometimes not. It depends on how it was engineered.
    Batteries sound just fine. Those UPS models doesn't sound good though.

    2 Gateway MX6124 - Windows XP SP2
    3 Asus EEE PC 701G4 ~ 2GB RAM ~ 16GB-SDHC
    2 Asus EEE PC 702G8 ~ 1GB RAM ~ 16GB-SDHC
    Windows XP SP2 ~ Xandros Linux - Puppy - Ubuntu
    BillW50, Jan 5, 2009
  9. Charlie Hoffpauir

    westom1 Guest

    Low voltage never damages any properly designed electronics. An
    industry standard even 35 years ago used this expression in voltage
    regions of that chart: "No Damage Region". Other standards discuss
    undervoltage only in terms of how long that voltage can be too low
    before a computer halts. Damage is not even an option. If low
    voltage caused damage, then power off also causes damage.

    All 120 VAC computers are required to operate OK even when voltage
    is only 90 volts. Most all my electronics designs routinely cut out
    at 85 volts. Another even discovered:
    Yes, it is routine to lower voltage on electronics - to even learn
    how low voltage can drop before electronics turns off. Power the
    computer from that UPS. Damage is not possible if the computer's
    supply meets so many standards including one from Intel.

    That light bulb should have dimmed to half intensity if your numbers
    are correct.

    Another test might string light bulbs on the UPS output to learn how
    many watts are actually too many. For example, a 650 watt UPS unable
    to power larger than 300 watts of lights implies half the UPS inverter
    has failed - would also explain that low voltage.

    Without a O'scope waveform, further definitive replies here are not

    Some have suggested one reason why a UPS in battery backup mode may
    fail. Because spikes output by UPSes are so large, then a power strip
    protector connected to that output may damage either the power strip
    or UPS inverter.

    Neither low voltage nor the very 'dirty' electricity output by a UPS
    in battery backup mode can harm any minimally acceptable computer.
    However we are only asking what has failed. Bottom line: that UPS
    obviously is hardware defective.
    westom1, Jan 5, 2009
  10. Charlie Hoffpauir

    M.I.5¾ Guest

    A cheap multimeter (either analogue or digital) will not correctly read the
    modified square wave output (often wrongly described as modified sine wave)
    of a UPS when it is running from batteries. Such a meter detects the
    absolute average value of the output but is scaled to read the RMS value
    *for a true sine wave only*. I would expect a US sourced UPS to read around
    85 volts on such a multimeter. The correct instrument to use is a true RMS
    indicating meter but low price meters are never of this type. The battery
    supplied RMS output voltage is seldom exactly the same as the line voltage
    and is often slightly less. Switch mode power supplies supplied by the UPS
    will rarely, if ever, complain.

    Note that any supplied equipment that contains a mains transformer will have
    variable results. It may work, it may not work. The transformer may
    overheat. It all depends.
    M.I.5¾, Jan 5, 2009
  11. Thanks for your very useful response.

    Additional comments inserted below....

    My guess is that is just about how much it dimmed. I'd compare the
    intensity change to that of switching a dual filament bulb from 100 w
    to 50 w. output.
    I'll definitely try this, but my guess at this time is that you have
    accurately diagnosed my problem.
    My "setup" is that I have the UPS powering a device that sits under
    the monitor, containing multiple outputs and switches to power the
    computer, monitor, and accessories like powered speakers. Obviously,
    that is essentially a protected power strip.... so I have probably
    damaged the UPS units.
    Since you mentioned that someone reported still powering a TV at 37
    VAC, I am going to try to use one of the UPS units to power my
    satellite modem (I'm on Hughesnet) and my local network switch. If the
    low voltage keeps them "on-line" they won't be a total loss for me. If
    not, I'll salvage the still usable batteries and dispose ot the two

    Again, thanks for all the suggestions.
    Charlie Hoffpauir, Jan 5, 2009
  12. Charlie Hoffpauir

    westom1 Guest

    37 volts was an anomaly. Only provided as an example that 120 VAC
    appliances can operate at much lower voltages. Most appliances work
    down to 90 volts, claim to operate only down to 95 or 100 volts, and
    typically operate as low as 85 volts.

    We typically use a variac to learn how low that appliance will
    work. That is acceptable for electronics. Small motor appliances
    often are not so forgiving and may even be damaged by low voltages -
    ie a 10+% voltage drop. Also small motors may be harmed by a UPS in
    battery backup mode because that modified sine wave. Electronics are
    more robust.

    Good luck with your experiments and resulting learning.
    westom1, Jan 5, 2009
  13. Yes, I'm understanding that if the "damaged" UPS units work with the
    electronics (modem and network switch) that it is probably OK to use
    them for those occasional line outages, but I won't attempt to use
    them for amything like a DirecTV video recorder, which might have the
    drive motor damaged if run for a time at a low voltage.
    Charlie Hoffpauir, Jan 6, 2009
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