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Observations on a UPS - follow up to a previous post

Discussion in 'Electronic Repair' started by Doc, Aug 13, 2007.

  1. Doc

    Doc Guest

    Recently I asked about suggestions regarding a UPS. I ended up
    getting an 875 VA 525 Watt "Geek Squad" model from Best Buy - yeah,
    yeah, everyone says Geek Squad stuff is overhyped junk, but at $69 on
    sale, the price seemed right.

    It seems to handle my 2 computers fine - a PIV 2.4 gig and a PIII 933
    mhz sharing a monitor. With both machines and the monitor on, the
    onboard readout shows them well below the unit's max capacity, drawing
    about .250 - .260 kw (which I assume translates to 250 - 260 watts) ,
    with an estimated run time of 9 minutes with both computers. More than
    enough to get me through short hit outages with both machines running.

    Interesting to note how much of a difference the monitor makes.
    Without the monitor - a 17" MAG CRT, the draw for both computers
    drops under 200 watts and the estimate run time for the 2 computers
    goes from 9 mins to 15mins. Over 20 mins with just one computer
    running but no monitor.

    Since this thing has a built-in watt usage meter, any reason I
    couldn't hook it up to say a refrigerator or TV to check how much
    wattage they're using?
     
  2. I would avoid hookihg it up to a motor driven appliance, as these generate
    powerful surges when turned off that can blow semiconductor components. The
    TV is fine.

    Bob Morein
    Dresher, PA
    (215) 646-4894
     
  3. Interesting to note how much of a difference the monitor makes.
    My experience -- at least where I live -- is that the power is off for a
    fraction of a second, or hours. There's rarely anything in-between.

    Than main advantage of an SPS -- again, in my area -- is protection against
    the tenth-of-a-second glitches that have little or no effect on anything
    else, but cause the computer to drop out. I've had as many as five or six in
    a day -- imagine having to restart the computer each time, not knowing if
    another might occur and slap you down again!

    If you constantly save your work, a hard shutdown won't usually hurt you.
    But it's always nice to have enough time -- during an extended power
    outage -- to shut down the machine "rationally".
     
  4. Arno Wagner

    Arno Wagner Guest

    The price is all wrong. Nobody can build a decent product with
    these specs for that price. You cannot even buy the components
    needed in decent quality for that price.
    And with the el-cheapo battery in there, that figure will be down to
    <1 minute in no time. And you would be well advised to test the
    claim. Software can be made to lie to you, you know.
    A) the watt-meter is likely very crappy, given that a good AC
    watt-meter costs more than this whole thing. They likely do a
    current average and then some magic correction. Can be 50% off
    or more even when used as intended. B) this device is
    not intended to support motors.

    Arno
     
  5. Doc

    Doc Guest


    Well, it was a sale price. I'm not sure that anything they sell there
    is "top of the line".

    I'm going by the readout on the front of the gizmo, though it does
    have software that gives many of the same readouts along with some
    other tasks.

    A test to find out how long it will actually run the computer sounds
    like a good idea.



    Maybe, but a lot of people seem to swear by the Kill-A-Watt meter,
    which can be had all day for around $25 online, eBay etc.
     
  6. James Sweet

    James Sweet Guest

    Yeah CRT monitors take a lot of juice, it's one of the reasons flat panels
    are so popular, though I still prefer a good CRT as it looks slightly better
    to my eyes.

    Sure you can plug in other items, though motorized appliances will probably
    not particularly like the modified sine wave those things put out.

    Your best bet for that is to buy a Kill A Watt or similar device, they're
    only about 25 bucks and will do so much more. You get accurate measurments
    of watts, volts, amps, volt-amps, power factor, and accumulated kwa and you
    can plug in anything you want.
     
  7. James Sweet

    James Sweet Guest

    That's a good way to kill the battery, these things tend to really punish
    batteries, after a few complete cycles they're often pretty well toast. You
    should be fine to try it for a bit, say 5 minutes without issues.


    EE friend of mine compared one to a $2500 power analyzer at work, found that
    the Kill A Watt performance is pretty much inline with the specs printed for
    it. It's not as good as the professional equipment, but it's really very
    impressive for what it is and certainly adequate for consumer use. The
    wonders of modern microelectronics, it's amazing what they can do with one
    inexpensive chip and a handfull of passive components. I still remember when
    a pocket calculator was $300, then a few years later $50 would buy one just
    as effective, and not long after that they were under $20 and those are all
    more capable than large machines costing many thousands just a few decades
    earlier.
     
  8. Arfa Daily

    Arfa Daily Guest

    But be aware that in general, these cheap 'power' meters are expecting
    'traditional' sine-draw loads. I have seen wildly inaccurate standby figures
    being given for equipment, by eco-campaigners that have been let loose with
    one. A lot of modern equipment that makes use of switch mode power supplies,
    handles standby mode by brief bursts of full draw operation. This can
    confuse a simple power calculating algorithm that's expecting continuous
    draw. Also, the draw by many cheapo switchers is very asymmetric and
    'dirty', and may also not produce a true reading.

    I wouldn't connect a UPS to a fridge. These things are notorious for pulling
    a short-term startup current of tens of amps, as they get the compressor
    turning over. The UPS would probably fall over before being able to supply
    this, and might, as someone else suggested, even sustain damage.

    Arfa
     
  9. Doc

    Doc Guest


    In general, I'd say that's my seat of the pants impression too, though
    not always. I also notice they'll often come in clusters.

    The transformer - if that's the correct term for it - big gray
    basically cylindrical unit on top of a power pole - near my house blew
    once. Powerful **BOOM** and a huge column of flame. Not sure what the
    fuel for the flame was, do they have oil in them? Also a bit
    disconcerting since anyone nearby surely would have been in jeopardy
    from flaming debris.

    Needless to say, power was out for a while on that one.
     
  10. Doc

    Doc Guest


    Seems I've heard an occasional complete drain-down and recharge will
    extend the life of a rechargeable battery, that being constantly
    partially discharged and recharged is what shortens their life. Not
    so? Does it depend what kind of rechargeable it is?
     

  11. It does depend on the battery. Early Lithium-Ion batteries benefitted from
    the occassional full discharge, and Nickel-Metal Hydride batteries may
    benefit from it. Lead-Acid batteries (like is in your car) have major issues
    if they are completely drained, these are also the common battery in cheap,
    well, just about everything. Newer Lithium-Ion batteries and Nickel-Metal
    Hydride batteries have the controls in place so they don't benefit from a
    complete drain. The Lithium-Polymer batteries that are beginning to appear
    in some places do not benefit from complete drains, nor do they have
    problems with overcharging, and now that they've gotten the self-ignition
    problems eliminated look to replace just about everything but lead-acid.

    So know your batteries, and you know the necessary behaviors, but really the
    only problem ones are Lithium (non-rechargable) and Lead-Acid (damaged by
    full drain).
    Joe
     
  12. Arno Wagner

    Arno Wagner Guest

    Hmm. Interesting. I trust he did this right and tested non-ohmic
    loads such as a PC PSU as well?

    Arno
     
  13. Seems I've heard an occasional complete drain-down and recharge
    You're thinking of nickel-cadmium batteries. The lead-acid batteries used in
    these power supplies can be crippled or destroyed by a "full" discharge. Try
    to avoid it.
     
  14. Arno Wagner

    Arno Wagner Guest

    Ugh. Putting them up for each individual hous is a very, very
    historic way to do it.
    Yes, for cooling. If it was an old transformer, you might have
    giotten a nice load of Dioxins for free there...
    The right way to do this is to use bigger transformesr for 10-100 houese
    and to bury 3-phase AC lines. A lot more expensive, but pays off
    in the long run, since you have less problems. And all these ugly
    poles and transformers will vanish.
    I can believe that.

    Arno
     
  15. Lead-acid batteries (like is [sic!] in your car) have major issues
    The _only_ consumer products I've owned that used lead-acid batteries were
    an early Sony Discman, and two APC SPSs. They are not common in consumer
    products. They provide relatively high capacity at a low cost (which is why
    they're used in SPSs and UPSs), but they are too-easily damaged by a full
    discarge. I accidentally ruined a $45 batter for the Sony D-T10.
     
  16. My experience -- at least where I live -- is that the power is off for a
    Yes. The glitches are rarely isolated events.

    Around my area, wind storms often cause sustained outages in areas where the
    lines are above ground.
     
  17. David

    David Guest

    I have a "Kill-A-Watt" and it appears to display true RMS
    for voltage and current readings. The voltage reading for a
    modified sine wave from a standard UPS displays the actual
    RMS voltage. I do not know what crest factor it can handle
    but displays power factors of considerably less than unity
    for most consumer electronics with DC rectifiers off of the
    line voltage. It is a very nice unit for the price.

    David
     
  18. Arfa Daily

    Arfa Daily Guest

    But that's my point. You can't have a 'true' sine-based RMS figure for power
    consumers that draw a pulsed current. Just because it is a sine wave that's
    *available*, it doesn't mean that the load will draw anything like a
    sinusoidal current, from it. The only items that will are those that are
    totally 'passive' in nature, such as light bulbs. Even power supplies that
    are transformer based, are likely to draw current in pulses from the
    available sinusoidal supply, and switch mode power supplies, on which most
    modern consumer electronics are based, most certainly won't draw a
    sinusoidal current from the supply.

    Arfa
     
  19. Scott Dorsey

    Scott Dorsey Guest

    It does not extend the life. Back in the seventies when NiCd packs had
    memory effect, folks were recommending deep discharge. But today, you
    are more likely to wreck a NiCd pack by reverse-charging a cell that way.

    The cheap UPSes use gel-cells, which are gelled-electrolyte lead-acid
    batteries. They are better at surviving deep discharge than NiCd packs,
    but they still don't like it. Consequently, most equipment that uses
    them will shut off when the battery voltage drops too low, to prevent
    damage. Electronics are cheaper than batteries. Bigger UPS units use
    liquid-electrolyte cells so you can check the battery condition with a
    hydrometer periodically, and they also have a pulsed charging system that
    prevents sulfates from building up on the plates. The Wal-Mart cheapies
    probably do not.
    --scott
     
  20. David

    David Guest

    Arfa,
    I know that the current draw on these things is anything but
    sinusoidal. My point was that the "Kill-A-Watt" seems to
    actually compute the RMS value for that complex current
    waveform as well as non-sinusoidal voltage waveforms.

    David
     
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