Pure Sine Wave UPSes for New Dell PCs

Discussion in 'Dell' started by Daddy, Apr 8, 2010.

  1. Daddy

    Daddy Guest

    I had to give myself a basic education on alternating current, output
    waveforms and active PFC power supplies just to be able to ask this

    It all started because I heard that new Dell PCs need a new kind of UPS
    (uninterruptible power supply.)

    It's a fact: To comply with regulations, Dell now includes something
    called an active-PFC power supply with their PCs. I also understand that
    users and power companies benefit from PFC, as does the environment.

    The problem is, active PFC power supplies supposedly need current with a
    pure sine wave output - and a Dell technical rep told me that all new
    Dell computers need this - but virtually all UPSes for home use have a
    stepped approximation of a sine wave.

    Has anybody priced a UPS with pure sine wave output? Those buggers are

    On the other hand, according to APC: Starting in mid-2008, all APC
    Back-UPS (home and small office) products were revised to better handle
    load requirements for PFC devices...allowing the majority of Back-UPS
    being manufactured now to handle most (not all) PFC loads within their
    wattage range much better than older units. Their output is still
    step-approximated, however, and APC still finds the occasional PFC
    device that they have trouble with.

    Here's where I throw up my hands. Do I really need to pay an
    arm-and-a-leg for a pure sine UPS, or is most any properly sized UPS
    'good enough'?

    Daddy, Apr 8, 2010
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  2. Daddy

    Tom Lake Guest

    Not good enough. For the XPS 435T/9000, at least, it absolutely won't
    work with a stepped approximation. You really do need a true sine wave.

    Tom Lake
    Tom Lake, Apr 8, 2010
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  3. Daddy

    Daddy Guest

    In fact, I just finished a 'chat' with a tech from APC. They recommend a
    pure sine wave UPS for the Studio XPS 9000, and I think my 8100 is
    similar enough for the same recommendation.

    Even APC's least expensive sine wave UPS (from their Smart UPS line) is
    more than a third of what I paid for my PC in the first place! And
    although I haven't looked at other makers, I can't imagine that their
    sine wave UPSes are so much less expensive.

    This sounds to me like a big consumer backlash that is waiting to
    explode. Dell does not warn potential customers: "Attention - If you buy
    this PC you will also need an expensive UPS to protect it." And it's not
    only Dell's problem...any new PC with an active PFC power supply is
    going to need an expensive UPS.

    I can buy a new PC for the price of a properly-sized UPS for my system.
    This whole thing is just too surreal. The UPS makers must be drooling.

    Daddy, Apr 8, 2010
  4. Daddy

    Daddy Guest

    Thank you once again, William, for your comprehensive and informative
    reply. Please see my reply to Tom Lake. Like you, I find it hard to
    swallow that new PCs *need* this expensive type of UPS.

    Daddy, Apr 8, 2010
  5. Hi!
    No. A *properly designed* power supply will work with a UPS that has a
    stepped approximation to a sinewave output. I've done this often
    enough with various power supplies that have active PFC circuits to
    say with reasonable assurance that it will work.

    I maintain that Dell is cheapskating on the quality of their power
    supplies, and they may have a nasty backlash from doing so. (But then
    again, I'm a pretty big believer in "do it right the first time" for
    stuff like this.)

    There's also the PS/2s...I have a herd of those and some are hooked up
    to UPS units with stepped approximation to a sinewave output.
    Sometimes the power supply harmonizes a little bit when on battery
    power, but they work. The late model 400 (actually 399.1!) watt power
    supply has an active PFC circuit and it seems to get along fine on
    power from the average UPS. (Some people do report power ups and power
    downs, but I have never been able to duplicate this.)
    It's not cheap or particularly easy to design a UPS with true sine
    wave output. What an AC generator does just by virtue of its
    mechanical design a UPS must do electronically. The complexity of the
    circuit is much greater--if you ever get a chance, compare the two
    designs sometime.

    I couldn't think of the term last night, but a lot of really old UPS
    designs put out a simple squarewave and don't even bother trying to
    make it look like a sinewave in any way.

    There were some exceptions--I had a very nice (and old!) APC 1200VA
    UPS with true sine wave output. A lot of BIG UPS units have true sine
    wave outputs. Here comes your money saving tip--even today you can
    find these and they are typically priced on a "if you can carry it you
    can have it basis". That is because the batteries in them will be
    totally dead. Good quality car batteries or deep cycle marine
    batteries can usually serve as replacements, although you may have to
    buy a battery box and wire up external cables.

    That was exactly what I did with that APC unit. It took 48 volts worth
    of input power to its inverter, so I wired up four big car batteries
    in series. The thing would run a moderately sized 120 volt room air
    conditioner or washing machine, although it had a hard time starting
    either one.

    The same thing works with many smaller UPS units as well, although
    sometimes the charging circuit flips out and won't do its job. The
    older APC UPS units sold from the mid to early 90s handle a battery
    retrofit perfectly. I'm using several that have been converted to
    operate from a lawn tractor battery. One of them is at the heart of a
    backup lighting system--it is connected to several CFLs. These sit
    idle until the power goes out--at which point the UPS goes to battery,
    a contactor with a normally closed contact goes closed and the backup
    lights come on. With a few 60W equivalent CFLs, the whole shebang runs
    for at least two hours with ease.

    Of course, if you do this you have to be wary of the fact that you're
    dealing with high current circuitry that really won't understand how
    you were just curious and wouldn't touch THAT again! Even one car
    battery contains enough stored energy to weld, cauterize, start big
    fires, etc. You must be sure that any wiring you do is safe and will
    stand the load placed on it.

    Oh, and charge sealed lead acid batteries in a decently ventilated
    area only. Otherwise explosive hydrogen gas would build up.

    William R. Walsh, Apr 8, 2010
  6. Daddy

    Daddy Guest

    Very interesting, William, as usual. But a lawn tractor battery is not
    an option for me. Nor can I imagine how I would explain it to my wife.

    Daddy, Apr 8, 2010
  7. Daddy

    Daddy Guest

    I have made my decision, based on further research.

    The issue concerning a UPS and a power factor corrected power supply
    arises when the power supply recovers from a temporary power shortage.

    A PFC power supply can have a high "inrush current" -- the amount of
    current it draws when first switched on. A highly efficient power supply
    (with apparent power approx. equal to actual power) can draw as much as
    100% of its full power for an extended period of time (approx. 50 ms.)

    A UPS that delivers its output power in a sine waveform is more likely
    to provide power for long enough vs. a UPS with a stepped approximation
    of a sine wave.

    Another factor in UPS selection is the transfer time. A PFC power supply
    can request power from the UPS in as little as 4 milliseconds. If the
    UPS has a transfer time longer than 4 ms, it may not be able to provide
    the power supply with power in time. (This entire discussions does not
    apply to an "online" UPS.)

    It's probably impossible to come up with accurate measurements for the
    actual inrush current and minimum transfer time of a given power supply.
    So, practically speaking, the only way to know for sure whether your
    computer is adequately protected is to 'pull the plug' from the wall
    socket. That's what I plan to do tonight.

    Daddy, Apr 8, 2010
  8. Daddy

    Tom Lake Guest

    I maintain that Dell is cheapskating on the quality of their power
    Not necessarily. The PS in the 9000 is rated for 475 Watts and puts out a
    true 475 Watts. I've seen some name brand supplies put out less
    than their rating.

    Tom L
    Tom Lake, Apr 9, 2010
  9. Daddy

    Daddy Guest

    Well, I conducted my little experiment...pressed the power button on my
    UPS to turn it off, and...my computer and monitor immediately shut off.

    That's not necessarily because my UPS doesn't produce a sine waveform.
    For one thing, at 550 VA, my UPS is way under-powered. For another, this
    sissy little UPS probably doesn't have a fast enough transfer time.

    By the way, don't waste your time asking Dell technical support about
    power supplies or UPSes. They don't have a clue.

    Daddy, Apr 9, 2010
  10. Hi!
    That's not quite what I'm getting at. How well filtered is the input
    for the supply? How well will it continue to operate under stressful
    conditions (like a low line voltage)?

    Meeting the published specifications for output is just one of many
    criteria. And while most of Dell's power supplies are of good quality,
    a comparison to something like a PC Power and Cooling unit would make
    them look cheap and maybe even a little flimsy. Given that Bestec
    supplies are showing up in some low end Dell boxen, I'd not be
    surprised to learn that even the higher end machines are having
    quality cutbacks here.
    Sure. And there are always dishonest no-name makers to worry about as


    That's the first of two that I've seen. After finding another one (in
    another eMachines computer), I see that whoever made it did do some re-
    engineering, mostly accomplished by adding more metal to the
    heatsinks. I guess they hoped this would make the supply live a little
    bit longer.

    The second one wouldn't even produce enough power to let the machine
    operate correctly, and I'd bet it wasn't pushing a load of more than
    perhaps 80-100 watts across all of its outputs.

    All problems disappeared upon replacement of the power supply with an
    honestly specified AGI 350 watt unit. The owner claimed that no one
    except Best Buy had ever serviced the machine. I don't have a high
    opinion of their service operations, but I'd hope that they would at
    least use decent quality, honestly specified replacement parts.

    William R. Walsh, Apr 9, 2010
  11. Hi!
    Actually, it sounds like it's because you turned it off. :)
    You should get a bigger one. An overloaded UPS won't always take it
    gracefully. I've seen overloaded UPS units go off with a bang,
    especially the cheaper ones.
    The power supply filter caps should bypass that problem, as they
    usually hold enough energy to see the power supply past little dips
    and sags. They only manage to hold about a second or so's worth of
    energy most of the time.

    William R. Walsh, Apr 9, 2010
  12. Daddy

    Daddy Guest

    This gives me an opportunity to ask this question:

    Since the 9000 has a PFC power supply - even though a Dell tech support
    rep assured me that "no Dell computer have PFC supply" - does that mean
    that its 475 watt power supply really delivers a maximum of 475 watts?

    Daddy, Apr 9, 2010
  13. Hi!
    That's not what PFC does. PFC tries to compensate for the fact that
    the components inside a power supply (particularly the capacitors and
    inductors) may mess up the relationship of voltage to current in an AC
    power waveform. In other words, your computer's power supply may be
    "polluting" the power line. With resistive loads (like heaters and
    such) the voltage and current are in perfect synchronization with one
    another, giving these devices a power factor of "1".

    Depending upon how it is loaded, the power factor of your PC's power
    supply can change. A passive PFC circuit performs a fixed amount of
    power factor correction and does not adapt to differing load

    Active PFC works by adjusting the level of power factor correction
    based on how hard the power supply is working. The idea is to get
    things as close as is possible to a power factor of 1 (the perfect

    Whether your power supply will meet its listed output is another
    matter entirely. The ratings of each major component--the switching
    transistors, rectifiers, transformers, capacitors and other stuff--
    must be considered. There must also be sufficient cooling for these
    parts, especially the rectifiers and switching transistors. Otherwise
    they will go "boom".

    See my other posting for a comparison of two other power supplies, one
    of them dishonestly specified. You can easily see how the honestly
    specified supply has much better build quality--it can more easily
    dissipate heat and the major components are larger, serving as a rough
    indicator that they are capable of more work.

    William R. Walsh, Apr 9, 2010
  14. Hi!
    The general rule is to multiply the current rating printed on the
    nameplate by three. That's your inrush current figure. As that rating
    is frequently a worst case rating, for a fully loaded machine doing
    everything at once, you'll have some headroom here.

    If you could find a meter with a sufficiently fast response time with
    a "peak hold" function, that could be used to figure it out at as

    A UPS is seldom if ever going to be powering your system from a true
    cold start (where inrush current would be an issue). Every ATX power
    supply I have ever seen keeps a small portion of its circuitry alive
    when plugged in (and the switch at the back, if there is one, turned
    on). The main filter capacitors are also usually kept charged in this
    case. So you really only have to be concerned about the average amount
    of power your system is using.

    There are inexpensive plug in meters that can tell you all of this
    quickly and easily. Most have multiple scales of measurement (watts,
    amps, line voltage, volt amps) that are reasonably accurate. The P3
    Kill-A-Watt is one such meter, and it is readily available. One of
    these can be a very worthwhile investment. Then figure about 20-30%
    headroom on top of that for your UPS capacity.

    The way I'd do it is to plug everything into the meter, power up all
    the equipment you want the UPS to protect, do something that runs your
    CPU usage up to 100% for a few minutes

    You should test your UPS periodically. Better units have a button to
    press for testing (a feature curiously absent from the plug strip
    types sold by APC, Tripp-Lite and Cyber Power) and even better units
    conduct timed self tests on a repeating schedule (usually every two
    weeks). Those that don't have a dedicated "push to test" button can
    sometimes be tested by pressing and holding the power button for a few

    Although I have never had a problem doing so, pulling the plug on your
    UPS to test it can result in the grounds for each piece of computing
    equipment entering a "floating" state. This does assume that the
    grounds are properly connected when the UPS is plugged in, as they
    should be. (This means that if your UPS has its "site wiring fault"
    light on, you need to find out why and have the problem fixed.)
    However, it is a guaranteed test.

    William R. Walsh, Apr 9, 2010
  15. Hi!

    ...., turn on all peripheral devices and take a reading with your meter
    set to report volt-amps (because that's how UPS units are rated).

    Don't put your printer on the UPS. Although inkjet printers are
    unlikely to cause trouble, laser printers will. The fuser demands an
    enormous inrush current whenever it fires, and this will overwhelm the
    inverter in all but the very largest UPS units, causing it to shut
    down (best case) or fail in an exciting way.

    William R. Walsh, Apr 9, 2010
  16. Daddy

    Al Dykes Guest

    I think you are deescribing the"Kill-A-Watt".

    I know of a case where a UPS wouldn't supply juice if it wasn't
    plugged into the utility mains. It was a "field day" exercise and the
    intent was to power a WiFi repeater off the grid.
    Al Dykes, Apr 9, 2010
  17. Daddy

    Daddy Guest

    I have learned several things from this entire exercise:

    1- Dell technical support reps don't know what a PFC power supply is,
    and aren't sure whether any Dell computer has one.

    2- Dell technical support reps don't really understand the published
    specifications for the computers they are supporting.

    3- None of the big UPS makers will come out and say: You can't use our
    home and small office UPSes if your computer has a PFC power supply.

    4- None of the formulas, online calculators or techniques to calculate
    or estimate the correct size UPS for your computer arrive at the same

    5- Nobody agrees on the correct method to calculate or estimate the
    correct size UPS.

    6- No OEM will tell you: If you are thinking about purchasing this
    particular computer, consider this: It will require a UPS that will cost
    you half as much as the computer itself for adequate power protection.

    7- No UPS maker will say whether they'll honor their warranty if you use
    a stepped approximation unit with a PFC power supply.

    I apologize for ranting.

    Daddy, Apr 9, 2010
  18. Hi!
    I am not sure why that comes as a surprise. To them, a power supply is
    a silver box with wires. They might know it has a fan or two inside.
    They also know that when power supplies in computers fail, you send
    out a new replacement.

    Few people do component level repair on power supplies. I've been
    incredibly frustrated in my attempts. The only reason I tried is
    because the supplies in question aren't made any more, and I've been
    losing them at a rate faster than I can replenish my supply. (In case
    you're wondering, the supplies are the 335 watt Delta SMP-332AB units
    from IBM PS/2 Model 95 computers. All I know about the failure is that
    the controller is being told to shut down, and that was what someone
    much better equipped than myself and more experienced had to say about

    And it's dangerous--switching power supplies can supply enormous
    amounts of electrical current, the high switching frequency can really
    bite if you happen to come in contact with something operating at that
    frequency and portions of the circuitry are directly line connected.
    That last one makes for an extremely dangerous environment, as the AC
    power in your home can deliver more than enough current to seriously
    injure or kill you.
    That's because it certainly *should* work. If I ever come into one of
    these Dell machines where the power supply doesn't "like" a stepped
    sinewave input, you can bet that I'll be doing a teardown.

    I'm deadly serious:
    although I usually don't go to the trouble of making web pages, or
    even ones really intended for public consumption.

    Anyone want to send me one of the PSUs for an exam? Private e-mail can
    be found from the above pages or wct <atsign> walshcomptech <dot> com.
    I'll return it to you fully reassembled, and it's unlikely to be
    damaged in the process because I take extreme care when doing these
    things. I will test it prior to returning it, and should it not work,
    I'll front the cost for a replacement.

    (Yes, that's only my word, but it's all you need as I take it quite
    Couple of explantions: 1) there's more than one way to skin a cat, 2)
    everyone has a different idea, 3) some are more truthful than others.
    I'd put more faith in a calculator constructed by someone who *uses*
    UPS units than I would someone who is *selling* them.
    See above.
    It'd cost them the sale, and maybe in the worst case, even land them
    in a court of law to defend their actions. When a computer from the
    competition can be proven to operate perfectly on stepped sinewave
    output, why won't theirs?

    Not saying that's correct, but you can be sure it's how the average
    consumer is going to view it.
    If the warranty to which you refer is the one that covers the UPS
    itself against any failures or issues, they don't really have a choice
    outside of snubbing the customer or coming up with an allegation that
    you were abusing the unit. There are some pretty strict laws governing
    what can and cannot be excluded or limited in a warranty, at least in
    the US. It's unlikely that the UPS would be damaged even if the
    computer failed to operate correctly from the power supplied by said

    As for any such "connected equipment warranty", these are practically
    worthless. You should not buy power protection equipment based on what
    any such policy might claim. I suppose that someone, somewhere has
    received a payout from one of these policies, but when you think about
    it, only a fool provides a multi-thousand dollar warranty for the few
    tens or hundreds of dollars that represent the profits from the sale.
    If you haven't, look at the fine print in one of those things
    No problem. Sometimes you just gotta speak your mind. :)

    William R. Walsh, Apr 9, 2010
  19. Daddy

    Brian K Guest


    Great summary. I'll wait for your recommendations.
    Brian K, Apr 9, 2010
  20. Daddy

    Greg S Guest

    The specs for my 6-month old Precision 3400 included the sine wave UPS
    recommendation. While the 375W PS is smaller than many (yet more than
    sufficient for my needs), my BACK-UPS ES 750 has always worked
    flawlessly with this machine. Just one user's experience -- YMMV, of
    Greg S, Apr 10, 2010
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