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Hacking UPS

Discussion in 'Electronic Design' started by aurgathor, Nov 30, 2004.

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  1. aurgathor

    aurgathor Guest

    I have a 650VA APC UPS (Back-UPS Pro 650)
    that has worn batteries (occasionally, it starts to
    beep and the red battery light comes ON) .
    The UPS is there to ride through brownouts and
    outages lasting usually less than 10 seconds (have
    quite a few of those) so if the batteries are less
    than perfect, I don't care as long as it can last for
    10 - 20 seconds.

    So, how does the UPS's circuitry determines if
    the battery is going bad? Is it simply a voltage
    measurement, or something more sophisticated?
    How difficult would be to modify the UPS to
    lower the treshold for a bad battery?

    Alternatively, how would the unit work if I were
    to connect a marine or car battery instead of
    the manufacturer supplied battery?

    TIA
     
  2. Ian Stirling

    Ian Stirling Guest

    Generally, just fine.
    If you put a much bigger battery in, you have to be careful of
    overheating due to the extended runtime.

    Old car battery from scrapyard is a really cheap way.
    Altering thresholds won't do much.
     
  3. Nico Coesel

    Nico Coesel Guest

    It will probably work. Beware though with the sealed batteries. An APC
    UPS will shut down when the batteries are completely worn out.
     
  4. Jerry G.

    Jerry G. Guest

    Mainly for safety reasons you should be using the proper battery. The UPS
    checks the battery by analysing the current load by pulsing it, and reading
    back the decay factor.

    If you start messing around by trying batteries that are not properly rated
    for it, there will be very little dependability. Also, if you put a battery
    with too high an amp hour rating, it will not get charged properly, and the
    result may be in damaging the UPS.

    As for protecting your investment, it is a bit skimpy for my taste that
    someone would not at least put in the proper battery in to their UPS.

    --

    Jerry G.
    =====

    I have a 650VA APC UPS (Back-UPS Pro 650)
    that has worn batteries (occasionally, it starts to
    beep and the red battery light comes ON) .
    The UPS is there to ride through brownouts and
    outages lasting usually less than 10 seconds (have
    quite a few of those) so if the batteries are less
    than perfect, I don't care as long as it can last for
    10 - 20 seconds.

    So, how does the UPS's circuitry determines if
    the battery is going bad? Is it simply a voltage
    measurement, or something more sophisticated?
    How difficult would be to modify the UPS to
    lower the treshold for a bad battery?

    Alternatively, how would the unit work if I were
    to connect a marine or car battery instead of
    the manufacturer supplied battery?

    TIA
     
  5. James Sweet

    James Sweet Guest

    Just be sure to put it in a plastic battery box, car batteries, particularly
    old ones are notorious for spilling leaking fluid if tilted, jostled or
    overcharged. Can make a real mess of carpet and subflooring real quick. A
    sealed deap cycle marine gel cell would be ideal.
     
  6. James Sweet

    James Sweet Guest

    It should charge just fine, it'll just take longer to fully charge.
    Lead-acid batteries aren't particularly sensitive. The proper battery for a
    UPS can be pricey, I have an old Trip-Lite that uses an odd size and it
    would have been around $100 to replace it, so I installed a pair of somewhat
    smaller surplus gel cells and it's been working flawlessly for several
    years. I say go for it and experiment, just use common sense with the wiring
    so you don't burn the house down.
     
  7. Joerg

    Joerg Guest

    Hi Jerry,
    This brings up a whole other question: Are there any low cost UPS that
    do use external 12V or 24V batteries? Or where you can add capacity by
    external connection? I know there are industrial ones but most are way
    out of price range for PC use. This would be nice to ride out longer
    outages without stopping work on the PC.

    We have an inverter 'mini suitcase' that is used for the fans of a wood
    stove in case power goes after we just put a load in the stove. This
    inverter with battery isn't a UPS but just a trickle-charged standby
    unit. Kept on the shelf just in case, like flashlights, bottled water
    and other emergency gear. It does, however, allow the connection of a
    large 12V battery for extended runtime.

    Regards, Joerg
     
  8. TheDragon

    TheDragon Guest

    I have several modded APC Smart UPS's

    Add rear contacts fused and parallel to the internal batteries.
    Then you can add any batteries you like as long as the voltage matches the
    originals. If you are extending the runtime, very good if you fit a fan to
    the grill inside, to cool the ccts inside.
    I have a smart APC 1500. It will run at 90% load for 8 hours. No problems at
    all.
    P.S I use 4 x exteral Chloride 100AH in a seriel parallel combo to give the
    needed 24v nominal.
     
  9. aurgathor

    aurgathor Guest

    Thanks for all who replied. I looked up the pricing on
    replacement batteries and found them kinda high for the
    capacity I'd get. Obviously, if I install external batteries,
    they'll be installed in a way that even if they leak, they
    can't cause much damage (crawl space ;-) . I'll also put
    in a fan that will turn ON if it the UPS is running on battery
    power, or charging the batteries.

    BTW, how do these sealed batteries degrade? Is it sulfating,
    or something else? Is there any way to reverse it to some
    degree, like charging it with a slightly higher current and/or
    voltage, or pulsing it? Again, if the batteries are not 100%
    and I only get half of the runtime -- I don't care. But waking
    up in the middle of the night because my UPS is beeping
    can be highly irritating. :-(
     
  10. Don

    Don Guest

    That, of course, depends on the UPS. Some just
    watch the potential at the battery REGARDLESS
    OF LOAD. Others apply a fixed (known) load and
    note how the battery voltage changes. Others
    *measure* the load and note the rate of change
    of battery voltage. Etc. The Back-UPS 650 Pro isn't
    a particularly "high end" unit so I wouldn't expect
    much sophistication, there. I'll have to look at the
    schematic to see what facilities *are* available to
    determine battery state...
    Again, it depends on the UPS and the battery chosen.
    Let's assume we stick with the same battery *technology*
    (i.e. lead acid) so you don't have to address differences in
    charging techniques, discharge characteristics, etc.

    Typically, the rate a battery is charged is related to the
    capacity of the battery. C/10 and C/20 are common
    rates. The higher rate obviously leads to greater
    *perceived* convenience though usually is tougher
    on the battery itself.

    One of the risks you run when replacing a battery with
    one of a different capacity (physical volume is a rough
    parallel to actual capacity -- for a given number of cells)
    is that the charger is probably designed with the
    *assumption* that a particular battery (capacity) is in place.
    Replacing it with a smaller battery could lead to excessive
    heating (in the battery) as the battery is now being charged
    at a "higher than typical rate". Replacing it with a larger
    (capacity) battery could lead to lengthier charge times.

    In either case, if the UPS monitors the charge cycle actively,
    it can erroneously deduce a battery failure ("Why is this
    battery taking so long to charge?" or "Wow! That battery charged
    awfully fast! I wonder if that's just a surface charge...")

    Using a "car battery" always poses the risk of outgasing which,
    if not vented well, can be a fire hazzard. Also, you have to
    worry about leaks, spills, etc. as these are not gelled electrolytes.
    And, of course, maintenance if the cells are not "mainetenance free".

    I had a 3500W unit that ran off 120VDC. I considered using
    a set of (10) auto batteries as a cheap way of getting "capacity".
    Of course, 10 batteries aren't likely to fit in the living area.
    And, with the high charge rate that the UPS used, I was
    fearful of putting them in the garage -- 10 batteries potentially
    venting into an enclosed space with open sources of ignition
    (think gas water heater, automobile, etc.) seemed like an
    insurance claim waiting to happen!

    So, the only real alternative would be to locate the batteries
    outside the garage and run 120VDC through the wall. Then,
    run AC from the UPS into the house to support the loads.

    But, that means building a shelter to keep the batteries out of the
    sun, rain, etc. And, protecting against wildlife chewing on
    the wiring, etc. Way too much work!

    So, I now use lots of little UPS's. Since outright *outages* here are
    rare (a bigger concern are the "2 second wink-outs" you mentioned),
    a 500VA - 650VA unit by each critical load is quite adequate.
    And, when the machine in question is powered off, there is no
    need for the UPS to run at all! (A 3500W UPS wastes a LOT
    of power just *idling*!)

    The Back-UPS 650 Pro *wants* an 11AHr battery (based on volume).
    But, a nice 7AHr will do just fine for you (though you will have to
    "pad" it a bit to prevent it from flopping around inside). At most,
    that should run you $15 - $18. I think you can even buy the 11AHr
    battery for around $20 ("off brand").

    What is an outage -- even a 2 second "reboot" -- worth to you?
    If it is NOT worth $18, then why are you bothering with a UPS
    at all?? (sort of like the folks who spend $50 on a tape backup
    system -- that they only use once a month -- and then complain
    when they have had a crash and discover last backup they made
    is "unreliable")

    <shrug>

    --don
     
  11. One of the 12 cells of your batteries was overcharged - and is
    destroyed. Unfortunately you can not replace this cell in a sealed lead
    acid battery. Other methods of repairing it are not possible.
    Batteries in UPS degrade mostly because the cells are not balanced.
    All are connected in series, and over time the voltage over the cells
    is getting different - because of little mechanical or chemical
    differences in each cell.
    You can increase the lifetime by lowering the charge voltage. Normally
    this is 2.3 volts per cell (or 27.4 for 12). Lowering this to 2.27 will
    reduce the available capacity a little, but the lifetime a lot.
    But the problem is - how can it be changed in the UPS?

    Another way would be a balancing circuit for each cell (ensure that
    each cell has no more than 2.3 volts). But with the sealed batteries
    you have no access to the connectors of each cell.

    Sulfating is another issue, but this takes much longer at room
    temperature. I have a torch with a sealed lead acid battery that I
    charge once a year. It is still ok! The sulfating is also regularly
    removed by the test cycle of the UPS (if there is any) or some drop
    outs.

    M.
     
  12. aurgathor

    aurgathor Guest

    Thanks for the great replies!! Very enlightening.

    I'll take apart the misbahaving UPS and check the
    batteries. If there's one that's a lot worse than the
    other 3, I'll probably replace it. If it's just a little
    worse than the others, I'll try to get a smaller (like
    1/3 - 1/2 capacity lead-acid) and parallel with it.
    If all are equally bad, I might just need to bite the bullet.

    I know that replacing/paralelling one is not a proper
    thing, but if Matthias is right, the UPS probably has
    1 bad and 3 OK batteries. When I have 3 bad ones,
    I'll replace them all. I have another one of the same
    UPS, so I might use those extra batteries left
    over when all old ones are replaced.

    I'll also look into a few other things when the UPS
    is open, like slightly decreasing the charging voltage,
    or making it more tolerant to marginal batteries.
    Assuming I can reverse engineer,or understand the
    circuit, which could be very difficult if it uses too much
    custom, or VLSI ICs.
     
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