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Problem with UPS

Discussion in 'Electronic Repair' started by P, Mar 18, 2007.

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  1. P

    P Guest

    Hi - wondering if anyone can point me in the right direction with this one.
    I have an APC BackUPS-RS 500 and it has recently been having issues. About
    three weeks ago it suddenly started giving errors on the front panel and I
    found that the battery had died (down to about 6v from the usual 13.8v).

    I couldn't get the battery recharged at all, so I replaced the battery and
    the UPS worked ok again. Then after a few days, I got the same problem
    again. This time I was able to fully recharge the new battery, put it back
    into the UPS and monitor it. The logs show that the battery is gradually
    being drained although it has never gone onto a battery condition (ie not
    lost mains power).

    Does anyone have any ideas where I might start to look in repairing this?
    I've found that I don't use the UPS that much since they upgraded our local
    mains power infrastructure, but if I can get it working again without
    having to buy new one that would be great.

    I don't really know much about how these things work, other than they have a
    battery and an inverter circuit. Any help would be appreciated.

  2. Ken

    Ken Guest

    I don't have your exact UPS, but most charge up the batteries whenever
    the AC is turned on and use those charged batteries when the AC fails.
    It sounds like your charging circuit is not functioning. Depending upon
    how knowledgeable you are about electronics, you might see if you can
    find a failure in that circuit. The first thing I would look for would
    be to determine if a charge voltage is being applied to the battery when
    AC is on. If that was OK, next I would look for a diode used for
    isolation of the charged battery. It could be you are discharging the
    battery through such a shorted diode. Of course it could be MANY other
    things. On the other hand, it might be better to buy a new unit.
  3. Jeroni Paul

    Jeroni Paul Guest

    It looks like the old battery shorted some cells and took away some
    fuse or protective resistor in the charging circuit. It might even be
    removeable without soldering.

    By the way when the 7 Ah battery on my UPS failed I replaced it with a
    96 Ah car starting battery. It just takes some more room but gives a
    much longer duration. The only thing to be careful is the inverter
    transistors that are running for a longer time don't overheat.
  4. Arfa Daily

    Arfa Daily Guest

    That's very similar to the problem I have with my APC Smart-UPS 700, and
    like yours, it seemed to occur after a worn out battery was replaced. The
    problem happens intermittently on mine, after it performs one of its
    periodic self checks. It's not "bad joint intermittent" - more "I'll let you
    down just for the hell of it" intermittent. Prior to it failing, all front
    panel indications are normal. After failure, it indicates low state of
    charge, and faulty battery. This is after it has attempted to power the load
    ( and failed I might add ) as part of the self check. About the only thing
    that I have come up with, is that it's a battery terminal issue. The reason
    that I say this is that the original batteries ( there's 2 of them in mine )
    had quarter inch terminals, with suitably matching spade connectors on the
    battery to battery jumper, and the main leads into the rest of the device.
    The replacement batteries, which were obtained for me by a friend, so not
    negotiable ( !! ), had the smaller terminals, so the original spades did not
    fit as well as they should. When these things go into load-power mode, the
    current drawn from the batteries is very large indeed, and it might just be
    that these connections are poor enough that under these conditions, as
    opposed to when the thing is just idling and trickle charging, there is
    sufficient voltage drop across the connections, for the system control micro
    to decide that the battery is faulty. It could of course be that one of the
    'new' - remember my friend got them, but they are supposed to be new ... -
    batteries is genuinely faulty. It's a case now of having the time and
    inclination to take the thing out of service again, to check it all.

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