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APC battery backup not working sometimes

Discussion in 'Electronic Repair' started by Peabody, Jul 9, 2012.

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  1. Peabody

    Peabody Guest

    This is an APC Model BE550G UPS. It's just a few months old, but
    has developed an intermittent problem that I'd like to fix if I
    can. I know if I send it back to APC it will just happen to be
    working then, and I will have accomplished nothing.

    The problem is that sometimes when the UPS switches into backup
    mode, no power gets to the plugged-in devices. It's apparent the
    UPS thinks it's supplying backup power (4 beeps every 30 seconds,
    just like the manual says), but it isn't. The battery shows as
    fully charged, with 27 minutes of run time available. And when it
    works, it works fine. So it's not the battery.

    I first noticed this during powerup of the UPS. At first,
    everything is on mains AC. Then it switches into backup mode as a
    test for a few seconds, then reverts back to mains AC. What I
    noticed was that my modem would turn on at first, but then turn
    back off when the UPS went into test backup mode, then turn on
    again at the end of the test period. Sometimes. Most days, but
    not every day.

    Then of course I tried a full test - unplugging the UPS from the
    mains, and all the devices shut down instead of continuing to run
    under backup power. But all of this is intermittent. Sometimes
    when I do the test, it works fine.

    I called support, and they had me reset the sensitivity of the UPS,
    and of course it started working then. But I strongly suspect this
    has nothing to do with sensitivity - after all, it's hard not to
    notice the mains dropping out completely.

    Logically, what this seems like to me is that everything is working
    ok, but the relay which switches over to supplying backup power to
    the devices has bad contacts that don't always make contact. I can
    hear the relay click when it goes into backup, and again when it
    reverts to mains, and I can hear that whether the backup power gets
    through or not.

    Well, I just wondered if anyone here has any experience with this
    kind of thing, and might offer some advice on what to try. I have
    already opened it up and made sure all the internal cable contacts
    are good, even tightened a couple just to be sure, but that didn't

    Any advice would be appreciated.
  2. Peabody

    Peabody Guest

    Jeff Liebermann says...
    Thanks very much for your reply, Jeff.

    The relay is a PCB style DPDT:

    12V coil
    8 amp contact rating at 250V

    I found the datasheet for this series relay, but not the
    exact "DCF" part, at:

    searching on the part number EMI-2P over on the left.

    But, I haven't been able to find anything equivalent at

    The relay is encased in plastic, so I doubt I can get
    inside, but I haven't desoldered it yet.

    I found 10 with a similar number for sale on Ebay for $79,
    but no singles.

    This is a really dinky little relay to be rated at 8 amps,
    which is probably why it is failing.

    If I could find a replacement relay, it would probably cost
    less to buy that than to ship the UPS back to APC - it
    weighs a ton.

    Of course while it would be nice, it wouldn't absolutely
    have to physically fit - I could bridge from the PCB holes
    to the relay with wire - but the coil and the rating would
    have to be right, as well as the speed I assume.

    Well, let me know if any solutions come to mind. Thanks
    again for your help.
  3. Peabody

    Peabody Guest

    Peabody says...
    Ok, I may have lied.

    On page 1896 of the pdf catalog, I find:

    Omron G2RL series
    8 amp rating, same size and pinout

    Omron part: G2RL-24-DC12

    Mouser part: 653-G2RL-24-DC12

    Looks like this should work. The only question would be if
    there is a speed issue - how fast it switches.
  4. Peabody

    Peabody Guest

    Jeff Liebermann says...
    Well, that one is silver/nickel per the data sheet. The
    AgSnO2 version would be RT423012, which DigiKey doesn't

    But this one:

    is silver/nickel with gold plating - per the datasheet.
    Would that be worth a couple extra bucks?
  5. Peabody

    Peabody Guest

    Jeff Liebermann says...

    I ordered this one today from Digikey. Came to $5.27 with
    shipping. It should be here Saturday or Monday, and I'll do
    the switch-out and see what happens.

    I guess there's always the possibility that the problem will
    turn out to be something else, but the fact that the problem
    is intermittent, and that the UPS behaves normally in all
    other respects, makes it seem likely that the relay contacts
    are responsible. But, you know, it's only $5 either way.

    I really appreciate your help with this.
  6. Peabody

    Peabody Guest

    Peabody says...
    The relay arrived this morning, and I've installed it, and everything
    works fine so far. Of course I don't know for sure that the relay was
    the problem because it was an intermittent problem to begin with. But
    I've gone through about a dozen tests with the new one and it hasn't
    failed to work. So I'd say this looks promising.

    I have to keep the old relay in case I ever need to send the unit in
    under warranty. So I won't be taking it apart. But, it does rattle
    when I shake it, which I think is not a good sign.

    Anyway, time will tell. Thanks again for your help.

    By the way, I assume the lead-free solder they're using now has a
    higher melting point than the 60/40 I use - it was a bear to get the
    thing unsoldered with my 30W iron. Ended up having to add some of my
    solder to the pins, then braid it off, two or three times before it all
    wicked up and the holes opened up.

    And Digikey is amazing. I ordered late Thursday afternoon, and it
    arrived in the mail Saturday morning, all for $2.20 postage. Hard to
    beat that.
  7. Peabody

    Peabody Guest

    Jeff Liebermann says...
    Well I'm going to declare victory and withdraw from the
    field of battle.

    It's been a week now, and the UPS has passed the boot test
    every morning without fail. And as luck would have it, in
    our 100-degree weather there have been two short-term power
    outages (two that I know of because I was at the computer
    each time) and the UPS switched into backup mode perfectly
    each time.

    So it appears the problem definitely was the relay, and my
    replacement operation was successful. And all for less than
    the cost of shipping the UPS back to APC. Plus, if
    something goes wrong in the future, I'll know what to do.

    Thanks very much for your help, Jeff.
  8. THX for the feeback.

    Saludos (an alle Vernünftigen, Rest sh. sig)
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