UPS turns off at load when on battery

Discussion in 'General Electronics Chat' started by sosaited, Jul 19, 2012.

  1. sosaited

    Thread Starter New Member

    Jul 19, 2012
    2
    0
    Hi.

    I have a 1000va UPS that I use for my Computer as their are numerous blackouts in my area. Recently I moved to a new location and for a few days initially, the mains voltage kept dropping too low (~170-200v instead of 220/230), during which time the UPS would go to the battery, but after it will run out in a few minutes, it will turn off (The on-battery indicating LED would turn off) but it would continue to beep and supply the same input voltage as it was getting to output (which didn't cause my computer to restart). This kept happening for about 7 days, after which the voltage was fixed (215-220v). But now since a few days, it is not charging the batteries fully (my own opinion, could be something else) as it turns off within a second or two after the power fails, if the computer is turned on when it happens. I have also noticed that one of its relay switches after few minutes of power returning, which I am guessing is the one that charges the batteries.

    I am posting its front side of the main PCB in the hope that someone can please tell me what is the purpose of the two VR at the bottom left, and if I can adjust any of them to make sure that it will charge the batteries fully, or if I need to check any other components with a multimeter. There are two 12v 7Ah batteries in it, one was at ~13v and the other at 11v after I had it connected to mains for more than 8 hours.

    P.S: When I checked its output volts on battery, without load; it was at 160-170v only.

    Thank you.

    http://i.imgur.com/XfgxI.jpg
     
  2. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    What is the battery voltage when the AC out is only 160-170V? Sure sounds like your batteries are either beyond useful service or are not being given enough time to charge properly. Can you check the amount of current being supplied to charge the batteries?
     
    sosaited likes this.
  3. #12

    Expert

    Nov 30, 2010
    16,298
    6,809
    Agree. 11 volts is a seriously empty battery. Either it isn't getting charged or it has gone bad.
     
  4. sosaited

    Thread Starter New Member

    Jul 19, 2012
    2
    0
    As I mentioned in my original post, this is my current hypothesis as well, partially judging from the relay switching after a few minutes of connecting to mains (which I am guessing is for the charging circuit).

    The current through the battery terminals when connected to mains was about 0.10A. P.D when UPS was on batteries was about 0.5-0.8v less than the already posted ones.
     
  5. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    First replace the bad battery. Most of the time it is the cause.
     
  6. BillB3857

    Senior Member

    Feb 28, 2009
    2,400
    348
    You still haven't answered the question of what are the BATTERY VOLTS when the unit is only putting out 160-170 volts, unless I missed it somewhere.
     
Loading...