16 x 12V SLA Batteries

Discussion in 'General Electronics Chat' started by philwalker, Oct 7, 2012.

  1. philwalker

    Thread Starter Member

    Aug 15, 2010
    41
    1
    Good evening all,

    I have recently acquired some old server rack mounted UPS's. These were given to me as their built in tested stated that one/some of the cells had failed and it was imperative the company could rely on the UPS's.

    The UPS's contain 8 12V SLA batteries (http://www.batteryweb.com/spec-sheet/bb-battery/HR5.8-12-T1.pdf).

    What is the best way to test these batteries, will a simple voltage check suffice?

    Also SLA Batteries are pretty new to me and i'm not too sure how to go about charging/maintaining ALL of these at the same time. How should these be looked after?

    Thanks, Phil.
     
  2. K7GUH

    Member

    Jan 28, 2011
    191
    23
    Test each battery individually under load. I use a 50 watt 12 volt camping incandescent bulb and an aging but accurate analog meter. If the battery is lower than 11.2 volts, it needs charging. If it is below 10.5 volts, it is a paperweight. I would not try to charge the batteries all at once. I have two chargers, each of which tapers off when the battery voltage is at or near full charge. It takes a while, but is 100% reliable and safe.
     
  3. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,980
    744
  4. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    If left unused for more than a few weeks all lead-acid batteries need to be maintained with a trickle-charge to prevent their failure from sulfation. After the batteries are charged you should be able to do that with all the batteries in parallel (if they are all good) if the voltage source is set to the proper trickle charge voltage (typically about 13.5V to 13.8V at 25°C).
     
  5. philwalker

    Thread Starter Member

    Aug 15, 2010
    41
    1
    Thanks for all of the replies.

    I have tested all of the batteries by using a 55W car headlight bulb as a load. The results are:

    #1: 11.9V
    #2: 11.9V
    #3: 5.1V
    #4: 11.9V
    #5: 12.2V
    #6: 11.9V
    #7: 12.2V
    #8: 11.9V
    #9: 11.9V
    #10: 11.9V
    #11: 9.5V
    #12: 11.9V
    #13: 11.6V
    #14: 11.9V
    #15: 11.8V
    #16: 11.8V

    Am i right in thinking that they all are good except for #3 and #11?

    Is it really as easy as connecting all these up together in parallel and applying a constant voltage? Do I need to monitor/limit the current? Can these be permanently connected to the charging voltage or should it be switched? I'm not sure what I am going to use these for but I can't let them go to ruin.

    Thanks, Phil.
     
  6. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    At least get each battery charged with a charger set to 14.5V
     
  7. philwalker

    Thread Starter Member

    Aug 15, 2010
    41
    1
    How do I do that? Just connect each battery up to a fixed voltage power supply? Do I need to worry about limiting current or anything?

    Thanks
     
    Last edited: Oct 9, 2012
  8. crutschow

    Expert

    Mar 14, 2008
    13,003
    3,232
    A dedicated battery charger could be used, but a power supply set to 14.5V will work also. You should limit the current to about 1/10 of the ampere-hour rating.

    After you charge them all individually you can connect all the good ones in parallel and float charge them.
     
  9. philwalker

    Thread Starter Member

    Aug 15, 2010
    41
    1
    Morning All,

    I have decided I would like to use 1 or 2 of the 12v batteries as a UPS to a CCTV system.

    The CCTV system runs on 12V DC at about 500mA peak.

    Is it quite straight forward to design a circuit to do this?

    I was thinking:

    AC - DC Power Pack (http://cpc.farnell.com/stontronics/t3527st/ac-dc-power-supply-13-5v-1-1a-2/dp/PW02898)

    |
    \|/

    Connected to two SLA Batteries connected in parallel

    |
    \|/

    From The Batteries to a low dropout 12V Voltage regulator (LM2940)

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    \|/

    To CCTV System,

    Does this seem like the outline to a workable system?

    Thanks, Phil.
     
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