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UPS battery

Discussion in 'Power Electronics' started by sudhakar, Jul 15, 2017.

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  1. sudhakar


    Jun 19, 2017
    In my UPS system have 12 v 120Ah Exid sealed lead acid battery 8 Nos.After 100% charge completed
    In battery supply feeding time , battery
    50% drain with in 4 or 5 minutes at 230v 2A load. Another 50% battery drained normally ( mean slowly depend the load ).
    Why first 50% supply drain fast?
    How to check and fill battery distal water in sealed lead acid battery?
    Thank you,
  2. kellys_eye


    Jun 25, 2010
    'some' SLA batteries have ports where you can lever out a 'lid' and refill cells - but not ALL batteries (SLA) have this. This is why they are called SEALED Lead Acid!!

    Your battery may be 'worn out' - they don't last forever and if they are over 3 years old they will be worse for storing energy. The constant trickle-charge they take eventually destroys the battery ability to maintain a charge.

    After 5 years you really should replace them.
    sudhakar and hevans1944 like this.
  3. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    You DO NOT check, add, or fill sealed lead-acid batteries with distilled water. That is why they are sealed.
    sudhakar likes this.
  4. ChosunOne


    Jun 20, 2010
    It sounds like your battery no longer is charging up to its rated capacity. If you're calculating your "50%" based on the rated capacity instead of its actual capacity after a lot of use, then your figures will be off.

    If you're draining your battery down completely when you use it, then your battery is not big enough for your application. Draining a battery down below 50% of rated capacity greatly shortens its cycle life, i.e., the number of times it can be recharged to its rated capacity, and you will need to replace it in much less than 5 years.

    There is no simple formula for how long your particular battery may last, because there is so much variation in how often and how long standby batteries are used. Ideally, you need a battery large enough that it is never drained below 80% of its rated capacity, if you want it to last for 5 years or more. If you discharg it many times below 50% of rated capacity, the amount of charge it will hold becomes less and less than the rated capacity.

    You might be able to find manufacturer specs on how to test the actual Ah capacity of your battery.

    My rule-of-thumb for testing a SLA battery is to leave a battery off its charger, no electrical activity for 5 days, then test the OCV (Open Circuit Voltage). After 5 days on the shelf, a fresh-from-the-factory fully-charged 12V (rated) battery should read about 13.2 VDC, i.e., 2.2 V per cell, and that indicates 100% of rated capacity is stored.

    The actual Ah charge stored is approximately proportional to the tenths of a volt beyond 2 volts/cell; i.e., a reading of 12.6V would indicate the battery is holding about 50% of its Ah rating (6 tenths of a volt being 50% of 12 tenths).

    I can't show you the math for this, I've just been using this method since I read it from an SLA manufacturer back in the late 70's and it's been an accurate predictor of whether a battery will hold up under use. Unfortunately, it's hard to apply in the field because it isn't practical to let a working battery sit on the shelf for 5 days

    you can make a less accurate measurement after 2 days, if you can leave it inactive (unplugged!) over the weekend to get a ball-park figure of your battery's storage capacity.
    Last edited: Jul 15, 2017
    bushtech, hevans1944 and sudhakar like this.
  5. sudhakar


    Jun 19, 2017
    Thanks for your reply,..
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