UPS over charging the battery-problem

Discussion in 'General Electronics Chat' started by tractable, May 26, 2010.

  1. tractable

    Thread Starter New Member

    Dec 30, 2009
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    Hi,
    I've installed a UPS for my house (220V mains), connected with a 12V car battery. In my area the daily power outage is 4 hours, max 1 hour at any one time and UPS remained fine providing backup during this.
    Yesterday I noticed that UPS is charging the battery for 6 hours while still charging it and battery is very hot. I opened the cell cover and saw water boiling inside, situation doesnt look good and I disconnected the UPS.
    I believe UPS is overcharging the battery and there is some problem in the cut out (when ups should stop charging), so can I fix it by opening the ups? Any one knows if its a simple matter of adjustment?
    I am a non-electrical person, have developed some basic circuits of telephone bell, fm transmitter many years ago.
     
  2. cjdelphi

    New Member

    Mar 26, 2009
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    What's the output voltage to the battery (d/c the batter) what's the voltage reading should be around 14.5v? voltage meter handy? when the battery reaches around 14.2v charging the UPS should switch to trickle type mode...

    Take a reading without the battery and then take a reading with the battery connected, it should NOT rise past 14.5v unless you want to see it possibly explode :)
     
  3. cjdelphi

    New Member

    Mar 26, 2009
    272
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    and my second thought is, the UPS, is it designed to be used on a car lead acid battery or a deep cycle battery? what's the manual say?
     
  4. tractable

    Thread Starter New Member

    Dec 30, 2009
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    Thanks cjdelphi,
    Outut voltage of UPS to the battery = 13.5 V,
    Output voltage of UPS with battery disconnected = 10.4 V
    Battery output if disconnected from UPS = 12.5 V
    Are these numbers looking fine..?
    At this moment battery is cool as it remian disconnected overnight.
    UPS is a china made and is common here to use with lead acid batteries.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
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    Automotive batteries will not last very long when used to power a UPS. They are not designed for that type of service. You need to use deep-cycle batteries.

    If the UPS is indoors, you must use sealed lead-acid batteries. Automotive and marine batteries will vent explosive gases during charging/discharging.

    Occasional overcharging for a short period of time (15-20 min) is OK. This is called an "equalization charge". It helps to remove plate sulphation and to mix up the electrolyte. However, it should not be allowed to go on for very long.

    You may have a shorted cell in the battery. After charging, let the battery sit for several hours. Then measure the voltage across the terminals. If you measure less than 12.5v, you probably have a shorted cell.

    If the battery is getting hot and the charging voltage is 13.5v, then you definitely have a shorted cell.
     
  6. tractable

    Thread Starter New Member

    Dec 30, 2009
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    sgtwookie, thanks.
    I'll keep battery disconnected overnight and see the voltages tomorrow...
    Battery is indoor and how can I seal this lead acid battery?
    If battery turns out good, I need to repair UPS. Just out of curiousity I have enough time at home and then rather repairing I'll go to upgrade it to a more powerful 1500 VA UPS. Currently it is 700 VA rated, Is there any article or book etc which I can use to do this?
     
  7. SgtWookie

    Expert

    Jul 17, 2007
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    You can also put a load on the battery, like an automotive headlamp, and then measure the voltage.
    You cannot seal a lead-acid battery that is not designed to be sealed.
    It will burst.
    Since you cannot seal it, and it will vent explosive gases, you must move it to a well ventilated area (outside).
    I'm betting that your battery is damaged; a shorted cell. It cannot be repaired. It needs to be recycled. Buy the correct batteries for indoor use, and deep-cycling.

    You may not understand the current requirements for a 700VA inverter.

    700VA at 220VAC is 3.182 Amperes RMS current.
    If the inverter is 85% efficient (which is a reasonable number for a good UPS), when operating from a 12v battery, you will need:
    700VA/.85/12v=68.63 Amperes current flow from the battery bank.

    Now if you want 1500VA with an 85% efficient you will need:
    1500/.85/12v = 147 Amperes. That is about the amount of current that it takes to turn the starter on a small automobile engine.

    How long do you think one battery will last with such a heavy load?

    Batteries will have their service life significantly decreased if they are routinely discharged below 70% of full charge.
    Batteries that are discharged to 50% routinely will have their service life reduced by 2/3 that of normal.
    Batteries that are discharged more than 50% will have a very short service life.
     
  8. tractable

    Thread Starter New Member

    Dec 30, 2009
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    That is important safety point, I'll relocate battery outside my lounge

    In last 3.5 idle hours, battery voltages are dropped to 12.35 V. Don't have spare bulb/load to put in, will see the voltage drop trend further.

    When there is power outage for 1 hour during the day, 3 fans (300 W), 2 tubelights(80W), two bulbs (60W) are running. Total = 440W
    W-hr / efficiency = 440*1 /0.85 = 517 Whr
    Required Amp-hr = 517/12 = 43 A
    Battery is rated 145 Ah, so in one hour I have not been discharging it to a great extent.
    For 1500 VA UPS you calculated 147 Amperes, means the battery is just sufficient for a ups of 1500VA?
     
  9. SgtWookie

    Expert

    Jul 17, 2007
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    Please do so.

    If left for about 10 hours, I will bet that it will drop to around 10.4 to 11v. This is an indicator of a shorted cell.

    You are discharging it by 29.6%, or 70.4% of it's maximum capacity.
    You said earlier that you have power outages that last up to 4 hours. In that case, you would need four times the battery capacity.

    If the battery is not immediately recharged, it will have a short service life. As I've mentioned before, an automotive battery is not appropriate for deep-cycle use as you are using it for. It will fail very quickly when used this way.

    No, it means that it is no where near sufficient. If you operate a typical lead-acid battery (even deep-cycle) until it is 100% discharged and then try to charge it up again, it will fail very quickly.

    You need to have enough battery capacity so that the batteries are never discharged more than 30% from their full "float" charge. It is not cheap to have such capacity, but it gets to be very expensive if you have to replace batteries every few months.

    If you buy enough of the proper size batteries to begin with, your operating and maintenance costs will go down.

    Keep in mind that there is an "overhead inefficiency" for charging lead-acid batteries. Even with the best battery charging/maintenance systems, you will only get back 70% to 80% of the power that you put into them.

    This isn't terrible, but it all adds up. You need to be aware of it.
     
  10. tractable

    Thread Starter New Member

    Dec 30, 2009
    16
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    sgt,
    Appreciate your detail replies. In morning today the battery voltages are 12.2 V, that is about 13 hrs idle time. Battery remained connected to ups but ups was disconnected from mains, I think this doesnt affect battery discharge. Seems UPS is the culprit, any suggestions on that?
    The 4 hours power outage is not in one go, it is 1 hour at any one time, total 4 times in 24 hours.
     
  11. SgtWookie

    Expert

    Jul 17, 2007
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    I don't know how capable your UPS is in recharging the depleted battery/battery bank.

    The discharge/charge cycle is very short. You will need much more capacity than you have right now. The sad part is, the people who are resorting to UPS's are making the problem much worse than it is now due to the inefficiencies involved.

    My best suggestion is to use candles and hand-operated fans when the power goes off. Then you will be helping the situation.

    What is the core temperature of the battery? You can measure it by placing a thermometer on the positive battery terminal. The hotter the temperature is, the less voltage is indicated for a full charge. However, the hotter the temperature is, the shorter the life of the battery.

    What is the ambient outside temperature where you are?
     
  12. tractable

    Thread Starter New Member

    Dec 30, 2009
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    Today the ambient is 44C, I am in office now and can check the battery terminal temperature on returning home.
     
  13. tractable

    Thread Starter New Member

    Dec 30, 2009
    16
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    Suspecting ups I took it to local electricion and when he connected his battery, surprisingly ups stopped charging, which was not the case with my battery at home. UPS inside looked very smple, a transformer and a board, the board is shown in pic here.
    [​IMG]
    His battery still connected, he tried to rotate the potentiometer named "charg full" but ups never started charging, now he thought there was something wrong with the board and it needed replacement.
    A new board was inserted, I brought home battery, which was connected , potentiometer adjusted and now it was working fine.

    On returning home, again ups keep on charging, I was wondering what has happened as everything was good at shop. While ups running I disconnected the load and good, now it stopped charging, load was re-connected and it remained dormant.
    I really suspect the problem was soemthing else but though now it rectified like I described.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    Did you measure the battery voltage after it had been sitting overnight?
     
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