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Battery Charging Voltage Jumping all over the place?

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  • Battery Charging Voltage Jumping all over the place?

    Battery Charging Voltage Jumping all over the place?

    Hello everyone,
    I just salvaged a small, 50AH FLA battery from a Tractor. The Battery has seen 2~3 calendar years. It was showing 11.38 Volts sitting on the shelf since 3 months so I thought it was good and I brought it for a bargain.

    I brought it home and connected it to my Intelligent charger which claims to support (Automatic)-

    Deep discharge Charging
    Boost Charging
    Absorbtion Charge
    Tricke Charge
    Equization Charge

    Automatic Charge Current and voltage regulation with Temperature compensated charging.

    The charger is currently showing "Boost charge" at about 12 Amperes. Problem is,the Charging voltage seems to Jump from 13.1v all the way to 14.2V (like under 10 sec) I hooked my DMM to the battery terminals which comfirmed the same.
    Sometimes the voltage also reaches 14.4v and the Charger goes into "Equalization Charge" but falls back to Boost charge at 13.5v or something odd.

    I would like to ask,
    What is the reason for this and is it safe? Shall i keep it connected for a day or two?

  • #2
    Normal for a PWM charger.

    WWW

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    • #3
      It means your batteries are old and need replaced. Your batteries have sulfated and the internal resistance has gone too high.
      MSEE, PE

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      • #4
        Originally posted by Sunking View Post
        It means your batteries are old and need replaced. Your batteries have sulfated and the internal resistance has gone too high.
        after few hours of charging the voltages seem to settle down near 13.6v. however as soon as charger is removed, the Battery falls back to 12.2v. shall I make a few more charging rounds?

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        • #5
          Try a EQ charge.
          MSEE, PE

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          • #6
            I tried a eq charge twice. it seems to be improving.

            the Battery voltage on charge is still jumping across 13.6v to 14.2v. if I draw a load it goes back to 12.3v.

            admirably, I connected the Battery to our DC load yesterday night and it ran Led street lights (load 4a ) for 5 hours before I switched it off. 20AH is decent progress for 50ah old Battery right?

            do you think it's sulpahation that's causing voltage jump?

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            • #7
              Voltage jumping rapidly, is likely a bad connection. Look for a hot wire/connection with an Infrared Thermometer.
              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

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              • #8
                Originally posted by Mike90250 View Post
                Voltage jumping rapidly, is likely a bad connection. Look for a hot wire/connection with an Infrared Thermometer.
                thanks mate,
                after cycling the Battery for 3 days (I'm using it on my DC circuit ) the conditions are 100 percent better.
                I ran the Battery down to 11.5v yesterday. in the morning with sun up, the Battery is slowly progressing from 12.8v and above... very stably. the charger shows'absorbtion charge' at 8-9 amps. 8 amps are good for 50ah Battery right?

                else how do we test the ah of Battery?

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                • #9
                  Originally posted by bhvm View Post
                  I ran the Battery down to 11.5v yesterday. in the morning with sun up, the Battery is slowly progressing from 12.8v and above... very stably. the charger shows'absorbtion charge' at 8-9 amps. 8 amps are good for 50ah Battery right?
                  If you are cycling down to 11.5v, stop doing that.

                  8 amps are actually bad for a 50ah FLA, especially one that is probably much less than that in real life due to the sulfation.

                  A *good* condition FLA can usually withstand no more than C/8, or in this case about 6.25A charge.

                  In bad condition, your 50ah battery could actually be much less than this, and 6.25A now would be beyond the C/8 spec. I'd stop wasting time on it.

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                  • #10
                    Originally posted by bhvm View Post
                    else how do we test the ah of Battery?
                    You cannot. Well not accurately anyway with DIY equipment. To do a capacity test requires the battery to be fully charged up. Then a constant current load is applied to the battery at a specified rate. Pro's apply a C/2 discharge rate and start a timer while monitoring the voltage. When the voltage reaches 1.75 volts per cell, the test terminates and time ended is recorded. So for example on a 50 AH battery apply a 25 amp load current and it takes .9 hours to reach 10.5 volts. So 25 amps x .9 hours = 22.5 amp hours. The tester will then look up the Discharge Curves published by the manufacture for the 2-hour discharge rate to convert and factor in Peukert Law effect. So in this case the manufacture would probable be around 45 AH @ the 20 hour discharge rate.

                    But here is the thing. DIY's do not have access to manufactures discharge curves because most of the batteries DIY's use do not have Discharge Curves being consumer grade products, nor can DIY's gain access to a programmable computer controller battery load box. The controller and load box cost 10's of thousands of dollars.

                    All a DIY can really do is try to apply a C/20 load and measure the amount of time it takes to get to 1.75 vpc. That means hanging around for 20 hours watching paint dry and when done is not accurate. But if there is significant loss of capacity will show up.
                    MSEE, PE

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                    • #11
                      thanks for the info

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