Please help me restore this old Lead acid battery

Discussion in 'General Electronics Chat' started by bhvm, Aug 12, 2014.

  1. bhvm

    Thread Starter Active Member

    Jul 16, 2009
    53
    2
    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.

    After 3 days for 'Cycling"-

    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?

    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?
     
  2. Polymorphism

    New Member

    Aug 10, 2014
    30
    2
    Your vehicle battery is not what we call 'deep discharge type'

    You will kill it with constant loads.

    The internal plates will bend.
     
    bhvm likes this.
  3. bhvm

    Thread Starter Active Member

    Jul 16, 2009
    53
    2
    Hello, Thanks for the super fast reply

    I am aware its a SLI battery and not a deep cycle one. I discharged 4A x 5 hours = 20AH. That still keeps 30AH in battery and shallower than 50% DOD. Its a junk battery anyways and I am trying to restore it.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,006
    3,232
    Sulfation which would increase the internal resistance of the battery so the charge current could cause a significant jump in the voltage due to this resistance and not due to the normal EMF of the cells. Sometimes just a long charge at a low current will eliminate some of the sulfation.
     
    bhvm likes this.
  5. Polymorphism

    New Member

    Aug 10, 2014
    30
    2
    I did an inverter kit 12VDC to 240VAC back in 1995.

    I killed two massive TRUCK batteries in a week.

    Running just an TV and 100W light bulbs.
     
    bhvm likes this.
  6. bhvm

    Thread Starter Active Member

    Jul 16, 2009
    53
    2
    Wow thats serious eh?
    Over my place its common to offer Truck batteries with inverters as a cost cutting measure. I never subscirbed to its view but still...

    I tried a spoon of epsom salt in each cell, Equalized it twice. The fully charged RESTING(4Hrs) voltage is 12.44V After a day of charging at 8A. I think a decent battery should have resting voltage near 12.6v?

    What does a 12.44v OCV voltage mean? Its definately not a shorted cell and the battery is holding charge overnight.
     
  7. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,788
    945
    It most definitely could be a shorted cell. A freshly charged battery can show an open circuit voltage of 13.8 to 14.4 for many days. This is a surface charge from the chemistry of the lead oxide and super oxide. Only a voltage while fully loaded will reveal the actual charge state. Fully charged and loaded should show 12.7 or 12.6. Anything lower than 12.0 indicates a shorted cell on a freshly charged battery.
     
    bhvm likes this.
  8. bwilliams60

    Active Member

    Nov 18, 2012
    722
    88
    Crutschow is correct. Sulphation has occurred over the period of dormancy resulting in internal high resistance. If it can be overcome, you need to charge this battery over a longer period of time (2 days) at a very low amperage (<2 amps). On the other side, 12.44 vdc represents roughly 75% charge and 12.6 vdc is 100%. Don't discharge it anymore or you run the risk of further damage.
     
    bhvm likes this.
  9. takao21203

    Distinguished Member

    Apr 28, 2012
    3,577
    463
    These batteries are not made for discharging at all, only to deliver very high currents when starting.

    If you do it, they will be ruined in a short time.
     
    bhvm likes this.
  10. bhvm

    Thread Starter Active Member

    Jul 16, 2009
    53
    2
    The Highest float voltage I've seen is 12.8v on very new batteries after 4hours of 'Sitting'. 13.8v seems too high to me.

    This old battery never seems to get 12.7 open circuit. max was 12.5v after an Hour of 'Sitting" after a charge. The good news is few days of restortion seems to work and the battery resistance is going down. The Charger is not Jumping anymore and battery takes a solid stable charge at 13A.

    How many hours of Sitting you recommend before taking another reading? Today the battery is disconnected from charger since morning and I will update the reading at night.
     
  11. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,788
    945
    If it is a flooded cell battery you can dump the electrolyte after it is fully charged. Empty it into a suitable sized plastic container. Don't spill or lose any. Using distilled water refill and rinse out the battery several times. You are wanting to gently wash out the cells and remove any loose material that has accumulated in the bottom of the cells. Gently. Vigorous shaking is not what I am suggesting, just repeated rinsing. Refill the battery cells equally with the acid electrolyte and add a small amount of water to make up any underfill condition. Never add extra acid unless acid has been spilled and lost.

    You should have some granular sandy looking residue left in the containers. Don't put this back in. :)

    Trickle charge the battery and you should see it recover full voltage in a few days. Do not charge it with high current. 5 of the six cells will already have a full charge.
     
    bhvm likes this.
  12. bhvm

    Thread Starter Active Member

    Jul 16, 2009
    53
    2
    Thank you for the detailed explanation,
    Yes its an FLA battery. I let the battery SIT for 24 hours and tested the OCV to be 12.33. Its on the low side but no shorted cells. I have currently put it on a float charge of 13.6v at very slow rate . I shall keep this for a week and let you know. I may try the electrolyte swap later on.
    Thanks.
     
Loading...