Possible Cause of SLA Battery Failure?

Discussion in 'General Electronics Chat' started by NM2008, Sep 14, 2011.

  1. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Hi,

    I was given a battery booster/jump start power pack to repair. The problem I was told was that it would not charge, and was told that more than likely it was the charger that was at fault.

    I tested the adapter/charger it was capable of putting out its rated 15V and under dummy load close to the rated 500mA.

    Checked the socket and plug everything seemed fine.

    Tried to charge it on my own reliable SLA charger and still nothing. When connected no current rise was seen on the ammeter.

    So I took it appart and found the that 12V 17Ah internal battery was discharged to 1V.

    Moved it around and noticed that the case was bulged and had split at some stage.




    This device is also relatively new and has been used/ charged and discharged only a couple of times.




    What I tought odd, was that there was no charge circuit within this booster pack to monitor overcharging/float charging..etc... the wall adpter literaly plugs 15v directly aacross the battery. I was always of the thinking that non smoothed power adapters were not suitable for charging SLA batteries.

    What I would like to know is has anybody else witnessed this type of battery failure before?
    What causes this type of failure........overcharging.....deep dis-charging, too much load on the battery?


    (On the blue label in photo 1 it can be seen that the device boasts 900A starting current, the positive negative tabs alone due to the thickness would barley stand 100A for 10seconds, let alone 900A for 1 second of starting, where did they get 900A amps from? the battery certainly is physical not capable of even producing 100A for 10 seconds.)


    Regards NM
     
    Last edited: Sep 14, 2011
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Chinese stuff. and oh yes, over charging.
     
  3. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Yes "Chinese stuff".

    But why couldnt they not fit something to prevent this from occuring, wouldnt this not be considered dangerous? Yet it has CE stamps and purchased from a reasonable reputable goods store.


    Could this have occured from been left on charge over night?
    Could the ripple in the supply adpter cause the battery to split?


    NM
     
  4. debe

    Well-Known Member

    Sep 21, 2010
    947
    184
    I have a simmilar unit & it certainly wont crank a 6cyl engine if the vehicle battery is totaly flat, ok if its at the slugish turnover point. Ive never used the supplied charger as it will eventually cook the battery. I use an automatic SLA mains charger & have had no problems with the battery. They are built to a price not quality.
     
  5. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    debe

    I have a similiar automatic SLA charger, which I have had for a while now its about 10 times the size of that wall adapter and has alot of control circuitry.

    Its amazing that the people who designed this device, practically chose to ignore the fact that its a little more complicated to charge one of these batteries, than just connecting two wires to it and hoping for the best.

    In that respect the charger they supplied with the product, ruined the product after very llttle use. Even a simple/cheap relay on a timer could have prevented this.


    In comparsion to the wall adpter which gives constant current does the automatic charger limit current nearing the end of the charge cycle?


    Thanks
    NM
     
  6. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    NM

    Batteries are like your dog, you will shorten his life if you over feed him or under feed him, your dog can't run for 10 blocks if you don't exercise him, If your dog gets to hot or to cold he is not going to do well.

    If you want a lead Acid battery to last, charge the battery to 14.8 volts and when the current drops to 1 amp it's full stop feeding it, watch out for thermal runaway. Exercise the battery or it will not remember how to put out 900 amps (advertising hype, with a condition battery it will put out 900 amps for a few seconds in a dead short), Lead Acid batteries want to live at 70 degrees.

    We use jump starters like that in our fleet of vehicles, we don't leave them pledged in and once every month or two we charge it at 14.8 volts until the current stop dropping, this will equalize the cells in the battery.

    My suggestion is to replace the battery, use the charger it comes with and unplug it when it's done charging, exercise it once a month with a load like a battery tester until it gets down to 11 volts under a 100 amp load and then recharge it. If it isn't used very often do a equalizing charge on it a couple times a year.

    Good Luck
     
    NM2008 likes this.
  7. #12

    Expert

    Nov 30, 2010
    16,346
    6,835
    You have not told enough for anyone to know if the automatic charger limits current near end of charge.

    I would like to say that ripple does not matter. Non-smoothed current will charge a battery properly.
     
  8. vrainom

    Member

    Sep 8, 2011
    109
    19
    Maybe the problem was the exact opposite, if it was left discharged for too long.
     
  9. Crispin

    Member

    Jul 4, 2011
    88
    2
    Is this irrespective of the size of the battery? 7Ah vs 270Ah?

    I've had a couple of batteries bulge due to the wall-wart chargers. Mine was 16something volts :(
     
  10. MrChips

    Moderator

    Oct 2, 2009
    12,451
    3,370
    This is an on-going problem and project of mine that I have not found the time to deal with. There are a number of concerns:

    1. An intelligent 3-stage charger that is reliable. I have $400 worth of overcharged SLA batteries all bulging from overcharging.
    2. A charger that charges batteries independently even when wired in series. One bad battery will result in the rest being over charged.
    3. Monitoring the temperature of each battery.
    4. Possibly a timer that shuts down the charger.
    5. More importantly the potential for a fire if left unattended.

    For the time being, monitor your batteries while being charged and do not leave unattended.
     
  11. iONic

    AAC Fanatic!

    Nov 16, 2007
    1,420
    68
    Yeah, overcharging, especially under adverse temperature conditions, the trunk of a hot car...etc. 15V @ 500mA will charge the battery, but is far too much to leave plugged in indefinitely. It's too high a float charge for both the rated voltage and current.
     
  12. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    The charger shown here is not the automatic one, this booster does not have an automatic charger.

    I said earlier that personally own an automatic charger.

    NM
     
  13. NM2008

    Thread Starter Senior Member

    Feb 9, 2008
    135
    0
    Smoke Maker

    Thanks for your response, good comparsion, batteries and the dog!

    You stated:
    "watch out for thermal runaway"
    By this do you mean with respect to current. As the battery cells internally heat they will take more current?

    Would I be correct in saying this?

    NM
     
  14. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    Some batteries have high internal resistance, especially bad ones or questionable ones. Pushing current through a battery with high internal resistance causes the heat, and the heat causes a increase in internal resistance, if you walk away and don't have a temp cutoff or alarm, bad things start to happen.

    So the answer is yes, current will start to increase causing more heat, and this keeps going until you hear your self saying what did I do. :mad:
     
  15. Smoke_Maker

    Active Member

    Sep 24, 2007
    126
    15
    YES, charge lead acid batteries to 2.466 volts per cell to equalize the cells.

    You do not want to equalize the cells every time you charge the battery, it's not needed. Charge the battery to 2.4 volts for a normal charge and equalize when needed.

    When batteries are in series you will know when they need equalizing, after a normal charge and rest period of 8 hours you can check the voltages and if the highest voltage to the lowest voltage is more than .02 volts per cell on a good pack of batteries it needs equalizing, as the pack ages you will need to raise that number.
     
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