Battery Failure Mode

Discussion in 'General Electronics Chat' started by GKP, Nov 2, 2014.

  1. GKP

    Thread Starter New Member

    Aug 15, 2014
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    Marine environment; house bank of batteries four 12volt AGM wired for 24volt output ; Charger 3 stage 100 amp with no thermal sensor; batteries all 6ms old
    Battery bank heat readings (on top of battery case with infrared heat gun) one battery reading 128F with localized reading at 141F over one cell; battery charger on; ambient temp. 80F
    Is this enough information to indicate a very low internal resistance in one cell as I have assumed?
     
  2. MrChips

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    Oct 2, 2009
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    For starters, I would try disconnecting and charging the batteries individually.
     
    Last edited: Nov 2, 2014
  3. kubeek

    AAC Fanatic!

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    If it was the case, it would be high internal resistance, not low.
     
  4. Dr.killjoy

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  5. #12

    Expert

    Nov 30, 2010
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    One cell heating up 1.43 times as much as its neighbors is a good indicator that you have already found the problem. 141F is in the, "burn your fingers" range, and that's only the case outside where the heat is.:eek:

    So, one bit of missing information is: How big are these batteries that you think you can push kilowatts through them?
     
  6. Kermit2

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    Feb 5, 2010
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    rated capacity = 25 amps for 257 min. @ 11.8/11.7 volts per cell.
    This is a very deep discharge.
    For my system I aimed for a 12.0/11.9 volt per cell final discharge point, which would be a liitle more than 50% discharge. I have 8D size batteries, weighing about 1 20 lbs. each, wired in series to make 48 volts. Since I only want a 50% discharge, I divide capacity by 2. work out new capacity 25 amps for 128.5 min.= 3212.5 divided by new discharge time; 12 hrs.(720 min.) equals new current limit; 4.5 amps. This is what i do to make my batteries last until next sunrise. charge rate is figured for a 5 hour span. they got me through a hurricane once with Air conditioning in one room, coffee, and TV and internet. The system you have described will have about 1/2 of the capacity, or just little less than 1/2.
    if you increase the amount of discharge you get more capacity but shorten bsttery life severely.
     
  7. GKP

    Thread Starter New Member

    Aug 15, 2014
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    These are 8D AGM 256 AH
     
  8. GKP

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    Aug 15, 2014
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  9. GKP

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    Aug 15, 2014
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    In order to get the house bank operational I took an identical battery from my start bank (we were in a remote location) and replaced the bad battery. House bank operated normally. Charger made it down to float voltage. But ....I then put the bad battery into the start bank thinking that it might still be good enough to start the engine and if it was not I would be able to use my parallel switch to start in any case. Wrong; could not even get the solenoid to click with the parallel switch engaged. This led me to believe that the bad cell must have really low resistance. Does this make sense?
     
  10. Alec_t

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    Sep 17, 2013
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    High resistance would make more sense, as Kubeek said in post #3.
     
  11. GKP

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    Aug 15, 2014
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    Sorry, I meant that the charger was capable of 100 amps. Charger output was around 28 amps of which 10.8 amps was going into the battery. Charger would not go into float mode.
     
  12. GKP

    Thread Starter New Member

    Aug 15, 2014
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    I
    Please explain. If high internal resistance my paralleling the second starting batteries should have worked. If the cell had high resistance the whole bank (2 batterers in series for 48 v) just acts like a reduced output bank (normally dead battery)

    I am trying to get a handle on the failure mode so I can ascertain if I have a problem with my parallel switch system.
     
    Last edited: Nov 3, 2014
  13. Lestraveled

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    May 19, 2014
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    Two reasons:

    - When you used the battery to start your engine and it failed to do so, this indicates a cell with high resistance.

    - The higher the resistance of a cell the more heat it will dissipate. Wattage (heat) = Amps squared, times resistance. The cell with the highest resistance produces most of the heat.
     
  14. kubeek

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    Sep 20, 2005
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    What do you mean by parallel switch? Please show a diagram of how the batteries are acutally connected together. I think everyone was imagining a simple series connected bank of batteries up to this point.
     
  15. Dr.killjoy

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    Apr 28, 2013
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    How did you figure you got 24v from 4 12v batteries in a serial configuration ???
     
  16. kubeek

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    Allright, missed that.
     
  17. Kermit2

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    if the charger stayed in full charge mode snd could not reach float voltage levels, i would suspect a SHORTED cell in the battery. the high temp in in one cell further confirms the shorted out condition. being AGM type it is not possible to wash out the cell and remove the short.
     
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  18. Dr.killjoy

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    Sorry I had to jump on that cause normaly you guys lose me really fast with the over overwhelmed knowledge you guys have..
     
  19. Lestraveled

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    I suspect he meant series parallel configuration. Pretty standard.
     
  20. GKP

    Thread Starter New Member

    Aug 15, 2014
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    Correct
     
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