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24v battery bank questions

Discussion in 'Technical Discussion' started by Chris W, Mar 28, 2012.

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  1. Chris W, Mar 28, 2012
    #1
    Chris W

    Chris W Member

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    Location:
    stuart florida
    good evening from HOT and humid fortaleza brazil.i have just takin over a 95ft expidition yacht that has been laid up on the hard for 14 monthes. she has been plugged in but very ofter the power goes out and the inverter kicks on , i think the inverter battery bank has been way down for some time. i have 8 big dekka 8d batts wired up into a 24volt bank. in taking off all the terminals to clean and tighten everything i found the one side of the bank,fwd4 of 8, that is connected to the negitive side of the charger to be holding 11.6-11.9v. while the other side,aft4 of 8,connected to the positive side of the charger to be holding 12.2-12.8v... they are properly layed out,wired,maint free batteries. i dont know why one side of the bank would show such a voltage difference. also found 2 of the pos terminals that are joined to the neg side of the other batts to be heavily covered in that white powdery crap. what is this stuff? and why would it only be on 2 out of 16 terminals,the rest looked like new. thanks for any thoughts.. charger seems to be putting out properly,i would think with it wired up as a big bank it should have one voltage throughout? i like mysteries as much as scooby doo.
  2. Freespool, Mar 28, 2012
    #2
    Freespool

    Freespool New Member

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    Hey Chris,
    I guess I will need to fly down and help you get underway.
    Sounds like a cell going bad in the set with lower voltage. Does one seem a little swelled up or hotter than the rest?
    The white stuff is corrosion on the terminals. If you switch to AGM batteries the terminals stay nice and clean.
  3. Chris W, Mar 28, 2012
    #3
    Chris W

    Chris W Member

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    Location:
    stuart florida
    thanks for the prompt reply. these are all agm batts. none hotter than any other,and the 2 batts that had the corrosion had higher voltage than the ones next to them. i will be replacing them in lauderdale in afew monthes but i just like to know why things are the way they are.
  4. Capt J, Mar 29, 2012
    #4
    Capt J

    Capt J Senior Member

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    The heavy corrosion is usually from acid leaking through the terminal and the battery is bad. Usually this occurs from an overcharging situation or could be from a very heavy discharge situation (pulling a lot of amps at once for a good period of time). The reason you are seeing voltage differences is because I am sure you have a bad cell in 1 or 2 of the batteries in that bank. The best thing to do is disconnect the terminals on each battery and load test it with a load tester. However, if 1 battery is bad, the entire bank of batteries needs to be changed. If they're AGM's you can also tap the sides of the batteries lightly with a hammer and you'll probably find a few that have been boiled dry and therefor bad.

    If the ones with the heavy corrosion have higher voltage, the battery connected next in line may be bad and it's drawing high amperage from the good one.
  5. CSkipR, Mar 29, 2012
    #5
    CSkipR

    CSkipR Member

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    My suspicion is the batteries on the weak side are going bad or one is bad. Charge them for 24 hrs and then measure voltage, disconnect and then see which batteries the voltage drops on. If any are bad the voltage will drop every few hours.
  6. Capt Ralph, Mar 29, 2012
    #6
    Capt Ralph

    Capt Ralph Senior Member

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    Yep
    You have a bad battery (or more) on that bank.
    Load test them all separately. If you don't have a battery toaster, use a string of light bulbs, a fan or ships dc lights to create a repeatable test load. Use this load and volt meter to find the best batteries on hand. Rotate them (top & bottom bank), charge them up and test them all again.
    Your end result should end up with an evenly charged set of batteries. Don't try to ad a bad battery in thinking it's better than nothing, it will keep the other batteries from preforming correctly.
  7. Capt Ralph, Mar 29, 2012
    #7
    Capt Ralph

    Capt Ralph Senior Member

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    Another thought
    Does your charger have 2 leads (negative and +24 volts) or 3/4 leads (negative, +12 and then +24 volts).
    I can imagine a fuse blowing somewhere and a bank not getting charged.