Battery Bank Question

54d18
54d18 Solar Expert Posts: 81 ✭✭✭
in General Solar Power Topics #1
Hi All, I have a battery bank consisting of 8 6v batteries, 225AH each, connected as 12v.
I have a set of bus bars that each set of batteries connect to for my 12v.
I was checking the charging current, and notice that one set of batteries was getting only1.2A,
while the other 3 sets were all at about 8A, would this be indication of a failing set of batteries?

Thanks,

T
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Comments

  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    Not necessarily, a parrallel connected bank should be connected with the load and charging diagonally opposite to avoid imbalance, if you could,  provide a drawing of how the batteries are connected, this would enable  all to determine what it is you have.
    Having 4 parrallel strings is not desirable,from a ballance point of view, also include if they are flooded or AGM, if flooded the specific gravity of the string accepting a lower current, could mean it is in a higher state of charge than the others, details, the more the better 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.  
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Or it can be a loose/corroded connection or cable. Or a bad cell/battery.

    Assuming you have the bank wired correctly:

    www.smartgauge.co.uk/batt_con.html

    Use a volt meter and check the battery voltages while charging/discharging/resting (look for one battery "different" than the rest). You can also use the volt meter (set to 2 volt or 200 mVolt full scale) and check wiring/connections for high resistance (higher voltage drop) while charging/discharging (looking for bad connection or cable).

    And a hydrometer to check the specific gravity.

    How old is the battery bank? Have you had any problems with the batteries before?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • myocardia
    myocardia Solar Expert Posts: 118 ✭✭✭
    edited September 2017 #4
    This is the link that Bill meant to provide:
    http://www.smartgauge.co.uk/batt_con.html
    DoD= depth of discharge= amount removed from that battery   SoC= state of charge= amount remaining in that battery
    So, 0% DoD= 100% SoC, 25% DoD= 75% SoC, 50% DoD= 50% SoC, 75% DoD= 25% SoC, 100% DoD= 0% SoC
    A/C= air conditioning AC= alternating current (what comes from the outlets in your home) DC= direct current (what batteries & solar panels use)
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  • 54d18
    54d18 Solar Expert Posts: 81 ✭✭✭
    #5
    I knew there would be some good info here, my setup is pretty much the same as method 3,
    except that the common points are on bus bars, and the batteries are 2 6v in series to make
    12v on the bus bars.
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  • myocardia
    myocardia Solar Expert Posts: 118 ✭✭✭
    edited September 2017 #6
    I'm not able to access their site right now. They seem to be under a DOS attack of some sort. Anyway, if both the negative and the positive leads that are going to the bus bars come from the same battery (and a single set of two 6V batteries in series is the same as one 12V battery, in this instance), that is your problem. You are charging only one battery, and then later sharing it's charge with the other 6 batteries/3 strings. While using power, you will be using only one pair of batteries, and then having the other 6 attempting to recharge them, slightly afterward. Use and charge the positive connection from one corner, and the negative connection from the opposite corner, to mitigate the imbalance.    edit: BTW, a lot of times it's easier to use from one set of corners, and charge to the opposite set of corners.
    DoD= depth of discharge= amount removed from that battery   SoC= state of charge= amount remaining in that battery
    So, 0% DoD= 100% SoC, 25% DoD= 75% SoC, 50% DoD= 50% SoC, 75% DoD= 25% SoC, 100% DoD= 0% SoC
    A/C= air conditioning AC= alternating current (what comes from the outlets in your home) DC= direct current (what batteries & solar panels use)
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    Myocardia,

    There is a typo in your link... Here is the correct one (and it seems to be working fine):

    http://www.smartgauge.co.uk/batt_con.html

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • myocardia
    myocardia Solar Expert Posts: 118 ✭✭✭
    #8
    BB. said:
    Myocardia,

    There is a typo in your link... Here is the correct one (and it seems to be working fine):

    http://www.smartgauge.co.uk/batt_con.html

    -Bill

    Hah! I had transposed "gauge" into "guage"! :D Thanks for pointing that out, I will correct it in the original post. After looking at battery configuration #3, it sounds as if you have either a corroded or loose connection in your battery bank, as Bill/B.B. mentioned earlier, assuming that all 8 batteries are the same age, of course. Since you already know which battery pair has the lower amperage, the problem is going to be in one of the connections with that pair. Don't forget that the pair has 6 connections, BTW.  The four on the batteries themselves, plus the two on the bus bars. With DC, it only requires one of those 6 to not be making a good connection, and the amperage to/from the battery will be lower.
    DoD= depth of discharge= amount removed from that battery   SoC= state of charge= amount remaining in that battery
    So, 0% DoD= 100% SoC, 25% DoD= 75% SoC, 50% DoD= 50% SoC, 75% DoD= 25% SoC, 100% DoD= 0% SoC
    A/C= air conditioning AC= alternating current (what comes from the outlets in your home) DC= direct current (what batteries & solar panels use)
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  • 54d18
    54d18 Solar Expert Posts: 81 ✭✭✭
    #9
    I plan to have a better look this weekend while at the camp,
    clean and inspect all connection and go from there.
    I will post any noticed issues and results.

    Thanks for the feedback,

    T
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  • 54d18
    54d18 Solar Expert Posts: 81 ✭✭✭
    #10
    I checked each batteries voltage while charging at close to 30A,
    each battery was 6.7-6.8V except the 2 in the string that were not
    taking as much current, the voltage on these 2 while charging was 6.2 and 7.2

    I have removed them from the bank, and saw that the voltage of each went immediately down
    to 5.7 and 6.

    I hope to see some improvement in the system come next weekend.
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