weakest battery at +INV terminal normal ?

whitestrabbit
whitestrabbit Solar Expert Posts: 39 ✭
in Off Grid Solar & Battery Systems #1
I have 8 6V Deka L16 batteries wired in series to an XW6048 inverter/MPPT @ 48V.
I noticed my weakest battery per SG readings is the one tied to the positive inverter cable. It is consistently 0.010-0.020 less than the rest. I have tried two different batteries in this location and it is the location not the battery. The battery moved away from +INV goes up in SG, and the one moved to +INV becomes the lowest SG in the string. Is this normal ?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: weakest battery at +INV terminal normal ?

    I am not sure why that would be true==Other than if there is a temperature issue (cell gets less cooling next to vent, connection to battery get hot for some reason like dirty or smaller gauge wire).

    Are the the cell temperatures the same across the bank when charging/discharging?

    -Bill :confused:
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • whitestrabbit
    whitestrabbit Solar Expert Posts: 39 ✭
    #3
    Re: weakest battery at +INV terminal normal ?
    Are the the cell temperatures the same across the bank when charging/discharging?

    My temp sensor is only on 1 battery so haven't actually measured temperature for each battery separately. I can check. All batteries are sitting on a concrete slab floor which should keep the temperature fairly consistent (slab/ground in this area I think stays around 55F year round) and are connected with 4/0 cable. One of the cables is from a different manufacturer than the rest and slightly longer but all are 4/0.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #4
    Re: weakest battery at +INV terminal normal ?

    It does not sound like the reason... You can, when the bank is under heavy load or heavy charging, just carefully touch the terminals and see if any of them are warm (no rings/jewelry!!!).

    If you have a bad connection / cable -- They can get warm / hot under heavy loads.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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