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Question about absorb & SOC

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  • Question about absorb & SOC

    Just for learning a question about charging lead acid.

    We know PV = current source and usually one charges with +/- C/10 charge rate.

    When during the charge proces OCV reaches nearly the charge-setpoint, saturation proces starts, and when the current <= C/33 the battery = FSOC.

    Ive read that when saturation begins the SOC is usually 80-90%.

    If for example we charge a 12v 100Ah @ 14.4v and Ri = 0.015 with C/10 saturation starts @ 14.25,

    (14.4 - 14.25) / 0.015 = 10.0A.
    (14.4 - 14.26) / 0.015 = 9.33A

    OCV = 14.31 amp = 6A..etc..etc.. right???

    I've read that when you charge with a (much) higher charge rate the SoC @ absorb can be 60-70%.

    So how do I relate the SoC @ absorb with the different charge rates ? Can someone explain me , preferably with a simple calculation. Thanks in advance.
    Last edited by GeorgeF; 07-24-2021, 02:16 PM.

  • #2
    It's simple. but not.'s_law

    The faster you remove energy from a battery, the less capacity it has.
    The faster you recharge a battery, the less full it is, and then you have to have a longer Float to complete the charge

    And maybe someone else has a better answer. This has been the main problem with FLA batteries ( all LA ), solar can get them up to 80% in a day, but that last 20%, the sun has started going down.
    Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A



    • #3
      Im aware of Peukerts Law. Is it not so that the energy and thus also capacity is still there but due to the (high)discharge rate the battery can "not give" the energy. When we charge we want to fill the battery with current. So, if due to peukert effect we can not fill the energy , ok. Thats is then a reasonable explanation. Thanks.