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Query on my battery bank's state of charge

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  • Query on my battery bank's state of charge

    Hi all,

    It's been a while since I was here and thanks to those that helped with giving me advice. I've got my solar power system up and running in the last 2 days but I was wondering if someone could help me clarify a question I have about my battery's SOC.

    This is my system which I'm testing with x2 100W 12V panels:

    24V battery bank (x2 100Ah 12V Casil sealed lead-acid batteries)
    MidNite Classic 200
    Victron Phoenix inverter 24v 1200W (not running it anywhere near full capacity)
    x2 100W 12V solar panels

    The advice I received was that the majority of first-timers are going to ruin their batteries - so these two were picked up new but on the cheap (someone was moving so I got a good deal). Last time I was told that these were primarily for telecommunication purposes and not to expect too much out of them. I figured they would be good to learn on.

    In the Classic I entered that the battery was 100Ah and 24V. I have a Whiz Bang Jr linked to the classic and when I set it up it showed me that the SOC was 100% - this surprised me because the voltage (with only the classic being powered) was 24.2V. I had in my mind around 12.7V = 100% for each battery in the series giving 25.2V or so if full.

    This is the link to the battery pdf http://www.casilbattery.com/products...ductId=83.html

    Also I'm using the default bulk, float and equalize on the midnite (28.6V, 27.2V, 28.6V respectively) - if anyone has any suggestions based on that pdf, I'm all ears. Thanks!

    This image shows the MidNite panel - it was under a small load at this point.

    Capture.jpg
    Last edited by DavidH; 10-22-2020, 07:57 PM.

  • #2
    The only true way to tell state of charge accurately is to use a refractometer.. everything else is pretty much just an estimate based on external values and established constants.. Hydrometers can get you very close, but a refractometer is better. Of course, with a sealed battery, using either meter to test acid levels is not practical.


    I'm not sure about your wizbang device, but it might have a setting for battery voltage or need some kind of calibration. A lot of systems out there perform their own self-calibration based upon the first full charge/discharge cycle.

    Sorry, wish I could be of more help.

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    • #3
      Is there a question? If you want to know your batteries SOC, read it with a hydrometer.
      MSEE, PE

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      • #4
        "If you want to know your batteries SOC, read it with a hydrometer"

        Is that possible on an SLA battery?

        I too am looking for a way to more accurately know my battery's SOC.

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        • #5
          Originally posted by Mattboyrdee View Post
          "If you want to know your batteries SOC, read it with a hydrometer"

          Is that possible on an SLA battery?

          I too am looking for a way to more accurately know my battery's SOC.
          Unfortunately a sealed battery's SOC can't be measured using a hydrometer. So the only way to get an estimated SOC value is to measure the voltage after the battery has been resting for more than a few hours after charging. An even then it is just an estimated value.

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          • #6
            Bummer. I thought that would be the case but was hoping otherwise.

            Thanks.

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            • #7
              You can get a fancy meter that counts watts in and watts out, and if you use the right loss factor in the meter, you can get pretty close, but after a couple months watching a volt meter, you can figure in your mind, what the SOC is from the voltage. With my bank, (NiFe, not lead acid) I run the generator at 52V. Happy at 60V and full after absorb at 67V
              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

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

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