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Hydrometer reading VS Percent SOC?

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  • Hydrometer reading VS Percent SOC?

    Today we have another overcast day here in Western TN. The Hydrometer reading this morning was 12.35 which is a little on the low side. My Whiz-bang
    JR shows 93 % SOC it was 100 % percent yesterday at Sundown. I am not sure that the Whiz bang Junior is accurate. I assume there is no calibration? Hey
    all this is new to me - I understand most of the concepts, but batteries are a mystery. I currently have voltage settings as per manufacturer. Yesterday I
    increased the float voltage from 52.1 to 54.4 which is standard for the classic 150's. My thinking is that I will get a higher rate of charge on the batteries. I have
    also noticed that with 3 classic 150's sometimes they take turns charging and one or 2 of them will go into retain mode! Another factor is my battery temperature
    is at 58 degrees F. My shop runs very little load and when I go in for the evening my inverter will read about 80 watts which is very lightly loaded. What other
    setting should I be looking at on the 150's? How do I know that my whizbang junior is calibrated correctly?

    Thanks for the help,

    Bill

    ps -would love to talk to someone on phone or ham radio - I have a lot of questions!
    1kwGrape,6kwSharp,3CL150
    XW6048-440 ah @ 48vdc

  • #2
    SOC voltages are mostly useless. Only a Temperature Corrected Hydrometer can tell you the SOC accurately in real time.

    The SG is temperature dependent. If the battery temperature (not air temperature) is above or below 77 degrees F can fool you into incorrect readings. You will have to look at your specific manufacture of your battery but typical Temperature Correction Factor goes something like this: below 77ºF subtract points (0.03 per 10ºF), and above 77ºF add points.

    On your controller if you have Temperature Compensation, use it. It works in reverse with respect to SG. As the battery temp falls below 77 degress, the voltage set point goes up. As temperature goes up, voltage goes down. Consult you battery manufacture for the correct Compensation. Typically it goes something like: Subtract 0.005 volt per cell (VPC) for every 1°C above 25°C or add 0.005 volt per cell for every 1°C below 25°C
    MSEE, PE

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    • #3
      Originally posted by Sunking View Post
      SOC voltages are mostly useless. Only a Temperature Corrected Hydrometer can tell you the SOC accurately in real time.

      The SG is temperature dependent. If the battery temperature (not air temperature) is above or below 77 degrees F can fool you into incorrect readings. You will have to look at your specific manufacture of your battery but typical Temperature Correction Factor goes something like this: below 77ºF subtract points (0.03 per 10ºF), and above 77ºF add points.

      On your controller if you have Temperature Compensation, use it. It works in reverse with respect to SG. As the battery temp falls below 77 degress, the voltage set point goes up. As temperature goes up, voltage goes down. Consult you battery manufacture for the correct Compensation. Typically it goes something like: Subtract 0.005 volt per cell (VPC) for every 1°C above 25°C or add 0.005 volt per cell for every 1°C below 25°C
      US battery says subtract 0.028 for every 10 degrees above 80F and add 0.028 for every 10 degrees bellow 80F. I will figure it out
      tomorrow. Need to convert to Celsius! It was a rainy - poor solar day here in West TN. Should be better tomorrow!
      1kwGrape,6kwSharp,3CL150
      XW6048-440 ah @ 48vdc

      Comment


      • #4
        Originally posted by BMAD View Post
        US battery says subtract 0.028 for every 10 degrees above 80F and add 0.028 for every 10 degrees bellow 80F.
        I assume you are talking about SG and not voltage. Nothing to convert if your thermometer uses Fahrenheit
        MSEE, PE

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