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max float voltage on a brand new gel 24v battery system

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  • max float voltage on a brand new gel 24v battery system

    this is my first solar system,
    145w, 24v panels
    two 12v gel batteries working at 24v, 40ah each
    pwm controller
    300w inverter.


    During the first days of use the batteries showed 27v as the floating voltage, during the days afterwards
    this voltage increased to 28, and even 29v. I'm a bit concerned that this number might be too high. ?

    the controller is a cheap chinese pwm controller with an LCD and temperature compensation, it doesn't show the temperature so I wouldn't be surprised if it doesn't have
    a temperature sensor.

    thank you!
    Last edited by ariel; 02-28-2017, 10:35 PM.

  • #2
    What does the battery owners manual say the float voltage should be? 27 sounds about right, but I think there is something else going on..

    My guess is you are using more power in a day than you panels can replace. That puts you in Charging Deficit. So what you are seeing is your controller is going through 3-stage charging of Bilk/Absorb, and if the batteries get fully charged goes to Float. Bulk Absorb voltages are up around 29 to 30 volts. Once the charger determines the batteries are fully charged, will then go to Float which is 27 volts. Your battery is never getting fully charged back up because you are using more than the panels can generate.

    If I am correct, in a few days if you keep using power, you will have a DEAD battery and a brand new Boat Anchor. Think of it like money. You have $100 and open a bank account. You make $20 a day, but spend $40 a day. In 5 days you are broke and have no money. That leaves you three options.

    1. Get a better job that pays more than $40 per day
    2. Cut back spending to less than $20 per day.
    3. Die

    Don't feel to bad, 99% of the folks who come here have the exact same problem.
    Last edited by Sunking; 02-28-2017, 05:30 PM.
    MSEE, PE

    Comment


    • #3
      hello!
      thanks for the didactic, cool answer.

      the battery's manual says 13.5-13.8 v/pc float charging. how we take this to 24v?

      I was unaware of the 3-stage charging!
      I think in my case the relation between solar panels power-batteries-and consumption is fine, the problem was that I haven't let the batteries charge enough so to go back to float, I've been over consuming since I thought that the battery was getting over charged and need it to release its juice asap.

      I'll be carefully inspecting the charger and see how it develops in the next days!

      thank you!

      Comment


      • #4
        Originally posted by ariel View Post
        hello!
        thanks for the didactic, cool answer.

        the battery's manual says 13.5-13.8 v/pc float charging. how we take this to 24v?
        You are good with words, but suk at math. Double it. 27 to 27.6 volts.
        MSEE, PE

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        • #5
          oh, I thought that it shouldn't be as easier as to double it. thanks

          this morning the batteries showed to be charged at 27 but as soon as the panel received sunlight it stared to increase until 29.
          I realised that when it was cloudy it the battery charge went down to 27. now in the night is 26.6.
          all of this without having any load
          are we talking of a crapy charger here?

          thank you!

          Comment


          • #6
            Originally posted by ariel View Post
            oh, I thought that it shouldn't be as easier as to double it. thanks

            this morning the batteries showed to be charged at 27 but as soon as the panel received sunlight it stared to increase until 29.
            I realised that when it was cloudy it the battery charge went down to 27. now in the night is 26.6.
            all of this without having any load
            are we talking of a crapy charger here?

            thank you!

            the lcd readout on your charge controller is a good indicator of charge voltage when the system is charging, when a battery is done charging (or night comes for solar), your lcd is showing battery voltage which will be high after charging and then drop over quite a few hours until it reaches its true stable voltage, what you are seeing is a temporary surface charge. Make sure your battery is fully charged, then remove it from all chargers and loads, let is sit overnight and check the voltage next day, that will give you a good indicator of your batteries actual full charge voltage.

            Comment


            • #7
              thanks for the Advice LETitROLL,
              I followed your advice, yesterday evening the battery monitor says 28v, I disconnected the battery from any loads and its charger.
              this morning each battery showed to be equally charged at 13.16v, so i guess the batteries have been charged efficiently however
              in the batteries manual it shows the float charge to be 13.5~13.8 V/PC, shouldn't I have the batteries charged within this range?

              thank you!

              Comment


              • #8
                Originally posted by ariel View Post
                thanks for the Advice LETitROLL,
                I followed your advice, yesterday evening the battery monitor says 28v, I disconnected the battery from any loads and its charger.
                this morning each battery showed to be equally charged at 13.16v, so i guess the batteries have been charged efficiently however
                in the batteries manual it shows the float charge to be 13.5~13.8 V/PC, shouldn't I have the batteries charged within this range?

                thank you!
                That all seems that it is in the right ballpark, the battery will never be up at the float voltage after sitting, float voltage is suppose to be higher so that it can cause current to flow into
                the lower voltage battery.

                Comment


                • #9
                  thank you LETitROLL!

                  Comment

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