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  • Charging batteries

    Hi. I'm new here and need some help.I have a battery bank of 3 strings of 8 batteries 6 vdc each for a total of 24 6 vdc batteries in a 48 vdc configuration. I'm trying to figure out how well are the batteries charged. At 6pm the batteries are still pulling at least 15 amps. It looks to me like if they were fully charges it would pull much less.

    Any help will be greatly appreciated.

  • #2
    You do not say what the amp-hour rating of the batteries is. Nor what voltage the charge controller is set to. Nor what your total panel wattage is. It is commonly accepted that many solar battery charging systems do not deliver enough power to keep the battery bank fully charged on the basis of the limited time solar power is being produced.
    A reasonable end of charge current for lead-acid batteries will depend on the capacity of the batteries. And the battery voltage after it has been without load or charging current for three or four hours can give a rough idea of the state of charge. But the very best indicator is the specific gravity of the electrolyte, compensated for temperature.

    If you can fill in more of the details of your system, we give you a much more specific answer.

    SunnyBoy 3000 US, 18 BP Solar 175B panels.

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    • #3
      Ok. Thanks.

      Batteries are 225ah x 3 strings= Total 675 ah
      Panels 280w x 15= 4200 watts
      Charge controller is Midnite Solar classic 150 set to absorb at 59.1 volts for 3 hours and to float at 57.1 vdc
      the Temp comp is set at -5.0 mV, The output limit is set at 88 amps, the input limit is set at 99 amps, The max vdc is set at 61.4

      I will soon add a second charge controller with 3 panels 375 watts each.

      If I missed something please let me know.

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      • #4
        Originally posted by ltnhawk View Post
        It looks to me like if they were fully charges it would pull much less
        Correct sir. It could mean the batteries have not fully recharged, or you have a shorted cell. So you have 6-volt batteries. Get a volt meter out and measure each battery voltage. If one has a shorted or weak cell will be obvious as its voltage will be much lower than the others. You should see if at float voltage roughly 6.8 volts.

        If battery Voltages are equal as they should be next thing to check is your controller voltage settings and make sure they are correct and not too high over charging battery.

        If all above checks out, then they are not fully charged and operating normally.
        Last edited by Sunking; 06-01-2020, 05:03 PM.
        MSEE, PE

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        • #5
          The batteries are new. Today I realized something that I had not noticed before. I was just looking at the controller side only but when I subtracted what the inverter was using the difference was less than 2 amps which if I am reading correctly means that the batteries were fully charged. Please let me know if my appreciation is correct.

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          • #6
            Originally posted by ltnhawk View Post
            The batteries are new. Today I realized something that I had not noticed before. I was just looking at the controller side only but when I subtracted what the inverter was using the difference was less than 2 amps which if I am reading correctly means that the batteries were fully charged. .
            Pretty darn close, when fully charged and Floating will only draw a few milli-amps. Did you give them a Initial Charge before placing in service?

            MSEE, PE

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            • #7
              Not exactly. They were almost full. The technician installed them.

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              • #8
                OK fire up the generator and give them a good 24 hour EQ charge.
                MSEE, PE

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                • #9
                  Thanks

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