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  • Charging and discharging at the same time

    Good day,

    I have a completely off-grid small solar setup with the following components:

    A. 4 Units of 160W, 12V, 8A Mono Solar Panels, arranged in this order -
    Panel 1 & Panel 2 connected in series = Panel A (24V, 8A)
    Panel 3 & Panel 4 connected in series = Panel B (24V, 8A)
    Panel A + Panel B connected in parallel = Panel C (24V, 16A)
    Total = 640W, 24V, 16A

    B. 2 Units of 200AH, 12V Batteries connected in parallel.
    C. 1 Unit of 700W, 12V Inverter
    D. 1 Unit of 12/24V, 30A MPPT Solar Charge controller.

    The combined panels (Panel C) is connected to the charge controller, which in turn
    is connected to the batteries. The inverter is also connected directly to the batteries.

    I get an average of 5 hours of sun light daily, and my batteries are fully charged in about 8 hours (less than 2 days).

    My question now is:

    Supposing my batteries are fully charged at about 13.4V, on a hot afternoon with the sun shining bright
    and am running on the system, am I running from my batteries or from the solar panel?

    It seems am running off the batteries as they are usually depleted. Is this suppose to be so?
    Considering that the hot sun is up, shouldn't I be drawing directly from the panels and not the backup battery?

    Thanks in advance



  • #2
    If your load is les than the array output you would be running of the panels with the batteries serving as load levelers absorbing the spikes from the load.

    If you load is greater than the arrays output you would be running off of both.

    WWW

    Comment


    • #3
      I do see a problem with your set up. You have 640watts charging a 12 volt battery with a 30amp MPPT Charge controller.

      Unless I am wrong 640 watts would be converted into 53 amps trying to charge a 12volt battery which exceeds that 30 amps charge controller. So unless you are using the all excess power from the panels on your loads you could be causing an issue with the CC which may be why your batteries are not charing.

      Comment


      • #4
        Originally posted by SunEagle View Post
        I do see a problem with your set up. You have 640watts charging a 12 volt battery with a 30amp MPPT Charge controller.

        Unless I am wrong 640 watts would be converted into 53 amps trying to charge a 12volt battery which exceeds that 30 amps charge controller. So unless you are using the all excess power from the panels on your loads you could be causing an issue with the CC which may be why your batteries are not charing.
        Didn't catch that. Even if he's using more than 30Amps the charge controller is only going to allow 30A through. He may as well have bought a 30PWM and saved some money as the undersized controller is wasting about as much as a PWM would with all the panels paralleled.

        WWW

        Comment


        • #5
          Thanks WWW

          SunEagle yes you are seemingly correct if u assume the direct P = IV; that is 640 / 12 = 53.3A. However the panels have a rated current of 7.43A and Short Circuit current of 8.17A. Hence its actually just 16A. Perfectly within the safe range of the controller.

          @WWW true, PWM might have been saved me cash, however I go a great deal and also plan to expand in the future

          Comment


          • ButchDeal
            ButchDeal commented
            Editing a comment
            even if you are right that is 16A at 24V, you are charging at 12V.... thus your CC is undersized.

          • Wy_White_Wolf
            Wy_White_Wolf commented
            Editing a comment
            With a PWM controller amps in equals amps out. With an MPPT watts in equals watts out. It works like a DC-DC converter changing the excess voltage to amperage. So with 640 watts (14.86 @ 42 volts about) going in you should have 640 watts (45 amps at @14 volts) coming out. But your charge controller is limiting it to 30 amp output. Basically it is throwing away 1/3 of your array.

            WWW

        • #6
          Originally posted by shups View Post
          Thanks WWW

          SunEagle yes you are seemingly correct if u assume the direct P = IV; that is 640 / 12 = 53.3A. However the panels have a rated current of 7.43A and Short Circuit current of 8.17A. Hence its actually just 16A. Perfectly within the safe range of the controller.

          @WWW true, PWM might have been saved me cash, however I go a great deal and also plan to expand in the future
          The amp rating of a Charge controller is based on the output and battery voltage not the input amperage.

          So if you are charging a 24volt battery you can use up to 720 watts ( 24v x 30amps = 720 watts). If you charge a 12volt battery you can use up to 360 watts (12v x 30 amp = 360 watts).

          Comment


          • #7
            Hmmm undersized How so?

            The Solar Charge controller is a 12/24V hybrid. Using a multimeter, voltage from the combined panels is about 36V (max).
            If I connect back to the CC and measure the voltage from the controller I get a reading of between 12V - 14V max.

            Then again, I am not an expert hence why I am on this forum seeking guidance & knowledge. Really appreciate your comments.

            Thanks

            Comment


            • ButchDeal
              ButchDeal commented
              Editing a comment
              that means that it is capable of outputing at 12V or 24V one or the other.
              But regardless of the output voltage only 30A. so at 12V it only puts out HALF the power as at 24V.
              your 16a equation at 24V input side translates to 32A at 12V output.

          • #8
            Originally posted by shups View Post
            Hmmm undersized How so?

            The Solar Charge controller is a 12/24V hybrid. Using a multimeter, voltage from the combined panels is about 36V (max).
            If I connect back to the CC and measure the voltage from the controller I get a reading of between 12V - 14V max.

            Then again, I am not an expert hence why I am on this forum seeking guidance & knowledge. Really appreciate your comments.

            Thanks
            Once you connect the CC to the battery it will determine what the proper voltage it needs to delivery. It will then determine what the maximum input wattage it can handle. A quality CC will ignor or clip the excess wattage which just wastes it. A low quality CC may not have that type of protection and get damaged.

            What is the make and model of your CC?

            Comment


            • #9
              So YOU ARE OK with turning your 640 watts of panels into 200 watts? You are better off throwing 4 or your panels in the trash. They are not doing anything.

              Anyway to answer your question batteries cannot and do not charge and discharge at the same time. Just like saying your rcar is accelerating and decelerating at the same time,, Impossible. Batteries can only be in 3 states:

              Charging
              Discharging
              Floating

              In a properly designed system at mid day the panels generate excess power. Some goes to the batteries for charging, and the rest goes to the loads to turn your LIGHTS ON.
              MSEE, PE

              Comment


              • #10
                Dear SunKing, I do not understand your comment about "So YOU ARE OK with turning your 640 watts of panels into 200 watts".
                I am here for an education and would appreciate that, hence my request. Can you please explain rather than being sarcastic about
                trashing my panels.

                SunEagle, its a Chinese brand with brand name imprinted in Chinese but every other thing is in English, something like this...
                http://www.aliexpress.com/cheap/chea...ontroller.html

                Thanks

                Comment


                • #11
                  Originally posted by shups View Post
                  Dear SunKing, I do not understand your comment about "So YOU ARE OK with turning your 640 watts of panels into 200 watts".
                  I am here for an education and would appreciate that, hence my request. Can you please explain rather than being sarcastic about
                  trashing my panels.

                  SunEagle, its a Chinese brand with brand name imprinted in Chinese but every other thing is in English, something like this...
                  http://www.aliexpress.com/cheap/chea...ontroller.html

                  Thanks
                  I am not sure which of those is your CC but the only one I recognize as a true MPPT is the Tracer 40A one and it states that 500 watts it the maximum allowed panel wattage for a 12volt battery system. Since you have wired you 2 12v batteries in parallel that is the type of battery voltage your system is set up as and 640 watts is too much for it.

                  Comment

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