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Powering the loads while charging the battery

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  • Powering the loads while charging the battery

    This question may sound stupid to you but i'm new to solar tech. In a battery based off grid PV system where al loads are AC loads (lights, tv, radio...) using MPPT charge controler, inverter, is it possible to power the loads and charge the battery bank at the same time? If yes, can someone explain how does it work exactly, and if some specific type of components need to be used? Thank you.

  • #2
    To perhaps self answer your question, spend about 30 seconds looking for a thread started 08/01/2018 @ 0730 by Endeavor with the title "Dumb question about battery use and charge".

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    • #3
      Batteries will only take the amount of current that they are willing to take, at that moment. We influence it by selecting the battery-bank voltage. Thus we have a 'Bulk-charge' voltage, a 'Float charge' voltage, and an Equalize voltage. At any set voltage the amount of current flow into the batteries will change according to their needs.

      If you make more current than what the batteries need the extra is available to go to loads.

      Much of the time, my panels produce more than enough for my batteries and my load.
      4400w, Midnite Classic 150 charge-controller.

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      • #4
        It is called Kirchoff's and Ohms Law in action. There is nothing for you to control, the system self regulates itself via Kirchoffs and Ohm's Law.

        Think of the battery as a pressurized air tank where the air can flow either into or out of the tank depending on what the pressure (voltage) is doing. Now think of the Panels/Controller as an air pump where air current (electrical current) can only flow in one direction, out to either the Battery, Load, or Both. Think of the Load as a valve to vent pressure out out to atmosphere with an adjustable valve we control know as the power switch to turn something on.

        Now assume it is a bright sunny day at noon with Battery fully charged up to full pressure and the output Load valve is closed. No air curents flows because it has no where to go and pressure has equalized. Controller has pumped air and pressurized the air tank to capacity of 14 pounds. In other words no air current is flowing system is collecting dust.

        Now we crack on the Load Valve and let air out. Not much just enough to make a fan motor move. As soon as we open the valve, air current flows, and the pressure begins to drop, but the Controller is already on line applying pressure and the pump starts pumping again supplying all the air we are letting out of the Load Valve. Close the Load valve, air current and controller pumps stops because it is at the pressure set point. No air current means system collects dust.

        Now we open the valve wide open. Controller pump cannot keep up, pressure drops, and now the compressed air tank now makes up for the shortage by keeping the pressure up allowing air current to flow. Then we close the valve down to normal low air flow, controller now is pumping in more air than what we a letting leak out and keeps running until the pressure reaches set point of 14 lbs and shuts off.

        There was nothing in our control or anything we can add to improve what physical law takes care of for us.

        Kirchoff Law on the system is the NODE formed by where the Controller, Battery, and Load all connect together which is the battery Term Post. Kirchoff's Law states all current flowing through the Node must algebraically sum = 0 amps. Current from the Controller can only flow one direction and always negative numbers. Battery air flow current on the other hand can be either Negative or Positive because air current can flow in or out of tank. So when you sum the 3 paths of air current can flow will always equal 0. Ohms Law is the pressure and air flow rate.
        Last edited by Sunking; 08-05-2018, 11:25 PM.
        MSEE, PE

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        • #5
          Originally posted by Newbie88 View Post
          This question may sound stupid to you but i'm new to solar tech. In a battery based off grid PV system where al loads are AC loads (lights, tv, radio...) using MPPT charge controler, inverter, is it possible to power the loads and charge the battery bank at the same time? If yes, can someone explain how does it work exactly, and if some specific type of components need to be used? Thank you.
          Yes. No specific components needed.

          If your batteries are discharged, and your solar system is supplying more current than your loads need, your battery will charge.

          if your batteries are at least partly charged, and your solar system is supplying less current than your loads need, your battery will discharge.

          All that happens inherently without you being required to do anything.

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          • #6
            Thank you all for the answers.

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