6 Replies Latest reply on Feb 15, 2019 2:13 AM by Pavel.Simon

    connecting different batteries to PV system

    bjornderian

      I have a PV system and a lead acid battery bank already attached with a solar charge controller. I want to charge a portable Lithium ion battery using excess energy during the day.

       

      Is it possible to charge the portable battery without going through a dc to ac inverter and another ac to dc charger which would decrease efficiency? basically, charging directly from DC with another battery already attached to the charge controller.

       

      If yes, how? and what do I need

        • Re: connecting different batteries to PV system
          genebren

          A lot will depend on your solar system specification and wiring.  Typically, the panels are connected in serial strings to get a high enough DC voltage that they do not need to add a voltage doubler on the front end of the power inverter.  Then extra panels are add in parallel circuits to add additional current.  Depending on the voltage range of you DC output of the solar array, you can get DC-to-DC convertors that will handle 150-400V inputs to provide 5V to 12V outputs. This would provide the correct range for many Li-Ion chargers.  What you will be missing in such an arrangement is the Peak Power tracking capability and protection circuitry that is built into the inverter.  If what you are dealing with is your excess capacity (beyond the lead acid battery bank), concerns of efficiency is sort of a moot point, as unless you are selling back your excess, the energy was not going to be captured anyway, so maybe an AC based charger would work fine.

           

          Gene

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            • Re: connecting different batteries to PV system
              bjornderian

              genebren  wrote:

               

              Depending on the voltage range of you DC output of the solar array, you can get DC-to-DC convertors that will handle 150-400V inputs to provide 5V to 12V outputs. This would provide the correct range for many Li-Ion chargers.  What you will be missing in such an arrangement is the Peak Power tracking capability and protection circuitry that is built into the inverter. 

               

              Thank you for your response in advance. I still have some questions left unanswered. How would the circuit be arranged, would it be okay to connect it directly to the DC bus after the MPPT charge controller. How would connecting it this way interfere with the Peak Power tracking capability of the charge controller?

               

              SInce I will be charging the li-ion only when the lead acid is full, what device would I need to shut off the connection to the lead acid and switch to the dc to dc controller-> li-ion charger automatically?

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                • Re: connecting different batteries to PV system
                  genebren

                  These are some great questions.  The answers to these questions would need very deep analysis of the actual equipment and the system interconnects.  This is not something that I could answer just by a rough description of your setup.  The simplest way to charge some Li-Ion batteries would be to connect a A/C powered charger to the output of the system.  This would allow all of the system's protections and features to operate as normal using excess energy to charge your extra batteries.  You could potentially be able to automate the charging by monitoring the charge status of the lead-acid batteries and switching on the Li-Ion charger when the storage batteries are full.

                   

                  If you wanted a more efficient and integrated approach your best approach would be to contact the manufacturer of the inverter system to see if they have any recommendations.

                   

                  Gene

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                  • Re: connecting different batteries to PV system
                    Pavel.Simon

                    Unfortunately there is missing information for proper answer:
                    1. with portable Lithium ion battery - do yo mean 5 V USB powered device?
                    2. lead acid battery bank - are they 12 V or 24 V setup? Or even other voltage?
                    3. current charge controller: is it already equipped with some "intelligence" to let you know, that lead acid battery bank is full? Or is standard without some type of communication possibility?

                     

                    More details give possibility to better answer. But in general, yes it is possible, but there would be need more additional circuitry to be done.

                     

                    Better one picture than 1000 word:diagram and questions

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                      • Re: connecting different batteries to PV system
                        bjornderian

                        Pavel.Simon  wrote:

                         

                        Unfortunately there is missing information for proper answer:
                        1. with portable Lithium ion battery - do yo mean 5 V USB powered device?
                        2. lead acid battery bank - are they 12 V or 24 V setup? Or even other voltage?
                        3. current charge controller: is it already equipped with some "intelligence" to let you know, that lead acid battery bank is full? Or is standard without some type of communication possibility?

                         

                        More details give possibility to better answer. But in general, yes it is possible, but there would be need more additional circuitry to be done.

                         

                        Better one picture than 1000 word:diagram and questions

                        To answer your questions:

                        1. I would mean something bigger, a 24V li-ion battery. something to power an electric boat

                        2. Lead acid battery bank they are 48 V setup

                        3. It's an MPPT charge controller so it has 'intelligence' and know when the battery is full

                         

                        Here's a picture of my proposed configuration: (by comm port you mean ethernet??)

                         

                        Would this work, I'd like to also have the possibility to charge the batteries in parallel (If I have multiple). Would it cause confusion to the chargers?

                          • Re: connecting different batteries to PV system
                            Pavel.Simon

                            A: by comm port you mean ethernet?? - it could be ethrnet, but RS485 or RS232 is fine too. Different type, different approach to connect, but result should be similar.

                             

                            B. MPPT Charge Controller: I am afraid, that your diagram shows, that it cannot be connected like that. Charger controller is doing what is require to do - control charge. Usually it has three electric "ports" and some others (USB, comm port ...).

                            1. electric - for PV panels

                            2. electric - to connect batteries (there is made some magic, and even low cost charger could detect what battery is connected, at least voltage level). And different type battery has different charging diagrams and details. You cannot mix different chemistry there, you would kill both battery...

                            3. electric - LOAD port. There controller tries to driveller constant voltage (depends on settings). And when on port 2 (battery) it finds, that battery is empty, it switch off this port. You can plug there LOAD: DC/AC inverter (grig-on, or off-grid), you could connect anything other, but remember, that is unreliable supply - when battery on port 2 is empty, it will be powered down (switch off).

                            Result: on your picture is DC Bus 48V. But it is not how charger controller works...

                             

                            Reason, why I asked for comm port, is, that this communication could inform you, that Lead battery is full, and you could connect another charger to PV. Depends on intelligence of your charger, you have possibility to connect it to load port (num. 3 above), or you would need to reconnect directly PV panels to different charger.

                             

                            What type of controller do you have?

                             

                            My type of charger controller has those connection:

                            It is low cost, but as you can see, only one battery port, and battery chemistry is set by menu. Lead acid has different from Li-ion.