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  • Parallel batteries

    Hi all
    I am currently setting up a off grid system i plan to use on my house and since looking on this forum have some concerns because i plan to parallel my batteries
    I have 32 6volt 125ah batteries i managed to get for free in good condition
    I currently have them set up in 4 banks for 48v 500ah supplied by 1000watts of panels and a outback fm80 charge controller to supply power to a shipping container untill i build the house
    Will the batteries be ok in parallel? i have the + and - terminals of each bank wired to common points so it isnt in a ladder setup
    Would it benifit from connections between the banks at 12v 24v and 36v points? i was planning to do this anyway so i could run small 12v loads from different points of the entire 48v bank

    Thanks

  • #2
    Originally posted by johnno113 View Post
    Hi all
    I am currently setting up a off grid system i plan to use on my house and since looking on this forum have some concerns because i plan to parallel my batteries
    I have 32 6volt 125ah batteries i managed to get for free in good condition
    I currently have them set up in 4 banks for 48v 500ah supplied by 1000watts of panels and a outback fm80 charge controller to supply power to a shipping container untill i build the house
    Will the batteries be ok in parallel? i have the + and - terminals of each bank wired to common points so it isnt in a ladder setup
    Would it benifit from connections between the banks at 12v 24v and 36v points? i was planning to do this anyway so i could run small 12v loads from different points of the entire 48v bank

    Thanks
    Hi john,

    You will have far more problems with your batteries with four strings in parallel than if you had built up the same total energy storage using larger lower voltage batteries (such as 2V each).
    Since you already have the batteries, you will have to watch them carefully during use to make sure that they share current as evenly as possible. Look at the guidelines at http://smartgauge.co.uk/batt_con.html for more details.

    For lead acid batteries, it is generally not a good idea to make ladder type interconnections, even at only some of the steps.
    SunnyBoy 3000 US, 18 BP Solar 175B panels.

    Comment


    • #3
      Originally posted by johnno113 View Post
      ...Would it benifit from connections between the banks at 12v 24v and 36v points? i was planning to do this anyway so i could run small 12v loads from different points of the entire 48v bank

      Thanks
      Very bad idea. It would very quickly create an out of balance situation between strings and even batteries in the string. If you need lower voltage get a DC-DC converter.

      Another problem is you solar array is not large enough to properly charge that size of bank. The most it can supply is about 20amps. LA batteries should be charged at C/8 to C/12 rate with C/10 usually being ideal. C/10 would be 50Amps in a 500AH bank.

      WWW

      Comment


      • #4
        Originally posted by johnno113 View Post
        I have 32 6volt 125ah batteries i managed to get for free in good condition... I currently have them set up in 4 banks for 48v 500ah supplied by 1000watts of panels and a outback fm80 charge controller
        You o not have enough panel wattage to support your batteries. A 48 volt 500 AH battery needs at minimum 2000 watts, and optimum 2500 to 3200 watts.

        Would it benefit from connections between the banks at 12v 24v and 36v points? i was planning to do this anyway so i could run small 12v loads from different points of the entire 48v bank
        No just asking forbid trouble.
        MSEE, PE

        Comment


        • #5
          Thanks for all the advice
          I will avoid tieing the strings like i planned and have ordered a dc-dc conerter to get the 12v output i was after
          when i use this system on the house i plan to upgrade to 4000watts of panels but at the moment i am not using much load only 1-2 kwh per day and the 1000watts of panel manages to charge it and go into float, is this ok or sould i have more panels and more amps to correctly charge the batteries?

          Comment


          • #6
            Originally posted by johnno113 View Post
            Thanks for all the advice
            I will avoid tieing the strings like i planned and have ordered a dc-dc conerter to get the 12v output i was after
            when i use this system on the house i plan to upgrade to 4000watts of panels but at the moment i am not using much load only 1-2 kwh per day and the 1000watts of panel manages to charge it and go into float, is this ok or sould i have more panels and more amps to correctly charge the batteries?
            As long as you have enough time between uses or low enough usage to get the battery into float at least every couple of days, you might be OK.
            But even then you will probably want to use a generator or other power source for equalizing and more important for stirring up the electrolyte to prevent stratification. That is one reason for having higher current available from time to time.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

            Comment


            • #7
              Your 1Kw PV array will be a trickle charge (20A) for a 500ah bank (if you calculated the bank size correctly).

              If all you are doing is keeping the batteries on charge, and maybe some light loads on weekends, you should be OK. Give the batteries a slosh once a month, to stir up the electrolyte, if you can.
              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

              Comment


              • #8
                ok so it sounds like they will be ok with the 1000watts as they have been getting to float
                the batteries are Yuasa UXH125-6FR 6volt 125ah and i have 32 of them
                i dont know alot about these batteries if there is any regular maintenance to be done on them?

                Thanks

                Comment


                • #9
                  Originally posted by johnno113 View Post
                  ok so it sounds like they will be ok with the 1000watts as they have been getting to float
                  the batteries are Yuasa UXH125-6FR 6volt 125ah and i have 32 of them
                  i dont know alot about these batteries if there is any regular maintenance to be done on them?

                  Thanks
                  Since those are sealed (AGM?) batteries, you cannot check cell specific gravity, nor do you need to keep the electrolyte levels up.
                  So the main "maintenance" is to check voltages regularly to make sure that you are not going down in State Of Charge (SOC).
                  They also do not need electrolyte "stirring" to prevent stratification since there is no free electrolyte.
                  SunnyBoy 3000 US, 18 BP Solar 175B panels.

                  Comment


                  • #10
                    Originally posted by johnno113 View Post
                    ok so it sounds like they will be ok with the 1000watts as they have been getting to float
                    the batteries are Yuasa UXH125-6FR 6volt 125ah and i have 32 of them
                    i dont know alot about these batteries if there is any regular maintenance to be done on them?

                    Thanks
                    My concern for you (besides the high number of batteries in parallel) is their age and life expectancy under your current "trickle charge" process considering you stated you got them for free and in "good condition".

                    Comment


                    • #11
                      Originally posted by johnno113 View Post
                      ok so it sounds like they will be ok with the 1000watts as they have been getting to float
                      the batteries are Yuasa UXH125-6FR 6volt 125ah and i have 32 of them
                      i dont know alot about these batteries if there is any regular maintenance to be done on them?

                      Thanks
                      They are designed to be floated as backup batteries. Usually they only last for 100 to 200 cycles when put in service as deep cycle batteries. Telecomm companies dump them on people so they don't have to pay for there proper disposal.

                      WWW

                      Comment


                      • #12
                        Originally posted by Wy_White_Wolf View Post
                        They are designed to be floated as backup batteries. Usually they only last for 100 to 200 cycles when put in service as deep cycle batteries. Telecomm companies dump them on people so they don't have to pay for there proper disposal.

                        WWW
                        Amend, I have done it for 35 years.
                        MSEE, PE

                        Comment


                        • #13
                          ok so it sounds like the batteries i have arent the best for this setup
                          previously they were used in a HV switch yard as backup batteries for about 2 years constantly on charge
                          would keeping the DOD at about 10-15% help the life expectancy alot as they arent designed to be discharged frequently?
                          i was planning to only use about 3kwh from them and have enough pv to fully charge them every day which would keep them in this range
                          Thanks for all the advice

                          Comment


                          • #14
                            Originally posted by johnno113 View Post
                            previously they were used in a HV switch yard as backup batteries for about 2 years constantly on charge
                            That is what they are designed to do, remain in float service and used in Emergencies. They can be discharged deeply and quickly, they just don't have a lot of cycles in them.
                            MSEE, PE

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