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  • question on inverter/charging setup

    HI Everyone,

    Its nice to be a member of this forum where a lot of experts seem to give advices to people like us.

    I live in India , southern part, lots of sun!!.

    I have 8x 250W all 24 volt solar panels.. I am in the process of mounting them at my roof.

    I have a Charge controller which is 48V / 50 AMPS rating and which I believe is suitable for the 2KV system.


    My home already has a domestic Inverter from Su-kam . It is 3.5KV and needs 48V battery. ( I have 4, 12V batteries connected in series, 200 AH each : so 200 AH at 48v )

    As soon as I setup the panels I believe the setup is straight forward.. connect the panels to charge controller and the output from charge controller goes to battery.

    My problem however lies with my Inverter's Charging facility..


    My inverter will charge batteries automatically at 12AMPS or 16AMPS and I cannot turn that feature off .

    So when i connect my panels to battery , I believe it will overcharge them .. 12AMPS from inverter + output from the panels ( approx 30AMPS+ ? )


    My batteries are Lead acid and not sealed. I m worried it may reduce life of batter or even kill them/cause an accident.


    My idea to prevent this for now is to switch off the Mains (utility) during all the morning like 8am - 6pm to be safe. Inverter wont charge batteries for sure ONLY when the utility is cut off.

    Instead of this manual function is there anyway to do it better .. like using a circuit or device? .. so when the charge controller has an output > 10 Amps , the mains are auto disconnected?


    Expecting the opinions from experts.

    Please do ask if you have any questions to make this clear. Forgive me if i am not very clear in explaining this.

    Mods please move this post to appropriate topic if i posted it at wrong one.

  • #2

    Re: question on inverter/charging setup

    Re: question on inverter/charging setup

    Welcome to the forum.

    I would not be worried about over-charging the batteries. The inverter has a built-in charger, but it should be a regulated charger. When does it activate? At a minimum Voltage and/or whenever AC IN is present? Usually such is the case, and the Voltage level can be set.

    You've got a good estimate on the panel output. With an MPPT controller that array would probably manage 32 Amps maximum. If the inverter's charger can't be shut off the maximum total current would be 54 Amps which is 27% of the battery capacity (if truly 200 Amp hours). This would only occur during Bulk charging, and only if the array has full sun at that time. Usually it would start out charging in the morning and the batteries would reach Absorb before the panels are capable of their maximum output.

    I'm putting a lot of caveats in this post because I don't know the exact specs of any of the equipment.

    I will say that if this is like other hybrid GT inverters that battery bank at 200 Amp hours total is very small for a 3.5 kW inverter. Doubling the size of the battery bank would solve all the problems at once.

    Comment


    • #3

      Re: question on inverter/charging setup

      Re: question on inverter/charging setup

      Originally posted by Cariboocoot View Post
      Welcome to the forum.

      I would not be worried about over-charging the batteries. The inverter has a built-in charger, but it should be a regulated charger. When does it activate? At a minimum Voltage and/or whenever AC IN is present? Usually such is the case, and the Voltage level can be set.

      You've got a good estimate on the panel output. With an MPPT controller that array would probably manage 32 Amps maximum. If the inverter's charger can't be shut off the maximum total current would be 54 Amps which is 27% of the battery capacity (if truly 200 Amp hours). This would only occur during Bulk charging, and only if the array has full sun at that time. Usually it would start out charging in the morning and the batteries would reach Absorb before the panels are capable of their maximum output.

      I'm putting a lot of caveats in this post because I don't know the exact specs of any of the equipment.

      I will say that if this is like other hybrid GT inverters that battery bank at 200 Amp hours total is very small for a 3.5 kW inverter. Doubling the size of the battery bank would solve all the problems at once.
      Thanks for your reply.

      To answer your question, it is a regulated charger , it activates depending on the battery level automaticaly.

      Inverter has a small LCD where it shows me some status on battery level as well as if its charging / charged state.

      I can reduce the charge current of my inverter to 12A, and if i get 30A from solar panels , thats 42A, total ( may happen around noon and only if (the battery not charged and the AC IN is up))

      I dont know the type of my Inverter . This is the from their website/catalog.. they seem to lack most of the important info that you look for anyway

      http://www.su-kam.com/Upload/Uploade...-Revised-1.pdf

      Comment


      • #4

        Re: question on inverter/charging setup

        Re: question on inverter/charging setup

        with all due respect marc, i think you made a math error as 2000w of pv at 48v could possibly produce about 42a through an mppt cc.

        you are right to ask us on the concerns of overcharging as that could at the least increase the maintenance to the batteries or at the worst warp a few plates. personally, i think you need more battery capacity as a 3.5kw inverter should at a minimum have 350ah in battery capacity due to ripple voltages that could develop. if you double the battery capacity then you fix both possible problems.

        now i am going on the assumption here that all else is fine with the install. for instance what many persieve to be 24v pvs actually aren't suitable for charging 24v battery banks as the vmp needed is not 24v+, but more like 35v+. this is a problem for a controller that has a limit of 48v as the number of pvs needed for pvs that contain 60 cells to charge up a 48v battery bank would be 3 and would exceed the safe area of your controller.

        maybe to be sure you should list the specs for your cc and your pvs.
        NIEL

        Comment


        • #5

          Re: question on inverter/charging setup

          Re: question on inverter/charging setup

          Another question :

          My batteries are like 6 month old, Is it possible to add another set of 4 batteries to this? I was told by someone to not mix old/new batteries,etc.

          Adding 4 more 200 ah batteries would cost me close to 1K$ lol at India. So I would prefer not to..

          But if i did do that, Is it possible for me to go almost off-grid? I am using close to 20-25KWH a day. with more panels sometime in future?

          Comment


          • #6

            Re: question on inverter/charging setup

            Re: question on inverter/charging setup

            Looking over the information, this would appear to be a standard UPS unit. It will cut in if AC line Voltage goes too low or too high (a good feature to have in areas where the grid is erratic in function). It does not back-feed the grid.

            The charger is regulated, and only comes on when the batteries fall below a certain (not defined in the info) set point. This should work fine, as the solar would keep the batteries up most all the time and the grid presence would keep them from being drained by supplying the load power. If the grid goes down, it isn't there to power the charger so there's no risk of over-charging.

            The only issue here I can see is possibly getting 32 Amps from the panels, which is a 16% charge rate on the 200 Amp hour batteries. That's a bit high, but they probably will take it for short periods every now and then. If the charge controller is not of the MPPT type you probably won't see even that much current, and you may have a problem with the panel Voltage (250 Watt panels are likely to be 30 Vmp, which means you need at least three in series to provide enough Voltage to charge a 48 Volt battery bank. Four in series would put the V in at 120 and the controller may not be able to handle that or handle it properly).

            I see nothing horribly wrong so far. Do you have the specifications on the panels and charge controller?

            Comment


            • #7

              Re: question on inverter/charging setup

              Re: question on inverter/charging setup

              i don't see a problem with adding the batteries at 6 months if the present ones have not been abused and have been maintained properly.

              no you can't go off grid with that much to be required of it because it is recommended to not exceed 50% dod to preserve battery life. half of a 400ah battery bank is 200ah and at 48v is 48v x 200ah = 9600wh. with a good deal conservation you could make this work for off grid. keep the grid as back up even if you make a go of it off grid as stuff happens.

              i am still concerned of the pv and cc specs to be sure there isn't a problem here.
              NIEL

              Comment


              • #8

                Re: question on inverter/charging setup

                Re: question on inverter/charging setup

                Niel;

                I did the standard derating and nominal system Voltage formula: 2000 * 0.77 = 1540 / 48 = 32
                This is usually close enough to max on an MPPT under most circumstances.

                Definitely go for reducing loads as much as possible. That's a strategy that works no matter what the power source.

                Comment


                • #9

                  Re: question on inverter/charging setup

                  Re: question on inverter/charging setup

                  Originally posted by Cariboocoot View Post
                  Looking over the information, this would appear to be a standard UPS unit. It will cut in if AC line Voltage goes too low or too high (a good feature to have in areas where the grid is erratic in function). It does not back-feed the grid.

                  The charger is regulated, and only comes on when the batteries fall below a certain (not defined in the info) set point. This should work fine, as the solar would keep the batteries up most all the time and the grid presence would keep them from being drained by supplying the load power. If the grid goes down, it isn't there to power the charger so there's no risk of over-charging.

                  The only issue here I can see is possibly getting 32 Amps from the panels, which is a 16% charge rate on the 200 Amp hour batteries. That's a bit high, but they probably will take it for short periods every now and then. If the charge controller is not of the MPPT type you probably won't see even that much current, and you may have a problem with the panel Voltage (250 Watt panels are likely to be 30 Vmp, which means you need at least three in series to provide enough Voltage to charge a 48 Volt battery bank. Four in series would put the V in at 120 and the controller may not be able to handle that or handle it properly).

                  I see nothing horribly wrong so far. Do you have the specifications on the panels and charge controller?
                  Panels are close to this spec. except that it is 250.. values must be pretty close though.
                  http://www.suranaventures.com/images...es/SVL-230.pdf

                  I cant the pdf for my exact panel which is 250.


                  Charge controller is from a company in China, RemotePower, I literally sat with them in their office before purchasing this at Beijing when i was touring China last month.

                  Product manual only says it is 48v/50Amps and it is PWM and not MPPT.

                  Is there any other parameter that you would look for ? I can ask the company in an email and My friend works there and I can get answers pretty quickly.

                  Comment


                  • #10

                    Re: question on inverter/charging setup

                    Re: question on inverter/charging setup

                    Originally posted by Cariboocoot View Post
                    Looking over the information, this would appear to be a standard UPS unit. It will cut in if AC line Voltage goes too low or too high (a good feature to have in areas where the grid is erratic in function). It does not back-feed the grid.

                    The charger is regulated, and only comes on when the batteries fall below a certain (not defined in the info) set point. This should work fine, as the solar would keep the batteries up most all the time and the grid presence would keep them from being drained by supplying the load power. If the grid goes down, it isn't there to power the charger so there's no risk of over-charging.

                    The only issue here I can see is possibly getting 32 Amps from the panels, which is a 16% charge rate on the 200 Amp hour batteries. That's a bit high, but they probably will take it for short periods every now and then. If the charge controller is not of the MPPT type you probably won't see even that much current, and you may have a problem with the panel Voltage (250 Watt panels are likely to be 30 Vmp, which means you need at least three in series to provide enough Voltage to charge a 48 Volt battery bank. Four in series would put the V in at 120 and the controller may not be able to handle that or handle it properly).

                    I see nothing horribly wrong so far. Do you have the specifications on the panels and charge controller?
                    I was actually planning to have 2 panels in series each to create 48V set and create 4 sets and use parallel connection to add all that and bring it to charge controller..

                    Im now worried it may not work?

                    Comment


                    • #11

                      Re: question on inverter/charging setup

                      Re: question on inverter/charging setup

                      ok. even so the 32a + 12-16a from inv = 44a-48a and is way too much for a 200ah battery bank that is probably undersized for the size of the inv in the first place. ok i'll conceed that requirement as it is a ups inv and they aren't meant to be run all out for short periods of time. overcharging on his batteries can still happen.

                      the concerns on the solar setup are still real as he indicated he has 8 pvs and if they are 72 cell pvs then i'll agree they are 24v pvs that having 2 in series could charge a 48v battery bank. if the pvs are of the 60 cell variety he'll need 3 in series to get the proper voltage to be high enough and that necessitates an mppt controller that can handle much higher input voltages. he speced 48v for his cc and we don't know if that is input or output. that max input v rating is important and what the cc type is is also important..
                      NIEL

                      Comment


                      • #12

                        Re: question on inverter/charging setup

                        Re: question on inverter/charging setup

                        Originally posted by niel View Post
                        with a good deal conservation you could make this work for off grid. keep the grid as back up even if you make a go of it off grid as stuff happens.
                        My interpretation of the OP's intention (FWIW) is that he has a grid-driven UPS and is either trying to extend the runtime of the UPS off the batteries during the day or is trying to reduce his power bill as long as he has the panels anyway.
                        I think that he would like to keep the grid connection regardless, either for at night or for better charging, and will actually be powering his loads from the grid whenever it is present.
                        But we need to see inverter/charger specs and get clarification from the OP in any case.
                        Sunny Boy 3000US, 18 x BP Solar 175b panels, installed 2009.

                        Comment


                        • #13

                          Re: question on inverter/charging setup

                          Re: question on inverter/charging setup

                          To make things real clear..

                          You are mostly right anyway.

                          My state at india has terrible utility power.. sometimes it is off like 14 hours a day and works only for 8-10 hours

                          So I am like trying to go off-grid ( as a long term- final goal) but in short term I just need to reduce the power bills..

                          They are raising the power costs while providing less and less power lol..

                          Most of my usage is during the nights as I work at night online most of the days.. even though I have 3.5 KW inverter, I run it only for like 20-max 30% load So thats prob around 1-1.5 KW I believe.

                          I would try to get the specs exactly from the manufacturers and product manuals,etc.

                          Regarding the number of cells in PV, I can just count it if it helps!.

                          Comment


                          • #14

                            Re: question on inverter/charging setup

                            Re: question on inverter/charging setup

                            Now you have problems.

                            A 250 Watt panel will not have the same electrical specs as a 230 Watt; that 20 more Watts has to come from somewhere, either higher Vmp or higher Imp. Probably a bit of both.

                            But in either case these panels with their 30 to 32 Vmp will not work to their best on any battery system because the Vmp is going to be 'wrong'. With a 48 Volt system you want the array Vmp to be around 70. Two of these panels in series would be too low, three would be too high. This is because the PWM type charge controller can not adjust the array Voltage down to a suitable level for charging; it delivers the current, and the power difference between that current at the panels' Vmp and that current at the battery Voltage level is simply lost.

                            With eight panels you have only one array configuration that would use all panels and provide enough charging Voltage for a 48 Volt system: two parallel strings of four. You might as well say two parallel strings of three because all the power from those fourth panels will be lost.

                            So you get this:

                            One string of three panels in series: Vmp 90, Imp 7.6 (power loss approximately 90-70 * Imp or 152 Watts for the string)
                            Multiply by two strings and the charging current is now only 2 * 7.6 or 15.2 Amps. A far cry from the 32 you could get with all panels on an MPPT controller.

                            You can not use four strings of two in series because the Vmp of the strings would only be 60 or so. Throw in some heat and wiring losses and you no longer have enough Voltage to meet the charging needs of a 48 Volt system (usually Absorb Voltage would be 57.6 to 59.2). This means the batteries might never full charge from solar, resulting in shortened battery life.

                            Comment


                            • #15

                              Re: question on inverter/charging setup

                              Re: question on inverter/charging setup

                              maybe we should stop our speculation and just wait for him to list out all of the pv and equipment specs and how he proposed to have it all arranged. then we can be more specific on what works or what doesn't work.
                              NIEL

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