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  • PV Combiner Box for 24 Panels

    So I am shopping for a combiner box for 24 panels (possibly but unlikely 28 or 32).

    If anyone sees this and can spare a minute... am I doing this right?

    If I connect these 24 panels in 6 x 4s groups, I'll need box with at least 6 inputs.

    The panels current (Imp) is 5.72 Amp, the voltage (Voc) is 21.6V.

    The current for each inputs would be 5.75 Amp

    My total current output: 6 x 5.72 = 34.32e Amp

    My each and combined Voc: 4 x 21.6 = 86.

    Would Eco LLC 6 string pv combiner box with 10A inputs, 60A output be a good choice and would 40ft of #8 cable be okey to use for the run to charge controller?

    Thanks!

  • #2
    Originally posted by Bozant View Post
    So I am shopping for a combiner box for 24 panels (possibly but unlikely 28 or 32).

    If anyone sees this and can spare a minute... am I doing this right?

    If I connect these 24 panels in 6 x 4s groups, I'll need box with at least 6 inputs.

    The panels current (Imp) is 5.72 Amp, the voltage (Voc) is 21.6V.

    The current for each inputs would be 5.75 Amp

    My total current output: 6 x 5.72 = 34.32e Amp

    My each and combined Voc: 4 x 21.6 = 86.

    Would Eco LLC 6 string pv combiner box with 10A inputs, 60A output be a good choice and would 40ft of #8 cable be okey to use for the run to charge controller?

    Thanks!
    I would put the Combiner Box next to the Charge Controller and run #4 from the CB to the CC and run #12 from each string to the combiner box if that's an option. 60A is too much for #8 especially for a 40' run.

    Do you already have your Charge Controller? Why such low voltage? 4x 6s would be more manageable. What's the fuse rating on the panels? If it's 15A you could even run 3x 8s w/o fuses.

    Comment


    • #3
      Sorry, I'm new at this; don't understand some things you're saying.

      I will have charge controller Victron 150/100 in about a week.

      Why 60A from CB to CC? The Eco CB is rated at 60A out but my total (lmp) current from the panels would be 34.32A with 6x4s, the way l am figuring.

      What is fuse rating of the panels, where would I look for that? Are you talking about short circuit current? If so, it's 6.24. Thanks!

      Comment


      • #4
        Originally posted by Bozant View Post
        Sorry, I'm new at this; don't understand some things you're saying.

        I will have charge controller Victron 150/100 in about a week.

        Why 60A from CB to CC? The Eco CB is rated at 60A out but my total (lmp) current from the panels would be 34.32A with 6x4s, the way l am figuring.

        What is fuse rating of the panels, where would I look for that? Are you talking about short circuit current? If so, it's 6.24. Thanks!
        Oh... I apologize... I keyed in on the '60A'; Yes #8 be ok for ~35A. Not sure how cold it gets where you are... but if you think a string of 6 panels would stay <150v even on the coldest day 4x 6s would be a better configuration.


        The fuse rating is the max fault current the string can accept. It's usually 15A. If this was true you could have 3x 8s without fuses but your Victron would not work. I think your setup is fine. Enjoy
        Last edited by nwdiver; 07-03-2019, 12:49 AM.

        Comment


        • #5
          If you used a more conventional 150V input charge controller, or even a Classic 200, you could run 6 panels in series (depending how cold it gets), and parallel into a 4 channel combiner box.
          6S = 132Voc 4P = 23A Put the combiner close to the panels, and you can run # 8 cable 40' from combiner

          Do the math on your wire costs vs controller costs.

          I missed your battery voltage - what's the output voltage of your controller? 24V would be 106A, 48V would be 53A to the batteries

          here's what my excel sheet says (working at 24v)

          6s4p_trial.jpg


          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


          • #6
            Originally posted by nwdiver View Post



            . If this was true you could have 3x 8s without fuses


            Wrong, three strings still need fusing.

            IMHO placing the combiner next to the CC just about defeats the purpose of using a combiner. 99% of the time the combiner should go at the array so that you can transition to a single set of less expensive wire, in conduit for protection
            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

            Comment


            • #7
              Thanks!

              My main concern is safety -- electrocution.

              Is 6s more dangerous than 4s than 2s, providing everything else stays the same?

              Comment


              • #8
                Higher voltages offer more chance of a more server shock, and are also more likely to sustain an arc should that occur.

                Therefore, TECHNICALLY, 6s is more dangerous than 4s or 2s... But it's all about managing risks. If you're aware and your equipment is properly certified for the voltage you just need to know not to unplug connectors while current is flowing, and don't touch anything energized.

                Comment


                • #9
                  Originally posted by littleharbor View Post
                  Wrong, three strings still need fusing.
                  With regular ~9A 60 cell panels, yes. But it you have a low amp panel like SunPower that only puts out <6A and it's rated to 15A you can run 3 strings w/o fusing. Fusing is required to prevent a fault in one string from exceeding the ampacity due to the other parallel string back feeding the faulted string. 6+6 < 15A.


                  Originally posted by Xplode View Post
                  Higher voltages offer more chance of a more server shock, and are also more likely to sustain an arc should that occur.

                  Therefore, TECHNICALLY, 6s is more dangerous than 4s or 2s... But it's all about managing risks. If you're aware and your equipment is properly certified for the voltage you just need to know not to unplug connectors while current is flowing, and don't touch anything energized.
                  I'll take the risk of higher voltage (so long as it's <600v) over higher amps any day of the week...

                  Comment


                  • #10
                    Originally posted by nwdiver View Post

                    With regular ~9A 60 cell panels, yes. But it you have a low amp panel like SunPower that only puts out <6A and it's rated to 15A you can run 3 strings w/o fusing. Fusing is required to prevent a fault in one string from exceeding the ampacity due to the other parallel string back feeding the faulted string. 6+6 < 15A.
                    How about these panels?

                    [TABLE]
                    [TR]
                    SPECIFICATIONS [/TR]
                    [TR]
                    [TD]Maximum Power: 100W[/TD]
                    [TD]Maximum System Voltage: 600V DC (UL)[/TD]
                    [/TR]
                    [TR]
                    [TD]Optimum Operating Voltage (Vmp): 17.9V[/TD]
                    [TD]Open-Circuit Voltage (Voc): 21.6V[/TD]
                    [/TR]
                    [TR]
                    [TD]Optimum Operating Current (Imp): 5.72A[/TD]
                    [TD]Short-Circuit Current (Isc): 6.24A[/TD]
                    [/TR]
                    [TR]
                    [TD]Weight: 16.5lbs[/TD]
                    [TD]Dimensions: 42.2 X 19.6 X 1.38 In[/TD]
                    [/TR]
                    [/TABLE]

                    I

                    Comment


                    • #11
                      Originally posted by Bozant View Post
                      How about these panels?
                      Maybe... hopefully there's a 'fuse rating' on the name plate. If it's 10A you need fuses for 3 strings in parallel. If it's >15A then you don't. But you'd need a different charge controller to run 3x 8s anyway...

                      There's a lot of confusion around the purpose of DC fusing. If it's impossible for the circuit to ever exceed the fuse rating... a fuse would be useless. If you have a string with a 6.24A Isc with a fuse rating of 15A you cannot exceed 15A with 3 strings. The highest current you'll see during a fault is ~12.5A. Maybe ~14A if it's a super hot and super bright day....

                      Most 60 cell modules are ~9A with a 15A fuse rating. If there's a fault on the 3rd string it could see >18A so fuses ARE required with 3 or more strings.
                      Last edited by nwdiver; 07-03-2019, 05:46 PM.

                      Comment


                      • #12
                        Screen Shot 2019-07-03 at 3.34.32 PM.png

                        Comment


                        • #13
                          Originally posted by nwdiver View Post
                          I'll take the risk of higher voltage (so long as it's <600v) over higher amps any day of the week...
                          Thanks! My understanding is that connecting panels in series doesn't change the current, only voltage of the string. So, regarding my question, wouldn't Amps be irrelevant?


                          Comment


                          • #14
                            Originally posted by nwdiver View Post

                            Maybe... hopefully there's a 'fuse rating' on the name plate. If it's 10A you need fuses for 3 strings in parallel. If it's >15A then you don't. But you'd need a different charge controller to run 3x 8s anyway...

                            There's a lot of confusion around the purpose of DC fusing. If it's impossible for the circuit to ever exceed the fuse rating... a fuse would be useless. If you have a string with a 6.24A Isc with a fuse rating of 15A you cannot exceed 15A with 3 strings. The highest current you'll see during a fault is ~12.5A. Maybe ~14A if it's a super hot and super bright day....

                            Most 60 cell modules are ~9A with a 15A fuse rating. If there's a fault on the 3rd string it could see >18A so fuses ARE required with 3 or more strings.
                            Yes, thank you very much again. I just looked: "Max series fuse rating -- 15A"

                            Comment


                            • #15
                              Originally posted by Bozant View Post
                              Thanks! My understanding is that connecting panels in series doesn't change the current, only voltage of the string. So, regarding my question, wouldn't Amps be irrelevant?

                              I would prefer 3x 8s over 6x 4s because amps into the controller would be half as much.

                              Comment

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