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  • Getting ready for panels

    and looking for confirmation here. Is the following design ok?

    This is an RV install
    10x 12v panels @ 22.81 voc, 2S5P
    Overall, 10 lines to combiner box. Longest run will be 10 meters, but I'd like to stick with 6awg for all runs.

    Is this the best or even an acceptable way to do this? are there better options?

    solar.png

    Thank you

  • #2
    First off you need to make sure each parallel "string" is fused properly in the combiner box.

    Next you really should perform a voltage drop calculation for the longest "round trip" run based on the Vmp & Imp of the 2 series wired panels of that string and make sure it is less than 2%.

    So what is the spec for each 165 watt panel? Vmp, Voc, Imp, Isc.

    If the Voc is 22.81v then my guess is that each panel has a Vmp ~ 18v and an Imp ~ 9amps so it is very possible that #6 wire should work on the 10 meter run for a pair of those panels.

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    • #3
      Hi. I used an online calc and it indicated that I should use 5awg for the longest run, but I'm going 6awg so I can buy a bulk 100'. By 'fused' are you being literal? This would be a solar combiner box and it looks like there are screws to secure the solar runs.

      I chose these: http://www.ebay.com/itm/271885508220 because of their width. Specs are there but I went over them first with Midnite Solar (Classic 150).

      I'm gathering the setup is ok, which is great.

      Comment


      • #4
        You are going to like this. OK you are using 2S 12 volt 165 watt panels right? That puts your Vmp = 36 volts and Imp = 8.8 amps. I will use 9 amps for for room and 2% voltage drop at 33 feet only requires:

        10 AWG @ 1.7% Voltage drop
        12 AWG @ 2.9% Voltage drop

        You are pissing away a lot of money using 6 AWG which gives you 0.8% drop. In reality you will never be pumping 8.8 amps. More like 7 amps. Save some coins, weight, and space using 10 or 12 AWG. The smaller wire is a lot easier to work with. 12 AWG is good to 20 amps so safety is of no concern.

        6 AWG cost $1/foot
        12 AWG cost 20-cents/foot.

        How many feet total for all 6 runs. Gets expensive real fast.

        Since I own copper stock, I say use 1/0 AWG.
        Last edited by Sunking; 02-23-2017, 05:19 PM.
        MSEE, PE

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        • #5
          Ha, thanks. I thought 5-6 was overkill but that calc disagreed. Never heard of anyone wiring their panels with 5 AWG!

          Edit: Much better product at 50% savings. I like it! http://www.ebay.com/itm/400246316396
          Last edited by -TX-; 02-23-2017, 05:50 PM.

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          • #6
            Originally posted by -TX- View Post
            Ha, thanks. I thought 5-6 was overkill but that calc disagreed. Never heard of anyone wiring their panels with 5 AWG!

            Edit: Much better product at 50% savings. I like it! http://www.ebay.com/itm/400246316396
            Well odd numbers do exist in AWG tables, but no one uses them. Where are you? Reason I ask is you used Meters instead of feet. Thus you may need to convert to metric cable cable gauges.

            I still say use 1/0 or even better 750 MCM.

            MSEE, PE

            Comment


            • #7
              Originally posted by -TX- View Post
              Hi. I used an online calc and it indicated that I should use 5awg for the longest run, but I'm going 6awg so I can buy a bulk 100'. By 'fused' are you being literal? This would be a solar combiner box and it looks like there are screws to secure the solar runs.

              I chose these: http://www.ebay.com/itm/271885508220 because of their width. Specs are there but I went over them first with Midnite Solar (Classic 150).

              I'm gathering the setup is ok, which is great.
              While the electric code mentions that a pv system with more than 2 items (panels or strings) in parallel require fuse protection for each "string", it really smart to protect your good panels if you develop a short on one set it could back-feed into the others, so the fuses are there to protect them.

              You can build a combiner box like the one I made. It was not cheap but IMO it cost less to build then to purchase.


              Comment


              • #8
                Originally posted by Sunking View Post

                I still say use 1/0 or even better 750 MCM.
                That would be copper right? lol
                2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                Comment


                • #9
                  Originally posted by Sunking View Post

                  Well odd numbers do exist in AWG tables, but no one uses them. Where are you? Reason I ask is you used Meters instead of feet. Thus you may need to convert to metric cable cable gauges.

                  I still say use 1/0 or even better 750 MCM.
                  Texas. longest run is 10 meters, shortest is 3 meters. I've already ordered that cable which is fine if it works or not. Easy enough to test the furthest string once installed, and if it's too low changing to higher gauge for it alone won't be difficult.

                  Comment


                  • #10
                    Originally posted by SunEagle View Post

                    While the electric code mentions that a pv system with more than 2 items (panels or strings) in parallel require fuse protection for each "string", it really smart to protect your good panels if you develop a short on one set it could back-feed into the others, so the fuses are there to protect them.

                    You can build a combiner box like the one I made. It was not cheap but IMO it cost less to build then to purchase.

                    So you would recommend that I add 10a fuse protection in every PVC box that I'm installing to house the 5 branch connectors? That's sound.

                    Comment


                    • #11
                      Midnight has some pre-fab combiner boxes, and I like using DC, Switch Rated Breakers instead of fuses. Touch-Safe fuse holders are just that, touch safe. They will arc ferociously if used to open a circuit under load

                      20160821_132247cc.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

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                      • #12
                        I looked at a few of those but couldn't find one that was 1) small 2) practical outdoors. I think I spent more time trying to find an alternative to the combiner box. Why can't I just combine my strings together like I have my batteries, along a busbar?

                        Edit: For that matter is it really necessary to use branch connectors and MC4? Using butt splices I could decrease the size of the PVC boxes planned to house branch connectors. Not sure why that would be frowned upon.
                        Last edited by -TX-; 02-23-2017, 08:56 PM.

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                        • #13
                          Originally posted by littleharbor View Post

                          That would be copper right? lol
                          Yes, tinned with silver.
                          Last edited by Sunking; 02-23-2017, 10:41 PM.
                          MSEE, PE

                          Comment


                          • #14
                            Originally posted by -TX- View Post
                            I looked at a few of those but couldn't find one that was 1) small 2) practical outdoors. I think I spent more time trying to find an alternative to the combiner box. Why can't I just combine my strings together like I have my batteries, along a busbar?

                            Edit: For that matter is it really necessary to use branch connectors and MC4? Using butt splices I could decrease the size of the PVC boxes planned to house branch connectors. Not sure why that would be frowned upon.
                            The fuses or circuit breakers (which is a better choice) are there to protect the good panels (or strings) from a short circuit caused by bad panels or bad wire to those panels. Using a bus bar subjects all of the panels to the same short circuit without anyway to open the circuit and isolate the problem to just the bad string.

                            I understand that adding the overcurrent protection is a PIA and can be costly but in the end you will be saving you from replacing all of the panels that can be damaged if you don't have oc protection.

                            Comment


                            • #15
                              If I can get breakers into this combiner box I ordered I will, otherwise this is what I'm planning. There will be 5 of these rows.

                              Serial PV.png

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