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Sizing cable from solar controller to bank, what size breaker?

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  • Sizing cable from solar controller to bank, what size breaker?

    Hey folks,
    I'll have 3 327w PV mods on the roof of my sprinter. Each will have a 20A inline fuse and a go to a Victron 150/85 MC4. Should I plan on the max amps of ~82 at 12V and get an 80A breaker? Can I size slightly higher incase I upgrade the panels to 360w/370w if I can ever source them, and put a 90A breaker in there? Or am I doing something wrong?
    Cheers!

  • #2
    What voltage is your battery bank ? I think you are going to need a MPPT controller to match those panels to the battery voltage, and in that case, you wire panels in series
    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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    • #3
      If those are Sunpower E20-327 panels I would keep them in parallel being that the open circuit voltage is so high. Unless you are going with a 48 volt system the voltage of these panels is plenty high enough to work with your Victron MPPT controller. You will need to fuse each panel (combiner box is best)and if you are going to use a circuit breaker for your array to CC circuit you need to size it and your wiring from combiner to CC appropriately for the total array amperage
      Last edited by littleharbor; 03-24-2018, 11:18 AM.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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      • #4
        So, my controller has 3 MC4 port pairs on it. Rather than combining them in parallel (series is too much voltage for the controller), I can just wire each panel right to the controller separately. It does mean more holes in the roof, more fuses, and more breakers. I might forgo separate breakers, and just get some switchable fuse holders from work from bad combiner boxes (I'm at a solar field right now),

        My output voltage is 12. What size breaker/fuse should I get from controller to battery bank?

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        • #5
          As to the holes in the roof you might find these entry glands useful. Amazon or ebay is a good source.

          Look on the data label on the panel, it will give you fusing info.

          double entry gland.jpgsingle entry gland.jpg
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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          • #6
            I already ordered up some entry glands. I actually prefer the ones with a lip at the bottom so I can throw some screws in there as well.
            ​​​​​​I don't mean the fuse between the panel and controller. I mean the fuse between the controller and battery bank. I'm guessing 90a, with a wire gauge that can handle more. Or am I wrong?
            Last edited by Withalligators; 03-27-2018, 09:38 AM.

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            • #7
              Originally posted by Withalligators View Post
              I already ordered up some entry glands. I actually prefer the ones with a lip at the bottom so I can throw some screws in there as well.
              ​​​​​​I don't mean the fuse between the panel and controller. I mean the fuse between the controller and battery bank. I'm guessing 90a, with a wire gauge that can handle more. Or am I wrong?
              These have a broad area inside the perimeter for sealant. I Would use 3M 5200 sealant in this application. It is a really strong adhesive. Screws wouldn't be needed. The only reason I showed these is that you could put both side by side for 3 strings.
              90 amp sounds fine if you can find one 100 may be easier to locate. The fuse or CB if for the protection of the wire so your wire's ampacity needs to be higher than the protective device.
              Last edited by littleharbor; 03-27-2018, 10:41 AM.
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024

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              • #8
                I'm having trouble finding 100A 12V breakers, that aren't crappy looking. Any suggestions?

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                • #9
                  Here are DC breakers in many sizes & styles. http://www.midnitesolar.com/products...tName=Breakers
                  Get the right housing to mount it in, DIN rail if needed.

                  Don't cheap out and use a glitzzy automotive stereo breaker that will burn up
                  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


                  • #10
                    In addition to MS, Eaton make good DC Breakers up to 1000 volt rating up to 1200 amps. If you want the really good stuff telecom and utilities use GE Critical Power both Bullet Nose and Snap In
                    MSEE, PE

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                    • #11
                      Here's a question that's probably stupid. Does voltage matter? The output from my controller to my batteries will be 12V at up to ~100A. I can easily find 100A DC breakers, but they're all rated at 150V and up. Is that ok for my purposes?

                      Comment


                      • #12
                        Originally posted by Withalligators View Post
                        Here's a question that's probably stupid. Does voltage matter? The output from my controller to my batteries will be 12V at up to ~100A. I can easily find 100A DC breakers, but they're all rated at 150V and up. Is that ok for my purposes?
                        So what is the problem? The 150 volt breaker is a maximum voltage. 12 volts is less than 150 volts. No problem.

                        Sort of like an elevator with a 3000 pound capacity. You do not have to weigh 3000 pounds to get in and ride. If you do weigh 3000 pounds, you will not find me within a mile of you, and you will find yourself alone in the elevator.
                        Last edited by Sunking; 04-20-2018, 12:22 AM.
                        MSEE, PE

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                        • #13
                          Haha, thanks. I'll try and stay under 3000lbs for you.

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                          • #14
                            From your first post you're saying the controler is a victron 150v85A.
                            Why you want a braker on the output rated at 90-100A? If the max safe output of that controler is 85A why you go higher than that? What protection will offer the higher rated fuse?
                            I have the same controler in a 48v system with a 75A fuse on the output.
                            By the way, those controlers can limit output Amps via settings , so you can reduce it to whatever you want and have more PV for overcast moments.

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