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  • Fuse on the panels. Yes or no?

    Hi everyone.

    I'm about to put solar panels on my caravan. I'll have 6x 60w in parallel going into a junction box and then into circuit brakers. I've read mixed opinions whether to fuse the panels before the junction box. Some say yes if more then 2 panels, some say no need. What do you think? If yes, what sort of fuses do you use? Something waterproof I suppose.

    ​​​​​​Thanks for any tips.


  • #2
    Fuses are not required unless you have more than 2 parallel strings.
    MSEE, PE

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    • #3
      get a 6 circuit box with breakers. When you replace the first fuse, you exceed the cost of breakers.

      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

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      • #4
        Originally posted by Sunking View Post
        Fuses are not required unless you have more than 2 parallel strings.
        Thanks for your reply. So is 5 panels going into one line (in parallel) considered as 1 string? Therefore no need for a fuse?

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        • #5
          Originally posted by Michal View Post

          Thanks for your reply. So is 5 panels going into one line (in parallel) considered as 1 string? Therefore no need for a fuse?
          No that is 5 strings of panels meaning you need an expensive combiner, fuses, larger and more wire.
          MSEE, PE

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          • #6
            [QUOTE=Mike90250;n379428]get a 6 circuit box with breakers. When you replace the first fuse, you exceed the cost of breakers.


            That's very neat Mike! I do prefer circuit breaker to fuses too but I already have one inside the caravan - between the controller and the junction box on the roof. I don't want to have another box (circuit breaker enclosure) on the roof. That's why I was thinking about the inline fuses. But more and more people say I don't need them. So I'll probably leave it as it is.

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            • #7
              [QUOTE=Michal;n379649]
              Originally posted by Mike90250 View Post
              get a 6 circuit box with breakers. When you replace the first fuse, you exceed the cost of breakers.


              That's very neat Mike! I do prefer circuit breaker to fuses too but I already have one inside the caravan - between the controller and the junction box on the roof. I don't want to have another box (circuit breaker enclosure) on the roof. That's why I was thinking about the inline fuses. But more and more people say I don't need them. So I'll probably leave it as it is.
              With 5 parallel strings fuses are required, plus a 6th fuse after all 5 are combined.
              MSEE, PE

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              • #8
                Originally posted by Sunking View Post
                No that is 5 strings of panels meaning you need an expensive combiner, fuses, larger and more wire.
                I already have the junction box where it all goes into one. So inline fuses wouldn't do the job you reckon? Plenty of wire, that's not a problem.

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                • #9
                  Originally posted by Michal View Post
                  I already have the junction box where it all goes into one. So inline fuses wouldn't do the job you reckon? Plenty of wire, that's not a problem.
                  I can't help you much as you have built a trap to box yourself in.

                  You have a prime number of panels for which in your case there is only one possible configuration, all in parallel. Only prime numbers that work at 1 and 3 in which gives you at leat two option of all in series or all in parallel. Last option anyone wants is parallel.

                  Lastly I bet money you bought a PWM Controller and that traps you to wiring your panels in parallel and sacrificing 40% of of your power. With MPPT you harvest maximum power and can wire your panels in series which allows you to take advantage of the efficiencies of higher voltage, less and smaller wire, and no expensive hardware like fuses and combinder, junction boxes and all the headaches that comes with it.

                  You built yourself a trap and not a dang thing anyone can do for you. Bet you are going to parallel batteries too.

                  Only thing I can tel you is loose one panel and replace the PWM controller with a real MPPT controller. Wire the panels 2S2P and you will have a full 200 watts. No need for any fuses. Keep what you got and you turn your 250 watts of panels into 165 watts. You heard me correctly, loose a panel and you gain power with a MPPT controller.
                  Last edited by Sunking; 06-27-2018, 04:43 PM.
                  MSEE, PE

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                  • #10
                    Originally posted by Sunking View Post
                    I can't help you much as you have built a trap to box yourself in.

                    You have a prime number of panels for which in your case there is only one possible configuration, all in parallel. Only prime numbers that work at 1 and 3 in which gives you at leat two option of all in series or all in parallel. Last option anyone wants is parallel.

                    Lastly I bet money you bought a PWM Controller and that traps you to wiring your panels in parallel and sacrificing 40% of of your power. With MPPT you harvest maximum power and can wire your panels in series which allows you to take advantage of the efficiencies of higher voltage, less and smaller wire, and no expensive hardware like fuses and combinder, junction boxes and all the headaches that comes with it.

                    You built yourself a trap and not a dang thing anyone can do for you. Bet you are going to parallel batteries too.

                    Only thing I can tel you is loose one panel and replace the PWM controller with a real MPPT controller. Wire the panels 2S2P and you will have a full 200 watts. No need for any fuses. Keep what you got and you turn your 250 watts of panels into 165 watts. You heard me correctly, loose a panel and you gain power with a MPPT controller.
                    Ok. thanks mate. You're right with the PWM but it comes with a semi-DIY Lithium battery kit I'm buying. They provide the battery and all the gear, I provide the panels and wiring (I don't have to pay for that, a bonus) and install everything myself. I prefer MPPTs too, I have one on my foldable kit, but I trust these guys so I believe it'll be all good.

                    But thanks for your help and time anyway. Appreciate it.

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