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Advice on fuses for this circuit

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  • Advice on fuses for this circuit

    Hi,

    So I'm slowly getting closer to getting everything I need for the solar power system. I'm seriously considering getting the Midnite Solar MNDC 125 Mini 125 Amp DC disconnect enclosure as I think it'll make everything neater and easier for me. Since this uses breakers I'm wondering if anyone can give me advice on whether fuses are still needed with this circuit and if so where?
    I had read the Terminal Fuse Blocks from Blue Sea Systems come recommended, but would a fuse at the battery terminal be recommended if I have the breaker? If that terminal fuse is needed then I'm probably going to need a work around as the battery hole is 5/16 (M8) and the hole at the end of the Blue Sea Terminal Fuse block is 3/8 (M10).

    I've attached a picture of the circuit - the MNDC-GFP is not needed as I understand that my Midnite classic 200 has this protection built-in. I'm also unaware of what the Field Install - yes or no, is beside the charge controller. I've chosen 125A as the inverter has an inbuilt fuse rated at 150A - so I would rather the breaker went before that fuse ever blew.
    Thanks

    - Just for clarity, I have 24V 100Ah battery bank, Midnite classic 200, 1200 24V Phoenix Victron Inverter. PV array to be x3 330W.

    Circuit Diagram.PNG
    Last edited by DavidH; 08-18-2019, 05:45 PM.

  • #2
    The fuse at the battery, protects the wires between the battery and the the 125A breaker

    The wire diagram looks like a Midnight product, and they assume certain things will be installed ?

    What you want to avoid at all costs, is allowing PV voltage into the Classic Charge Controller, with out a battery connected. The Classic output is OK to have a disconnect breaker on it, but again the battery terminal fuse (i like to use the Dual Fuse model) is what protects the wires. I use a 200A fuse for the inverter and a 30 or 50A fuse for the charge controller - whatever makes sense for the wire size.

    But your 200A battery fuse will not protect the 8 ga wire from the controller to the 60A breaker.
    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


    • #3
      So the diagram comes from the Midnite MNDC 125 DC disconnect enclosure and maybe they do assume other things are installed. Ok, so to prevent PV voltage into the Classic without a battery connected would you recommend the circled breakers (See attached diagram) to be two pole so that turning off one turns off the other? Maybe a two pole breaker like this one? I'm not overly familiar with the different types of breakers. Screen Shot 2019-08-18 at 9.28.39 PM.png

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      • #4
        Been thinking about this, - how do you protect the charge controller if the fuse at the battery positive blows? I know with breakers you can use two pole, so the opening of one circuit could open the PV circuit into the controller but if a fuse blows you don't have that option.

        Comment


        • #5
          Originally posted by DavidH View Post
          Been thinking about this, - how do you protect the charge controller if the fuse at the battery positive blows? I know with breakers you can use two pole, so the opening of one circuit could open the PV circuit into the controller but if a fuse blows you don't have that option.
          You have to over-engineer the battery - CC cables & breaker so it's not easily violated..

          If the CC develops a massive internal fault, and blows a breaker, you have stopped a fire anyway, and the controller was already dead before disconnecting from the battery. Now you have to make sure the enclosure the Cc is in, can resist the flaming box long enough for the PV breaker to open.
          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 Mike90250 View Post
            You have to over-engineer the battery - CC cables & breaker so it's not easily violated..
            Ok, over-engineer it is!
            I've a safety question about MidNite Solar breakers that are rated for 150VDC. If I have 1 PV string (3 panels in series each with a VOC of 48.74V) that gives a total voltage of 146.22V, am I correct in thinking that a breaker on the PV +ve input rated for 150VDC will not be sufficient and I should get the next one up which is rated at 300VDC?

            Comment


            • #7
              Yes, your VOC will be over the 150 V rating. I think the 300V ones may be a pair of ganged breakers in series !! Sometimes this HV stuff gets expensive
              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


              • #8
                Ok thanks. Haha, it definitely does start to add up - I'm seeing the prices pretty much double once you go about 150V!

                Comment

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