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  • DC fuses, what size?

    Hi,
    Great forum site, my first post.

    My system contains a Giant 48 volt 4 kW Invertor / Charger (MTTP)
    4 x 120 ah batteries (series connect to 48 volt)
    4 x 250 (24 volt panels)
    Projected load 300Wh per day.
    I will have a generator back up.

    Questions are;
    What size fuses do I need to protect the DC ?
    I've yet to purchase the panels, is 24 volt preferable to 12 volt ?
    Should I series the panels ?

    Thank you

    PS I live in Australia, so my appliance voltage is 240 Volt.

  • #2
    Originally posted by Oruro View Post
    Hi,
    Great forum site, my first post.

    My system contains a Giant 48 volt 4 kW Invertor / Charger (MTTP)
    4 x 120 ah batteries (series connect to 48 volt)
    4 x 250 (24 volt panels)
    Projected load 300Wh per day.
    I will have a generator back up.

    Questions are;
    What size fuses do I need to protect the DC ?
    I've yet to purchase the panels, is 24 volt preferable to 12 volt ?
    Should I series the panels ?

    Thank you

    PS I live in Australia, so my appliance voltage is 240 Volt.
    Howdy and welcome to Solar Panel Talk.

    I dont know about the fuse size but I know you are generally better off with standard grid connect style panels they are generally best option. yes generally series the panels but Im no designer so someone else that knows a bit more might chime in at some stage to help you out.

    P.S Im in Adelaide where are you if your in SA you can call www.solarwholesalers.com.au week days to get some prices perhaps a bit of advice on your system, cheers

    Comment


    • #3
      Originally posted by Oruro View Post
      Hi, Great forum site, my first post. My system contains a Giant 48 volt 4 kW Invertor / Charger (MTTP) 4 x 120 ah batteries (series connect to 48 volt) 4 x 250 (24 volt panels) Projected load 300Wh per day. I will have a generator back up. Questions are; What size fuses do I need to protect the DC ? I've yet to purchase the panels, is 24 volt preferable to 12 volt ? Should I series the panels ? Thank you PS I live in Australia, so my appliance voltage is 240 Volt.
      The panel wiring depends on the type and model charge controller you purchased. Usually an MPPT type has a higher DC voltage input when allows you to series wire panels. A PWM type is geared more for parallel panel wiring which requires fusing if you have more than 2 or 2 sets in parallel. So what is your charge controller, what is the Isc rating of those 250 watt panels and how far will the panels be from the CC. From that info both DC fuse and wire sizes can be calculated.

      Comment


      • #4
        DC fuses, what size?

        Originally posted by SunEagle View Post
        The panel wiring depends on the type and model charge controller you purchased. Usually an MPPT type has a higher DC voltage input when allows you to series wire panels. A PWM type is geared more for parallel panel wiring which requires fusing if you have more than 2 or 2 sets in parallel. So what is your charge controller, what is the Isc rating of those 250 watt panels and how far will the panels be from the CC. From that info both DC fuse and wire sizes can be calculated.
        Thanks SunEagle, My CC is an MPPT (not MTTP as I said in my opening).

        The ISC rating of the individual panel (24v 250w) is 8.49 Amps.

        The panels will be maybe 5 meters (15 foot) from the CC .

        The fuse rating I'm also looking for is the one to the battery bank as well as from the panels to the CC, I've been told 160 Amp - what do you think?

        I don't have the panels yet, should I go with 12v or stick with the 24v as planned?

        Thankyou.

        Comment


        • #5
          The fly in the ointment (flaw in your plan) is that the inverter is way too large for the batteries.
          48 volt 4 kW Invertor / Charger (MTTP)
          4 x 120 ah batteries (series connect to 48 volt)
          Projected load 300Wh per day.
          That large of inverter, (4Kw) will consume a fair amount of power over 24 hours. quite likely more than your 300wh load would be)
          [25w overhead x 24h = 600wh just in inverter load.

          With such a small load, look for a smaller inverter which will greatly reduce your tare losses.
          (or maybe you have plans to have larger loads later)

          Batteries:
          4 x 120 ah batteries (series connect to 48 volt)
          48V x 120ah = 5,760wh of storage, so you are well within the capacity of the batteries to handle the 900wh daily load IF your inverter standby draw is only 25W.
          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 Oruro View Post
            Thanks SunEagle, My CC is an MPPT (not MTTP as I said in my opening). The ISC rating of the individual panel (24v 250w) is 8.49 Amps. The panels will be maybe 5 meters (15 foot) from the CC . The fuse rating I'm also looking for is the one to the battery bank as well as from the panels to the CC, I've been told 160 Amp - what do you think? I don't have the panels yet, should I go with 12v or stick with the 24v as planned? Thankyou.
            I would stay with the "24v" panels since they are usually a better match for both an MPPT CC and a 48v battery bank. -------------------------Depending on what the max DC voltage input of that CC you might be able to wire all 4 of those panels in series to it. Technically you will not need any fuses between the series wires panels and the CC. You only require fusing if you wire more than 2 panels or sets of panels to a combiner box. Since you only have 4 panels unless you have to wire them all in parallel you will not need fuses between them and the CC. --------------------------The wire and fuse size between the CC and the battery bank is determined depending on the Amp Rating of the CC. A 40Amp CC requires wire that can carry more than 40 amps and a 40amp fuse to protect it. --------------------------A 48volt 4000 watt inverter can draw up to 84 amps so the wire and fuse between the batteries and inverter needs to be greater than 84 amps and the fuse needs to be less than what the wire can carry. That is how the fuse will protect the wire.--------------Hope that helps you a little.

            Comment

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