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  • Battery Bank Fuse

    After a little research I would like to go with one of those nifty Blue Sea battery terminal fuses.

    Aside: except the one I have picked out here seems to be a slightly different model than the ones I have seen posted before.
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    After a little more research on fuse sizing I'm back to the forum with a question.

    Here goes:

    From a previous thread [BB I believe]:
    Battery Fusing:
    Typically, the maximum expected current * 1.25 (or 1/0.80) for rated fuse/wiring/breakers. For example a 1,200 watt inverter running on a 12 volt battery bank (100 amps "nominal" becomes):
    •1,200 watts * 1/0.85 inverter eff * 1/10.5 volts minimum battery voltage * 1.25 NEC factor = 168 amp fusing/breakers/wiring
    And round up to next standard fuse/wire (175-200 amp in this example).

    OK, Before I start, my Flexpower 1-6 (48v, 230VAC panel) comes with a "175ADC breaker" and a "80 amp charge controller breaker" (dont know if that helps) and a "VFX3048E" inverter.

    What will be my maximum expected current. No idea really (pretty economical fridge, freezer, lights, blender)...lets go with 3000 watts (I think around the inverter max).

    3000w*1/.85*1/42V (battery cutoff for a 48v bank)*1.25= 105 amps minimum circuit.
    I'd then go for a 150 amp fuse.

    I just need one battery fuse, right? My bank is one string of eight 6volters. This fuse should be screwed on to the battery + terminal that leads to the inverter....?

    Am I on the right track my friends, or just still con-fuzed?
    Surfpath
    Last edited by Surfpath; November 22nd, 2012, 17:28.
    370AH RE Trojan Bank, 48V/230VAC Outback Flexpower 1 Panel (incl FNDC/RTS), 2kw PV . 100% off-grid

  • #2

    Re: Battery Bank Fuse

    Re: Battery Bank Fuse

    That looks like a piece of hardware for mounting an external fuse, not the same as the nifty Blue Sea holders.

    If it were me, I'd size the inverter wiring for the maximum current (111 according to my calculations) which would be 2 AWG and size the fuse for the more likely expected 60 to 70 Amps. So that would be 100 Amps. The best source of info for this would be the inverter manual itself; hard to beat factory recommendations!

    And yes you only need one fuse on one battery string, and standard practice is to put it on the (+) side.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

    Comment


    • #3

      Re: Battery Bank Fuse

      Re: Battery Bank Fuse

      On the Amazon link I supplied the model number correlates to the Blue Seas' "Terminal fuse block 1 terminal stud"
      The Amazon photo looks similar but perhaps more...basic?
      Hmmmmm..
      Last edited by Surfpath; November 21st, 2012, 19:41.
      370AH RE Trojan Bank, 48V/230VAC Outback Flexpower 1 Panel (incl FNDC/RTS), 2kw PV . 100% off-grid

      Comment


      • #4

        Re: Battery Bank Fuse

        Re: Battery Bank Fuse

        I guess they look odd with the fuse removed.

        I'm used to seeing them like this:
        Attached Files
        1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

        Ohm's Law: Amps = Volts / Ohms
        Power Formula: Watts = Volts * Amps

        Comment


        • #5

          Re: Battery Bank Fuse

          Re: Battery Bank Fuse

          Originally posted by Cariboocoot View Post
          If it were me, I'd size the inverter wiring for the maximum current (111 according to my calculations) which would be 2 AWG and size the fuse for the more likely expected 60 to 70 Amps. So that would be 100 Amps. The best source of info for this would be the inverter manual itself; hard to beat factory recommendations!
          Cariboocoot, if the DC breaker for the inverter is 175 amps, shouldn't the fuse be at least that large? I presume that the cable from battery to inverter must be sized with an ampacity greater than 175 amps, and I don't think 2 AWG is adequate.

          --vtMaps
          4 x 235w Samsung, Outback fm60 & vfx3524 & mate, Midnite E-panel, four Interstate L16, Trimetric monitor, Honda eu2000

          Comment


          • #6

            Re: Battery Bank Fuse

            Re: Battery Bank Fuse

            From the Flexpower 1 manual:

            Battery Positive (+) Minimum conductor size= 2/0 AWG, Breaker size 175 Adc
            PV Positive (+) Minimum conductor size= #4 AWG, Breaker size 80 Adc

            Dont know if that helps
            370AH RE Trojan Bank, 48V/230VAC Outback Flexpower 1 Panel (incl FNDC/RTS), 2kw PV . 100% off-grid

            Comment


            • #7

              Re: Battery Bank Fuse

              Re: Battery Bank Fuse

              Originally posted by vtmaps View Post
              Cariboocoot, if the DC breaker for the inverter is 175 amps, shouldn't the fuse be at least that large? I presume that the cable from battery to inverter must be sized with an ampacity greater than 175 amps, and I don't think 2 AWG is adequate.

              --vtMaps
              You can undersize supply lines provided you know they are undersized and you keep the relation between wiring and circuit protection so that the CP always gives out first.

              Those were minimal power requirements I was quoting. If you go with maximum output at minimum input for sustain operation you get quite different numbers indeed!

              The Flexpower numbers are its maximums, which are not necessarily what are needed for a particular install. For instance 175 Amps continuous on nominal 48 Volts is 8.4 kW - nearly 3X the inverter's rated capacity. The 80 Amp rating on the controller side fits with an 80 Amp controller.

              This is why it's always best to go with the specs supplied by the manufacturer of the device supplying or using the power, and make sure everything in the connections is up to that rating.

              Clear as mud? That's normal for wiring/fuse sizing questions.
              1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

              Ohm's Law: Amps = Volts / Ohms
              Power Formula: Watts = Volts * Amps

              Comment


              • #8

                Re: Battery Bank Fuse

                Re: Battery Bank Fuse

                More detail from the page in the manual
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Size:  33.9 KB
                370AH RE Trojan Bank, 48V/230VAC Outback Flexpower 1 Panel (incl FNDC/RTS), 2kw PV . 100% off-grid

                Comment


                • #9

                  Re: Battery Bank Fuse

                  Re: Battery Bank Fuse

                  Which inverter are you using? Outback FX3048T?
                  Refer to install manual: http://lib.store.yahoo.net/lib/wind-...FX-install.pdf
                  Page 38: DC Input Current - Rated Power: 75 Amps
                  Not 175 Amps.
                  1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                  Ohm's Law: Amps = Volts / Ohms
                  Power Formula: Watts = Volts * Amps

                  Comment


                  • #10

                    Re: Battery Bank Fuse

                    Re: Battery Bank Fuse

                    Also look at Page 51: Recommended Wire Sizes By Length.
                    For full power at lengths up to 10 feet one way Outback indicates 1/0 only on the 3048. That actually has an Ampacity rating of 150, and they recommend it to keep the V-drop low under maximum power circumstances. A 3kW 48 Volt inverter just does not draw that much current. OB's figure for "typical" is in fact only 60 Amps. Does that number look familiar?
                    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                    Ohm's Law: Amps = Volts / Ohms
                    Power Formula: Watts = Volts * Amps

                    Comment


                    • #11

                      Re: Battery Bank Fuse

                      Re: Battery Bank Fuse

                      Originally posted by Cariboocoot View Post
                      Which inverter are you using? Outback FX3048T?
                      Refer to install manual: http://lib.store.yahoo.net/lib/wind-...FX-install.pdf
                      Page 38: DC Input Current - Rated Power: 75 Amps
                      Not 175 Amps.
                      In his OP he wrote that he has the vfx3048E (50 hz 230 volt). I couldn't find on Outback's site any specs for DC input current. I did find that its AC overload capacity is surge to 5750 VA and 4800 VA for 5 seconds. The Flexpower system which his inverter is part of does include a 175 (not 75) amp DC breaker. I have no idea if a 75 amp breaker would trip on those overloads.

                      --vtMaps
                      4 x 235w Samsung, Outback fm60 & vfx3524 & mate, Midnite E-panel, four Interstate L16, Trimetric monitor, Honda eu2000

                      Comment


                      • #12

                        Re: Battery Bank Fuse

                        Re: Battery Bank Fuse

                        Guess what? 3kW AC out is 3kW AC out, whether at 120 VAC 60 Hz or 230 VAC 50 Hz. When drawn off 48 VDC the current is the same.

                        The Flexpower has the capacity to handle a lot more inverter than that. 175 Amps will never trip from normal use and is way over-sized for that inverter.

                        A 2812 will draw about 240 Amps at max, so the 175 Amp breaker is under-sized for that. A 3524 will draw about 145, so 175 Amps is just about right for it.
                        Why they put a breaker that big on that 3048 inverter I don't know. You could run two of them off that. For some reason this seems to be the smallest breaker offered with the FP units.

                        Which begs the question that if you buy a pre-wired unit like this, why are we trying to calculate breaker sizes at all?
                        And also brings up the issue that if you are running with a 175 Amp breaker do not under-size the wire at all. You must use 1/0 minimum or preferably 2/0 wire. Otherwise the wire can fry before that breaker will trip.

                        Of course that inverter can go up in flames before that breaker will trip too. Seems dumb to me. I didn't design it, though. And I do always say you can't beat the maker's recommendations.

                        In this case I could be wrong about that.
                        1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                        Ohm's Law: Amps = Volts / Ohms
                        Power Formula: Watts = Volts * Amps

                        Comment


                        • #13

                          Re: Battery Bank Fuse

                          Re: Battery Bank Fuse

                          FWIW my Midnite prewired ePanel with an Outback 3648 inverter also has a 175 amp breaker- which seemed too large to me. I did use 2/0 cables though for that reason.
                          Array 1: Sanyo HIT225 X 8 on Wattsun tracker. Array 2: Evergreen ES-E-225 X 12 on shed roof. Midnite e-panel with Outback GVFX3648, FNDC and Classic 150 X 2. 436 AH AGMs. Honda eu2000i X 2. Outback PSX-240 autotransformer. Remote monitoring and control with HP netbook running UltraVNC, Wattplot, Midnite local app and Cumulus weather station software. Waiting to be installed: PowerSpout ME120 microhydro turbine and 3rd Midnite Classic 150.

                          Comment


                          • #14

                            Re: Battery Bank Fuse

                            Re: Battery Bank Fuse

                            MidNite, run by the guys who invented most of Outback's equipment in the first place, sensibly offers an E-panel with 125 Amp breaker for 48 Volt inverter.
                            1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

                            Ohm's Law: Amps = Volts / Ohms
                            Power Formula: Watts = Volts * Amps

                            Comment


                            • #15

                              Re: Battery Bank Fuse

                              Re: Battery Bank Fuse

                              Originally posted by Cariboocoot View Post
                              MidNite, run by the guys who invented most of Outback's equipment in the first place, sensibly offers an E-panel with 125 Amp breaker for 48 Volt inverter.
                              Right, some of the bare ePanels they sell have 125 amp breakers but all of their ePanels that are prewired with 48V inverters have 175 amp breakers. As you point out, that seems too high. The question is why do they do it this way?
                              Array 1: Sanyo HIT225 X 8 on Wattsun tracker. Array 2: Evergreen ES-E-225 X 12 on shed roof. Midnite e-panel with Outback GVFX3648, FNDC and Classic 150 X 2. 436 AH AGMs. Honda eu2000i X 2. Outback PSX-240 autotransformer. Remote monitoring and control with HP netbook running UltraVNC, Wattplot, Midnite local app and Cumulus weather station software. Waiting to be installed: PowerSpout ME120 microhydro turbine and 3rd Midnite Classic 150.

                              Comment

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