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Thread: Battery Bank Fuse

  1. #1
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    Default 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.
    Click image for larger version. 

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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 at 16:28 PST.
    370AH RE Trojan Bank, 48V/230VAC Outback Flexpower 1 Panel (incl FNDC/RTS), 2kw PV . 100% off-grid

  2. #2

    Default 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

  3. #3
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    Default 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 at 18:41 PST.
    370AH RE Trojan Bank, 48V/230VAC Outback Flexpower 1 Panel (incl FNDC/RTS), 2kw PV . 100% off-grid

  4. #4

    Default Re: Battery Bank Fuse

    I guess they look odd with the fuse removed.

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

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

  5. #5
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    Default Re: Battery Bank Fuse

    Quote 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

  6. #6
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    Default 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

  7. #7

    Default Re: Battery Bank Fuse

    Quote 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

  8. #8
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    Default Re: Battery Bank Fuse

    More detail from the page in the manual
    Click image for larger version. 

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

  9. #9

    Default 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

  10. #10

    Default 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

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