What fuse to protect battery's

tom12
tom12 Registered Users Posts: 8 ✭✭
in General Solar Power Topics #1
My inverter internally has a 240 amp fuse. If I use a 300 amp class t fuse and there a short in unit will it protect my battery bank or If I use a anl fuse and there is a short will it protect my 2 6v battery's wired in series to make 12v please let me know as soon as you can. thank you
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  • unyalli
    unyalli Solar Expert Posts: 121 ✭✭
    #2
    Re: What fuse to protect battery's

    You don't fuse to protect equipment you fuse to protect wire. What size wire and for grins what inverter?
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  • tom12
    tom12 Registered Users Posts: 8 ✭✭
    #3
    Re: What fuse to protect battery's

    2/0 wire and power bright inverter
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  • unyalli
    unyalli Solar Expert Posts: 121 ✭✭
    #4
    Re: What fuse to protect battery's
    tom12 wrote: »
    2/0 wire and power bright inverter
    Power bright 300, 1500, 50,000,000? c'mon man.
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  • tom12
    tom12 Registered Users Posts: 8 ✭✭
    #5
    Re: What fuse to protect battery's

    It's a 2,200 w surge 2400
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: What fuse to protect battery's

    Basic math:
    • 2,200 Watts * 1/0.85 inverter eff * 1/10.5 battery cutoff voltage * 1.25 NEC derating = 308 Amp minimum Branch Circuit rating

    Realistically (i.e., as the batteries age, less than full charged, etc.), the maximum you could draw from 2x 6 volt @ 220 AH "golf cart" batteries (flooded cell) would be:
    • 12 volts * 220 AH * 1/5 hour discharge rate = 528 Watts of DC power max continuous
    • or 220 AH * 1/5 = 44 amps max continuous current
    • 12 volts * 220 AH * 1/2.5 hour discharge rate = 1,056 Watts of DC power max surge (seconds to minutes)
    • or 220 AH * 1/2.5 = 88 amps max surge

    If your battery bank is larger (AH rating), you can adjust the numbers.

    What is the maximum power you want to draw from the AC Inverter--If less than 2.2 kWatts, you can always put a smaller fuse/breaker in the branch wiring.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Dragonlady5
    Dragonlady5 Registered Users Posts: 19 ✭✭
    #7
    Re: What fuse to protect battery's

    ANL fuse is fine for protecting wires, Some inverter manufacturers specify Class T (fast blow) fuses, this characteristic is not required for wire protection, an ANL or CNL fuse will protect the wire in case of a short as well as a T class fuse and is a lot less expensive.

    Since you have 2/0 wire a 300 Amp could be used.
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  • tom12
    tom12 Registered Users Posts: 8 ✭✭
    #8
    Re: What fuse to protect battery's

    can a 350 amp fuse be used and still be safe?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    Re: What fuse to protect battery's

    Here is the NEC table for wire size vs amperage (conservative in conduit):

    http://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

    Marine wiring vs amperage (less conservative):

    http://www.acbsphl.org/Tips_and_hints/ABYC_Wiring.htm

    350 Amps is a bit large even for Marine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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