fuses on battery banks

Everlong
Everlong Solar Expert Posts: 36 ✭✭
in Solar Beginners Corner #1
I have 6 batteries in total, 3 banks, for 24v. I have a fuse between the main cable going to the inverter, and batteries.

What to use for the three banks, so each bank is fused? What amperage of a fuse?

After 100hrs of running my meter shows 2.6kwh
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: fuses on battery banks

    How much current is expected? 100 Amps? 50? 150?
    Individual battery bank string fuses should be as large as the main inverter fuse. Some would argue it should be 1/3 in such a case, but if the current draw shifts or one of the fuses blows then the other(s) take on more load. The purpose of these is to prevent massive discharge in the event of a dead short like a dropped wrench. That's why the Blue Sea terminal fuses are a good choice: minimizes the unprotected connection area.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #3
    Re: fuses on battery banks

    As Marc says--How much current do you need?

    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).

    Note, if you will never use "1,200 watts" from your inverter--But "600 watts" max load instead, you certainly can derate the wring/fusing without an issue.

    I don't believe that battery banks always equally share current--And as he says, if a string failed, the other two will carry more current.

    The absolute maximum fuse--Basically the maximum current that you would have flow through the wiring (and battery bank). If you have 14 awg wiring--then 15 amp fusing.

    If you have 4/O cabling, then around 195-260 amps (NEC) up to 445 Amps (Boating standards).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Everlong
    Everlong Solar Expert Posts: 36 ✭✭
    #4
    Re: fuses on battery banks

    Im running 4ga wires between batteries, my loads will not go beyond 300w,

    Where could i purchase blue sea components?
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: fuses on battery banks

    :confused: 300 Watts on a 24 Volt system? Why? Normally you're looking at 50 Amps (1200 Watts) and up for battery wiring. 300 Watts is less than 15 Amps @ 24 Volts. 4 AWG can handle 60 to 100 Amps (depending on the install). Seems a pretty light load for a 24 Volt system.

    Blue Sea equipment is usually available at Marine supply or RV stores.
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  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    #6
    Re: fuses on battery banks
    Everlong wrote: »
    Where could i purchase blue sky components?

    Here you go.

    I just purchased one of these from them. I haven't installed it yet but looks well made.
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  • Everlong
    Everlong Solar Expert Posts: 36 ✭✭
    #7
    Re: fuses on battery banks

    Im assuming its blue sea not blue sky ;)?
    Yes, i only run led christmass lights of my pv system:)

    My initial plan was to run 0ga wire;) for less loss;) but i have ran into issues with connectors/fuses etc....;)

    LoL, i know ;)

    And as for 24v, i got a good deal on these 235w sharp panels(2), and thats where it all started..
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
    Re: fuses on battery banks

    Yeah, I just went back and fixed that through.
    Blue Sea makes the nifty fuse holders & battery switches.
    Blue Sky makes charge controllers.
    Two different companies.
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  • Everlong
    Everlong Solar Expert Posts: 36 ✭✭
    #9
    Re: fuses on battery banks

    Found some of these on ebay for 18$, anyway, did you see the price of these fuses? Pretty expensive!
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  • mtdoc
    mtdoc Solar Expert Posts: 600 ✭✭
    #10
    Re: fuses on battery banks
    Everlong wrote: »
    Found some of these on ebay for 18$, anyway, did you see the price of these fuses? Pretty expensive!

    $18 for the fuse holder? Good price. $20 at Hogdes Marine - see link above.

    The cheapest place I found the fuses at is Waytek. LINK

    $5.28 per fuse. Shipping is more but if you order other things as well it works out to pretty cheap.
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  • freedj
    freedj Registered Users Posts: 15 ✭✭
    #11
    Re: fuses on battery banks

    After reading this thread I installed one of the blue sea terminal fuse holders on my battery and couldn't be happier with the product. I have a pretty simple system and so I don't have a breaker box by my battery. I had considered going with one of the baby boxes and a breaker but the blue sea solution fit inside my battery box and was also less expensive. I got the double holder since it was only $3 more than the single and allows for future expansion.
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