Fusing for a 48V/415Ah battery bank

ctann
ctann Registered Users Posts: 12 ✭✭
in Off Grid Solar & Battery Systems #1
Hi all,

Working through the last steps of my 4kW off-grid solar design. I had a question on battery bank fusing.

My design is based around a Magnum Mini Panel, which includes a 175A breaker between the Battery bank and the Inverter, and a 100A breaker between the battery bank and the Charge Controller. The battery bank will be in a separate outdoors enclosure, less than 5' of cabling (run through conduit) to the panel, and will be wired with 2/0 cable (between the 8x6V batteries, and between the battery enclosure and the Magnum panel).

As I understand it, that is all that is necessary per code. However, I see some discussion on inline fusing in the battery string, with a recommendation of an inline fuse in the middle of the string, to prevent catastrophic failure. It seems the cable has a max ampacity of 190A.

Any comments on this? Good/Bad idea to include a 190A inline fuse in the middle of my battery bank? Would it be code compliant? From further reading, it looks like an external fuse holder and fuse would be required, rather than one of those bolted in-line fuses...

Thanks,
              Chris.



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Comments

  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #2
    175 amp breaker is all that is needed for 2/0 wiring on batteries in a single string. Where in the world did you hear about another fuse in the bank?
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Fusing at the battery bank is a good idea if you have parallel battery strings (typically 3 or more parallel, one fuse/breaker per parallel string).

    Technically, the fuse/breaker is to stop high current from the battery bank from starting a fire if there is a short. Typically, the battery bank fuse/breaker is relatively close to the battery bank (one marine spec. is 18" max recommended, as I recall)--Basically, you want the over current protective device as close to the power source as practicable (i.e., fuse 10' from battery--there is more likely a cable short before the fuse, than if the fuse is 1 foot from the battery).

    A single breaker for the battery bank is also nice to turn off all power to/from the battery in an emergency and/or if you shut down the building while going away for a month (prevent battery bank from being taken dead). However, if you go away for more than one month at a time, a flooded cell battery bank should have some sort of solar charging to keep it from self discharging and sulfating.

    Fuses and Breaker are their to protect the wiring from excessive current if there is a short. Each wire that "leaves" the positive battery bus should have a fuse/breaker sized to the wire (i.e., 14 AWG may have a 15 or 20 amp fuse).

    Breakers are nice--They can both be fuse and a power switch. Fuses themselves generally are not great for "turning off" power (in some cases, fuse holders used as "switches" have caught fire--The holders are not protected against arcs if used as a switch).

    Good quality fuses are not cheap and can be pretty large. If you decide you want a battery based fuse, these holders from Blue Sea are pretty nice:

    https://www.bluesea.com/products/category/16/72/Fuse_Blocks/Terminal_Fuse_Blocks (the first two with the "red" covers are nice for battery installations).

    Note the holders generally do not come with the fuses themselves.

    -Bill

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • ctann
    ctann Registered Users Posts: 12 ✭✭
    #4
    Dave Angelini said:
    175 amp breaker is all that is needed for 2/0 wiring on batteries in a single string. Where in the world did you hear about another fuse in the bank?
    Right here: http://forum.solar-electric.com/discussion/5564/fusing-of-battery-bank

    I suppose now I look again that is really about limiting in parallel strings. I was actually trying to figure out how to hook up parallel strings to multiple Magnum inverters, even though that is not what I am doing short term.

    But good to know my original understanding was correct, and I don't need more than the planned 175A breaker...
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  • HarryN
    HarryN Registered Users Posts: 9 ✭✭
    #5
    Hi, I am assuming that you are using a breaker like the midnight solar MNEDC175 or MNEDCRT175?  Were you able to find an enclosure for this breaker?

    I am looking for an enclosure that can handle 3 each parallel circuits (3 of these F class breakers)

    Just out of curiosity, in a nominal 48 volt system (which can peak up to nearly 60 volts), does a breaker like this really require a UL rated enclosure, or can it just be mounted inside of any rated electrical box or even just a heavy duty electronics project box?   I want it all to be at least NEC and if possible meet ABYC or RV industry specs if at all possible.

    Thanks



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  • davemac
    davemac Registered Users Posts: 39 ✭✭
    #6
    BB. said:

    Good quality fuses are not cheap and can be pretty large. If you decide you want a battery based fuse, these holders from Blue Sea are pretty nice:

    https://www.bluesea.com/products/category/16/72/Fuse_Blocks/Terminal_Fuse_Blocks (the first two with the "red" covers are nice for battery installations).

    Note the holders generally do not come with the fuses themselves.

    -Bill

    This is what I went for for my 24 V 225aH Trojan T105 battery bank.

    The BlueSea block fuse is a tidy solution that is located on the +ve terminal and also helps in providing a convenient point for attaching the battery monitoring circuitry that certain controllers, GFPD's, shunts and same-such devices require.

    The little block fuses are well stocked at marine stores everywhere.
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  • ctann
    ctann Registered Users Posts: 12 ✭✭
    #7
    Hi all, sorry, just saw the previous question:

    "Hi, I am assuming that you are using a breaker like the midnight solar MNEDC175 or MNEDCRT175?  Were you able to find an enclosure for this breaker?"

    I am actually using "Magnum Panels", which come included with the breakers. I think that Midnite also has suitable enclosures ("BabyBox").

    Regards,
                    Chris.
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  • ColoradoSolar
    ColoradoSolar Registered Users Posts: 63 ✭✭
    #8
    I was just looking at the Blue Sea fuse blocks and they can only handle voltages up 58v so they don't seem like a good option for a 48v battery bank. Since I am in the process of installing my new system and looking for a battery fuse (will have a breaker near the inverter) what are others using to fuse their 48v bank?

    Thanks,
    Eric
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #9
    ctann said:
    "Hi, I am assuming that you are using a breaker like the midnight solar MNEDC175 or MNEDCRT175?  Were you able to find an enclosure for this breaker?"

    I am actually using "Magnum Panels", which come included with the breakers. I think that Midnite also has suitable enclosures ("BabyBox").
    Chris, The larger breakers used for inverters have different mounting than the Din rail of the baby box. Midnte Epanels or Magnum panel boxes are designed for other breakers as well.

    https://www.solar-electric.com/catalogsearch/result/?q=magnum+panel

    https://www.solar-electric.com/catalogsearch/result/?q=E-panel
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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  • ctann
    ctann Registered Users Posts: 12 ✭✭
    #10
    I this what you are looking for?

    http://www.midnitesolar.com/productPhoto.php?product_ID=123&productCatName=Small Breaker Boxes&productCat_ID=10&sortOrder=3&act=p

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