Battery storage placement??

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camelback75
camelback75 Registered Users Posts: 4 ✭
in Solar Beginners Corner #1
Retiring and heading up to SW Colorado next year. Going off-grid, in the process of new home construction, and have a mechanical room in the livable basement. I'd like to put my batteries in this mechanical room, if I can do it safely of course. The battery enclosure would be sealed and vented to the outside. I'm also considering AGM's. Is this a definite no-no? Has anyone seen this done? Thanks for the feedback!
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Battery storage placement??

    Welcome to the forum.

    You've already hit on the secret to success: "The battery enclosure would be sealed and vented to the outside". No worries then, even with FLA's. Many of us off-gridders have the batteries inside and their storage compartment vented to the outside. They won't freeze if kept charged.

    AGM's would not need to be sealed up and vented out, but they usually will cost more per Amp hour . And since it's more likely something will go wrong with the first set of batteries (because of getting all the "bugs" worked out of the system and getting a feel for what you're doing) the flooded cells are mostly recommended for starting out, unless they have to be in living quarters (like RV/camper applications).
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #3
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    Re: Battery storage placement??

    Many people put a forced air fan to vent their battery boxes--Attach a small fan to a solar panel or set charge controller to turn on when the battery is floating/equalizing/over 14 volts charging.

    Also, look at the access to your basement. For a large PV installation (>100 kWH per month), you may be looking at 200-300+ lb batteries/cells--Or even at 1,000-2,000 lb batteries if you use fork lift batteries.

    You will need a place to unload the batteries from the truck, get them to the basement, then moved into your battery bank.

    Probably do not spend too much time/money making a box/enclosure that just fits your battery bank. Who knows what size/configuration batteries you will be installing in ~10 years from now.

    And keep your other stuff away from the battery bank... Flooded cell will out-gas and may spread electrolyte around--causing corrosion issues. AGM/Sealed batteries do not normally vent--but can if overcharged and/or as an age related failure.... So, I would suggest that you treat AGM with similar respect to flooded cell batteries.

    Lastly, I am not a fan of lots of parallel strings of batteries. I suggest getting large AH cells (6 volt, 4 volt, 2 volt) and creating 1 series string vs small 12 volt batteries in 4 or more series/parallel strings. It does take work to make sure that parallel strings of batteries properly share charging/discharging current, requires extra fusing/breakers for safety, and additional monitoring--more batteries to check, monitor string current in each parallel string, etc....

    Fortunately, you can get a pretty cheap DC current clamp meter (this $60 one from Sears is about the cheapest, useful, DC clamp meter I have seen) to monitor charging/discharging current in each parallel string. I would suggest 2-3 parallel strings is about the maximum for easy maintenance. People have done more, happily, but I would avoid it if possible.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • marsofold
    marsofold Solar Expert Posts: 45 ✭✭
    #4
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    Re: Battery storage placement??
    BB. wrote: »
    It does take work to make sure that parallel strings of batteries properly share charging/discharging current, requires extra fusing/breakers for safety, and additional monitoring--more batteries to check, monitor string current in each parallel string, etc....
    I would suggest 2-3 parallel strings is about the maximum for easy maintenance. People have done more, happily, but I would avoid it if possible.

    -Bill

    It would be dangerous to have battery string fuses inside the battery box (due to H2). It would seem to me that the only way to fuse each string outside the box is to have one cable of each string (same polarity) exiting the box to meet with its fuse mounted externally. The other side of each fuse than would join to form a larger common cable going to the inverter & charge controller. For me with six batteries/three strings that would mean four cables exiting the battery box (the one - main & three + string cables). This is messy enough that I have to wonder if I really need to do it. Do golf cart batteries die by forming dead shorts? Would anything less really matter? Thanks for any advice...
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
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    Re: Battery storage placement??

    It is not dangerous to fuse batteries within the box. Fuses are sealed; when they blow there is no open spark potential. The only other danger of spark ignition is from bad connections, and that risk is there always.
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  • marsofold
    marsofold Solar Expert Posts: 45 ✭✭
    #6
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    Re: Battery storage placement??
    Cariboocoot wrote: »
    It is not dangerous to fuse batteries within the box. Fuses are sealed; when they blow there is no open spark potential. The only other danger of spark ignition is from bad connections, and that risk is there always.

    Are you ABSOLUTELY certain of this? If you say yes, then although it seems scary I'll do it. I've been getting by with not fusing the individual strings, although I always felt uneasy about it. P.S.: I'll be using this site's 110 amp inverter fuses for each string.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #7
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    Re: Battery storage placement??

    No, I do not believe you will find explosion proof (rated) fuses or breakers for solar PV applications (at not least any easy find, cheap to purchase).

    It would be better to mount them on the outside of the battery enclosure (and it would keep acid mist away too--typically a bigger issue with flooded cell batteries).

    Lead acid cells can fail shorted pretty easily--but I don't think a shorted cell would trip a several hundred amp breaker/fuse in a typical battery bank.

    I would plan on fuses/breakers in parallel battery banks as more of protection of failed electrical connections (shorts) and/or dropped tool situations.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #8
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    Re: Battery storage placement??

    They're as safe as anything can be.
    BTW, Blue Sea actually makes fuse terminal blocks which are designed to bolt directly to the battery post. They go with their marine rated battery fuses.
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  • marsofold
    marsofold Solar Expert Posts: 45 ✭✭
    #9
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    Re: Battery storage placement??

    OK, then I'll chance it. For simplicity I'd just bolt the fuses directly to the battery posts. Then bolt the 2-gauge inter-battery cables to the other side of the fuses. The big inverter fuses are rigid enough to support both their own weight and the end of the attached cable.
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  • camelback75
    camelback75 Registered Users Posts: 4 ✭
    #10
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    Re: Battery storage placement??

    Thanks guys ! I'll no doubt be back with many more questions.
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