what is the best way to rig 32 piece 12v 9a battery for a battery bank?

biglots88
biglots88 Registered Users Posts: 3
in Off Grid Solar & Battery Systems #1
Hi all, first time poster, I just got a used APC server backup unit and find 32 12v batter in it just want to know how to rig them
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #2
    Re: what is the best way to rig 32 piece 12v 9a battery for a battery bank?

    there isn't any good way to wire 32 9ah batteries for a battery bank. this is just too many batteries. it would be better to actually buy larger capacity batteries and deal with that.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: what is the best way to rig 32 piece 12v 9a battery for a battery bank?

    It depends on what you want to do (UPS, off grid power, etc.).

    In general, I would highly recommend that you do not series/parallel a bunch of 12 volt 9 AH batteries into a large battery bank. There are just a whole bunch of wiring, cost, and battery maintenance issues with such a design.

    You would be better off defining your needs (watts, watt*hours, etc.) first, then making a single string of XXX AH batteries (2/4/6/12 volt) in series.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • biglots88
    biglots88 Registered Users Posts: 3
    #4
    Re: what is the best way to rig 32 piece 12v 9a battery for a battery bank?
    BB. wrote: »
    It depends on what you want to do (UPS, off grid power, etc.).

    In general, I would highly recommend that you do not series/parallel a bunch of 12 volt 9 AH batteries into a large battery bank. There are just a whole bunch of wiring, cost, and battery maintenance issues with such a design.

    You would be better off defining your needs (watts, watt*hours, etc.) first, then making a single string of XXX AH batteries (2/4/6/12 volt) in series.

    -Bill

    They are now pre-rigged in 4 steel box in series/parallel setup in 48v 18a each box, just see if I should break it down, plan to use it off grid to run a 1000w -2000w inveter if that is ok
    I know it is better to have bigger battery but since I already have this free, just want to use it
    Thanks for the in put
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: what is the best way to rig 32 piece 12v 9a battery for a battery bank?

    A good place to start would be to purchase a Kill-a-Watt type power meter.

    Put the meter on each load you want to run from the inverter for ~24 hours--Then you will know your kWH/Day requirements.

    A 72 AH @ 48 volt battery bank is not very large. Using rules of thumb for generic lead acid flooded cell batteries:
    • 72 AH * 48 volts * 0.85 inverter eff * 1/8 rate of discharge = 367 watt average recommended AC load
    • 72 AH * 48 volts * 0.85 inverter eff * 1/2.5 rate of discharge = 1,175 watt maximum AC surge (for a few seconds)
    • 72 AH * 48 volts * 0.85 * 0.50 maximum battery discharge = 1,469 Watt*Hours = 1.47 kWH recommended draw from battery bank before recharging

    Typically, the smaller batteries used in UPS systems are GEL or AGM type batteries--Which can sustain much higher power/surge ratings--But typically only for 15-30 minutes until batteries are "dead". And, the batteries would need to be replaced ever 1-2 years if subjected to very many cycles like that.

    Also, if GEL, they typically have a maximum rate of charge of C/20 (5%). Above that level, they are easily damaged/ruined. So--it would take a minimum of ~20 hours to recharge a GEL bank from "dead"... Other types of batteries can be recharged in the 5% to 13% rate of charge (or even higher for AGM).

    So--What are the loads/needs you wish to fill with such a system?

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • biglots88
    biglots88 Registered Users Posts: 3
    #6
    Re: what is the best way to rig 32 piece 12v 9a battery for a battery bank?

    well if the put all of them together is not a good idea, another thinking is i want to put some light and fan at my plastic shed in my backyard, here is what i want to have

    2 x 12v 10w LED light (one will turn on at night and run about 8-10hr a day) and one will be on by the switch
    1 x 12v 3w LED dome light turn on by switch if need

    1 x 12v (0.2a) fan that turn on on the day time to suck the hot air out from inside the shed

    may be I can beak the set down and use few of the 12v battery for this project? 2 12v in parallel? Is one 10w panel enough to charge this setup?
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  • techntrek
    techntrek Solar Expert Posts: 1,372 ✭✭✭
    #7
    Re: what is the best way to rig 32 piece 12v 9a battery for a battery bank?

    I use an APC UPS, the way APC wires them all up from the factory is with clips that attach directly to the gel-cell batts. I ditched those and wired up 16 flooded lead-acid in their place (mine is 192 volts nominal). Way more watts for the buck, although with the maintenance required I'm debating on going back to the gel-cells when my current bank is ready to be replaced. BTW, most models can be easily adjusted/reprogrammed if you want to modify the float voltage, you just need their proprietary serial cable.

    Click on the link in my signature if you want to see something else interesting I'm doing with the APC. ;)
    4.5 kw APC UPS powered by a Prius, 12 kw Generac, Honda EU3000is
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