48v string w/GC batteries charging voltage

Stdyhand
Stdyhand Solar Expert Posts: 33 ✭
in Solar Beginners Corner #1
I'm still doing a lot of research but starting to lean towards a 5kWh bank using the 30 amp Midnight Solar KID CC and a 48v battery bank using Samsclub GC batteries with 232 amp hours. The reason for the GC batteries is because this will be my first time using solar offgrid so less of a loss IF I did mess up though I am confident I understand enough now to avoid a disaster. Furthermore, within 2-3 years I will get a larger bank, second KID, and have double the panels for charging and the GC batteries will get moved and used in another application so they don't go to waste.

My question is what is a good starting voltage for absorb and what voltage would be used for float? With GC batteries from Sams Club I don't expect to be able to simply call up the manufacturer and get this information but I'm sure several people have used these.
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #2
    Re: 48v string w/GC batteries charging voltage

    I would think you could use the presets for the type of batteries they are (flooded lead acid? last time I purchased they had 220amphours) I think I was using 28.4 for absorption and 27.2 for float and 31V for equalizing, in a 24V system, but that's from my faulty memory...

    Check the FAQ's?
    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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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #3
    Re: 48v string w/GC batteries charging voltage

    Hi Stdy ..,

    Be certain that you have and use a Hydrometer.

    A good place to start on a 48 V bank is;

    57.6 Absorb
    52.6 Float
    62 - 62.5 EQ

    Also be certain to use a Battery Temperature Sensor on the KID, and, ideally ALL charge sources.
    My opinions, Good Luck, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
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  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #4
    Re: 48v string w/GC batteries charging voltage

    GC-2's charge really easy and they are very predictable in how they react. In picking a starting point, you'll have to take in consideration what dod you use, the number of sun hours available and the amount of panel and amps available. Watch the SG's for a couple days and make small changes. I'd start at about 57.5 - 58 V Bulk / Absorb for a hour and 53 - 54 V float. If your only pulling them 10-20% the bulk will be short, at 30-40% you can increase the Bulk voltage a few tenths and / or add a little time to the absorb, again it'll be based on the SG's. If your having long floats you'll see a small SG increase from it. The next question you need to ask yourself is what target is my SOC I plan to reach on a daily basis ??, I like at 90-95% and keep 100 % within striking distance and go there at least once a month. You can get there with a simple Voltage and time change on your daily charge regimen or with a short EQ.
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