Battery choice question

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azrc
azrc Solar Expert Posts: 43 ✭
in Solar Beginners Corner #1
What are the advantages/disadvantages with going for a larger Ah battery rather than adding another string of smaller batteries? Longer life? Less maintenance?...

Just curious because the T105 batteries seem to have a significantly better $/Ah ratio.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,447 admin
    #2
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    Re: Battery choice question
    1. Fewer cells to check/water (3 strings, 3x as many cells to check).
    2. Fewer electrical connections/issues with balancing current between parallel strings. Fewer circuit breakers / fuses (should be one per parallel string).
    3. Easier to diagnose problems... A weak cell / battery in a set of parallel connected battery banks is not as obvious.
    4. Weak/shorted cells can damage parallel connected strings (discharging other strings) or weaken series connected cells (no charging current in string with open cell).
    5. With a 12 volt battery paralleled into 12 volt bank... Most batteries do not have exposed cell bus bars where you can easily measure each cell's voltage (checking for balanced charging/loading). With 6 volt batteries or higher voltage strings--it is easier to find problems with a voltmeter by measuring cell to cell or battery + to - terminals to look for voltages that are out of the norm.
    I tend to think that parallel string of 4 or more batteries are difficult to maintain and the bank can fail sooner because of the above issues.

    However, our host (Windsun) has said that he finds that series or parallel connected battery banks both last well (with good maintenance).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
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    Re: Battery choice question

    I think it's much easier to manage a single series string, than parallel strings, exception being only 2 batteries - then simple diagonal wireing does the trick.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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