Battery bank merging question

System
System Posts: 2,511 admin
in Advanced Solar Electric Technical Forum #1
I have a bank of 4 trojan 105's at 24V runing a small solar backup system.

They have been hooked up for about 6 months and they were built in May of 07.


I have used the back up system twice but never has the bank been below 24.4V and has a light trickle from ~600w of Evergreens through a MX-60


I am ready to up size (XW4024 or 6048 with 1.2-1.6 KW of Evergreens) and just got 8 more T105's that were built last month.

I will either run 24 V with 3 strings or get 4 more batts and run 2 strings of 48V.

Would I be OK to merge the batteries into the same bank being they have had so little use?
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  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    #2
    Re: Battery bank merging question
    SKYWLKR wrote: »

    I will either run 24 V with 3 strings or get 4 more batts and run 2 strings of 48V.

    Would I be OK to merge the batteries into the same bank being they have had so little use?

    If I was going to do this, I would get 4 more and go with 48V. Series banks are less susceptible to current hogging than parallel. With 48V, and only 2 parallel strings the current (and the resistance imbalances) will be less.

    I would equalize each battery individually, BEFORE placing it in the strings, so that everything is all fully charged (all those batteries, may take a day or two, running generator) before you wire them up. And be sure to switch the inverters & chargers to 48V before you connect them to the bank.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

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  • System2
    System2 Posts: 6,290 admin
    #3
    Re: Battery bank merging question

    I have a large auto motive charge I can charge pairs with or I have a smaller 10/20 amp charger that I can set to 6V for individual.

    I have access to Household grid power

    I am leaning towards adding another four but it will be a MAJOR Tight squeze for my batt box, as in no air space at all where the batts touch...

    It gets a bit warm here in Souther Louisiana in the summer but the tightness would be great for winter...
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