Battery bank modification

Arkansasoffgrid
Arkansasoffgrid Solar Expert Posts: 117 ✭✭
in Off Grid Solar & Battery Systems #1
Currently have 8 GC2s that are 215 AH, these are 6 months old, only used a total of 27-28 days. My dilemma is whether to add a parallel string of these to total 430 AH for about $700, or spend $2600 on a single string of 8 L16s @420AH. The current GC2s have never been below 75%, and other than those few intermittent days of use have always been sitting in float mode. What say you??
8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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Comments

  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    #2
    Re: Battery bank modification

    Personally I like GC-2's, they are easy to charge and manage and have a reasonable life / cycle span and cheap. Stratification is rarely a problem. What would you do with the ones you have now ??
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  • Alaska Man
    Alaska Man Solar Expert Posts: 252 ✭✭
    #3
    Re: Battery bank modification

    I've been told, but have never done it, that you can add to your existing string if it less then a year old. Also one string is better than two in parallel.
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  • 2twisty
    2twisty Solar Expert Posts: 199 ✭✭✭
    #4
    Re: Battery bank modification

    I guess it all depends if you want to expand later. 2 strings is the usual maximum recommended around here, so if you ever think you might want more than 430Ah, spring for the L16s now and expand later. If you think that the GC2s will last you long enough for them to wear out before you need more, then go with the GC2s

    I just expanded my 8 GC2s to 16GC2s. Got a friend planning a larger system and is going with 16 L16s.
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  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    #5
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    #6
    So 6-7 months isn't to old to add 8 more in parallel?
    Any specific test to perform on batteries to check "life in battery"?
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #7
    If the bank is less than 1 year old, adding parallel batteries is usually not a big issue.

    If the bank is 3 or more years old, then it could be an issue.

    It is not that the batteries will not work... It is that batteries have different ages. And you could end up 3-5 years down the road with needing to make the choice of replacing the "old batteries" or the whole bank.

    Also, new batteries (after they have cycled 20-100 times) have a lower resistance than older batteries--So the new batteries can tend to cycle more current through them vs the old/paralleled batteries. So, the newer batteries can age a bit faster too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Arkansasoffgrid
    Arkansasoffgrid Solar Expert Posts: 117 ✭✭
    #8
    Would you "mix" the strings with old & new batteries, or have a string of old & a string of new in parallel?
    8-420AH US Battery L-16s, Midnite Classic 150cc, Whiz Bang Jr, Magnum MS4448PAE inverter/charger,  4590w Canadian Solar panels. Honda EU2000i generator.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #9
    For a series string, the AH capacity of the string is only the value of the weakest battery.... If you have a some 200 AH new batteries and some older 180 AH (20% degraded)--Then the string is only 180 AH.

    Also as batteries age, their self discharge rate goes up (from 0.0x% to 0.x% or even 1.0 to 2.0%). The older batteries in the string will require "more" equalization current vs the new batteries in the strings. The new batteries would see more stress from equalization (controlled over charging) and damage trying to "leak current" to properly equalize the older batteries.

    So, personally, I would try my best to keep series strings of identical batteries. And I would prefer to mix Old and New Parallel strings of batteries together (one set of old series string batteries in parallel with the new set series string of batteries). Not ideal, but I think better.

    -Bill "trying to keep the English clear" B.
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • xsnrg
    xsnrg Registered Users Posts: 10 ✭
    #10
    Another approach would be to sell your good string of GC-2s to somebody else close by (save shipping), then use the funds to offset the cost of the L16s. This way you still have just 1 string, and the extra amps
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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #11
    I've never added new batteries to old, but think I might add them intermixed, I think we had a member here (Olsen? good with wind) who recommended this to maintain equal resistance among strings.

    When doing this it is recommended to equalize the old batteries before adding new.

    Also comes the questions about the added capacity...

    Do you need it?
    Do you have or are you adding solar(or other charging sources) to maintain the added capacity?
    Will you have a balance system?

    Often people add battery capacity thinking they will have more available energy, when they end up with an unbalanced system, having too little charging capacity to maintain the battery health. This leads to costly under charging and even ruining old and new alike.
    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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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #12
    Sorry, I missed your system info, you should be fine with 18, 255 watt panels....
    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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