2v battery in 24V bank giving different readings

lazza
lazza Solar Expert Posts: 336 ✭✭✭
in Off Grid Solar & Battery Systems #1
HI All

After a nightmare with a host of failed 12V monoblock batteries, we've made a strategic decision to only install 2V OPzS stationary batteries. I always knew they were better, but we cant be dealing with battery problems 7 days a week, so going for the safest option, and having to convince clients to splash out for everyone's piece of mind.

However, to my great concern :s , after a few weeks of installation, i was measuring the voltage of the 2V cells in 24V battery banks, only to find that one battery was reading less voltage than all the rest. That is to say, 11 batteries were at 2,25V in float, one was only at 2.14V. 

I've noticed this anomaly in more than 1 system. They are TAB batteries and I expect them to be all equal in both density and voltage!!

Does anyone know why this might be??

Thanks for any advice
Larry
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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    What sort of equalization are you doing (voltage and current)?

    What is the rate of charge of the battery bank? Are there significant loads during the day time (such as A/C, water pumping, etc.)?

    -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 ✭✭✭✭✭
    #3
    battery values will always drift, so EQ cycles once a month are needed, Unless the cell has gone bad.
    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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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #4
    HI. Thanks for the replies.

    In this installation the maximum charge is around 45A for around 420Ah C10 batteries. So it's correctly sized. No heavy loads.

    I think the monthly equalizations from the Victron MPPT must have sorted out the difference because we went back to it and all the batteries appear to be perfectly equal now, both in float and in discharge- so that's a relief!

    I did notice this anomaly in another installation with TOPzS batteries. The only problem is the charger there doesnt allow for equalization charges. I'll see how that has got on when we next visit. See if it was the equalizations or general usage that permitted the readjustment.

    Cheers
    Larry


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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Note that the 10% rate of charge "we use here" is based on C/20 battery AH capacity specification.

    A C/10 battery "looks smaller" than a C/20 AH spec'ed battery.

    Check with the mfg. specifications for charging. It may not be 10% rate of charge--Technically, you may need an 11% to 14% rate of charge if using C/10 AH capacity--Not a big deal (only 1%)--But need to look at your battery's manual to verify.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • lazza
    lazza Solar Expert Posts: 336 ✭✭✭
    #6
    Ok, thanks Bill
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