batteries show high SG

castilloj
castilloj Solar Expert Posts: 208 ✭
in Off Grid Solar & Battery Systems #1
Hey guys , I'm not sure if my Hydrometer is bad , but I'm noticing some of my batteries have high SG. I have a refractometer coming net week to double check the accuracy of the SG. But is there something that i can do?
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Re: batteries show high SG

    What have been your temperature corrected readings for SG been?

    I understand that some tropical locations will use a bit weaker electrolyte (batteries will have a longer service life?)--So reading high is a bit strange.

    From this thread, the range of Electrolyte Specific Gravity seems to be:
    Specific Gravity vs Applications
    1.285 Heavily cycled batteries such as for forklifts (traction).
    1.260 Automotive (SLI)
    1.250 UPS – Standby with high momentary discharge current requirement.
    1.215 General applications such as power utility and telephone.

    As mentioned earlier, the specific gravity (spgr.) of a fully charged industrial battery, or traction battery, is generally 1.285, depending on the manufacturer and type. Some manufacturers use specific gravities as high as 1.320 in an attempt to gain additional Ah capacity, but at the cost of a shorter cycle life.

    ...

    Higher Gravity = vs Lower Gravity =
    More capacity / Less capacity
    Shorter life / Longer life
    Higher momentary discharge rates / Lower momentary discharge rates
    Less adaptable to "floating: operation / More adaptable to "floating" operation
    More standing loss / Less standing loss
    So, where do your readings fall in the above scale... And I would guess that a difference of 0.030 SG or less is nothing to panic over.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
    Re: batteries show high SG

    Noticed that you mentioned that SOME of your batteries had high SG.
    Are these high SG batteries in series with others that do not have high SG?
    If so, you may have some bad batteries that won't come up to full voltage, thus resulting in the overcharging of the good ones in that string.
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  • RCinFLA
    RCinFLA Solar Expert Posts: 1,485 ✭✭✭✭
    #4
    Re: batteries show high SG

    Depends on what type of battery you have and how is initially charge formed by manufacturer.

    Some batteries when new, again depending on manuf. & type, may be initially set with electrolyte on the high side, SG in the 1.300 range.

    The SG will drop after a several cycles as the positive plates gets fully formed (Lead dioxide coating).

    Batteries used for starting and high surge current may have their SG set high.

    Higher SG make battery provide more capacity but shortens lifespan.
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  • Fullpower
    Fullpower Solar Expert Posts: 69 ✭✭
    #5
    Extreme High Specific Gravity

    I have just ( 13 september)put a new bank of (12) 2Volt 1200AmpHr Rolls Surrette S-1590 cells in service. Of the dozen cells, two had S.G. 1.310, and one cell has S.G. 1.340
    These gravity measurements are verified with two glass bulb hydrometers, AND a refractometer.
    Rolls tech service said to run them in for a few cycles, and see if they converge.
    so far I have them down to approx. 50% state of charge, most cells in the 1.200 range, except the highest one is holding 1.265
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: batteries show high SG

    You can also estimate the battery specific gravity by measuring cell (or bank) voltage at ~77F/25C:

    Specific gravity = single-cell open-circuit voltage - 0.845 (example: 2.13v – 0.845 = 1.285)
    Or
    Single-cell open circuit voltage = specific gravity + 0.845.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Vic
    Vic Solar Expert Posts: 3,208 ✭✭✭✭
    #7
    Re: batteries show high SG

    fullpower,

    From what you mentioned, you have the batteries down to 50% SOC. This one-half of one cycle, as you have described it.

    Perhaps you have run a number of full cycles. BUT, if not, Be certain to not leave the bank at 50% SOC for more than a day or so.

    It can be a bit difficult to run cycles on a bank, but if your inverter is on-line, of course 120 V electric heaters work well for the discharge.

    Have also built a DC Load Bank for the purpose of quickly discharging a bank (to 60-70% SOC), in order to cycle it.

    Most batteries that we receive are not completely finished, and need some number of cycles for the each of the cells to settle in to their final SGs when fully charged.

    This is just my experience. Perhaps am assuming too much. 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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  • Fullpower
    Fullpower Solar Expert Posts: 69 ✭✭
    #8
    batteries show high SG

    Waiting for a sunny day.
    I have had a couple absorb cycles, 29.6 volts, for maybe 7 or 8 hours, spread over a few partly cloudy days, but SG's are all over the place.
    from 1.22 all the way up to 1.275.
    I had a short, 2 hour equalize at 31.8 volts a few days ago, after the second absorb cycle finished, but never really got much gassing, and several of the cells did NOT make full charge.
    mostly sunny today, hope to get some amps in them. will check all gravities tonight.
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  • abrockca
    abrockca Solar Expert Posts: 72 ✭✭✭✭
    #9
    Re: batteries show high SG

    Just curious - what are the date codes on your Surrettes?
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