Add acid when batteries are charged or discharged???

olNick
olNick Registered Users Posts: 5 ✭✭
in Off Grid Solar & Battery Systems #1
Hi,
Think first post here. Totally off grid.
Commissioned a set of used OPzS, 12v, 600AHr bank for my home about 10 months ago.
Without getting into details, my SP is low, ~1.18 - 1.2.
OPzS should be about 1.24-6.

My question:
I have low capacity and want to add acid to bring up the SP. Should I add acid when batts are charged (as much as possible) or discharged?

Please do not tell me what should have been done/never add acid etc... ( I know...) commissioning was during full COVID lockdown etc. emergency needs,nNo acid, no hygrometer etc..., no options etc.

regards,
Nick
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  • mcgivor
    mcgivor Solar Expert Posts: 3,854 ✭✭✭✭✭✭
    #2
    The acid concentration is a reflection of state of charge, being less dense is an indication that the sulphur is attached to the plates rather than being in solution. Acid should not be added to increase the SG, the battery needs to be charged completely even if it means going multiple days without power, there are not many options other than having  a generator  with a high capacity charger.

    You know what you shouldn't do, but want to know if you should, but don't want to be told you shouldn't

    Charge, charge and charge some more until the SG rises, there is no other realistic solution, the batteries were filled with the correct concentration during manufacturer, only add distilled water to adjust levels after charging or to cover the plates if required.


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  • olNick
    olNick Registered Users Posts: 5 ✭✭
    #3
    Hi,
    A little clarification is in order.

    The batts were used and came to me empty. The electrolyte was removed to make removal easier (lighter).

    I recommissioned the batteries according to the manuf. procedure.

    I got the SP wrong for reasons stated, no shops to buy acid etc.

    I charged them for 2 1/2 days, at C20 till the SP and voltage stopped rising.

    This is where I am at.

    Do I add acid now to bring SP in line, and essentially re-commision/recharge?

    If so, add acid when batts are CHARGED as much as possible, or when they are DIS-CHARGED.

    Before I toss them, as the capacity is low.

    tx,
    nick
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,626 admin
    #4
    No battery engineer... But my suggestions:
    • You have been cycling the battery bank by at least 25% capacity daily/regularly?
    • If yes, do a full charge and Equalize the bank (EQ charging at ~5% rate of charge checking SG every hour until all cells reach maximum SG reading--Sounds like where you are at now).
    • Dump/save existing electrolyte.
    • Next choice--Buy/mix new batch of electrolyte to battery specification of 1.260 and fill battery to cover plates
    • Or, add sulfuric acid to existing electrolyte and bring up to 1.260 SG (as always, add concentrated sulfuric acid to water/electrolyte, do not add water to conc. sulfuric acid as an explosion can occur--Use gloves/safety shield, etc. when working with acid).
    • Cycle battery bank and see what happens.
    I guess you could add sulfuric acid directly to the battery cells--Use a plastic hose to draw down the electrolyte level and refill with acid, then EQ (gassing will mix the electrolyte and acid).

    Then you get into the math... What is the volume and SG of the electrolyte, and what is the SG of the sulfuric acid (1.84 SG for "pure" sulfuric acid--Have no idea what you would be adding). You could work out the ratio of x liters of weak electrolyte @ x.xxx sg and y liters of sulfuric acid at y.yyy sg ... 

    If you know the volume of the battery and SG of the sulfuric acid, we could try doing the math (I did it once here years ago--Cannot find it right now). It is probably easier and safer to do the "mixing" outside of the battery (mixing acid in a "confined space" that may contain hydrogen and oxygen--Could get exciting).

    If the batteries are truly and well "sulfated" (fluffy gray lead sulfide has converted to hard black crystals)--Then the batteries will not see any recovered capacity (sulfation is a permanent loss of capacity).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • olNick
    olNick Registered Users Posts: 5 ✭✭
    #5
    Thanx all for the replies,

    I can calculate and adjust SP by removing existing and replacing w/ new electrolyte that I have which is 1.28 SP.
    I had ordered concentrated H2SO4 but they sent me nitric :-( so I just got the ready mix at the battery shop.

    the main thing I get here is to fully charge before mixing/replacing.
    Thanx for that.

    nick
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