Specific gravity of electrolyte in new battery

jprokos
jprokos Registered Users Posts: 8
Hi,

I was perusing this site while trying to find an answer to my particular situation (couldn't find an answer anywhere). I should tell you that I am living in Nepal, an American, and having trouble with my four 180 AH "Exide Inverter Plus" batteries. When I bought the batteries, two years ago, I took a specific gravity reading after giving them a full charge and it showed 1.200 on the hydrometer. That was when the batteries were brand new. I thought it was odd that all the literature that I could find said the electrolyte should be 1.265 and mine weren't. The voltages of the four batteries however were ~12.7 volts at the store when I bought them, and after charging and measuring at rest after I had them home and hooked up. I guess my question is, since these are made in Nepal under license from Exide, is this a gimmick or possible unscrupulous behavior by the dealers here. What benefit could they possibly get by keeping the electrolyte diluted? They give a 12 month full and then prorated 12 month warranty on the batteries for a total of 24 months. The batteries weren't exactly cheap at $250 each.

I noticed today that within 15 minutes of the grid power going off (we have load-shedding/blackouts every day in Nepal) the individual battery voltages dropped down to 12.3 V! The system is 360AH @ 24V and I was using about 400 watts for the duration of the black out. I do have a record of all the individual cell voltages and their SG.

The reason I ask is that I want to avoid this on the next purchase. Maybe I should insist on buying batteries dry and mix my own electrolyte next time?

In the mean time what can I do to squeeze one more year out of these batteries? I have read that if absolutely necessary you can charge the batteries, then equalize, then dump all the electrolyte and refill with fresh. Right now it appears I am getting false voltage from the batteries and they have become sulfated.

Any help?

Comments

  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Specific gravity of electrolyte in new battery

    Having a rested, open circuit voltage of 12.7 vdc indicates fully charged.

    An SG reading of 1.200 is not possible with an open circuit, rested voltage of 12.7 vdc. I would guess the SG measurement was in error.

    For a lead acid cell, the open circuit rested voltage per cell is very close to SG + 0.845.

    An SG of 1.200 would yield a per cell voltage of 2.045 volts or 12.27 vdc for a six cell battery.

    As to your voltage drop. If the cells have been on float for a long time the initial discharge will have a voltage dip before it begins to rise again. You might have this condition.

    Try discharging the batteries a bit more and see if voltage rises then starts dropping again due to normal discharge profile. At a discharge rate of 10-20% AH rating in amps, the voltage dip recovery should occur within 15 minutes of starting initial load.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Specific gravity of electrolyte in new battery

    Here is a thread on Hydrometers and how best to use them.

    I understand that some tropical locations will use a bit weaker electrolyte (batteries will have a longer service life?).

    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
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Specific gravity of electrolyte in new battery

    Voltmeters, hydrometers, and thermometers all have tolerances, and one could be high, the other low, and did you use thermal compensation for the hydrometer readings ?
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