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  • #16
    Originally posted by A.K. Boomer View Post
    You got me there,,, I thought his battery would have been as basic as they get...

    so once the sulfates get knocked off they dissolve instead of clogging up the bottom plates and shorting them out?
    Nope, if they fall off it is lost capacity, the sulfate is not very soluble in the electrolyte. If they lodge somewhere, might cause shorted plates.

    There usually is a little space at the bottom for sufficient electrolyte , and some stuff will fit there, I suppose.
    CNC machines only go through the motions

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    • #17
      I don't want to say its is not sulphation, as suggested by some on this thread, but i have 98% doubt that it is sulphation.
      I can report :
      in '60s and '70s I while in engineering school, I worked as a gopher in an auto dealership.
      One job was to test all the 12V batteries.
      In those days, the cells could be accessed via either screw caps on each of the 6 cells, or by a click off cover.
      Also, the lead links were either uncovered or just under the soft pitch.
      The immediate test was to use a "battery hydrometer" ( I see they are still available, although I have not used one in 30 years).
      The second test was to use a pronged device "cell discharge tester" which applied a resistor across each cell and it had a cell voltmeter.
      The second test was almost never used.

      In almost 100 % of cases, the safer hydrometer test would pick up a dead cell immediately.
      That is, the specific gravity on 5 cells would be almost identically charged, and one cell would be discharged.
      Opinion:
      If the failure mode was sulphation, I doubt that sulphation would occur on just one cell, and further, i would say thet the overcharging
      mentioned on this thread would quickly destroy the good cells, and also liberate hydrogen.

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      • #18
        Originally posted by wombat2go View Post
        I don't want to say its is not sulphation, as suggested by some on this thread, but i have 98% doubt that it is sulphation.
        I can report :
        in '60s and '70s I while in engineering school, I worked as a gopher in an auto dealership.
        One job was to test all the 12V batteries.
        .....
        In almost 100 % of cases, the safer hydrometer test would pick up a dead cell immediately.
        That is, the specific gravity on 5 cells would be almost identically charged, and one cell would be discharged.
        Opinion:
        If the failure mode was sulphation, I doubt that sulphation would occur on just one cell, and further, i would say thet the overcharging
        mentioned on this thread would quickly destroy the good cells, and also liberate hydrogen.
        A single cell at low gravity, and all the others at normal gravity suggests a shorted cell. Lots of reasons for that.

        Overcharging does not "quickly destroy" cells of flooded cell lead acid batteries such as we are discussing. Other types may be "quickly destroyed" by various mechanisms, though. It's a bad idea to overcharge, or too deeply discharge, lithium-ion cells, for instance.

        Overcharging WILL eventually cause a problem due to corrosion of, or possible "forming" of the grid frame material, which is not supposed to be involved in the battery reaction. When the regular battery material is fully charged, fully converted, and charging is continued, the lead alloy frame may be converted to active material over time, weakening the frame, or it may just be attacked by the electrolyte. Eventually, the battery fails by having only a tiny fraction of the original capacity. This is because the frame has broken due to the weakening, disconnecting a large section of the grid, with its active material (lead dioxide PbO2 paste). When a cell gets to having only a thread of material connecting a large section of the plate to the contact, a heavy current can melt through that thin section and disconnect the plate.

        I would point out that overcharging occurs on ALL cells, just a little later in the case of ones which happen to have a bit higher capacity than the others. But, the same charging current goes through all cells, so if you keep charging when the battery is already charged, you will get to the point where you are overcharging every cell. That will probably gas the battery and tend to dry out cells.

        When one cell is discharged, an others are good, it may be due to the cell shorting. That can be due to an insulator failure, or a particle of conductive material wedged between plates, possibly active material that fell off due to sulfation.

        Since overcharging drives off water as oxygen and hydrogen, drying out the cells, it can be a cause of shorting. Dry material can loosen and fall off, lodging between plates and eventually penetrating the insulator, causing a short. In that case of overcharging, it is likely to be "charged", and therefore conductive, material.

        "Sulfation" does NOT occur in a battery that is being actively used, being regularly charged and discharged. It occurs in a battery that has been "sitting", or in one that is never fully charged. It happens quickly when the battery sits in a discharged condition, because the sulfate is already present, and can immediately begin re-crystallizing. If the battery is charged, then it self-discharges over time, taking longer to get to a "sulfated" condition.

        Sulfation can lead to shorts also, because the recrystallized sulfate may "grow" the plate, and force some portion through the insulator to cause a short.
        Last edited by J Tiers; 07-23-2017, 11:19 PM.
        CNC machines only go through the motions

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        • #19
          Not automotive, on telephone power supplies and power station cold start DC etc,
          the standards for regulation of the 1600 Amp 50 Volt DC lead acid banks were Float 2.15 ~ 2.25 V,
          Boost I recall, was about 2.35 Volt. The specs on DC ripple current were tight for 2 reasons, one was battery life, and one was noise on the phones.
          Production test of every rectifier included psophometric test to the CCITT curve.

          On AC outage, the battery bank would take the exchange load.
          I still have notes in my diary here..."A floated battery will come back to 60~80% in 24 Hrs, after 120 Hrs nearly to full capacity.
          From a chemical point of view it is best to boost charge every so often"

          To protect against failure of the regulation there were ( I think 2) independent overvolt trips and tell tale pointers on the meters.
          I am not sure how often the banks were boosted, and it was done while the banks were on -line.

          On automotive side, sometimes a regulator would fail and the battery would "cook" in a short time. The indicator of that was the sulphurous stink under the hood
          or "bonnet" as it was called in Australia, when the car came into the shop. In those days batteries came packed in a box with a container of electrolite.
          They were "wetted up" and boost charged. ( maybe 10 to 15 minutes ?).

          I also worked for a time on the diesel electric submarines, each 2 V lead acid cell was about 4 foot tall
          and had a short circuit capacity of about 2 million Amp, and a lifetime across 2 refits, about 8 years.

          I don't know what type of cells are used in these applications now,
          I suppose distant memories of the Lead Acid tech. are of not much use these days.

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          • #20
            Note that comment about boost charging. That was to assure that the cells were fully charged.

            Solar charge devices often have an "equalize" setting, which is to assure all cells are fully charged, even ones that have a bit more capacity than the others.
            CNC machines only go through the motions

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            • #21
              wombat2go, I bet the dead cells were always in the center & not the end cells of the battery if you can remember as the inner cells get hotter in use than the outer ones.

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              • #22
                Flylo, that was in 1969 years and I don't remember.
                I do remember having battery problems in a fast boat I had - dead cells and getting towed home etc.
                I contacted the manufacturer and got onto a tech guy who knew about vibration.
                He told me to change from marine batteries to tractor batteries of same capacity because those from his company
                had much stronger supports for the plates and were otherwise the same. -no more problems

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