Theory on Equalization Damage

RCinFLA
RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
I have searched web and have not found any substantial explaination on overcharging damage to lead acid batteries.

The term of 'shedding' lead is often used but other then plate erosion there does not seem to be further explaination.

I was given two relatively new batteries by a friend that asked me if I could revive them. He said his new charger overcharged them. He said they got warm and boiled off a great deal of water.

When I tested them with hydrometer I was surprised to find the fluid looked like graphite power was mixed in with electrolyte. I emptied all electrolyte, filled with distilled water and gave it a normal charge to ensure I pulled any lead sulphate out of plates. I then replaced with new fresh electrolyte. The cell voltage was way off normal and batteries self discharged almost as fast as I could charge them.

So here is my theory. The 'graphite' appearence must have been fine lead or lead oxide particles. I did save some of the original contaminated electrolyte and it did settle out to bottom of jar in several days. I unfortunately did not have access to a way to identify the material. I guess it could also be grid material but I am inclined to believe not.

The second part of theory, perhaps more controversial, causing high leakage is lead/lead-oxide particles being driven into the separator material to a point of creating a leakage path directly through the separator material. I contribute this to poor separator material used in these batteries and the high driving current during the overcharge.

I be interested if someone has found more info, or opinions, on such failures. There are quite a few folks out there doing equilization after equilization trying to balance their cells' specific gravity reading.

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Theory on Equalization Damage

    i am curious in that he stated he consistantly overcharged these batteries with high loss of water. did he replace water constantly or did he allow it to go below the plates? my old wally world batteries did get overcharged as well (slowly cooked and below the plates) and showed matter floating. they catastrophically failed on me not long afterward as i assumed it to be from sulfation, but never gave it a thought about failing in another fashion.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Theory on Equalization Damage

    I think it occurred in a one time (one or two day) event of overchargng.

    I also considered that it might be plate warpage punching through separator but I would expect inability to get any voltage from a dead short cell. After the flushing and refilling with new electrolyte, the consistancy of the leakage and drop of SG across all the cell were more like a uniform resistance leakage.

    I also considered the powder build up at bottom of plates. I flushed as much of the junk out as I could, considering a fifty pound brick, by about 12 flushes with water turning the battery upside down. A lot of the powder came out and quantity did taper off significantly after all the water flushes.
  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    Re: Theory on Equalization Damage

    What you are seeing with the particles is the plate erosion - positive grid corrosion - you speak of. It is quite common in batteries that have been chronically overcharged. There is no fix for it.

    I am betting that when you replaced the electrolyte that the specific gravity was way off of normal.
  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Theory on Equalization Damage

    The Battery Technology Handbook might shed some light on eq damage:
    http://www.scribd.com/doc/4738495/Battery-Technology-Handbook

    I couldn't find anything with a quick scan through it, but it has a lot of indepth detail about how lead acids behave and how they should be treated.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Theory on Equalization Damage
    Windsun wrote: »
    What you are seeing with the particles is the plate erosion - positive grid corrosion - you speak of. It is quite common in batteries that have been chronically overcharged.

    Thanks,

    Is the particulates primarily lead or corroded support grid material?

    I have some of the same Wally world batteries. They last me 4-5 years but I notice if I try to equalize just a little, the electrolyte starts to darken within 10-15 minutes of about 6-8 amps @ 15.5- 16.0 vdc. (After normal full charge).

    I have thrown 20-25 amps at them for an hour and half when they have been discharged to 60%-70% state of charge with no clouding of electrolyte or ill effects.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: Theory on Equalization Damage

    From what little I understand of battery chemistry--When equalizing, the split hydrogen and oxygen molecules tend to go different places. The hydrogen tends to out-gas into the air... The Oxygen tends to bind into the positive plate and create lead-oxide. This causes the positive plate to swell and can sometimes be seen as bulging battery walls and seeing the positive post(s) being forced up through the top of the battery case.

    The part I am not sure about is how fast this happens (a few weeks to months of excessive equalization--or over the period of years).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Theory on Equalization Damage

    Like making hydrogen and oxygen in electrolysis, the oxygen comes off the positive plate and hydrogen off negative plate. I guess with hydrogen being a smaller molecule in free state it probably permeates out to top surface faster.

    I know you don't really want to have raw grid exposed to electrolyte, especially in presents of oxygen bath. I previously only associated exposed grid to old battery or over discharged battery. Normally the grid will have been rebuilt up with lead during normal recharge process.

    Perhaps with a thin plate of marine or starting battery, the thin lead coating does not provide enough barrier to grid from the oxygen gas. Or possibly a poor pasting process leaves some of grid exposed originally from the factory.

    The only difference I can think (relating to grid corrosion) of between a fast rate recharge and fast rate overcharge is the amount of oxygen creation in the over charge.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Theory on Equalization Damage

    Did some more reading on the subject.

    You'd think after 150 years a corrosion resistance grid would have been developed. Problem is quite complex. There is dissimilar metal alloy issue, and battery is basically a metal plating tank and the positive plate is the ejector source. The best protection seems to be just thick positive plates to provide a greater lead oxide barrier to the grid.

    Other item I came across is the tight bracket on a permanent float use case. On a 12v battery below 13.6 v is bad for negative plate sulphation, above 13.8 v is bad for positive grid corrosion.

    Perhaps this is where pulse charging might help. Run a low average float voltage to avoid the positve grid corrosion and pulse charge to keep the negative plate from sulphating. Seems pulse charging does not generate as much free oxygen.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Theory on Equalization Damage

    rc,
    if you run tests, i would be interested in hearing of the results as i'm sure others here would be also. are you also going to test differing pulse rates?
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Theory on Equalization Damage

    Sure, the only thing I can prove in the short term is pulse charging pulls up SG from recharge of sulfate while still keeping a low average battery float voltage.

    I have several batteries that have been maintained at 13.8v for about 4-5 years but some cells are showing 1.20 to 1.25 SG.

    I am beginning to think the low SG is due to positive grid corrosion.

    I also read in one article that some cycling is essential to recoat positive grid. These batteries have had little cycling as they are primarily used in UPS function for momentary power outages.

    I have lowered float to 13.2v knowing they will sulfate but hopefully extend positive grid life. When SG lowers some I will try pulse charging on them.

    Does anyone know reason of lower SG due to grid corrosion? I can do impedance check to judge grid corrosion.
  • trkarl
    trkarl Solar Expert Posts: 33
    Re: Theory on Equalization Damage

    Hi RC,

    This may be of interest to you. I have a 12v bank of Surrette 6cs17ps batteries that I cycle about once every week or two to keep them from stratifying. Maybe your batteries kept on float for 4 yrs or so have stratified and caused your sg to drop at the top of the batteries?

    Anyways, I used to keep them floating at about 13.2v with the inverter in between cycles. Also when I would shut off the inverter, it's a ProSine 2.0 not that it matters, I would use a battery tender float/ charger to keep them floating. Well I wanted to get a desulfator for floating. So I bought this:

    http://www.thebatteryminder.com/12vbatteryminder-p-58.html

    It says one of the features is:

    "3 stage (constant current bulk, constant voltage absorption, pulse width modulated float).

    Well when I charged the batteries the sg would get to 1.265 and would stay there. I usually check the sg of a few batteries in my banks every couple days just so I know what is going on with them . Well after the bank was floating with the battery minder the sg came up to just above 1.270. Was this a fluke? I don't know and need to repeat this a few times to see what happens but I had never seen the sg come up with batteries floating before. Maybe the pulsing during float actually did something useful. I don't know. I just thought you might find this interesting.
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: Theory on Equalization Damage

    They are not stratified. They get a bulk once or twice a week after the typical grid flickers. (their feeding two stacked SW4048's)

    One guy I know had DR1524 with two legs of US battery U-225 golf cart batteries. His float was correct and he equilized them once every other month. Two years old and they went high resistance with grid corrosion. Now when he trims his hedge once a month he does it on the inverter power to exercise the batteries a little.

    I'm getting degradation in Rs of battery. With relatively good SG, worse cell is 1.205, this usually indicates the Rs degradation is due to grid corrosion.