Sulphated battery recovery two 7 Ah VRLA results.

Discussion in 'Electricians' Talk' started by MGW, May 13, 2018.

  1. MGW

    MGW Well-Known Member

    Father-in-law had a stair lift, he switched it off, the batteries (7 Ah VRLA) went flat half way up stairs, it would not power up or down and no instructions on how to release the brake. So fitted two new batteries with the idea of charging the other two latter, however they went missing, only to be found three months latter on his death.

    So tried to charge with a Lidi battery charger, the only charger designed to charge small batteries which I have, however on switch on it hits 15 volt and switches off again.

    So cheated, put one battery at a time in parallel with at 75 Ah battery, and one battery of the pair seemed to recover after some 3 days. Tested both batteries by trying to power a cool box, one seems to work, other dropped to 6 volt in seconds.

    So now both VRLA batteries in parallel and the charger was alternating between 0.1 amp and 0.8 amp at 14.4 volt it drops to 0.1 amp and at 12.4 volt it returns to 0.8 amp you can see [​IMG] the bump around 1 pm where batteries were tested on the cool box, by 20:20 the charge rate started to rise, by 23:20 full 0.8 amp which continued for 3 hours then started to tail off again. Now 12:30 sitting at 13 volt. I have not seen this sudden change before, one hour will not take any charge next hour taking full charge, however in the past I have not powered the battery charger through an energy meter to be able to see it.

    It has take 5 days to get the battery to recover, not tried to measure Ah capacity I would guess it is reduced, but seems 4 days nothing happened then all happened in 4 hours.

    Interested to hear comments.
  2. JP.

    JP. Screwfix Select

    I would say that it took 4 days to overcome the battery internal resistance, and once that occurred then rapid charging (or relatively rapid charging) took place Mr M..I would think that the amp hour capacity of the battery has dropped substantially, this would be confirmed with the relevant test. Interesting stuff m8.
    MGW likes this.
  3. Bob Rathbone

    Bob Rathbone Well-Known Member

    Not only do these batteries sulfate, and that goes hard on the plates when left, but the acid is held in a pad between the plates, this dries out over time as the cells gas and vent. Breaking down sulfate requires a higher start voltage and a close watch on current, as it will rise quickly as soon as the hard sulfate starts to break up and expose the plate surface to the acid. More often than not these batteries do not survive being left discharged.
    MGW likes this.
  4. spinlondon

    spinlondon Well-Known Member

    Some Motorcycle trickle chargers have a desulfate mode.
    Don’t know if it does much?
  5. MGW

    MGW Well-Known Member

    The charger does have this de-sulfation mode, however to hold the voltage down to use this the battery has to absorb so much charge. What was found was the battery would be charged by pulses to de-sulfate, until it reached the critical voltage when normal charging starts around 11.5 volt, and then the volts shoot to 15 volt and the charger auto switches off.

    Once by connecting in parallel I had charged it a bit more, then it again started to pulse charge, 0.8 amp until 14.4 volt then 0.1 amp until volts dropped to 12.4 volt then back to 0.8 amp again. It does seem this pulse charging worked, as the battery did recover.

    Although my portable radio will take 8 x C cells which can be charged in the radio, these are no where near 7 Ah more like 1.2 Ah plus lower voltage so not as much output, so getting these cells working means they are both light enough to carry and leak proof so seem a good option to power my old FT290R radio, may even power the IC290 radio although think 30 watt is asking a bit much.

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