Lead Acid (VRLA) how long before one says it's US?

Discussion in 'Electricians' Talk' started by MGW, Jun 9, 2018.

  1. MGW

    MGW Well-Known Member

    I have been going through my late mothers and father-in-laws stuff, and there are a number of small VRLA batteries which have been flat for some time. I started with a pair originally used for a stair lift, 7 Ah each, the 3.8A Lidi charger would not recharge them as it went over voltage, so I put them in parallel with a 75 Ah leisure battery which also needed recharging, because it is a so called "Smart" charger I could just leave it on 24/7 however I powered it through a wifi connected energy meter one of the MiHome Energenie range so I could monitor progress with the PC.

    I was surprised, I expected a gradual recovery, this was not the case, after around 10 days within 2 hours the charge rate went from 0.1A to 0.8A and then held at 0.8A for 6 hours, then slowly back to 0.1A over another 2 hours. The charger has 4 charge rates, 0.1, 0.8, 3, and 3.8A and once charged it will jump to 0.8A when volts drop to 12.8 volt and back to 0.1A once voltage reaches 14.4 volt, so the lead in and out was a mark/space switching between the two rates, not an analogue rise and fall. Both the 7 Ah batteries did the same, and once that charge had completed they seemed to be fully functional.

    So second battery was in a power bank, 20 Ah this had not been left flat for so long and took just two days, so now second 20 Ah battery this one out of a wheel chair, clearly looking at the 7 Ah batteries I must give it two weeks, and since this one has been left the longest it will likely take the longest to recover. However at what point do I say scrap it?

    As a radio ham I do use 12 volt batteries so these fully sealed batteries are great, but I have been dumping old batteries mainly US because at some point over charged and dried out, but until this year I did not have a charger where I could look back and see charge rates change, so I was unaware of this point where the battery suddenly recovers. I thought it was a gradual thing. So asking if others have tried reviving sulphated batteries, and what they found?
     
  2. spinlondon

    spinlondon Well-Known Member

    Do you have a battery tester?
     
  3. MGW

    MGW Well-Known Member

    Not for such a small battery, however the 2 x 7 Ah batteries were able to power a cool box once they recovered, so they clearly are usable.

    I had expected to see a gradual recovery however, this 9 days accepting no charge then 9 hours and fully charged is some thing I have never noted before, it may have happened, but until I was able to monitor the power used by the charger over time, I was unaware of this.

    Hence the question.
     
  4. spinlondon

    spinlondon Well-Known Member

    It may be that once enough of the lead sulphide has been converted, the released acid helps speed up the conversion of the rest.
    I can’t say that I have noticed a rapid change, but prolonged trickle charging has resulted in revival of battery condition.
     
  5. Bob Rathbone

    Bob Rathbone Well-Known Member

    The issue with any lead acid battery is sulfating during discharge, the sulfur is from the sulfuric acid, that's why the SG drops on discharge. Normally this is a soft layer on one plate of the cell and is easily dissolved back into the acid when the cell is charged. If the cell is left in a discharged condition for a long period, the sulfate hardens and becomes difficult to drive back into the acid solution. With wet cells this is possible in many cases, but with the acid trapped in the fleece like plate separators in the sealed cell, and the fact that the cell may have lost moisture previously, it is far more difficult to restore the dry type cells. Look on the web for the 'Battery University', it's full of useful stuff.
     
    MGW likes this.
  6. MGW

    MGW Well-Known Member

    Thank you the "Battery University" is good. I served my apprenticeship as an auto electrician, back in the early 70's, and it does seem we are lacking in our education, even then we got a home work question, "Why does the battery voltage drop" I still don't really know the answer for lead acid, the chemical formula is same at start to finish, so why does the voltage stay the same like in the Daniel cell? I could find why the zinc/carbon cell voltage drops, and had to assume same for lead acid.

    To inspect to find out what has happened means we destroy the battery, so in real terms we just guess. I know ripping off the vent cover, and removing the valves (rubber caps) and putting a couple of drops of pure water in the cells can revive to some extent VRLA batteries where they have been over charged, however over charged batteries are very different to abandoned batteries, the latter should not be short of moisture.

    In the past I would give a battery 24 hours, if no improvement, then dump, however the two 7Ah batteries off the stair lift I knew what had happened to them, the battery charger had been switched off, and they had discharged completely with the lift in centre of the run. With the British stair lift my mother had, there were instructions on how to release the brake and wind it back to station, but with the German one my father-in-law had I could not find how to release the brake, so it was visit to Electrofix and two new batteries, with the intention of then recharging the old ones, however they went missing, only to be found on his death. I was so busy, I put them on charge and forgot about them until after the funeral. And the graph drawn by the MiHome monitor showed how the charge was suddenly accepted rather than gradually.

    The power bank found in his garage (20Ah) did a similar thing, so it seemed worth while trying to charge another VRLA 20Ah battery which was in my late mothers wheel chair.

    The problem however is to charge it, it needs another battery in parallel, not a problem to start with, I have other batteries needing a charge, but now they are fully charged and the Lidi battery charger is showing 14.5 volt and supplying 0.1A I think in spite of very low charge rate, holding a battery at 14.5 volt is not good.

    On disconnecting the second battery the volts hit 15 volt and switch off the charger completely, the volts then decay and as they drop below 3.5 volt and the charger displays error.

    So giving it another 24 hours OK, but giving it another 7 days not so sure, however I do have a known faulty battery, which I really should dump, although it will still drive the motor mover on the caravan, so has been kept so if we arrive back home with a discharged battery we can still get caravan into the drive, so I will use that one to give it a little longer.

    But question remains, how long to give before I give up?
     
  7. Bob Rathbone

    Bob Rathbone Well-Known Member

    I scrap them after a day and a half on charge.
     
  8. robertpstubbs

    robertpstubbs Member

    I know very little about batteries so can't give any advice.

    I have some 20 year old DeWalt 18V batteries that wouldn't charge in a yellow DE9116 charger, but when put in a black DE9108 charger would hold some charge. I would love to know why that is.
     
  9. MGW

    MGW Well-Known Member

    NiCad and NiMh batteries are completely different to lead acid. As are the chargers, there are a number of ways to work out when battery is fully charged, one is Delta V where the charger looks for a voltage dip as it becomes fully charged, another is temperature, electrical energy is constant and to start with it is converted into chemical energy, once this is complete it turns into heat, so once battery gets warm, it's fully charged. There is also the trickle charge method with warning to charge for 18 hours only.

    The lead acid charger I use has 4 charge rates, it starts at 3.8A, then 3A, then 0.8A and finally 0.1A and the changes are triggered by the voltage. There are other methods to stage charge batteries, and also pulse charge the latter common with solar panels. Even today engine management so battery only charged if under 80% or car on over run.

    Electric vehicles, be it golf trolley, mobility scooter, fork lift, or milk float, want to recharge the battery fast, they also use stage chargers, normally three stages, flat out to 80% or voltage limit, then last 20% slower so as not to damage battery. You note missed out electric cars, as not lead acid batteries.
     
  10. robertpstubbs

    robertpstubbs Member

    I did start by saying "I know very little about batteries". Now I have woken up a bit more, even I know the difference between NiCad/NiMh and lead acid.
     
  11. MGW

    MGW Well-Known Member

    Well started charging 2 pm Friday 8th June, today connected up last of other batteries that require charging, I expect it will take all day at just 0.8A, so that battery should come off charge tomorrow, that's only 4 days, and last time over a week before the VRLA recovered, the disconnected voltage is raising, I have a battery pack which could also do with a re-fresh charge, so if the battery voltage is enough to hold in anti reverse connection relay I will also charge that pack, but don't want to damage good batteries due to over charging, so just two days left.
     
  12. MGW

    MGW Well-Known Member

    Well now a week, battery still not responding, the charger between 7.5 and 10.5 volt would normally pulse the charge, this is suppose to help revive a sulphated battery.

    However I can't connect the battery on its own, as the charger detects is as a faulty battery and simply will not charge it.

    When I was trying to revive the 7 Ah batteries I found the voltage was varying between 12.8 and 14.4, at 14.4 the charge rate drops to 0.1A and at 12.8 it returns to 0.8A so in fact it was pulse charging, however at the moment even 0.1A is holding the voltage above 12.8, all my batteries other than this one 20 Ah one are fully charged. When I was reviving the 7 Ah batteries I had other batteries not fully charged so I could get the pulse.

    So how important is the pulse? Do I need a 0.2 amp load to get it to pulse, or is the pulse really not required?
     
  13. MGW

    MGW Well-Known Member

    I was two quick, 5:21 there was a pulse of 0.8A, again 10:21 so it seems it is at last taking some charge, to get that pulse volts must have dropped to 12.8 volt, once the charge rate increases then voltage soon reaches 14.4 volt so it drops back to a 0.1A charge.
     
  14. spinlondon

    spinlondon Well-Known Member

    When you are charging two batteries, are they in series or parallel?
     
  15. MGW

    MGW Well-Known Member

    They are in parallel, the charger will just say "err" if good battery not connected in parallel, I am told the CTEK is better at charging sulphated batteries, but they are 3 times the price. Today I thought it was going to charge [​IMG] the picture shows four spot readings and how I got three periods of charging, now sitting at a lower voltage 13.3 volt where before the activity it was 14.3 volt, and on disconnecting the voltage falls to around 4.5 volt where before around 3 volt.

    The numbers are watts input to charger, since current either 0.8 amp or 0.1 amp output, since volts have dropped watts have also dropped. I was a little worried at 14 plus volts, to my mind a bit too high, but 13.3 volts is fine, so I will just leave it for some more time.

    Once the open circuit volts for the VRLA hit 7.5 volt, I can take the leisure battery out of the circuit.
     
  16. boardey

    boardey New Member

    Local tip, and put them in the correct container.
     
  17. MGW

    MGW Well-Known Member

    You are likely correct, at least for the 20 Ah battery, but the 7 Ah batteries took so long, yet seemed to fully recover, in the past 24 hours if nothing to the skip. But it was 10 days before the two 7 Ah batteries started taking a charge, and when they did they took all the little charger could give until near fully charged.

    So now on day 11, with 7 Ah in parallel as other wise charger locks out, and have been sitting at 12.9 volts for at least 2 days with charger not showing any current draw.

    Reading the charger instructions it should alternate between 0.1 and 0.8 amp, at 12.8V goes to 0.8A and at 14.4V drops to 0.1A, however once battery has been at higher voltage for some time charge rates drops to zero, but that function is not documented, so I will give it two weeks, however the 7 Ah batteries were pulsing between the two charge rates which should help with sulphated battery, but this 20 Ah is just static at 12.9 volts.
     
  18. MGW

    MGW Well-Known Member

    Update, battery charges and batteries moved to new house, the revived VRLA 7 Ah batteries were given away with stair lift, so I now have the two less than year old 7 Ah VRLA batteries and the old 20 Ah VRLA on charge, it seems to hold the voltage at around 13 volt, the energy monitor tells me every so often the charger goes from zero to 0.1A charge rate, for around 1 hour every 6 hours.

    The 20 Ah battery will not charge unless in parallel with one of the 7 Ah batteries, however disconnected the open circuit voltage seems to have risen in 2 volt steps, at moment it will show 8 volt open circuit, with a 6W bulb as load quickly drops to 4 volt which is seems to maintain.

    If as I had expected 4 cells have part recovered, and 2 cells are still holding out, then really don't know what has happened to those 2 cells, if they were open circuit then the bulb would not glow with 4 volt across it, and if closed circuit then it would over charge the 4 part recovered cells.

    OK I know the 20 Ah battery is unlikely to recover, however doing no harm being left on charge. Using a 500 mA 6W battery charger with no regulation other than that of the transformer the voltage exceeds 15 volt in seconds, also the open circuit voltage jumps up within minutes, the battery states standby charge 13.5 to 13.8 volt, and cycle charge 14.4 to 15 volt, and the Lidi charger auto shuts down at 15 volt.

    What I would like is for the Lidi charger to go into pulse charge mode, however it will not do this. The 20 Ah is showing signs of recovering, but as you can see started 8th June, so around 58 days it has been on charge, there was the move where it went off charge for a short time, but 8 weeks on charge and not recovered.
     

Share This Page