Re-charging VRLA which have been over discharged?

[ericmark]

A stair lift has been unplugged, plugging back in the batteries would not recharge, quick cure new batteries, however I suspect the only fault with old batteries is over discharged.

Now I have an old unregulated battery charger, however 12 amp is rather over the top for a 7 Ah battery, but my smaller chargers seem to have a safety device built in which results in it displaying Err (Which I assume means Error) when I select charge.

I am using this Lidi charger however most chargers designed for small batteries are the same, in motor cycle mode limited to 0.8 amp designed for batteries 1.2 to 14 Ah.

Only way I can charge the battery is to connect it in parallel to my 75 Ah caravan leisure battery, it does not seem to want to charge them stand alone. It states Err shown if over 15 volt (or under 3.5 volt) now although 0.8 amp is not much, however for 7 Ah maybe still too high?

So what I am wondering is the battery simply faulty, or is the charger not suitable? As said batteries were working fine until stair lift switched off. But I have not really got much experience with such small batteries.

 

[bernardgreen]

When a battery is over discharged the best way to recover it is a slow trickle charge over several days, preferably from a constant current source that will increase it's voltage as the battery recovers. Otherwise a variable voltage power supply with a suitable series resistor and manually adjust the voltage from time to time.

Forcing too much current to speed the recovery can have un-expected and potentially hazardous consequences,

 

[securespark]

CTEK chargers are brilliant at giving life back to "dead" batteries.
As long as you have a minimum of 2V there.
I had a battery attached to my Octavia that was kaput. It was winter time and the voltage was sub 2V, so I was out there with a hairdryer, warming it up. As soon as it was 2V+, I whacked the CTEK on it in "reconditioning" mode and it brought it back to life. Took ages, but it worked a treat.

 

[ericmark]

I have now connected both batteries in parallel so 14 Ah under 7.4 volt it sees it as a 6 volt battery, and over 10.3 volt it starts the main charging system at 3.8 amp. However between the two voltages it starts pulsing the battery icon which I assume means pulsing the charge.

As soon as it starts to do the main charge the voltage goes over 15 volts so it switches off again. So every 1/2 hour I am pushing the mode button and restarting the pulse charge.

I have been told a few times how good the CTec chargers are, however I already have two Lidi battery chargers and with a 65 Ah battery the Lidi charger is spot on, it is only when trying to charge the little 7 Ah battery where it has a problem.

For the price of a Ctec I could buy new batteries so hardly seems worth while.

Looked at instructions and it seems lowest charge rate is 0.8 amp, with a 65 AH battery this is nothing, however with 7 Ah just 1/10th Ah rate, this may be OK with good battery, but not for one sulphated.

 

[333rocky333]

I recently had to sort a stairlift for a relative, they left it off as it was due removal, after being off a day i switched it back on and it bleeped and didnt work, when i googled it, it seems a common thing for them to fail if switched off then they con you into buying batteries, i just removed them and read about 3 volt each, i stuck my batteries on a normal car charger and every ten minutes took them off and checked the voltage and felt them in case they got hot, after about 30 minutes the voltage was up about 12 volts, refitted them and they appeared ok, i left it overnight for the machine to further charge them itself, it then moved fine, I then had to reset the limits with info from the net, they came and removed it and never said a word about the batteries

 

[ericmark]

The batteries were swapped for new. However I would like to use the old batteries. One idea is a portable power supply. But don't really want to pay out until sure idea will work. So step one is batteries to experiment with.

My idea is using existing equipment to be able to recharge battery for caravan with car cig lighter socket. Idea is whatever car is used for day out, they all have cig lighter socket, so plug in inverter, then power battery charger from inverter, which will charge battery.

However until tried not sure if enough charge will transfer to be any real use. 14 AH is not much, but if it will run central heating and water pump over night, that is enough to keep things running until next camp site will huck up.

Also when not in caravan they will run my radio. Don't want a large battery which can spill acid in car, but small sealed batteries present no real danger, no different to carrying wheel chair with batteries in for what car is designed for.

So have a 150 watt inverter and two Lidi battery chargers, so if batteries will start working likely can charge two batteries so could get 7.6 amp total although that would mean larger batteries. But step one is will the concept work?

Anyway I have put battery one in parrellel with 75 AH caravan battery, Tomorrow likely swap to other battery. If I can revive them, then I can move to next stage. If concept works then move to making a proper box to hold everything.

 

[JohnW2]

Anyway I have put battery one in parrellel with 75 AH caravan battery,

Is the 75A one charged? If, so, I would have thought that putting a small 'discharged' one in parallel with it (without any diodes) would carry a risk of the big one frying the little one, wouldn't it?

Kind Regards, John

 

[ericmark]

Is the 75A one charged? If, so, I would have thought that putting a small 'discharged' one in parallel with it (without any diodes) would carry a risk of the big one frying the little one, wouldn't it?

Kind Regards, John

Not really, with split charging there was a worry that on cranking it would draw current from second battery overloading cables and relay, so relay was connected to warning light of alternator so it could not back supply power when cranking, also of course no limit to how much power can transfer between batteries so I would fit a fuse. As an experiment I tried fitting just a 10A fuse, it did not rupture, so connected an ammeter to monitor, then realised why split charging did not work that well.

I found with a 110 AH battery on start I may get 20 amp into second battery, but a minute or so latter this had dropped to less than 5 amp, what I tried was to fit 3 x 1A diodes to alternator to replace the 3 diodes used for warning lamp on Lucas ACR alternator, and used the original 3 diodes which were same size as main diodes as a second output, this worked well, the charge rate for second battery was same as prime mover battery.

However Bosch and Delco alternators did not have large diodes for warning lamp, so could not be easy converted. Today with engine management switching off the alternator converting the alternator is a non starter. The blocking diodes worked with CAV 440 regs where you had hi, med, low terminals but useless with alternator with built in regulators.

So the modern method is DC to DC inverters, which are rather expensive.OK with a Sterling DC to DC inverters you have float charge to prime mover battery 13.8 volt and stage charging to second battery or pulse charging. So a narrow boat can charge the three domestic batteries at 110 amp from two engine alternators however not really an option with caravan, very few cars have two alternators and the cables required to take that power to caravan would be rather heavy.

Since we like going out on push bikes, often use two cars, so tow car not used once on site, so want some thing which can be recharged with either car, and not too heavy. Not sure if the idea will work, theory is OK, but practice may show I have missed some thing.

Really with chargers I have need batteries 14 AH or larger so I can use full 3.8 amp, also having to press button to start it charging is not ideal, but want to test idea before spending money.

Charger is powered from an energy meter, so remotely I can monitor charge rate, at the moment two watt, at 84 watt/hour it seems likely it will take two days per battery, so it will take some time before I know if batteries have recovered.

 

[ericmark]

After a lot of messing around I finally got it to charge the two 7 Ah batteries in parallel, it alternated between 0.8 amp and 0.1 amp for around an hour, then settled at 0.8 amp. The switch between the functions is voltage dependent, 7.5 ~ 10.5 it should alternate 0.1 to 0.8 amp, 10.5 to 12.8 it should charge at 3.8 amp, and 12.8 to 14.1 it should charge at 3 amp, then 14.1 to 14.4 at 0.8 amp and then it should drop to 0.1 amp, should the battery voltage then drop to 12.8 it will resume charging at 0.8 amp this is the pulsing I was getting. However at 15 volt it switches off, and the time delay between reaching voltage and switching is too great, so to start with before it was getting to the 0.1 amp stage it was hitting 15 volt and switching off.

It would seem although the battery charger states for batteries 1.2 Ah to 120 Ah with two setting manually selected below or above 14 Ah, for small batteries the switching delay is too large. With the 75 Ah battery when that was allowed to fully discharge the pulsing 7.5 to 10.5 volt worked, but with the small batteries it just hits 15 volt and switches off.

Anyway seems I now have a 7 Ah battery to play with. Update one of the pair has come back to life, it will run a cool box which is a reasonable load, and recharge going through the stages. The other one drops to 6 volt with cool box load, and recovered to 8 volt, on trying to charge at first it pulses as it should, the volts start to climb, then it shoots to last stage and then slowly the volts fall, as the charger returns to 0.8 amp volts shoot up and charger switches off.

 

[ericmark]

This was a surprise. Although I have tried to renovate many sulphated batteries, I have not used this type of charger before or had a device monitoring the progress. The graph shows how I discharged both batteries then returned them to charge with the bump just after 12:00, this is where the charger was pulsing between 0.1 amp and 0.8 amp as the voltage keep rising and falling, it then settled at the 0.1 amp charge rate until 18:00, at this point the second battery of the pair started to accept a charge, at 20:21 (can read on monitor software exact times and input to charger) the charge rate started to rise 4W, by 22:21 (dot half way up) it was an average of 11W the charger was actually swapping between 0.1 amp and 0.8 amp it was the mark/space ratio which was changing. By 23:21 it was drawing 15W so charging at 0.8 amp which held until 02:21 after which again mark/space ratio changed and average current started to fall, 3:21 down to 10W and 4:21 dropped all the way to 2W.

To recap started to charge on Wednesday had to put batteries in parallel with a 65 Ah battery to get battery charger to hold on charge, as otherwise it detected over voltage and auto switched off. So the first 7 Ah battery to recover one could not see the graph as masked by the 65 Ah battery, it took two days to be able to charge just the two 7 Ah batteries, and neither could be charged on its own only charging two would the voltage hold below the 15 volt cut off point. Then one of the pair seemed to be working as expected, it would run a cool box used to load the batteries, so paired them up again to see if second battery would also come up. The surprise is the delay where I was convinced the battery was useless, then a sudden change where it accepted charge.

It has taken 5 days for the pair of batteries to recover, the major problem was any standard car battery charger could bang in 8 amp and cause the battery to explode, so wanted a battery charger with low output, however the safety features on the Lidi battery charger used (switched off once 15 volt recorded) stopped simply clipping on leads and leaving. Had I had a constant voltage power supply to hand then maybe that would have worked, but only way I could generate a constant voltage was the 65 Ah battery in parallel.

I would have not spent so long with an unknown battery, but I knew why they had failed, the chair lift had been unplugged, the stair lift in question did not have a manual method to return it to charging station, so needed a second pair of batteries to get it to charging station. I had intended to try recharging the batteries the next day, but they went missing. So it was not until my father-in-law died that they were found.

I would question the whole idea of a 7 stage battery charger claimed to revive sulphated batteries which needs 7.5 volt in the battery to see it as 12 volt and start the charge, although the pulse charging worked, with such a small battery it jumped from pulse to 0.8 amp but before it could drop to 0.1 amp it had hit 15 volt so switched off.