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The abandoned leisure battery how to restore it.

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Main problem is sulphur gets harder over time, and the only way to turn it back into sulphuric acid  also takes time, I have had a battery seeming to do nothing for 2 weeks, then like as if some one had flicked a switch, it recharged.

 

However while the battery will take no charge, my Smart charger will not charge it, It trips on either under or over voltage, so some way we have to trick the charger into working.

 

Since the cells will not allow any power through them, if one cell is short circuit, we have no way of knowing. So we need some method to limit how much energy can be poured into the battery should it have a shorted cell, the on board caravan charger can often give 25 to 35 amp, which will fry a battery with a shorted cell, a 3.8 amp Smart charger will limit the current to safe limit, but often they simply will not switch on.

 

I use a 7 Ah valve regulated lead acid (VRLA) some times called absorbed glass mat (AGM) in parallel with the larger battery, this means the maximum power into the discharged battery is 84 watt (7 x 12) which will not over heat the battery too much, plus the 3.8 amp from the battery charger, clearly needs daily inspection, but should a cell be short circuit there will not be a melt down or explosion. 

 

I have not had a battery recover after 3 weeks on charge, I have after 2 weeks on charge, so would say after 3 weeks give up. But up to 2 weeks there is a chance it will come up again. And there are no signs before it recovers, it is like flicking a switch, I have a computer linked energy monitor, this monitors power into the charger, but power out is related to power in, so the computer shows a graph of charging rate, without having to watch any ammeter or volt meter.

 

So the Lidi charger I use has 4 fixed outputs, 0.1A, 0.8A, 3A and 3.8A plus of course zero. It will auto switch between zero, 0.1 and 0.8 amp, it will not return to 3 or 3.8 amp output without pushing buttons, this is great, as once battery starts to recover then no more than 0.8 amp, so no fried battery if there is a shorted cell. But below 7.5 volt it sees battery as 6 volt, so will not charge a 12 volt battery once below 7.5 volt and at 15 volt it assumes leads removed and switches off. Hence why using a 7 Ah battery in parallel.

 

It is very similar the the Ctek MXS 3.8 but not the same, it has some plus and some minus points. So I am starting this thread as likely there are loads of people with batteries which have been abandoned due to Covid-19 and will need reviving, so this allows people to share experiences and hopefully reduce the number of new batteries bought and also ensure reasonable safety. 

 

Even a 5 amp charger can cause a battery case to warp, DSC_3937.thumb.jpg.a3ef43f2e2a0e016424e91882db3c6c9.jpg This battery is a 35 Ah from a mobility scooter.

It was charged with the scooters 5 amp charger, it was inside a battery box so damage was not seen until I came to change the battery, so if this is what a 5 amp charger can do, think what the 25 amp charger built into caravan will do.  9 times out of 10 putting the caravan on the drive and plugging it in will revive the battery, normally a bad egg smell if battery is faulty, but nothing smelt with this one.  And you can't really inspect the battery once an hour for 2 weeks.

 

So only safe way is with a very low output charger.

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Plate sulphation due to a battery left in a discharged state for a time can never be totally eliminated, the longer it is left the harder and larger the crystals become.

 

It may successfully start to take a charge and appear to be fully charged and healthy,  however a test to see if  it performs as it should when under load, and monitoring when open circuit to see if it is capable of holding a charge may prove otherwise.

 

There are potions, myths and electrical devises that are supposed to, but can't be proven to remove sulphation, some of them have the potential to make it worse by causing detachment of the paste from the plates, which if it gathers in sufficient quantities in the sludge traps at the bottom of the battery to bridge + and - plates, will cause a soft short resulting in it not holding a charge.

 

However, it's well worth giving it a go, nothing is lost, it may not prove successful, but again it may revive it enough to be useable for the foreseeable future  as long attention is taken  to keep it fully charged.

 

With caravan batteries they may be useable for a long time after a car battery has to be replaced, the normal reason for a car battery to be changed is the inability of it to operate the high load of a starter motor,  with a caravan the highest load is the mover, if fitted, the day to day loads on the battery are minimal, especially on EHU , but more so if none EHU.

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I have a lab power supply which is adjustable from 0 to 30v and 0 to 5A, it's very versatile  for battery charging, but you have to understand what you're doing because it's just a dumb power supply not a smart charger.

 

In the case of attempting to revive a dead 12V battery, I'd set voltage to max 30V but limit the current to say  max 1.5A . The limiting circuits in the power supply work by Ohm's law, so it will automatically increase voltage until it's high enough to push a current of 1.5A into the battery.   A battery which has been discharged for a long time will have a high internal resistance, so even 30V may not be enough to push 1.5A through the battery as current equals voltage divided by resistance (Ohm's law). As the battery starts to revive the internal resistance drops, so the current will increase relative to voltage, both current and voltage are displayed on the power supply, so you can see this happening, if the battery is saveable you will see the power supply voltage drop to around 13 to 14 V to provide the pre set 1.5A max current, at this point, I'd set the max current to 5A and limit voltage to 14.5V and charge for 16 to 24 hours. If everything is OK the current supplied will gradually reduce as the battery charges at the limited max 14.5V. 

 

I use a linear power supply, no more expensive than a mid range battery charger but much more versatile for abnormal battery charging situations.

 

Ihttps://www.ebay.co.uk/itm/Lavolta-BPS305-Variable-Linear-Adjustable-Lab-DC-Bench-Power-Supply-0-30V-0-5A/191766020330?_trkparms=aid%3D1110009%26algo%3DSPLICE.COMPLISTINGS%26ao%3D1%26asc%3D20200220094952%26m

 

 I also have a regular battery charger for everyday use.

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Posted (edited)
18 hours ago, Weekend Traveller said:

I have a lab power supply which is adjustable from 0 to 30v and 0 to 5A, it's very versatile  for battery charging, but you have to understand what you're doing because it's just a dumb power supply not a smart charger.

 

In the case of attempting to revive a dead 12V battery, I'd set voltage to max 30V but limit the current to say  max 1.5A . The limiting circuits in the power supply work by Ohm's law, so it will automatically increase voltage until it's high enough to push a current of 1.5A into the battery.   A battery which has been discharged for a long time will have a high internal resistance, so even 30V may not be enough to push 1.5A through the battery as current equals voltage divided by resistance (Ohm's law). As the battery starts to revive the internal resistance drops, so the current will increase relative to voltage, both current and voltage are displayed on the power supply, so you can see this happening, if the battery is saveable you will see the power supply voltage drop to around 13 to 14 V to provide the pre set 1.5A max current, at this point, I'd set the max current to 5A and limit voltage to 14.5V and charge for 16 to 24 hours. If everything is OK the current supplied will gradually reduce as the battery charges at the limited max 14.5V. 

 

I use a linear power supply, no more expensive than a mid range battery charger but much more versatile for abnormal battery charging situations.

 

Ihttps://www.ebay.co.uk/itm/Lavolta-BPS305-Variable-Linear-Adjustable-Lab-DC-Bench-Power-Supply-0-30V-0-5A/191766020330?_trkparms=aid%3D1110009%26algo%3DSPLICE.COMPLISTINGS%26ao%3D1%26asc%3D20200220094952%26m

 

 I also have a regular battery charger for everyday use.

Interesting technique thanks. I might just get my army surplus PSU down out of the loft and give it a try.

 

I also saw some guy on YouTube and his method was to use a regular battery charger in boost or start mode multiple times for 10 minutes at hourly intervals.  Currently testing out this system as it seems feasible, the voltage is higher in boost mode. After a couple of goes, I got the internal resistance down from over 25 milliohms to 21 and the capacity has gone up by only 10 to 136 on a 265 CCA SAE battery I had lying around. I also used my Ring smart charger in a recondition (pulse) cycle inbetween. It's slow going.

 

I tested every battery I have and the best ones have an internal resistance around 4.5 m.ohms, anything over 7 and it's on it's way out apparently.

 

Probably battery salvage might only work on an unsealed battery as it's necessary to keep topping up any cell as water is lost. If it were a sealed battery it could just boil dry and die completely. It would also be possible to flush sediment out and replace the electrolyte on an unsealed battery. I'm no longer a fan of maintenance free batteries.

Edited by limecc

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8 hours ago, limecc said:

Interesting technique thanks. I might just get my army surplus PSU down out of the loft and give it a try.

 

I also saw some guy on YouTube and his method was to use a regular battery charger in boost or start mode multiple times for 10 minutes at hourly intervals.  Currently testing out this system as it seems feasible, the voltage is higher in boost mode. After a couple of goes, I got the internal resistance down from over 25 milliohms to 21 and the capacity has gone up by only 10 to 136 on a 265 CCA SAE battery I had lying around. I also used my Ring smart charger in a recondition (pulse) cycle inbetween. It's slow going.

 

I tested every battery I have and the best ones have an internal resistance around 4.5 m.ohms, anything over 7 and it's on it's way out apparently.

 

Probably battery salvage might only work on an unsealed battery as it's necessary to keep topping up any cell as water is lost. If it were a sealed battery it could just boil dry and die completely. It would also be possible to flush sediment out and replace the electrolyte on an unsealed battery. I'm no longer a fan of maintenance free batteries.

I'm no expert on batteries, however it would seem that getting initial current flowing through a neglected battery is what starts the process of resurrection if the battery is salvageable. Because the battery has high internal resistance when in a deeply discharged and probably sulphated state, it requires high voltage to get that initial current flowing, a regular battery charger will likely struggle to achieve those high voltages because they are outside the parameters required for normal battery charging, this is probably why you may have one on the charger for a couple of weeks before anything noticeable happens. If you have a power supply which is capable of sufficiently high voltage you can use brute force to induce that initial current flow which the battery charger can't manage. As long as you have a current limiting circuit set to a low current for the initial stage then you could put 100 volts across it and it will be perfectly safe, once the current starts flowing and the internal resistance of the battery starts to drop then the power supply will automatically reduce the voltage to maintain the current at the preset level.  

 

With a battery charger, it decides what happens, with a power supply, you decide what happens but you need to understand what you're doing!

 

I agree, maintenance free batteries are not for me, I don't understand how it can be an advantage not to be able to top up the electrolyte.

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There are maintenance free, and absorbed glass mat or valve regulated lead acid. Maintenance free has extra electrolyte and a system which tries to recombine the hydrogen and oxygen so water loss is reduced, but other than not needing to top up, no real advantage, they are still a flooded lead acid battery that means more electrolyte than required. 

 

The AGM or VRLA is a completely different beast, the acid is absorbed into a fibre glass mat and only just enough is used, there is no free electrolyte, the first advantage is they will not leak, and with stair lifts for example they are used on their side. The material can't physically fall off the plates and they can deliver a lot more power for given size, they can also retain the charge for longer, and no question they are a far better battery.

 

However they also have their down sides, in cars they are normally put in the boot to keep them cooler, and with stop/start technology no real option but to use AGM batteries, a flooded battery would not stand that for long. But they clearly must not be over charged, go onto Halfords web site and look at battery chargers and many say for all lead acid batteries, then a note at bottom not suitable for AGM batteries.

 

The Ctek charger is well known and most maybe all I have not checked are suitable for AGM batteries, in the main they are stage chargers, and as with most stage chargers some stages are current regulated not voltage, but voltage is very important as well. I use a cheap Lidi charger there is also Aldi version and after that Ring also do one, in the main the maximum output is 5 amp mine is 3.8 amp, Ctek do a special for caravans at 25 amp, it also has a special price, the Lidi charger does not work so well with caravans as it will only auto cycle 0.8 amp, 0.1 amp and off, once it has charged the battery, the 3.8A and 3A rates need you to press button again, it does however mean it will not over charge a battery producing high levels of hydrogen gas should a cell go short circuit, and it will charge both 6 and 12 volt, the Ctek cheap MUX 3.8 however will return to 3.8 amp, the Ctek D250SA designed for caravans costs around £230 so the MUX 3.8 is cheap when compared with that.

 

However I have some thing most people don't, I have an energy monitor which connects to my PC, it only shows power into the battery charger, not actual charge rate, but power in = power out plus heat, so nearly the same as power out. So from my PC I can see a graph of the charge rate. What was a surprise was what a sulphated battery charge curve looked like, first was a small 7 Ah battery, or actually 2, as the charger will not start charging under 3.4 volt and also switches off at 15 volt, so to charge I had to cheat and put a good and sulphated battery in parallel, so to start with good battery charges, once charged the charger switches off, and it remained off for nearly two weeks, then as if a switch had been flicked the sulphated battery started to charge, it took the chargers max output of 0.8 amp for around 7 hours, then 0.1 amp for last few and then off.

 

I at that time had a few sulphated batteries both flooded and VRLA (AGM) and they all did the same, just as if a switch was flicked, however one had a shorted cell, and this like all the others took no charge until a week or so, then as all the other cells took charge it was over charging due to shorted cell, at 0.8 amp no real problem, but in a caravan with a 25 amp voltage regulated charger this could cause an explosion. So the built in caravan charger is not really suitable for reviving the sulphated battery unattended, the bad egg smell will warn if you in the caravan, but unattended there is nothing to switch off the charger.

 

That is what likely happened to the battery in the picture, shorted cell caused over charging, the shorted cell may not even have been in that battery, as two in series.

 

But I have tried all sorts to bring sulphated batteries back to life, and some time is has worked, but now realise had I done nothing more than leave them on charge for an extended time they would have recovered likely better than putting 24 volt or anything else on them, it makes sense it took time to sulphate so taking time to reverse the process is only to be expected.

 

The problem with AGM batteries is old chargers were made before the battery, so when not suitable there is no warning, so I have a 90 Ah AGM battery for my caravan, it came out of the car, so cost nothing, and it is better than the 75 Ah that came with the caravan, but will the caravan charger damage it? So where with the 75 Ah when I could store at home it was left on charge 24/7, with the AGM it is only charged when caravan is used, since the AGM holds charge longer they are a good option when caravan is in storage with battery not being charged, but clearly needs to be no discharge, no alarm or radio memory, take the terminal off on one end, other wise you need to swap battery every month, and with a 75 Ah flooded and a 90 Ah AGM that was my intention,  once a month swap them, but the lock down stopped that, hence a totally flat 75 Ah not even 3.8 volt needed to start the battery charger, had to put 7 Ah in parallel.

 

Caravan-battery_upto8_28-06-20.jpg.62828e8776a09f2018b9a2bbf93d6efa.jpg This was the result, at around 10:30 I had noted it had started to take charge so pressed the charger button to put onto 3.8 amp charge rate, it is still taking 0.1 amp now, some 3 days latter and sitting at 13 volt. It will likely slowly rise in voltage but never hit the 14.4 volt at which the charger would switch off.

 

However with the smart charger I really don't need to monitor, it was just I have the energy monitor so did so out of general interest.

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