Recovering deep discharge lead acid battery - Page 1
Forum section: electronics / general

author: veedub565
author_rank: Frequent Contributor
timestamp: July 03, 2020, 02:29:28 pm
content: I have a 12v 110Ah lead acid "leisure" battery. It has been left for quite some time (months) and voltage is now at 8vIt may well be dead and unrecoverable, but I'm going to try.I connected a basic type charger on its low setting, after 20min I removed the charger and battery is now at 12.8vWith the charger attached it does not draw much current. Even with the charger set at High 8A I've confirmed with a multimeter, it only sucks about 0.5AQuestion is do I:go gently gently, and leave on low for a few days, a week, and see what happens.Go gently gently for a day or so and then up the current on the chargerOr just go in full power right away.I don't unfortunatly have a smart charger. Otherwise that would be the best option.

author: veedub565
author_rank: Frequent Contributor
timestamp: July 03, 2020, 02:30:27 pm
content: Also I checked and the plates inside are covered with distilled water, so it doesnt require topping up.

author: Gregg
author_rank: Super Contributor
timestamp: July 03, 2020, 05:04:35 pm
content: Go gently; but it depends a lot on your charger. If the charger isn't voltage limited, it will require a lot of monitoring. Basically you don't want to get the battery hot. You can check the cell to cell voltage by dipping acid resistant electrodes connected to your multimeter into the electrolyte of adjacent cells. Lead wire is ideal but lead based solder should work; use a loop to keep the flux out of the electrolyte.I'm kinda partial to the chargers that raise the voltage to about 14.5 and then turn off until the voltage drops to about 12.9 as this seems to allow heat to dissipate while giving enough power to kick some sulfates off the plates.

author: veedub565
author_rank: Frequent Contributor
timestamp: July 03, 2020, 05:37:08 pm
content: Sounds sensible, I've no idea if the charger is voltage limited or not. I would assume it is, but I don't know. I do have a decent bench PSU I could use instead if that might be better.I've unscrewed the caps for each cell, and plenty of ventilation around it.

author: veedub565
author_rank: Frequent Contributor
timestamp: July 03, 2020, 05:40:57 pm
content: Just disconnected the charger and connected it to a DVM, it read over 20v, so I guess NOT voltage limited.With the battery connected voltage is 12.8

author: drussell
author_rank: Super Contributor
timestamp: July 03, 2020, 05:42:57 pm
content: What are the hydrometer readings on each cell?With still having 8v terminal voltage I would guess unless you have a shorted cell or something else physically wrong it is probably 80% chance recoverable to working....If they're all basically even, none way down like they were shorted, then yeah, essentially just put up to about 15v across it for a while until it starts drawing some current, then switch to a standard trickle charge for a few days and it will probably come back to life unless there is actual physical damage

author: drussell
author_rank: Super Contributor
timestamp: July 03, 2020, 05:47:41 pm
content: Quote from: veedub565 on July 03, 2020, 05:40:57 pmThat's good...It means the battery must be drawing something if it's pulling it down to 12.8....I would just leave it like that until it starts to gas out of any cells, it might take for a day or two if they're all still good at trickle rate like 12.8v...If only some cells start to charge or gas, then you're screwed, you have bad cells, but if they come up semi-equally, you're all good.... Just to a slow trickle charge for a few days then if some cells are still low, blast it with an equalize charge, high amps at, say 15-15.5 volts for an hour and see if the lower cells come up.... but that's after you've already bulk charged it and gone through essentially the "absorption" phase by trickle charging it for a couple days....More importantly, what current is the battery pulling from the charger? That's really all you care about at this point, not the voltage....

author: veedub565
author_rank: Frequent Contributor
timestamp: July 03, 2020, 07:03:30 pm
content: I'll need to buy a hydrometer as I don't have one.Its sucking about 300-500mA at the moment. I'll leave a couple of DVM's set up to monitor voltage and current.There's nothing physically damaged, and it was working fine a few months ago. So fingers crossed might have a chance.

author: Gregg
author_rank: Super Contributor
timestamp: July 03, 2020, 08:09:24 pm
content: The fact that it went up to 12.8V after a light charge means that you do have a chance of recovery but in any case the capacity will be reduced depending on how sulfated the plates are.Sometimes a lot of the sulfates can be dislodged by short bursts (10 to 30 seconds in 5 minute or longer intervals) of around 16V as long as the amperage doesn't become too great during the higher voltage interval.

author: tautech
author_rank: Super Contributor
timestamp: July 03, 2020, 08:48:19 pm
content: Trickle charge with a smart charger until it indicates full charge then apply a gassing charge of 15V for some hours and top up cells with distilled water.If you're lucky you can recover some charge capacity.When doing a gassing charge extreme care must be taken to provide ventilation and NOT provide any ignition sources.

author: trobbins
author_rank: Frequent Contributor
timestamp: July 04, 2020, 12:03:40 am
content: And buy a dedicated lead-acid battery charger. If you push the voltage higher than allowed then you run in to personal safety risks (stibine gas, explosion) as well as further degrading the battery.If your aim is to 'use' the battery then you really need to also do some controlled cycling so that you know what the battery can now provide as far as discharge. So that also means an under-voltage cutoff type arrangement, and an appropriate charger, otherwise you may end up losing the next few weeks of your life to babysitting a battery that you wish you had just gone and recycled immediately.

author: SilverSolder
author_rank: Super Contributor
timestamp: July 04, 2020, 12:09:42 am
content: Recycling it immediately is probably the right choice, based on many wasted hours in the past...

author: veedub565
author_rank: Frequent Contributor
timestamp: July 04, 2020, 09:24:50 am
content: Voltage has stayed the same, but current has gone up to about 1A now.I'm using an old Bradex 8 charger set to "low" which presumably limits the current. I'm guessing 8A on "High" and not sure what on "low"Would I be right in thinking I can check the voltage of each individual cell by clipping one DVM lead to the Neg post, and dipping the other lead into the electrolyte?I'm inclined to leave it on trickle charge for a few days, even a week, and see how it goes. If I manage to get a charge into it with the basic charger, then try a smart charger or desulphator on it afterwards to recover it a bit more.I understand when you say just ditch it, recycle it and buy a new one. And if it was my car or boat battery then yes I would do that. All I want to use this for though is to experiment with powering a HF radio. I don't really need it to recover 100% capacity, and it's not worth investing in a brand new one at the moment.

author: veedub565
author_rank: Frequent Contributor
timestamp: July 04, 2020, 09:34:00 am
content: Again just a guess, but am I going to see a pattern here..Draws very little current to start withDraws more current as it begins to recover and take a chargeDraws less current again as it becomes fully charged

author: tautech
author_rank: Super Contributor
timestamp: July 04, 2020, 09:44:56 am
content: If you can monitor the current draw all the better.No don't probe into the cells for fear of damaging plates.As the charge pushes/converts the sulfates from the plates more lead is exposed and more current is drawn to lift the SG of the electrolyte until such time it reaches optimum levels with a controlled voltage charge when current draw should fall to low levels of a few 100 mA.Technically the battery is charged at this point but its capacity is related to the condition of the plates and how complex the sulfate structures are.Old technologies max'ed out ~ 14.2V for max charge voltages but newer Cadmium and the like 14.4V is the target charge voltage......not to be confused with rested voltage which should be in the mid 13V.When fully voltage controlled charged, a gassing or maintenance charge can be applied to remove further simple sulfates in order to gain more capacity.Old dumb chargers would supply voltages into gassing regions if left unattended so aren't advisable to use on modern sealed batteries.If the current is rising connect a smart charger rather than leave a dumb charger connected. You can always hit it with higher voltages later.

author: veedub565
author_rank: Frequent Contributor
timestamp: July 04, 2020, 11:47:04 am
content: I'm going to have to buy a smart charger as I don't have one. I was hoping I might be able to save a few pennies and reuse this old battery, but I can see I'm going to need a charger to stand a chance of recovering itCharger costs about the same as a cheap new battery here, but then a cheap new battery will still need a decent charger buying for it.Does this one look ok to use, the store nearby has then un stick, I can go get one right nowhttps://www.halfords.com/motoring/battery-maintenance/battery-chargers/ring-12a-smart-charger---charge-and-diagnose-116453.html**EDIT**Found a better one, CTEK MXS 5.0 T

author: trobbins
author_rank: Frequent Contributor
timestamp: July 04, 2020, 12:17:53 pm
content: You need the charger to follow the battery manufacturers recommendations. You could try and find those recommendations for your present battery - there may be info on the battery, or google for it.Would you buy the same battery, and why?You need to define your actual application. Just saying it is to power a radio doesn't say anything about discharge rate, or discharge profile, or when you can recharge.Note that charging a 110Ah battery at 1A is going to take at least 110 hrs ball park of charging, and given the charge rate is C/100 nominal and the battery is poor, it may well take much longer - so say try 5-6 days, but it must be voltage limited (just in case), and then discharge it as per your application and confirm current and how long it takes to get down to say 1.8vpc.It's only once you know your application and the battery you are using, that you can adequately look at a chargers specifications and operating manual and work out if it can be set up to follow the manufacturers recommendations, and meet your recharge time requirements.Of course you can just 'wing it', but it's your money.

author: veedub565
author_rank: Frequent Contributor
timestamp: July 05, 2020, 11:04:05 am
content: So I tried a CTEK MX5 smart charger on it. It skipped through the desulphation and test phases and went to bulk charging phase (14.7v 5A)The battery started making some odd noise, not fizzing, more like an odd crack or clunk every now and then.After maybe 40min an hour I noticed spots of water/acid around 3 of the holes in the top of the battery. Clearly it's been spitting. Although the electrolyte never appeared to be boiling at any point.I'm inclined now to do as others have suggested and just recycle it and buy a new one. I'm not so sure it's really that safe now.Ah well, worth a try. At least I have a decent charger now for my new battery.

author: trobbins
author_rank: Frequent Contributor
timestamp: July 05, 2020, 12:57:57 pm
content: Quote from: veedub565 on July 03, 2020, 02:30:27 pmDid you add water at any stage before you started charging? Were you able to see the liquid level of all 6 cells?

author: veedub565
author_rank: Frequent Contributor
timestamp: July 05, 2020, 01:19:55 pm
content: I haven't added any water to it. I can see inside that water is covering the plates, but that's all. There doesn't appear to be any mjn/max mark.

author: Gregg
author_rank: Super Contributor
timestamp: July 05, 2020, 07:21:14 pm
content: A good way to measure the specific gravity of the electrolyte is a refractometer, something like this:https://www.tequipment.net/Mastercool/43705/Refractometers/BRIX/It only needs a small drop of electrolyte, is easy to read and less likely to get acid where you don't want it. It is amazing to see how many holes you might find in your clothes after washing them when messing with battery acid. The clothes look OK until they are washed.

author: veedub565
author_rank: Frequent Contributor
timestamp: July 07, 2020, 04:34:00 pm
content: I used one of the bulb type hydrometers to test it.Best cell was 1.20Worst cell was 1.15Rest were all about 1.17Ambient temp about 17degCWhen I was trickle charging it got up to 13.2v and was drawing about 600mA. Even with the charger on 8A setting it was only drawing about 1.6A so it didnt appear to be taking the chargeTrying to force it with higher power seemed to upset it and potentially damaging or even dangerous. That's why I gave up. Just buy a new one. The old one's still kicking about till I can be bothered to take it for recycling.

author: Gregg
author_rank: Super Contributor
timestamp: July 07, 2020, 05:00:21 pm
content: There is a good chance that the battery is beyond redemption. But you might want to give it one more try at low current so it doesn't spit out electrolyte. First make sure the the electrolyte level is at the recommended height above the plates by adding some distilled water. The spitting could be mitigated by a slightly higher level. The spitting is the result of large gas bubbles forming on and between the plates and rising quickly to the surface where they pop and spit. Probably the plates are either warped or greatly sulfated causing gassing in localized areas. If the plates are warped, they most likely will start to disintegrate and short the cell with further use, especially heavy charging. If they are just sulfated there is a chance that you could get rid of some sulfation and have a reduced capacity battery. A shorted cell will show low specific gravity, close to 1 (water is 1).

author: veedub565
author_rank: Frequent Contributor
timestamp: July 18, 2020, 06:41:28 am
content: I did give this one last try. After several days on trickle charge it was at 14.4v and taking 230mA.So I hit it with the CTEK smart charger again and it ran through all the stages no problem.I hooked it up to the radio, with a couple of DVM's to monitor volts & amps. The radio drew a steady 3.85A. Battery voltage started at 13.7v and after 17hrs was at 12.2vSo it looks like it does have some usable capacity left. I wouldn't rely on it, but good enough for what I want to do with it.

author: tautech
author_rank: Super Contributor
timestamp: July 18, 2020, 12:16:43 pm
content: Quote from: veedub565 on July 18, 2020, 06:41:28 amNice. Give it a few good cycles (not too deep) and you might gain a bit more capacity yet.