Attempt 'rejuvenating' old gel-cell lead-acid batteries with a bench supply?

[floobydust]

Um, don't forget these old batteries make hydrogen gas which explodes easily, along with the sulfur stink.
Any spark at the plates can make a bang, so I don't advocate massive overvoltage unless you've got safety glasses and a bin to contain the spray.

[duak]

I'll echo what Floobydust says about hydrogen gas.  I didn't do it with any of the rejuvenation experiments, but I did suceed in blowing the side out of an MC battery during quick charging.  I was young and lucky. 

Cheers,

[tautech]

Hopefully on the home straight now with the forward charge now commenced. See reply #14 for the ongoing logging:
https://www.eevblog.com/forum/index.php?topic=152765.msg1991789#msg1991789

[Circlotron]

Checking the results every few hours.
Go, little battery! You can do it!

[T3sl4co1l]

Two FYIs:

1. At 400mA, you're in basically no danger of heating up anything noticeably.  You can hold 10V * 400mA = 4W in your hand comfortably, though in that size it will be noticeably warm.  In a battery size, fuggeddaboudit.

If anything's being damaged, it will be chemically, and not apparent until you've done full charge cycles.  Examples: increased self-discharge, increased ESR (even at full charge), reduced capacity, poor capacity retention over time (maybe it's only good for a few dozen charge cycles after this; or maybe a thousand, good as new??).

2. Give or take enough charge, a lead acid battery is symmetrical.  Taking a reverse charge means you've fully reduced the lead dioxide cathode (if not in bulk, then at least the active surface), and are now producing hydrogen on it, while the other is being oxidized to lead dioxide (on the surface).  Lead dioxide tends to expand and flake off the surface of a bulk lead electrode, so I don't know how healthy this will be to the "sponge" structure.

So... we'll see what happens.

Tim

[cdev]

(You're adding the 0.6 volts or so voltage drop of the diode in series with them- right?)

About the safety of recharging batteries using a generic lab power supply, it's a good practice to put a diode in series with the battery you want to charge.  Many power supply have a crowbar circuit that shorts the output of the power supply when the voltage is bigger than what the power supply expects it to be.  This can happen by accident, or during a power outage.  Another reason is that a charged battery can deliver strong enough currents to melt wires and start fires.  If something goes wrong inside the power supply, and the output of the power supply short circuit itself, we'll also get a short-circuit on the battery we charge.  This can start a fire.
...

[tautech]

Checking the results every few hours.
Go, little battery! You can do it!

It's gunna ! ! 

Just in the time to grab this pic and compress it for posting the charge rate has fallen to 360mA.



Some battery rest to stabilize and load tests to come. 
But first....should we push the charge voltage a bit higher ?
Battery seems quite happy and cool.

Results to be documented in reply #14........

[Circlotron]

Yeah, 14.5V or so for half a day shouldn't hurt.
As to how low you should let the charge current drop to, not sure. It may not drop to as low a figure as what a "good" battery would. Just have to wait and see.

And that 13.8V is upstream of the diode of course, not the actual battery voltage...

[tautech]

Yeah, 14.5V or so for half a day shouldn't hurt.

TBH I'm reluctant to push the charge voltage so high just yet.
Sure that's just on the max of a cyclic charge limit whereas we've targeted the recommended max of a standby/float charge. It would appear that the battery is quite happy with the treatment it's been dealt so I'll maybe push the charge voltage to 14.2V (cyclic min) which going by recent behavior it should reach reasonably quickly. Further charge notes in reply #14.

As to how low you should let the charge current drop to, not sure. It may not drop to as low a figure as what a "good" battery would. Just have to wait and see.

We're down to 120mA @ 13.8V and charge current has slowed up dropping to the point where IMO it's mimicking normal SLA battery charging behavior.    At this point I'm really happy with what I've seen and logged however as they say 'the proof is in the pudding' and some discharge/capacity checks will tell us a lot about if your process is really worth its salt ! 

Now we have some logging about expected behavior the effort and process is relatively straightforward and almost 'set and forget'.
Thanks for 'being there' and keeping an eye on proceedings. 

Edit
Charge voltage bumped to 14.5V and current has only risen from 120mA to 250mA......and falling.
~3.15 pm @ 200mA recovery forward charge ceased.

[IanMacdonald]

A series diode will NOT protect a PSU from a reversed battery. Think about it for a moment: If the diode allows current to flow from the PSU +ve at 14v to the battery +ve, at say 13v,  then it will also allow current to flow from the unpowered PSU (0v) to the (reversed) battery -ve at -12v. The voltage drop being in the same direction. 

It will prevent a short if the PSU 'crowbars' the output. I've met one or two PSUs like that and basically it's a braindead idea since the short on the output can also damage a downstream regulator through back current from filter or decoupling caps.

To make a reverse polarity proof battery charger, you need an arrangement which will briefly tolerate reverse polarity on the output, and disconnect the output when that arises. If the PSU is current limiting it may meet the first criterion, depending on actual circuit, and a relay or mosfet can provide the disconnection. A horn with a series diode is also a good idea.  

Safetywise a gel cell should always have a fuse or polyswitch mounted directly on its case. That protects against frayed wiring starting a fire.

[Circlotron]

Initial/preliminary findings/summary.
~40-50% of battery capacity recovered from this method.

Unknowns
Will this battery hold charge for any useful period ?
Will these initial battery test results improve of degrade with further use ?

Further battery conditioning
Maybe some time on the desulphator built many years ago.

TBC..........

That's interesting. For sure, cycle it up and down a few times and see if things get better or worse.

[RoGeorge]

50% is better than no battery, so it worked somehow.   
Now, it would be interesting to see the self-discharge rate.  Charge the battery and leave it disconnected for a week, or so, then discharge it and compare how many Ah are still there after a week, or a month.

For the next battery, it would also be interesting to try a normal charge first, and see if the battery can store any charge at all, and if it can store some charge, to measure the capacity in Ah.  Then, to try the reverse charge rejuvenation, and see if there is any increase in how many Ah the rejuvenated battery can store.

[tautech]

And that 13.8V is upstream of the diode of course, not the actual battery voltage...

Oh, and all this talk about charging with a series diode.....that's for pussies !
Nothing like the risk of blowing something up to keep your mind on the job. 

50% is better than no battery, so it worked somehow.   
Now, it would be interesting to see the self-discharge rate.  Charge the battery and leave it disconnected for a week, or so, then discharge it and compare how many Ah are still there after a week, or a month.

We're on the same wavelength.....shame it's coming into summer and oh so many jobs are piling up.

For the next battery, it would also be interesting to try a normal charge first, and see if the battery can store any charge at all, and if it can store some charge, to measure the capacity in Ah.  Then, to try the reverse charge rejuvenation, and see if there is any increase in how many Ah the rejuvenated battery can store.

Oh you can be sure I'll be keeping my eyes out for further victims batteries especially any neglected and near new where IMO this rejuvenation method offers the best return for time invested.

[TerraHertz]

cdev, here's some pics of what the insides of dead SLAs look like: http://everist.org/NobLog/20180430_lead_acid_ruin.htm

What most people don't realize, is that in addition to sulfation of the plates (which forms a barrier to charge flow), there's another more serious effect, which is not reversible.

The current-carrying matrix of solid lead mesh within the plates, becomes embrittled and develops cracks. Even the thick lead conductors up near the battery top can crack right through. When you find a battery that is completely open circuit, or won't take more than a few mA of charge current, this is what's happened. Nothing you can do is going to repair those cracks.

I had a SLA from a big UPS, that seemed fairly OK. It had been left idle for a few years, but had only gone down to about 10V. Moving it, I put it down on the concrete floor. Then measured it again. Gone completely open circuit. The slight jolt had fractured an embrittled primary conductor path.

[tautech]

Tiny update on the 20Ahr SLA recovered and documented in reply #14.

After some unsuccessful attempts to start the jetski it came in and even with a jumper battery paralleled for additional grunt, it's still holding ~12.3V after a week sitting idle. It's been freshened charged a couple of times and although hasn't got the grunt of a sound battery it's proved the Circlotron SLA battery recovery method is certainly of some benefit.

Just popped it onto the same charger that was used for the recovery and @ 14V it drew 5A momentarily before quickly settling to 2.25A and now only a few minutes later to 200mA and still falling.

OC voltage is certainly a bit low and this battery will get some desulphator treatment that in the past has proven to lift battery open circuit voltages.
I'll come back to document those results when done and share some desulphator waveforms and the circuit.

[CJay]

Tiny update on the 20Ahr SLA recovered and documented in reply #14.

After some unsuccessful attempts to start the jetski it came in and even with a jumper battery paralleled for additional grunt, it's still holding ~12.3V after a week sitting idle. It's been freshened charged a couple of times and although hasn't got the grunt of a sound battery it's proved the Circlotron SLA battery recovery method is certainly of some benefit.

Just popped it onto the same charger that was used for the recovery and @ 14V it drew 5A momentarily before quickly settling to 2.25A and now only a few minutes later to 200mA and still falling.

OC voltage is certainly a bit low and this battery will get some desulphator treatment that in the past has proven to lift battery open circuit voltages.
I'll come back to document those results when done and share some desulphator waveforms and the circuit.

I'm intending to give it a go with some batteries over the Christmas break.

I'm beginning to regret letting go of the 480AHr 2V cells they removed from our old phone system now but 37Kg a cell is a bit much to transport

[tautech]

Status update on SLA recovered in reply #14
3 weeks idle = 12.0V (lower than satisfactory but OK for further attempts at improvements)

Freshening charge applied......13.8V.

[Circlotron]

^^ Watching with interest.

[m3vuv]

looks to me like a pointless exercise to me tbh,just my thoughts.

[Armadillo]

It's easy to get confused....example lack of charge AH, sulfatant and internal leak.

The first thing to do is to find out if the battery had internal leak, example it will hold the charge with enough decency or not.

Reliability of start up is important to me, no point keeping something that when you most want it, it's not delivering.

Dumpster it goes without a pain.

[Armadillo]

This subject on this old Rejuvenating will NEVER End.
Sooner or Later, there will be someone bitten by the Dracula and the subject resurface again and again and again.......
cause there are too many of them........

Not Dracula, dumpster lead acid batteries around.
These days, they seems to last for only a year, and the whole of the motorist industries dumps it, non stop every each year, about.

[Armadillo]

VRLA[AGM, Gel] , at 90F = Half Life but in reality 1 ~ 2 years.

It's burden to maintain and time waster, I prefer flooded cells, rock solid.

[tautech]

looks to me like a pointless exercise to me tbh,just my thoughts.

It's easy to get confused....example lack of charge AH, sulfatant and internal leak.

The first thing to do is to find out if the battery had internal leak, example it will hold the charge with enough decency or not.

Reliability of start up is important to me, no point keeping something that when you most want it, it's not delivering.

Dumpster it goes without a pain.

This subject on this old Rejuvenating will NEVER End.
Sooner or Later, there will be someone bitten by the Dracula and the subject resurface again and again and again.......
cause there are too many of them........

Not Dracula, dumpster lead acid batteries around.
These days, they seems to last for only a year, and the whole of the motorist industries dumps it, non stop every each year, about.

VRLA[AGM, Gel] , at 90F = Half Life but in reality 1 ~ 2 years.

It's burden to maintain and time waster, I prefer flooded cells, rock solid.

Best you both take some time to carefully read this entire thread and understand it !
Heaven knows, you might just learn something, I know I did and proved it !

Still more work to do on the 20AHr AGM.....with a desulphator, that in the past has lifted OC voltages even though the power that drove it was supplied from the battery it operated on. Yes, scary stuff ! 


Do come back when you have something useful to contribute.

[Armadillo]

Please don't because of Thirteen Thousands+ you bring people merry go around, or you have a commanding say and do not accept criticism.


I advice interested members to firstly check it is not internally leaked, other than sulfate or lack of AH before they even waste their time.


Whether I contributed, is not for you to judge.


 

[T3sl4co1l]

...What?

Tim