Author Topic: Attempt 'rejuvenating' old gel-cell lead-acid batteries with a bench supply?  (Read 11008 times)

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Offline cdev

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I have a bunch of old gel-cell batteries that all show voltages well below 12v.

Ive attached them at regular ijntervals to a cheap trickle charger meaning to try to rejuvenate them at some point. Now I am trying to declutter. Either I can fix them or I need to recycle them.

For years Ive been hearing that various techniques existed to desulfate them.

I've read all sorts of advice on this. But only had nice bench supplies accessible to me recently.

There is no time like the present.

What are peoples experiences and what can I do to try it using a bench supply with adjustable current?

 Is there any danger to the bench supply from doing this? Most of these batteries show voltages of 6-11 volts now. Some are lower.

They are gel-cell batteries like the ones from UPS's.
« Last Edit: November 23, 2018, 01:12:38 am by cdev »
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Offline BradC

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What are peoples experiences and what can I do to try it using a bench supply with adjustable current?

My experience? You will spend quite a bit of time learning that it's a relatively futile effort.
I won't say you are wasting your time, as time spent learning is never wasted.

My experience is that SLA batteries are generally a lost cause.
*Quality* batteries (like Japanese made Yuasa) can often be brought back from the dead if they have died from sulfation, but only at a fraction of their original capacity. Cheap Chinese SLA's generally don't come back to any meaningful capacity.

You won't damage your power supply, but you may well spend a lot of time reaching a similar conclusion. I've tried all the magic chemical tricks, and all the whizz-bang electronic de-sulfation techniques and am yet to find anything that actually works. Most SLAs I come across have died due to plate corrosion, which is a combination of time, float voltage and cyclic use. They have a limited life-span which is specified under best case conditions, and I've never found a device that maintains them at those conditions, so they all die faster than their design life.

I have some fabulous CSB 7AH batteries here that will still start a 4-stroke generator (so their impedance is still nice and low) but they are down to about 2AH at a 20C rate.
 
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Online CatalinaWOW

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BradC said it well.  My experience also.  Either recycle them or repurpose them.  I use them for weights when glueing things and other similar uses.
 
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Offline T3sl4co1l

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If you're not getting any current into them at 14.3V (or whatever the exact float voltage is for that type), they're dead dead.

AFAIK, the mechanism is sulfation cutting off current flow.  Sulfation is the state of full discharge, and something something crystal growth making it that much harder to get a charge going again.  Lead sulfate is an insulator.

The way electrochemistry works, or a lot of it anyway, is electrons being forced into or out of solution at the electrode surface.  These immediately form ions, radicals, whatever.  Example, there's organic chemistry that can be done with electrochemistry (I forget what; I think one is a radical decarboxylation, which turns two molecules of an organic acid into a paired up backbone, with the loss of two CO2's, probably as CO3(2-) in solution?).

So, lead sulfate being an insulator, it probably doesn't participate directly, and it has to be in a very small, thin form near the electrode surface, where it can be attacked by the ions and radicals at the surface, without having secondary reactions take over (namely, electrolysis of water -- loss of electrolyte volume, no actual charging).  Or it's a thin film, nanocrystalline or amorphous maybe, which is conductive over that distance (or capable of tunneling, say).  (Now I'm getting curious, and I wonder if there's an article that studied this?)

In any case, big crystals of the stuff, don't participate, or at least not very much.  And the more sulfate there is blocking off electrodes, the higher the internal resistance.  Which means not only is discharge current minuscule, but charge current as well.

And, low current means low charge rate.

The best you can do, AFAIK, is to float for an extended period of time (days, weeks... months?), at just enough voltage to effect the charging reaction, without causing electrolysis.  This doesn't leave much excess voltage to drive the reaction forward, and we're talking about large crystals not fine deposits, so it could take very long indeed.

In time, hopefully, the ESR falls, the charge capacity rises, and sulfate is reduced, at least the sulfate still sticking to the electrodes.  Hopefully any shedded sulfate, sitting at the bottom of the cell, isn't reduced and causes a short.

I'm not aware of any mechanism or science behind the more fringe recovery methods.  Surge voltage/current might be able to open up a shorted cell (preferably, applied across the cell in question, not the whole battery), but that's only a temporary trick.  I don't know that applying a large voltage (in either direction) would be able to, say, shake loose some sulfate.  Electrolysis -- producing bubbles -- might be able to shake some things loose, but this disturbs the metal sponge as well, also not recommended.

Mind that, of course, the stuff-moving-around only applies to a regular lead-acid, not a gel-cell.  Hopefully the gel will hold things in place better, but who knows how much can be recovered if any.  Definitely don't overvoltage them, which makes gas that doesn't have anywhere to go (or, I guess there's a catalyst in there to consume modest rates of gas, but not large amounts!).

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Offline BradC

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Definitely don't overvoltage them, which makes gas that doesn't have anywhere to go (or, I guess there's a catalyst in there to consume modest rates of gas, but not large amounts!).

As with all sealed cells, there is definitely a catalyst. If you pry the plastic top cover off the battery you'll see little rubber caps sitting over plastic pipe-spiggot thingies. These are actually relatively well calibrated pressure relief valves, and when you exceed the capacity of the catalyst to recombine the gasses you'll hear the battery fart as the cells push gas past the rubber caps. It can be quite disconcerting the first time you hear it happen, particularly when it's a relatively healthy battery that is being grossly overcharged and you hear all 6 cells popping off at random intervals.

The common internet "wisdom" is to take the caps off, poke a couple of drops of water back down there and put it back together again. The trouble is if you've been gassing the battery sufficiently to lose enough water to warrant doing that, you'll have caused significant plate corrosion and knocked a heap of capacity out of the battery in any case.

 

Online NiHaoMike

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One trick for reconditioning lead acid batteries involves a light dimmer set to about half, a mains rated capacitor (value depending on size of battery, 5-10uF motor run cap good for a car battery), and a bridge rectifier. Basically a crude pulse charger.
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Online tautech

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Good luck, cut your losses or spend an unhealthy amount of time trying to recover LA batteries.
Like pushing the proverbial uphill with a pointed stick !  :scared:

Went down this path ~15 years back and built and optimized a few desulphators the best of which was quite simple and was powered from the battery itself. Pretty neat to see battery voltages rise after an overnight zapping from 7A, 65V @ 1KHz however any significant capacity gain was always illusive and I now only consider desulfphation only as a LA battery maintenance exercise.

Better and more cost effective to properly manage and maintain batteries rather than try and shut the door after the horse has bolted !
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Online RoGeorge

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What are peoples experiences and what can I do to try it using a bench supply with adjustable current?

My experience? You will spend quite a bit of time learning that it's a relatively futile effort.

Same here.  Once damaged, those UPS batteries can not be recovered.  The best thing to do is to discard them at a recycle center.

Offline Circlotron

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Back in the early 90s I worked at a place that had a small warehouse full of UPSs, many of which had sat around for 4 or 5 years just waiting to be sold. They had 12V 6.5Ah and 24Ah batteries that typically measured about 2 volts. They would put new batteries in them before they were sold, so I had way heaps of batteries to experiment with.

The technique was refined to the following:
Reverse charge the battery at 2% of its Ah rating for 48-72 hours.
Then forward charge the battery at the same rate, again for 48-72 hours.
Absolutely under *NO* circumstances crank up the charging current!!! If you do, you will find one cell will get hot and then it’s all over, red rover. It’s junk.

Recovered many batteries that way including one 24Ah that I put in my Daihatsu Charade and it would easily crank it for several minutes continuous. Didn’t try to see how long till it quit.

So it can be done with batteries that were once good but just sat around for a long time,  but as for old worn out batteries, I don’t think so.
 
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Online RoGeorge

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Reverse charge the battery at 2% of its Ah rating for 48-72 hours.
Then forward charge the battery at the same rate, again for 48-72 hours.
Absolutely under *NO* circumstances crank up the charging current!!! If you do, you will find one cell will get hot and then it’s all over, red rover. It’s junk.

Never tried to reverse the polarity when charging a UPS battery.

Just to be sure I understood it correctly, let's take an example:
- take an old gel battery 12V/7Ah.  Measure the voltage with the battery disconnected.  It should be at least 2V to be good for a recovery try.
- charge it in reverse polarity at a current of 140mA for about 2-3 days.  After this, we expect to have the voltage reversed, so the red terminal is now the negative of the battery, and the black terminal is the positive one.
- charge with normal polarity at the same 2% current, in this example about 140mA for another 2-3 days.
After this, the battery might work again.  The recovery is not guaranteed for each and every battery, but some of them may be restored.

Once a recovery is successful, from now on we can use the battery at normal charge/discharge rates, without the 2% current limit, and without reversing the polarity at each recharge.
I'm curious to give this a try with the first occasion, did I understood the procedure correctly, please?
« Last Edit: November 23, 2018, 11:45:21 am by RoGeorge »
 

Offline Circlotron

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did I understood the procedure correctly, please?
Yep, 100%.
When charging reverse direction, have the charger set so the voltage won't creep up any higher than 13.65V for a 12V battery, same as a normal charge. And like I said, DON'T wind up the charge current!  :P
 
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Offline Rascal

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I was given one of those 12v solar panels advertised for car/boat/camping, and I often use that to attempt to rejuvenate old gel cells. I attach it and leave it for a few days to work its magic. Occasionally a few days may turn into a week or two if I forget.

More often that not the batteries appear to recover (certainly to some extent) I will quite happily use them.


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Offline CJay

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It can be done but it's unlikely you'll get full capacity.

I have had success and have measured (crudely) capacity at a fairly high percentage of original spec so those batteries were useful, others, not so much, you'll also need to test them on load if they appear to recover as I've had a few which looked great but just couldn't sustain the current drawn.

My recipe for 'success' is to give them a few solid thumps, base flat down onto a lump of wood, if you meause the current draw before and after you can often see an immediate increase, I guess it shakes loose sulphated material from the plates.

The Yuasa batteries seem to recover fairly well, charge at 13.5V for a 12V battery and watch the current as well as the battery temperature, it takes patience.

If you're expecting to get long life out of them, forget it and buy new, if you're only using if for non critical applications or just to see if it can be done then it might be worth the effort.

My absolute favourite lead acids are Hawker/Gates Cyclon, I've seen them recover from 0V terminal voltage to almost 'as new' capacity, excellent quality cells.
 
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Offline cdev

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Circlotron, thank you for this great info!

I think I saw one of your earlier posts. Thank you!
Your process is what I wanted to try out. Since I would just throw them away anyway.

Okay, I am going to try this on a dual cell gel-cell I have here - maybe a 7 ah gel cell, which is currently only delivering 4.5 volts. Its at least eight years old and was used in an alarm system until it died, then was used for low current stuff intermittently. I'm going to see what my bench supply does when I connect it up in series with it with the current limiting set to 150 ma..  Luckily the bench supply is built like a tank.

What should the current be set at for different size batteries? 

This is likely a process that would lend itself to optimization.

I have a bunch of different ones in different sizes.

I even have one old car battery, in a similar state of age. It was used in a car until it was retired around two years ago. Since then Ive kept it topped off with a trickle charger that was never meant to actually put the main charge on a battery, just keep it topped off. Now its showing 11 volts.

My bench supply can deliver up to 20v at 3 amps (x 2) So charging the car battery at after it recovers could be done, up to 3 amps - but probably best to try less, and also a reasonable voltage, no more than 13.6 volts? Its really cold today, and the cold has even inflicted the indoors. Outside its well into the negatives, way below freezing.

Ever since I read your original post Ive wanted to try this out.

Do I need to put it in a metal tray or something? Or do this in the basement? I would hate to have it explode on my dining room's nice hardwood floor!  But also good to have it close by so I can keep an eye on it and check on it. Maybe I will do the car battery in the basement, and do both in a metal tray.

Back in the early 90s I worked at a place that had a small warehouse full of UPSs, many of which had sat around for 4 or 5 years just waiting to be sold. They had 12V 6.5Ah and 24Ah batteries that typically measured about 2 volts. They would put new batteries in them before they were sold, so I had way heaps of batteries to experiment with.

The technique was refined to the following:
Reverse charge the battery at 2% of its Ah rating for 48-72 hours.
Then forward charge the battery at the same rate, again for 48-72 hours.
Absolutely under *NO* circumstances crank up the charging current!!! If you do, you will find one cell will get hot and then it’s all over, red rover. It’s junk.

Recovered many batteries that way including one 24Ah that I put in my Daihatsu Charade and it would easily crank it for several minutes continuous. Didn’t try to see how long till it quit.

So it can be done with batteries that were once good but just sat around for a long time,  but as for old worn out batteries, I don’t think so.

This is a semi worn out battery, I suspect. But what the hell.

Cheap thrills!  ;)
« Last Edit: November 23, 2018, 05:54:38 pm by cdev »
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Online tautech

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Back in the early 90s I worked at a place that had a small warehouse full of UPSs, many of which had sat around for 4 or 5 years just waiting to be sold. They had 12V 6.5Ah and 24Ah batteries that typically measured about 2 volts. They would put new batteries in them before they were sold, so I had way heaps of batteries to experiment with.

The technique was refined to the following:
Reverse charge the battery at 2% of its Ah rating for 48-72 hours.
Then forward charge the battery at the same rate, again for 48-72 hours.
Absolutely under *NO* circumstances crank up the charging current!!!
If you do, you will find one cell will get hot and then it’s all over, red rover. It’s junk.

Recovered many batteries that way including one 24Ah that I put in my Daihatsu Charade and it would easily crank it for several minutes continuous. Didn’t try to see how long till it quit.

So it can be done with batteries that were once good but just sat around for a long time,  but as for old worn out batteries, I don’t think so.
I've just got the perfect candidate to try this ^ !

A 12V MOTOBATT AGM 20AHr
http://www.motobatt.com/MBTX20U
CCA 310A, Capacity (10HR) 21 AHr

~3years old from a neglected jetski score !  ;D
Free standing open circuit voltage 1.7V  :o

A previous quick look at this battery a few days ago to see if it would take a charge was done with a reasonably modern LA charger that needs a residual voltage before it will charge and of course this battery wouldn't. Another dumb LA charger was connected also to bump the voltage up to where the smarter charger would latch and commence charging but when removing the 'bump' charger, charge was not maintained.

Normally I'd give this one up as stuffed but the case looks perfect without any swelling/bulging.

Circlotron battery recovery method.

Started NZ time = ~10pm 26 Nov.
2% x 20AHr =400mA reverse charge from a CC supply set to 13.8V, CC'ed down to 1.6V......will this work ?
Will check it several times/day and make any necessary adjustments if/when required.

Supply: MCH K305D (30V 5A SMPS) All charge voltages and current noted from the PSU display readout.
Discharge voltage and current measurements: Fluke 15B and Kaise analog meter.

The clock is ticking !

Reverse charge progress log:
ALL charging measurements .....PSU set to 13.8V and in current controlled (CC mode)
Measurements from PSU display readout unless otherwise specified.
0 hrs.      Voltage 1.6V @ 400mA reverse charge.
10 mins   Voltage 1.4V
15 mins,  Voltage dropped another 100mV to 1.3V.
20 mins,  Voltage 1.2V,
2 hrs.      Voltage 1.0V,  Battery cool to the touch.

7am 27 Nov
9 hrs.   Voltage 1.0V. Current 400mA stable and battery cool....no warm spots.
10 hrs. Voltage 1.3V.
11 hrs. Voltage 1.8V.
12 hrs. Voltage 2.4V.
14 hrs. Voltage 2.9V
17 hrs. Voltage 3.2V.
18 hrs. Voltage 3.7V. Current stable @ 400mA. Temp slightly above ambient, no hot cells.
19 hrs. Voltage 4.2V. Ever so slightly warm, will watch this closely and maybe reduce reverse charge current.
22 hrs. Voltage 5.5V. Still watching temps, no change from before.
23 hrs. Voltage 6.5V. Confirmed polarity reversal with a DMM.  :o
24 hrs. Voltage 7.5V Temp and current stable.

At the speed of reverse charging now I'll back off the current to 300mA until the morning when I can keep an eye on it every couple of hours.
Then I'll wind it back to 400mA and let it stabilize for a bit before continuing this log.

7am 28 Nov
After overnight reverse charging at the lower 300mA rate the battery was quite cool and @ 9.5V.

33 hrs. Voltage 10.3V. Reverse charge returned to 400mA.
34 hrs. Voltage 10.7V.
35 hrs. Voltage 10.7V. Interesting, have we reached some plateau ?
36 hrs. Voltage 10.7V. Battery still cool to the touch. PM sent to Circlotron for advice and Amps reduced to 100mA while I await his reply. 9.6V (slowly falling) @ 100 mA........7.7V now ~15 minutes later.

37 hrs. Voltage 8.1V @ 100mA with a still reversing charge.
38 hrs. Voltage 8.9V @ 100mA. With reply from Circlotron I'm lifting charge to 200mA (1% of C) to observe battery behavior.....9.4V. Will probably lift current more in another hour or so.
39 hrs. Voltage 10.2V @ 200mA reverse charge. (1% of C)
40 hrs. Voltage 10.3V. Current lifted to 300mA.....10.6V. Battery @ ambient temp.
41 hrs. Voltage 10.7V @ 300mA. Will it go higher or have we reached the 10.7V plateau again ?
42 hrs. Voltage 10.9V @ 300mA.
43 hrs. Voltage 10.9V @ 300mA.
45 hrs. Voltage 10.9V @ 300mA. Battery slightly warm. Will run until the morning, say ~56 hrs then leave to settle and measure OC voltage before deciding if more reverse charging needs be undertaken or to start the discharge prior to forward charging. Much will depend on results from another overnight reverse charge.
48 hrs. Voltage 10.9V @ 300mA. Battery slightly warm. Plan is to do some OC voltage measurements over maybe 30 minutes while the battery stabilizes before draining it prior to the forward charge.
Will also log the discharge which might at the end be able to indicate the success of this attempted recovery...or not. Till the morning....

10am 29 Nov
60 hrs. Voltage 11V @ 300mA. Reverse charge terminated.
Open circuit voltage after 10 mins 8V.
Nearing a stable but 'reversed' voltage 7.5V ~20 mins after reverse charge terminated.
7V and still very slowly falling.
6.75V and nearly stable reverse voltage.

Discharge commenced. 11.35 am
Load: 30W 12V sealed beam spotlight, 2.25A measured draw @ 13.2V.

Actual battery drain 1.3A
+10 mins   1.16A, 3.7V
+15 mins   1.13A, 3.3V
+20 mins   1.1A,   3.15V
+25 mins   1.08A, 3.1V
+30 mins   1.05A, 3V
+35 mins   1.01A, 2.75V  Starting to noticeably fall away.
+40 mins   0.95A, 2.4V
+45 mins   0.88A, 2V
+50 mins   0.8A    1.55V
+55 mins   0.74A  1.2V
+60 mins   0.69A  1.0V
+65 mins   0.64A  0.8V
+70 mins   0.6A    0.7V
+75 mins   0.55A  0.55V
+80 mins   0.5A    0.45V
+100 mins 0.25A  0.2V
+110 mins 0.21A  0.15V Battery now resting to observe any recovery....immediately to 1V then to 1.75. Will rest a further 5 mins......2.45V.
Further discharge started.
+15 mins   0.17A  0.125V
+65 mins   0.09A  0.06V


Forward charge commenced. 3pm 29 Nov
Target = ~13.8V with charge current falling indicating battery fully 400mA (2% of C rate) trickle charged.

0 hrs.      Voltage 1.3V @ 400mA
+20 mins Voltage 1.5V
+45 mins Voltage 1.8V
1 hr         Voltage 2.0V
2 hrs        Voltage 2.5V. Battery temp barely above ambient.
2.5 hrs     Voltage 3.0V
3 hrs        Voltage 3.2V
4 hrs        Voltage 3.8V
5 hrs        Voltage 5.0V
6 hrs        Voltage 6.5V
7 hrs        Voltage 8.0V  @ 400mA Reduced to 300mA for overnight. Battery cool.
12 hrs      Voltage 10.2V @ 300mA
14 hrs      Voltage 10.4V @ 300mA
15 hrs      Voltage 10.5V
23 hrs      Voltage 10.6V @ 300mA. Charge rate increased to 2% of C: 400mA = 10.9V.
26 hrs      Voltage 10.8V @ 400mA.
27 hrs      Voltage 10.7V. Battery barely warm.
30 hrs      Voltage 10.7V
40 hrs      Voltage 11.0V @ 400mA
41 hrs      Voltage 11.1V
43 hrs      Voltage 11.2V
@ nearly 44 hrs....75 min power cut. Measured OC battery voltage 11V. 1 hr later 10.8V.

Forward charge resumed (45 hrs) 1 pm. Voltage 11.0V @ 400mA.
46 hrs       Voltage 11.3V
47 hrs       Voltage 11.4V
56 hrs       Voltage 11.8V. Still @ 400mA and battery still cool.
65 hrs       Voltage 12.1V
66 hrs       Voltage 12.2V
70 hrs       Voltage 12.3V
73 hrs       Voltage 12.4V
76 hrs       Voltage 12.5V
78 hrs       Voltage 12.6V
87 hrs       Voltage 13.1V
88 hrs       Voltage 13.2V
89 hrs       Voltage 13.3V
90 hrs       Voltage 13.4V
91 hrs       Voltage 13.7V CC'ed voltage rising quite quickly now as we approach the 13.8V PSU setting.
Expecting to see the current (400mA) start decreasing soon after 13.8V battery voltage is reached.

~92 hrs
Midday Dec 2
Target voltage (13.8V) reached with battery draw current quickly reducing .....now 340mA.
93 hrs        Voltage 13.8V Current 230mA.
~30 mins later current 180mA.

Will leave charging @ 13.8V CC until no further current decrease is noticeable, then rest battery for an hour or so to get a stable OC voltage before attempting any discharge/capacity tests.

~95 hrs       Voltage 13.8V @ 120mA.
From discussion in reply #33 charge voltage has been lifted to 14.5V where current increased to 250mA and falling reasonably quickly. In just a few minutes down to 200mA.

I'm calling recovery forward charge finished at this time as the little further charge can/will be added to the battery. ie. insufficient to make any significant difference to upcoming load/capacity tests.

3.15pm Battery resting.
+5 mins     OC 12.75V
+15 mins   OC 12.64V
+30 mins   OC 12.6V
1hr            OC 12.56V


Discharge log 4.50 pm.
OC voltage 12.54V
Load: 12V 30W handheld spotlight.
Drawing ~2.2A battery voltage ~12.3V

Attempting a dual measurement histogram with SDM3065X bench DMM........

+30 mins  Voltage getting close to 12V and current just over 2A.
+50 mins  Voltage 11.9V   Current 2.07A
2hrs          Voltage 11.78V Current 2.04A
3hrs          Voltage 11.6V   Current 2.01A
4hrs          Voltage 11.38V Current 1.99A
Discharge stopped. Battery recovered to 11.62V


Battery returned to charge, target = 14V @ 1A CC (5% of C)

0hrs      Voltage 11.9V @ 1A
9hrs      Voltage 14.0V @ 0.1A
Charge stopped.
+2hrs static voltage 12.54V



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 or degrade with further use ?

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

TBC..........

Please note: ongoing edits throughout this post for text clarity and better understanding.
« Last Edit: December 03, 2018, 07:03:28 pm by tautech »
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Offline Circlotron

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I was thinking - when the time for reverse charging is up, discharge the battery down to zero before connecting to the psu for charging in the forward direction. If you don't do that, the battery supplying reverse voltage to the psu may damage it. Lots of current may flow through the rectifier diodes, filter choke and transformer secondary.

Apart from that, keep us posted!!!  :popcorn:

P.S. You should live-stream it on YouTube :-)
« Last Edit: November 26, 2018, 10:38:20 am by Circlotron »
 
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Online RoGeorge

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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.

I always put a series diode when using a lab power supply as a charger.  For my particular case, 2xST double diodes recovered from defective PC power supplies on a former processor radiator acts not only as series diode, but they put in parallel the 2 channels of a Rigol DP832 power supply for a bigger current when recharging a car battery.  In the user manual of DP832 is specified the series diode as mandatory when using the power supply as a charger.



 
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Offline duak

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I agree that it's a good idea to have a series diode to protect the power supply.  Even if the supply doesn't have overvoltage protection, it may be sensitive to voltage on its output.  For example, the Lambda LP-41x series utilizes a floating regulator design where the output voltage is determined by a variable resistor to the negative output.  If this resistor is turned to low resistance while the output voltage is held high, protection diodes in the regulator conduct and send excess current through the resistor and either damage or destroy it.  Quite a few other power supplies use a similar design, (hp in particular) and I suspect could be damaged too.

I whipped up a rejuventor using an 80 V supply, a capacitor bank and a power MOSFET switch to apply short high voltage pulses to the battery.  If the battery isn't too far gone, it'll often regain some capacity but it's only a temporary fix.  If more than one cell was heavily sulfated, nothing helped no matter how long I left it on.

Cheers,
 
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Offline cdev

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I'm glad you posted this because I am doing this as we speak.

I am not sure if I am seeing a crowbar activating or current limiting in my power supply. Because only 13 ma is flowing.

I am using a generic switching diode in series with the power supply.


I needed to verify the current limiting set point before starting - which I use an 8 ohm power resistor to do.  I just did this again to verify that my power supply is not broken. Its not.

When it is just connected to the resistor, it gets hot, unless I set the current limit to whatever.

A crowbar may be acting to prevent my reverse charging the battery?


 Trying to Google for that now. The manual does specify that one needs to use a fuse when using it to charge batteries.

There is no indication on my supply of any crowbar operation.

Normal operation is in constant voltage mode which displays a green LED.

Besides the current meter (digital) a red LED goes on when it current limits, it is currently off.

But it says nothing in the documentation about any crowbar indication if you don't have one of the add on interface cards it can be upgraded with. (I don't) I do think they indicate it.

I doubt if there is anything I could throw at this power supply that would damage it.

Its a real beast. But it is quite possible it could and would self-limit.

 Its more than 30 years old, but its still a current model, its still being sold. Which must be some kind of record.

« Last Edit: November 26, 2018, 08:15:50 pm by cdev »
"What the large print giveth, the small print taketh away."
 

Offline Gyro

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If all else fails, the scrap value of LA batteries is quite high. Check your local metal recycling company (not sure where on the planet you're located).
Chris

"Victor Meldrew, the Crimson Avenger!"
 

Offline cdev

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I could charge a large electrolytic capacitor.

How much voltage for 12 volt cells, and do you apply it in the forward or reverse direction?


I whipped up a rejuventor using an 80 V supply, a capacitor bank and a power MOSFET switch to apply short high voltage pulses to the battery.  If the battery isn't too far gone, it'll often regain some capacity but it's only a temporary fix.  If more than one cell was heavily sulfated, nothing helped no matter how long I left it on.

Cheers,
"What the large print giveth, the small print taketh away."
 

Online tautech

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I was thinking - when the time for reverse charging is up, discharge the battery down to zero before connecting to the psu for charging in the forward direction. If you don't do that, the battery supplying reverse voltage to the psu may damage it. Lots of current may flow through the rectifier diodes, filter choke and transformer secondary.

Apart from that, keep us posted!!!  :popcorn:

P.S. You should live-stream it on YouTube :-)
Yes I wondered where voltages and battery energy would be when we are ready to start the forward charge....I'll keep your comments in mind however there's a lot of battery behavior to record yet as we go through your recovery process. I haven't got a programmable load (Siglents one is not released just yet) however plenty of various wattage auto bulbs and 12V spotlights to drain the battery to nearly zero before we start the forward charge. Fingers crossed !
I'm not looking to continually create new posts instead opting for ongoing edits in reply #14 to record it all in a single post.

Starting to see a trend of rising reverse voltages now as the battery starts accepting the reverse charge.  :)
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Offline floobydust

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I asked wet lead-acid car battery "rebuilders" what they do, they replace the electrolyte with some special reconditioning Battery Chem or Epsom salt and then charge at the highest rate the battery can take, say 50A to break off the sulphate crystals. The battery is literally boiling and it's limited by temperature rise. They must save enough batteries to make a profit.

I think reverse-charging is silly. Sulphate crystals are very tough and I've never been able to do much with them regardless of time, current, polarity on lead-acid batteries.

Desulfators really need to hit the cells hard:
https://www.eevblog.com/forum/oshw/desulfate-regenerate-lead-acid-batts-a-new-diy-guide-overnight/
https://www.eevblog.com/forum/projects/guess-what-will-happen-battery-desulfation-experiment/

Even then, lead-acid batteries are basically always corroding when not charging, it's lead in sulphuric acid and the metals breakdown so no repair is possible:
http://everist.org/NobLog/20180430_lead_acid_ruin.htm
 

Offline Bud

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.  I use them for weights when glueing things and other similar uses.

That is what i use them for, too.  They also double as weights for exercising.
Facebook-free life and Rigol-free shack.
 

Offline duak

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cdev:

I applied the pulses to the battery in the forward direction.  The voltage was pretty much 80 V.  The capacitor bank was a few thousand microfarads of lowish ESR 200 VDC caps pulled from PC power supplies.  I initially tried to use an IRFP340 FET as a switch but it couldn't handle the current for bigger batteries.  I had some bigger STM FETs rated for a 100 A and 100 V.  I used a pulse generator to drive the gate at 10 to 100 Hz with a pulsewidth of 50 to 500 microseconds.  As the sulfate is converted, the peak current goes up and the power supply loads down.  If memory serves, I was getting 50 to 100 A pulses into a car battery.

About applying a reverse voltage to a power supply.  Many supplies have a diode on the output to limit the reverse voltage.  What the supplies actually do when this happens depends on the design.  I suppose some would be damaged right away, some would get really hot because the pass element has to dissipate more power than they were designed for and some might latch up.  I would apply the reverse voltage to the battery thru a power resistor sized to allow the power supply to develop the correct polarity voltage yet still deliver the charging current.

I haven't tried the reverse voltage bit, but it's an interesting idea.

Cheers,
 
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