Is my lead acid battery cactus? Experimenting with dead batteries i guess. - Page 1
Forum section: electronics / general

author: Refrigerator
author_rank: Super Contributor
timestamp: August 29, 2020, 04:20:25 pm
content: Been charging my homemade electric scooter an awful lot and decided to look into ways of recovering dead lead acid batteries.Got inspired to do some experiments so i rounded up all the junk batteries i had laying around.One in particular wasn't terribly bad, i started charging it at 3A and it rose to 14V within a couple hours, but after charging overnight it dropped down to 13.2V and won't go up.The battery has been abused by my dad's battery draining mercedes.I can hear fizzing from all around the battery, i think it's developing shorts in the cells, bummer.Is it possible to recover this or should i not bother? it's a "panther +30 hochleistungsbatterie" 95Ah.I don't really have lead acid batteries laying around since good batteries go into cars and bad batteries go into the recycling center for a discount towards a new one so there's no point in keeping old batteries.But i also want to experiment with renewable energy and lead acid seems like the best (most forgiving) chemistry to experiment with.BTW, i'm a battery noob.Ps: Also regarding the recovery methods, there seems to be a lot of hear-say on the internet so i'm spending my evenings reading scientific studies instead.

author: helius
author_rank: Super Contributor
timestamp: August 29, 2020, 06:22:24 pm
content: Quote from: Refrigerator on August 29, 2020, 04:20:25 pmApparently, because:QuoteIs a battery that is generating gas. All lead-acid batteries, whatever condition, do this when they are charged above 2.50 volts per cell. For flooded batteries, like yours, some gassing is normally desirable as it helps to mix up the electrolyte and clean deposits off the plates. For sealed AGM batteries, this process is not necessary and undesirable.If you can easily remove the plugs on the cells, you should do so to be able to look into the plates and determine A. if they are corroded, and B. if the water in the cells is at the correct level (should cover the plates but not be too high to risk spilling). Pure distilled water can be added to correct the level in each cell.QuoteScientific papers aren't textbooks: they are not written to educate the reader sufficiently to understand a topic.If your desire is to understand how to maintain batteries, you should read the manufacturers' manuals, which are very detailed.See, for example:http://www.exide.com/Media/files/Downloads/IndustEuro/Operating%20Instructions/Handbook,%20part%201,%20edition%206,%20Feb_%202012.pdfhttps://www.trojanbattery.com/pdf/TrojanBattery_UsersGuide.pdf

author: Refrigerator
author_rank: Super Contributor
timestamp: August 29, 2020, 07:33:51 pm
content: Just hooked another battery to charge and checked the panther and one of the cells does feel slightly warmer than the rest so i think it has a shorted cell.Before i unplugged the charger the battery had 13.3V on it that's at 3A charge for more than 24h.The voltage dropped to just a touch over 11V after it sat unplugged.I'll pop the caps tomorrow to check the cells.I also have another 95Ah battery (Varta made VW OEM battery) with a cell that's completely shorted and it started out the same as the panther, where it shorted during charging.The shorted cells do get warm during charging so maybe i can jam something through the filler cap hole to completely short them out to bypass the bad cell?Maybe gently poking/moving the plates around can clear the short?I was planning to dispose of these batteries anyway so might as well make the most out of them by experimenting some.Ps: the VW battery has transluscent case so i can see that the acid level is correct.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 29, 2020, 07:42:43 pm
content: Quote from: helius on August 29, 2020, 06:22:24 pm"The requested page could not be found."Also looks like i need to charge at a constant voltage rather than constant current so i might have to make another charger for CV at high amperage.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 29, 2020, 07:53:16 pm
content: Quote from: helius on August 29, 2020, 06:22:24 pmBut imo they can help quantify some things where as YT tutorials mostly just wing it.

author: helius
author_rank: Super Contributor
timestamp: August 29, 2020, 11:23:07 pm
content: Quote from: Refrigerator on August 29, 2020, 07:33:51 pmI agree that sounds like one cell is shorted. When batteries are abused, they shed spongy lead that drifts to the bottom of the cell. If it piles up high enough to touch the plates, that cell gets shorted out. I don't know of any way to repair this situation. Trying to extract the spongy lead seems difficult and dangerous, and the plates in that cell must already be pretty worn out.Quote from: Refrigerator on August 29, 2020, 07:42:43 pmThe initial stage of charge, "bulk absorption" is carried out at a constant current, with voltage limited to 2.45 V per cell. A current of C/3 is a good compromise between speed and battery lifetime, but faster and slower rates will also work. C/10 would be better for a deeply discharged or abused battery. So if the battery is 95Ah you should charge up to 9.5A.The second stage of charge, "float" is carried out with a constant voltage at around 2.35 V per cell. Yes, you descrease the voltage after it reaches 2.45V. This is what puts the final 10% of charge into the battery and keeps the plates in good condition.The third stage is "equalization" and puts a small current (C/20) at 2.70V into the battery for a few minutes. This generates gas at the plates (fizzing) and helps to prevent sulfation or stratification. It is only needed periodically such as once a month. The water level should be checked and corrected before equalization, and equalization should be repeated until the hygrometer reading of the cells stabilizes.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 30, 2020, 07:43:49 am
content: Well i did my first experiment with the VW battery, which was to whack the case where the bad cell is.And during the night the short cleared up but the cell is still slightly warm.Previously even after a day of charging it wouldn't go over 12V no matter what and this morning i found it at 14.2V.After i leave it unplugged for a couple minutes the battery still drops to below 12.5V which is not great, but previously it would drop to just a bit over 10V so it's quite an inprovement still.I guess lead acid batteries like some percussive maintenance from time to time.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 30, 2020, 08:11:27 am
content: Checked the panther voltage and after the night it settled down to 10.9V so it's not a happy camper.Might have to give it a little "nudge", if you know what i mean.Both of these batteries have been frozen over i think, since they've spent a couple winters discharged (the VW battery read 6V when i pulled it out of the scrap heap).But they both still have enough juice to melt wires if you short them out (i had to check).I might whip together a quick micro thingy to measure the capacity of these batteries.Also the bad cell in the VW battery feels just barely warm now so there might still be hope.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 30, 2020, 01:11:13 pm
content: Made the capacity meter with an arduino and a 5load and premared myself for lenghty wait for the results.Well it didn't take very long because the capacity of the VW battery was *drum roll* a whopping 842mAh.Yeah it's a sad puppy.A prime candidate for some magnesium sulphate experiments.But i don't have any now and the hardware store is closed so i might first do a cheeky reverse charge experiment instead.I've done some experiments with DIY lead cells and reversing the charge with each discharge is an easy way to form the plates.I've read in the abstract of one study that after reverse charging at 2 amps for 12 hours (i think*) for some number of cycles (i think*) they could recover up to 84% of the battery capacity.Also the panther battery now sits at 13.6V after i reconnected the charger to it so there seems to be something happening.*stupid me forgot to bookmark so i'm talking from memory here since i can't find it now.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 30, 2020, 02:28:01 pm
content: Panther battery has been stuck at 13.6V for a few hours now so i disconnected the charger because it seems to be only fizzling without any other improvement.I've made a few modifications and also lowered the cutoff voltage to 8V for my discharge. It was previously 10.5V for 6 cells but will now also work for 5 cells.That said, VW battery is discharging again and seems to be pretty happy at 10.3V at over 1 Ah on the clock now (after reset) so it does seem like i have a weak cell.After this i'll reverse charge this battery and re-test again.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 30, 2020, 10:04:02 pm
content: The VW battery had made a little over 5Ah before i accidentally nudged the breadboard and shorted something out, which cooked the onboard voltage regulator on the arduino nano.No big deal, i added a LM7805 and also tweaked the code to read the voltage more accurately and to also account for the 60mA that the arduino contraption draws.And since then the battery has cranked out almost 10Ah more. So about 15Ah in total.Pretty crap for a 95Ah battery but at least it's something to compare against later.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 31, 2020, 06:14:16 am
content: Hooked up an old tungsten headlight to the VW battery to drain it overnight.When i left it the voltage was about 7.9V, this morning i check the battery and the voltage is 9.2VThe bulb draws about 3.8A and it's been doing so for the past 7 hours.Batterizer eat your heart out because my batteries charge themselves.Don't know if this battery is blessed or cursedAnd there's no room for error here, because i terminated the battery discharge at 8.37V and that was with a 5load (1.6A @ 8V) and it makes sense that it would drop below 8V with a bigger load. But why did it go up?And let's say it's been drawing 3.7-ish amps over the 7 hours, that's almost 30Ah more.Ps: this also makes my Ah measurement completely irrelevant, because with such an unstable voltage i would be better off measuring Wh instead.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 31, 2020, 12:20:55 pm
content: Well the lamp thing might have been a fluke if the lamp disconnected when i wasn't looking, which would make the theoretical 30Ah Shrodinger's capacity.Anyways the panther battery has been discharging and had squeezed out just over 20Ah before i nudged the cable and my arduino reset.I used this opportunity to update the code to calculate Wh along mAh for a more accurate measurement. Also the panther battery seems quite happy at 10.2 V so it probably has a bad cell as well.But even with a bad cell if the battery cranks out more than 40Ah in total i'd be pretty happy with the results. Some 40Ah at 10V is still 400Wh.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 31, 2020, 05:29:07 pm
content: VW battery is comfortably sitting at -10.3V (yes, negative) and has been taking 3A in the opposite direction for some 8 or more hours.The whole battery feels warm. Will be fun to see how much juice i can squeeze out of it in reverse polarity.Meanwhile i took a UL7-12 battery, which had a weak cell that would limit the current of the whole pack.At first the battery would charge too quickly and would only give out 0.7A max. After that i added water to the cells and it would take more charge but would only give 1.7A max and under such load you could hear one of the cells sizzling.Added some magnesium sulphate solution to the bad cell, basically as much as there was free space still remaining in the cell and after charging the battery seems better.Testing max current would now overload my tester so it's over 20A, which is great. I stopped charging it over an hour ago but it's still sitting at above 13V so all the cells are ok.I've noticed that almost all of these non-spillable batteries die because they dried out (i've had 5 of them in total). And once they dry out they start producing huge amounts of white powder that i assume is lead sulphate. So much so that they eventually blow out through the case, i've already had two of these batteries do that.Checked the fluid level in the panther battery and all cells had fluid above the plates. Found the shorted plate, which was slightly lower on fluid than adjacent cells.Added ~30ml of battery electrolyte in hopes that the higher concentration would start sulphating the cells (yes, purposely sulphating).Sounds mad but what i'm after is for the acid to sulphate the bridge that is shorting the plates and to turn it into non-conductive lead sulphate, which would act as a separator of sorts. Well that's the hope, at least.Also the panther battery does seem like it was in a pretty good condition because it just keeps cranking out energy, i've already lost track of how many Wh it has churned out but it has been going for like what, close to 24 hours already?So i hope that i can somehow fix the shorted cell.

author: Refrigerator
author_rank: Super Contributor
timestamp: August 31, 2020, 09:02:19 pm
content: In case anyone's wondering, if you reverse charge your 95Ah lead acid battery to 10.3V it will have about 0.45Wh in it.

author: hendorog
author_rank: Super Contributor
timestamp: August 31, 2020, 09:17:53 pm
content: Quote from: Refrigerator on August 31, 2020, 06:14:16 amIt sounds like that bad cell has an intermittent short - from your earlier post where you whacked it. So it was shorted initially when you connected the lamp, then the short failed when a decent current started flowing. An extra cell coming online means an increase in voltage.This could also explain the excessive fizzing as the other cells will be exposed to over-voltage if one is shorted.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 01, 2020, 08:21:45 am
content: Well the VW battery has been charging (the normal way) at 3 amps overnight for about 11 hours now and it's been sitting at 10.3V for a while.Will have to see whether the voltage goes up as it should, perhaps it's just taking it's sweet time to re-plate the lead on the electrodes.I'll go pop the caps to check the voltages with the multimeter, just to make sure. But so far i hear no bubbling or fizzing at all.The area where the bad cell is feels just the slightest touch warmer but it's in the placebo area. But nowehere near as warm as it was during reverse charge, where it was very noticeably warm all across the battery.I'll be leaving for university today but i'll return on friday so i might just leave the battery to charge in the meantime.95Ah / 2.9A (i measured) = 32.7 hours but that's assuming a constant current charge, so let's say the battery will get some extra time for absorbtion.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 01, 2020, 11:36:37 am
content: Measured the voltages of each cell by holding one probe on the terminal and dipping the other in each cell ending on the other terminal, then repeating the same but from the other terminal.Starting at the positive:1.65V (this varies alot (1V to 1.8V) based on there and how deep the probe is)3.76V (holes 2 to 6)4.95V5.86V7.96V9.59V10.51V (negative terminal)Then from the negative terminal:0.55V (holes 6 to 1)2.61V4.71V5.56V6.85V8.91V10.51V (positive terminal)You might look at the one low reading and think that it's the bad cell but i compared this to known good cells in the panther battery and got similar results.And this is because the multimeter probe in electrolyte itself becomes an electrode and as evident by the very first measurement favors being the negative electrode.That said there's a steady increase in voltage across the board meaning that so far there are no obvious signs of dead cells.And that's good news, but it would be even better to find a way to recover the shorted cell in the panther battery just because all the other cells are showing so much life still in them.I've already confirmed through the same probe dip test that cell 5 in the panther battery is completely shorted out and by looking through the fill hole i can see that the plates are noticeably brighter than others, cell 3 also looks a little brighter.Cell 5 has already received some mechanical input (as Ben from applied science would say) but does not show any improvement. Also from inspecting the plates it looks like most of them have cracks so i don't want to bang this battery any more, otherwise i risk ruining the other cells.I think that perhaps it would be possible to drive a high enough current to clear the short, but this also risks burning a hole in the separator.My hope would be that the short would have a high enough resistance to allow enough voltage to build up to cause the cell to bubble up and then the bubbles would separate the plates from each other to clear the short. Simultaneously the electrolyte could help the short not overheat.But this method also means that other cells would get abused as well, ideally i would only want to blast the single cell.Of course before any of that i would need a charger that can supply more than 3A. I'm thinking my AC arc welder with an added bridge rectifier would work for a short pulse.Shorting the battery would also drive a load of current through the dead cell, but it would also reverse charge the shorted cell and from what i noticed when reverse charging the VW battery is that this produces all heat and no bubbles, so it would be counter productive.There are videos on YT that claim that blasting a car battery at some 200A for repeated intervals will make it like new. And while i don't necessarily agree with this, if i decide to go the high current route i can use that knowledge as an excuse to not feel as bad for abusing the battery so much.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 01, 2020, 12:51:20 pm
content: VW battery voltage seems to be increasing by about 100mV every hour or so and i don't feel any significant difference in temperature.The battery is cool to the touch and the area around the dead cell maybe feels less cold but it could very well be my imagination.Regardless, it seems better at least for now.Also the UL7-12 battery did recover in terms of max current but seems to have pretty poor capacity. With a 5load it only squeezes a measly 1.5Ah.I've previously (before the magnesium addition) left a 100load connected to the battery for an extended amount of time (overnight, so 12h approx) and it did not drop much in voltage (i think it was around 12.4 when i disconnected it) and kept the resistor nicely warm.I've also noticed that during discharge (5load) the battery voltage drops rapidly when it reaches 11-ish volts and plummets to 9.5-ish volts where it stabilizes again, indicating a weak cell, which could be the magnesium sulphate cell.These UPS (non spillable) batteries are AGM by their nature so cleaning them out or changing the fluid is not easy at all. I've also read that it's best to flush the magnesium sulphate solution after about 4-6 cycles so i might attempt something but i won't have my hopes up.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 01, 2020, 02:40:33 pm
content: The VW battery is now at 10.8V and if i put my ear right on the vent hole in the case i can just about hear the occasional bubble pop.Not sure if it's too early for it to be bubbling but i'll have to see how the battery behaves.So far around ~50Ah have gone into the battery.

author: helius
author_rank: Super Contributor
timestamp: September 02, 2020, 02:00:30 pm
content: AGM batteries are different in a lot of ways, since they have relatively little electrolyte (to be able to be turned on their side) and meant to be safely float charged for indefinite periods. You've shown a lot of resourcefulness but I'm not sure that trying to disassemble and reassemble them is such a good idea. The container needs to be quite strong to resist swelling and gas pressure (some pressure-release valves are set for 50 psi (3.5 bar)).

author: Refrigerator
author_rank: Super Contributor
timestamp: September 03, 2020, 05:14:14 am
content: Quote from: helius on September 02, 2020, 02:00:30 pmWell by attempting something i meant flushing fluid through the filler hole. I don't feel like taking lead acid batteries apart, too much of a mess.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 03, 2020, 03:52:37 pm
content: Came home early an immediately went to check the battery but shock horror, someone had unplugged the charger.But left the wires connected so it kept bleeding the battery through the charger. When i checked the voltage it was at 8.56V so it's not terribly horrible.Keeping a lead acid battery at low voltage causes sulphation, but looking at the bright side, the sulphation will help reduce the chances of the cells shorting again ...... is what i tell myself to not feel bad.Anyways i plugged the charger back in and after some charging the voltage is now at 11.5-ish volts, and i hear bubbling (which is good.....?).Might go blast the panther battery with high current but before that i'll go google some answers.Doing any of the potentially short clearing procedures is a one-way road so i don't want to get into trouble.Also my brother told me that the battery is rather new so clearing the short would mean a 100€ saved.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 03, 2020, 04:12:20 pm
content: The voltage on the VW battery quickly dropped to 10.5V and i decided to pop the caps to see what's going on inside.Cells1, 3, 41, 3, 5 and 6 are bubbling but cells 2 and54 are not meaning they're cactus.So i think we have a prime contender to get the high current treatment.I'll go give it a couple whacks on the side and go get the bridge rectifier wired up to my welder. If the short doesn't clear by the time i'm done then the battery will get zapped.Actually i'll zap it regardless because i just want to see what happens.The VW battery is old and trashy so abusing it is ok, i mean it sat in the scrap metal pile so there's not much to lose.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 03, 2020, 04:32:11 pm
content: After a whack the voltage got up to 11.65V, we'll see what a good zap will bring.Will also be a great opportunity to test the 50A diode bridge module i bought off ebay, since they (electronic components in general) are notorious for being counterfeit.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 03, 2020, 05:31:38 pm
content: And just like that the diode bridge is cooked, didn't release that much smoke but lord allmighty does it stink.I have a massive headache right now.But after i hooked the battery to the charger the voltage shot up to 12.4V so that's good, right?Pulled the diode apart and honestly expected to find four 1n4007's but instead found four rather large dies. Didn't measure but i estimate about 16mm2of area per die.Barely used the 60A tap on my welder before the bridge shorted, but i think i might have cooked one diode in the bridge when i accidentally touched one of the battery wires to an AC terminal.But i have 3 more of these bridges to burn.Will see how the batery behaves now. Popped the caps and the cells are not bubbling yet but they might be undercharged because they were shorted.Ps: the miasma of burned diode smoke is still lingering around me, this stuff is nasty.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 03, 2020, 05:57:59 pm
content: VW battery dropped to 12.3Vbut cell 4 has started producing bubbles.actually it does not yet.Will give this battery a hot supper tomorrow.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 04, 2020, 07:32:16 am
content: Cooked another one of those "50A" diode bridges just for good measure.Didn't help much so i pulled the diode half bridge from my DIY inverter welder since it has two IDW100E60 diodes in parralel that i can use.And oh boy did i cook the battery. It actually didn't even bubble much, and at close to 100A barely went over 16V.But that's just pulse current since it's a half bridge, but at least i'll know that the diodes aren't crapThe short, wherever may it be, has to be absolutely monumental now. I guess if i can't clear the short i can at least weld the plates together to lower the resistanceI'm thinking the reverse charge thing might have contributed towards the cell failure, if i remember right the lead that replates is loose and puffy so that coupled with the paper thin separator might have just excentuated the short.

author: Refrigerator
author_rank: Super Contributor
timestamp: September 04, 2020, 12:35:11 pm
content: I'll have to build an improved battery tester because the one i have now is too clumsy.For starters i have to hard code the resistance of my load so it's a pain in the arse if my load is not constant resistance, like a tungsten bulb, for example.And i don't have high power resistors for most cases.So if i want to dump more current out of the battery, because at 2A the discharge takes aaaaaages, i have to change both software and hardware = no bueno.Also the connections on the breadboard are not reliable at all and just wiggling the wires around messes with the measurement.