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Desulfation of flooded lead acid batteries with just a DC power supply.

Luk88

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I've read this new (20230 study about desulfating flooded lead acid batteries with just high voltage DC charge. It is very interesting as they tested just overvoltage on desulfating flooded lead acid. Many a company sells pulse desulfators, but if all we need is a bench power supply - that would be a great discovery.

They did a proper study with multiple batches of 30 batteries and they have microscope photos etc to prove it. So it seems legit. The study is: "A Novel Approach Using High Charging Voltage for the Restoration of Discarded Lead Acid Batteries" by Chee Hiun Lee, Jianhiu Wong, Yun, Seng Lin. It is available here: https://www.researchgate.net/public..._Restoration_of_Discarded_Lead_Acid_Batteries

the conclusion of the study is that we can desulfate and achieve close to 80% of capacity without the "inverse charge", we just apply overvoltage of 2.6V per cell. They tested with 2.67V and found it works too, but it removes too much electrolyte. 2.6V seems to be enough to desulfate without (too many) adverse effects.

2.6V per cell is 15.6V for a 12V battery. They did all their tests with tiny 7Ah discarded UPS batteries and the gist of it is to pump 15.6V(for a 12V battery) for 24h into it, then charge normally for 48h and its done. The current should slowly raise up till 0.5A (for a 7Ah battery). Of course they had a number of failures, all were caused by mechanical deformation of conductors causing shorts or disconnects.

I have 4 198Ah 6V batteries (for a total of 24V) which were left with no maintenance for 6 months in temperatures around 2C (they were fully charged before). All 4 show slight whitening of the plates. 3 sit at 6.3V one has collapsed to 5V. The one that was collapsed was charged fully and the capacity was tested at 1Ah only!

Then I tried 3h of this overvoltage treatment on the worst battery. And indeed the current raised up to about 4A. I then tested the battery and it tested as 19Ah. Promising, but far from the result I hoped. So I gave it additional 8h and I then noticed the remaining 3 batteries are sulfated too. So I connected them all 4 in a string and I gave them 30.2V from a constant current PSU limited to 10A. It has been about 8h more and the batteries are starting to get slightly warm. They are of course bubbling a lot and the plates look the correct color.

10A seems much, but considering they used 0.5A with a battery almost 20 times snmallert (and they do say it reached 45C temperature in the end) I think I'm OK. I'm planing to keep going to complete the 24h, then do a "normal charge" for 48h and do a capacity test.

Has anyone done desulfation of good, but sulfated batteries before? Also, in case anyone is interested, these appear to be lead-calcium alloy batteries. This does matter for the voltages involved. Sadly the researchers didn't specify what alloy of lead they did their experiments with. Perhaps I need to write to them to ask :)
 
We have been using this method for 13+ years with off-grid lead acid battery setups. In fact many manufacturers recommend equalize voltages in the range you are talking about. We have always told our customers to equalize once per month (that way it happens every 2-3 months.) and the proper way to do it is to hold that higher voltage for an hour or 2, then giv ethe battery a 10-15 min. rest and then check cell specific gravity to determine if done or if it needs another "shot". I have had scenarios where there was no equalizing ever done and after 2-3 years the batteries didn't have the capacity they should have had, so I got the customer to take the voltage up to those numbers and hold there for 4-6 hours, then wait a day and do it again. Maybe even 3 days in a row. Generally they ended up regaining capacity to close to new numbers. This was on 2-3 year old batteries though. Not on batteries that were 5+ years old!

  • For US Battery brand L16s and golf cart batteries we would use a voltage of 15.6V/31.2V/62.4V (for 12/24/48v systems respectively)
  • For Trojan brand L16s and golf cart batteries we would use a voltage of 15.8V/31.6V/63.2V
  • For industrial cell batteries we would use pretty well same voltage as the Trojans.

Most (or maybe all) forklift lead acid battery chargers actually take the voltage up to around 2.6-2.65V per cell and terminate charging once the charge amps stops dropping at that voltage. That would be happening on pretty well every charge cycle! Doing that on every charge cycle would cause premature failure in a solar type of application, but with a forklift type of usage profile, it does the trick to keep them going for a reasonable life-span.

Please note though, that this works best as a preventative maintenance thing, rather than a "get back my battery health" thing! And along with that, there are other things that wear out a battery, such as active material shedding. This happens with cycles, and also heat contributes to it. If you look inside a battery and the water looks brownish-reddish, your issues go deeper than sulfation! If you see grey buildup on your plates then you are dealing with sulfation. Generally speaking, when you have water discoloration, you aren't getting your battery health back, because the plates have lost their active material, therefore rendering them no longer able to create the chemical reaction need to store and produce electrical energy.

Personally, after dealing with hundreds (or really probably thousands) of lead acid batteries, and now working with lithium batteries for probably 8-10 years, I would never even remotely consider messing with lead acid for myself. (I know you mentioned lead-calcium, which I don't know much about.) I simply haven't seen a battery that comes even remotely close to giving LifePo4 a race in terms of performance and $$ pr kWh of life! Plus, with lithium there is no acid mess or corrosion to deal with!
 
Yes this is not a new process. I do this daily at work. Some manufacturers like Concorde call it a "conditioning charge"
 
Caution. If the battery has been severly degraded a short may have developed in one or more cells. The result will be that the battery gets hot. Very hot. I had one get hot enough to crack the case and leak acid.
To be safe it is best to current limit the power supply to 200 ma or less.
 
For instance, ill summarize what Concorde says - charge at a constant current of 10% C1 rate for 16 hours. Max voltage should be 17v for 12v or 34v for 24v batteries. The process may be repeated 3 times to achieve 80% capacity. If at any time the temp goes above 120F , let cool and try again.

This is a very common practice in the aircraft industry with valve regulated lead acids. Being in the aircraft maintenance world we cannot deviate from the instructions and experiment, but we have had good results raising capacity 20-30%. If your first cap check is below 50%, likely its not worth the effort. Other manufacturers use similar techniques, current is always limited based on battery size and voltage has a "ceiling" not to be exceeded. Towards the end of a condition charge you will likely be at the voltage limit with current reduced by default.
 
I’ve used a constant current charge on 48V golf cart batteries, but I only push about an amp for a few days till the battery voltage stops rising. Not sure if I’m getting good results, but all the cells are offgassing at the end. I’ve seen something about overcharging causing plate oxidation…
 
Wow, thank you for great, very helpful replies.

the proper way to do it is to hold that higher voltage for an hour or 2, then giv ethe battery a 10-15 min. rest and then check cell specific gravity to determine if done or if it needs another "shot"

How can you tell it is done by specific gravity? My most sulfated battery(one that later measured 1Ah out of 198 it should have) seemed almost fully charged when specific gravity was measured. Is it different in older sulfated batteries?

Generally speaking, when you have water discoloration, you aren't getting your battery health back, because the plates have lost their active material, therefore rendering them no longer able to create the chemical reaction need to store and produce electrical energy.
An I right to assume some cloudiness of the electrolyte during such high voltage desulfation/equalisation is expected? The mechanism some speculate is responsible for the improvement is not just dissolution of the sulfate, but shedding because of bubble formation.

Perhaps this is different in properly maintained batteries. As you said recovering an almost dead battery is a different thing and much less certain.

Personally, after dealing with hundreds (or really probably thousands) of lead acid batteries, and now working with lithium batteries for probably 8-10 years, I would never even remotely consider messing with lead acid for myself. (I know you mentioned lead-calcium, which I don't know much about.) I simply haven't seen a battery that comes even remotely close to giving LifePo4 a race in terms of performance and $$ pr kWh of life! Plus, with lithium there is no acid mess or corrosion to deal with!
Exactly, lithium is so much better... But sometimes we get lead for free (guess why).

I am switching to lfp. But I still have these batteries and the idea is to keep them as a power source if I ever need to heat up my lithium batteries if we have a freakishly cold temperatures and my basement ever goes below freezing while there is a power cut at the same time (these are usually the times when I discover a clogged jet on a generator :)

Caution. If the battery has been severly degraded a short may have developed in one or more cells. The result will be that the battery gets hot. Very hot. I had one get hot enough to crack the case and leak acid.
Yes, leaving these unattended is not a good idea, but how else do you do it for 24h as in the study paper? Perhaps doing a couple of hours at a time is the way to go as Cmiller describes.

Personally I do leave them unattended, but it's done in a building where an acid spill wouldnt be a complete disaster.

To be safe it is best to current limit the power supply to 200 ma or less.

This really depends on the battery size. Even with the study where they had tiny 7ah batteries they reported good results only with 0.5A of current (it is supposed to grow in time reaching that value towards the end).

I doubt you could do this process if you limited to 200mA. I was getting almost 2A when I started. Had I limited to 200mA the voltage would drop below the level needed.

If we scale this value to my 198ah batteries I should see 14A! But my psu is incapable of delivering that much so I limited to 10A. With no short in the cells this was enough to get them slightly warm to the touch(and properly stink up and acid-mist the room - despite two open windows). In the study they reached 45C.

I'd recommend to get a multimeter and with a constant current psu set a small current limit for example 200mA, way too high voltage (20v for a 12v battery) connect it and measure the voltage at the battery terminals. If it is what it should be leave it, if not increase the current limit until you get the right voltage. Then increase is to double that while lowering the set voltage to the target. This IMO would be a relatively safe method.
 
How can you tell it is done by specific gravity? My most sulfated battery(one that later measured 1Ah out of 198 it should have) seemed almost fully charged when specific gravity was measured. Is it different in older sulfated batteries?
I guess using specific gravity would pertain a little more to the "preventative maintenance" approach. When Equalizing for preventative maintenance you want to achieve 2 goals at the same time.
  1. Raise voltage to a controlled overcharge in order to overcome resistance "build-up" from the sulfation crystals, therefore being able to soften the crystals to induce shedding.
  2. Bring specific gravities back up to a "full charge" state. Specific gravity is directly related to the acid levels in the water, which is related to the charged/discharged state of the cells/plates.
  3. Create bubbles to help get those softened crystals to drop to the bottom of the battery case. Lead acid batteries actually have an empty section in the bottom of the case, below the cells, to allow sulfates and/or (plate shedding) active material to drop into without bridging between the cell plates.
Something to keep in mind is that when active material has been lost (plate shedding) the plates can no longer "work" properly, therefore even though specific gravity comes up to where it should be, you still don't have the usable capacity. A good analogy would be to compare to a bucket of water. As the battery cycles, essentially the top of the bucket slowly "wears down", therefore it can hold less water.
An I right to assume some cloudiness of the electrolyte during such high voltage desulfation/equalisation is expected? The mechanism some speculate is responsible for the improvement is not just dissolution of the sulfate, but shedding because of bubble formation.
Yes, that is correct. During Equalizing you will likely see cloudiness, in fact some bubbling occurring during normal charge is actually fairly normal. Using an absorb voltage just high enough to get a tiny bit of bubbling at the end of the normal charge cycle can actually be helpful as far as preventative maintenance goes! Before you start the Equalize process, when your batteries have been at rest for a few hours, is when the water being dark/discolored/black/reddish etc. is indicative of more issues. Basically permanent discoloration vs. "floaties".
Perhaps this is different in properly maintained batteries. As you said recovering an almost dead battery is a different thing and much less certain.
Often during Equalizing you will get some cloudiness even on properly maintained batteries, just because those bubbles stir up any "floaties" in the water.
Exactly, lithium is so much better... But sometimes we get lead for free (guess why).
Yep, I always say "if it's free, it's for me". 😄

Although, I don't consider myself a packrat though. Lol (my wife might say differently...)
I am switching to lfp. But I still have these batteries and the idea is to keep them as a power source if I ever need to heat up my lithium batteries if we have a freakishly cold temperatures and my basement ever goes below freezing while there is a power cut at the same time (these are usually the times when I discover a clogged jet on a generator :)
Sound like a great plan!
Yes, leaving these unattended is not a good idea, but how else do you do it for 24h as in the study paper? Perhaps doing a couple of hours at a time is the way to go as Cmiller describes.

Personally I do leave them unattended, but it's done in a building where an acid spill wouldnt be a complete disaster.
Another factor in keeping an eye on them is that I have seen batteries so hot that I was concerned they could almost light something on fire! Say a piece of paper falls down on them or something, and then if you get a spark or a flame, there will be a big bang! Equalizing creates LOTS of hydrogen! (I had 2 different customers blow a top off a battery after checking water levels with a lighter directly after charging...... :fp2💥 After the second one, I began specifically mentioning to customers not to check water levels using a lighter instead of a flashlight, lol.)
This really depends on the battery size. Even with the study where they had tiny 7ah batteries they reported good results only with 0.5A of current (it is supposed to grow in time reaching that value towards the end).

I doubt you could do this process if you limited to 200mA. I was getting almost 2A when I started. Had I limited to 200mA the voltage would drop below the level needed.

If we scale this value to my 198ah batteries I should see 14A! But my psu is incapable of delivering that much so I limited to 10A. With no short in the cells this was enough to get them slightly warm to the touch(and properly stink up and acid-mist the room - despite two open windows). In the study they reached 45C.

I'd recommend to get a multimeter and with a constant current psu set a small current limit for example 200mA, way too high voltage (20v for a 12v battery) connect it and measure the voltage at the battery terminals. If it is what it should be leave it, if not increase the current limit until you get the right voltage. Then increase is to double that while lowering the set voltage to the target. This IMO would be a relatively safe method.
Those times where we did a "recovery" of sulfated batteries, I sometimes even left an additional charger there to get more amps pumping into the batteries. If the sulfation is excessive, sometimes you need to pump pretty high amps in to get the voltage to rise high enough. For instance, we have had to adjust absorb voltage setpoints on Schneider inverters, because they never got the voltage high enough to finish absorb, therefore they never even transitioned into Equalize.

Excessive sulfation "eats up" the charge amps by making heat. (Remember, resistance in any electrical circuit creates heat, and sulfation creates resistance!) So sometimes you simply have to pump even more excessive amps until internal resistance is overcome to the point of pushing voltage high enough to get enough bubbling going on! Many lead acid battery manufacturers don't recommend higher charge amps than ~18-20% of battery AH for normal charge rate. So for 420AH 12V (2x US Battery L16s) that would be 420 x 0.18 =75.6A. I am pretty sure that I had times where I hooked up 2x Intellipower 45A chargers in order to get the voltage high enough. (With the Intellipower chargers, you can then insert a 15.9V plug. That does a good job of "cooking" the battery for a while!)

A number of years back we took a tour of the Crown Battery plant (I believe it was in Freemont, OH) and it was amazing what we learned from seeing the manufacturing process, as well as what they showed us. We were able to see cells and plates that had been tested in their labs, and they showed us the difference between sulfation, stratification and active material plate shedding. You can literally see these issues on the plates! Pretty cool!

Stratification, by the way, is when the batteries have not had enough "action" (for lack of a better term) and the water and electrolytes stratify, or separate and the electrolytes settle to the bottom. You then end up with a "gummed up" bottom 1/3 or so of the plates, and the result is permanent damage, as that portion will no longer be able to conduct properly, therefore you lose usable capacity!

Here are a few quick google search result pictures of stratification and sulfation.

1713276041984.png
1713276089460.png
1713276117733.png
1713276282861.png
 
ever goes below freezing while there is a power cut at the same time (these are usually the times when I discover a clogged jet on a generator :)
Generators only act up in your most vulnerable times. It's like it's their job to add stress to your life. :fp2

That's why i want to build (or buy.. nahh!) a generator powered by my Kubota tractor. That thing never breaks. Possibly hasn't broken in 45 years (ive only owned it for 2-3). Possibly never will!
 
Generators only act up in your most vulnerable times. It's like it's their job to add stress to your life. :fp2

That's why i want to build (or buy.. nahh!) a generator powered by my Kubota tractor. That thing never breaks. Possibly hasn't broken in 45 years (ive only owned it for 2-3). Possibly never will!
Ah, I have been hoarding this huge 3 phase 15kW squirrel cage motor hoping one day I can build a generator from it and I can hook it up to the pto of my tractor for power :) so I definitely get where you're coming from.
 

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