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Your method looks to be quite good at recovering capacity from cells designed to be abused. My question would be how many full cycles after recover is left.
Well, I have not done accelerated durability testing, post recovery. However, batteries have gone directly back into automotive service. I only have tracer data on my own 3 vehicles and close friends who have gotten batteries from me. All those results exceed the original OEM warranty periods. Perhaps 10 recovered batteries in all have tracer data. Of course, this is still anecdotal as I'd need at least a few score of tracer data to make claims with supported statistical confidence %.
In my testing I have done a few 100% discharges down to 10.5V when I was developing a prorated method/equation of Ah capacity evaluation. What I notice is that such abuse is bad for SLI batts. They lose about 5-10% of capacity each time they get cycled so deeply. I guess the paste/grid is too thin to support such discharge cycling. SLI batts are rated for 20% cycling.
WE made SOLARTECH's battery rejuvenator and they and others verified their claims. Although it was a slow unit , more important it was low cost and attached to the battery to work all the time the engine was running. The main difference was it was only 70A not 600A but rise time was 100x faster. It also did not boil the electrolyte. Outgasing is bad and over current can cause leaching of contaminant metals like Antimony into the electrolyte.
A good battery in a hot climate only lasts a couple years as sulfation increases with temperature and depth of discharge.
The theory is like an ultrasonic vibration to resonate the PbSO4 crystals to break down into a sediment at the bottom but if it floats as a plasma it can instantly short out a cells if the particles form a chain., so thermal monitoring is a safety requirement.
Most modern batteries (SLI) are low antimony with added selenium to refine the grid grain structure and calcium/tin for grid strength/creep resistance and reduced water consumption. Carbon black and lignin are added (to the paste) to improve conduction and reduce agglomeration of the leady oxide paste and barium sulfate is included to disperse the nuclei formation of the lead sulfate. All of these combine to a small % of the leady oxide in the paste.
I haven't seen any empirical evidence of ultrasonic vibration being the actual means of desulfation. If PbSO4 is mechanically forced into sediment then the H2So4 never recovers spec. gravity and the battery will fail. Some other mechanism is at play that places the sulfate ions back into solution. Sulfate that has become sediment is lost to the electrochemical process permanently.
The Grid /paste plates of SLI batteries can be <= 1mm and loss of paste integrity is a bad thing. Shedding lead sulfate actually also sheds previously active paste material that should be returned to active lead oxides during recharge.
In deeper cycle batteries with pasted plates up to 6mm thick this 'shedding' approach will expose fresh paste and appear to rejuvenate a battery. SLI batteries cannot tolerate much of that at all. Thus EDTA and other sequestration type approaches WILL work on thicker plate batteries while simultaneously degrading their total capacity. Thus such approaches are of limited usefulness. Repeated or excess doses will destroy a battery.
My tests seem to indicate that it is a combination of controlled heat and voltage that provides the energy to drive the stable sulfate back into ionic solution. Lead sulfate is inherently a passivating material and if it develops stable crystal growth the insulating islands of hard sulfate diminishes plate area and eventually 'shrinks' the battery's capacity. Once the physical micro geometry of the paste is compromised and its pores are filled with stable lead sulfate we have a failed cell.
Since lead sulfate crystal growth distorts the paste & grid, 'dissolving' (actually converting to lead/oxide and H2SO4) it sometimes leaves pockets behind as the lead oxide occupies less volume.
Once the sulfate is back in ionic form , ideally the plate/grid/paste needs to be reformed to compensate for the pockets left by the now 'oxide converted' large sulfate crystals. Thus some limited cycling of the battery via a sequence of discharge and slow charge will rebuild the micro structure of the paste surface to some extent, thus improving overall capacity.
Back in the 80s, I worked for a company that installed large UPS (20 to 150 KVA) for the large mainframe based computer rooms.
The biggest complaint always: Battery life. Those battery banks were expensive to maintain.
We used 500 lb 2V cells for the 48V UPS in our computer rooms, which were very high quality. The clear case to inspect the sediment and plates and cell S.G. balance was important. ( Telephone companies must remove/recycle these whenever they become mismatched even if they still have good life left. ) ( hint)
We only had problems with the emergency light batteries as I recall which were conventional small deep discharge types. We had Liebert UPS units.
I recall it was the antimony dendrites that can chain to short plates once the separator has worn. I experienced this effect once with a car in 1970. One second, it wouldn't turn over. then next time it started like new, thus disturbing the chain from the first attempt and allowing it to settle. Then repeating each day or so with occasional shorts causing outgassing until battery replaced.
You can inspect the health of the acid particulate contamination with a laser pointer and look for sparkles floating in acid. THe conductive particles will likely sparkle and the non-conductive particles will reflect light but more diffused.
Back in the early 80s, to achieve the kind of power I was talking about, one had to use a rotary converter, namely a DC motor coupled to an AC generator. A SCR chopper controlled the DC motor's speed.
Armature voltages were either 250 or 500 VDC.
To maintain 500 volts when the individual cells were at 1.9 volts each, required 264 cells, which we rounded to 250 cells. To achieve the desired speed with insufficient armature voltage, field weakening was also employed.
Anyways, lots and lots of individual cells to maintain.
I too have experience with a large ventilated battery room full of racks of clear case EXIDE batteries meant to backup a pair of IBM system 36 mini computers with 8" floppy disc storage dozens of 40 column monochrome monitors and a couple 'machine gun' daisy wheel printers. That was for AMOCO in 89/90. My job then was to convert that Sys 36 into a DEC ALPHA RISC based system running a version of UNIX.
We used 500 lb 2V cells for the 48V UPS in our computer rooms, which were very high quality. The clear case to inspect the sediment and plates and cell S.G. balance was important. ( Telephone companies must remove/recycle these whenever they become mismatched even if they still have good life left. ) ( hint)
We only had problems with the emergency light batteries as I recall which were conventional small deep discharge types. We had Liebert UPS units.
I recall it was the antimony dendrites that can chain to short plates once the separator has worn. I experienced this effect once with a car in 1970. One second, it wouldn't turn over. then next time it started like new, thus disturbing the chain from the first attempt and allowing it to settle. Then repeating each day or so with occasional shorts causing outgassing until battery replaced.
You can inspect the health of the acid particulate contamination with a laser pointer and look for sparkles floating in acid. THe conductive particles will likely sparkle and the non-conductive particles will reflect light but more diffused.
This sounds good, but do you have any advice for checking a maintenance free battery, the kind that dont open on the top? Or is there a way to open them up anyway ? (as they are the same just with closed top).
There is big money is in motive power batteries for hauling aircraft.
I verified the performance improvements of SOLARTECH's unit on a motive power expired battery by measuring ESR and S.G. all equalized and back to normal.
I see now they sold out to CANADUS in Ohio , who have sold units to Volvo which are now FCC certified for 24V trucks or 12V cars.
Maintenance -free , without a removable seal , are pretty hard to inspect.
They should just call them "disposable".
Sealed lead acid batts are trickier to recover. Tighter voltage management and reflex charging are required to manage gas evolution and to permit adequate oxygen recombination into water. I have recovered such batteries and I have also exploded one.
On a side note, I did a bit of investigation into using a colpitts oscillator with a tight coil (metal detector) to evaluate the reformation of lead from lead sulfate as a non contact means of evaluating battery charge condition. While it shows promise, so far each battery needs to be profiled in order to correlate SOC vs lead detected.
I need to spend a lot more time with that approach to come up with a viable SOC meter for general lead batteries.
EDIT: Congrats on being a part of that 'Volvo' tech Tony...they are a reputable firm!
No congrats to me ,although I did consult for Solartech about EMI solutions to AM problems for trucker driver complaints on long hauls for a bottle of Oban. C-MAC in Winnipeg built & test them in 5k batches, then the owner sold the company for more a million after I left and sold to Canadus who got the Volvo contract and Volvo got it certified. Not bad for an uneducated guy from Flin Flon MB. I was with him once when he refused his competitors in Taho who wanted to buy him out for a million, since he had the patent back in '99. Then they flew right back on their private jet.
I always thought SoC on flooded lead acid was 12.5 to 11.5 for 100% to 0% after a 5 minute light load to decay the charging voltage at 14.2.
There is big money is in motive power batteries for hauling aircraft and mismatched Telco 2V batteries.
I verified the performance improvements of SOLARTECH's unit on a motive power expired battery by measuring ESR and S.G. all equalized and back to normal.
The other thing about ESR as it rises rapidly as SoC goes towards 0 on every battery and aging as well. Solartech found the US Military was the biggest consumer of all battery types and were primarily interested in NiCad and other rechargables and found it worked.
As I recall the unit only drew about 5 watts of power and dumped the flyback pulse thru steering diodes in about 1% duty cycle meaning big energy pulses were delivered with 50 to 70ns pulse duration. This was limited by 70V MOV's to prevent shock on wasted SLI cells.
Interesting potential outcome of all this.
I am possibly going into a Ph.D. program to properly research the science of these 'reconditioning' methods. I've been doing mostly empirical 'science' so far and deriving postulations.
I'm doing the proposal for it now. This might lead to clear reproducible science.
That would be to investigate the effects of ultrasonic piezo electric vibrations on the battery?
When u say detection of EMF pulses......that sounds like using piezo transducers on the battery housing to detect sympathetic harmonics being induced in the battery plate/grid structure?
Sounds reasonable, but can u suggest a sensitive enough piezo device or should I propose a fixed light beam incident onto an attached mirror on the battery and then analyze the reflected 'modulation' of that beam with a phototransistor and preamplifier? That would fit into the methodology of the proposal.
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