Ummm maybe a chart but im on mobile @hummieee start a list and ill help populate it
Maybe come up with testing procedure to figure out what the effects are?
todo:
make a table with relevant info for cells, link the spec sheet, manufactures minimum voltage, manufactures qualifications such as how they believe it effects the cell performance and safety.
accepted practice for recovery, maybe qualified by manufacture or model as to procedure to recover cells
a procedure for testing recovery and how to determine the long term effects. maybe start collecting cells to specifically test. i have some testing equipment and can start on a few but i would like some input on how to test consistently and what data points will be the most valuable. maybe reach out to mooch but i dont wanna bother if i don’t have a good write up yet. don’t wanna false start if I’m just doing this solo as it will take me forever
I think the main point would be consistency of recovery - how do the cells perform after being recovered from the same voltage at which they were standing for the same amount of time, are they still consistent? And how does the voltage they are standing at influence their performance/ consistency afterwards? Another thing to test is how does staying different time intervals at the low voltage affect things.
My biggest worry (assuming a successful recovery) is that since we always top balance, little differences in capacity and IR can cause significant differences in voltage when you go deep into underdischarge territory. How much inconsistency will this cause in
Capacity at modest current
Internal resistance
How they handle higher currents, as it’s not just internal resistance that effects this. Do you need to derate the cell current so that the discharge curve doesn’t look like the cell is overstressed?
Do they become vastly different from each other after being recovered?
It’s probably also worth highlighting that no matter how many scenarios get tested, results will probably somewhat vary in each real world case so at best we can create a guideline but always proceed carefully and at your own risk.
Good points, im not set to test anything a higher current than just a few amps but i do have a consistent if not lab quality ir tester.
One thing i dont think can be controlled for at least initially would be sample size. All of the tests would be just a few cells donated and may not be representative and im not certain how to accomplish this without it quickly getting to be too large of a scope.
This is three tests in my opinion -
first would be testing for lowest voltage the cells would recover without obvious or measurable degradation, making the varrable the voltage they are dropped too and then time at that voltage kept consistent and then using the same recovery method - then testing for stable maximum charge voltage after a rest, ir, capacity, self discharge, and
then separately what effect the amount of time spent under voltage has.
Third would be the load they are placed under to get them to this level as my intuition would lead me to think sagging to a low voltage briefly would be less damaging than trickling down to a very low potential but i have no data
I’m not interested in going through every cell’s data sheet.
My point is simply to defend my statement that many cells allow charging from 1v with a trickle charge. Anyone who says I’m being dangerous and starts insulting me while it’s literally in the manufactures’ data sheets is a fivking idiot who likes to argue
Anyone who brings up a quote of mine from many years ago stating u can do this, while trying to mock me, is a total fuicking idiot.
Have you got a short list of cells you have recovered and what state they were at? Whatever links you have just slap them down. Grabbed the murata and 50s links already
I’ve only recovered p42 ironically as they’re not even one that state possible on their ridiculously small data sheet which has me wondering if they have something else somewhere.
But as I say I’m not interested in building this. I’m interested in figuring what’s possible. I was started on this quest to find what cells could be brought back from lv because batteryhookup said I could do it with the p42 they gave me that were low
Their statement was not related to a specific cell and that any ion could be brought back from 1v with a trickle.
Huh , any chance you could ask them where they got this info as it seems kinda suspicious. They have a pretty significant conflict of interest but that doesn’t mean they don’t have a real justification for their stance. They seem like pretty solid dudes
Considering ion cells of all types of chemistry (power or energy) have stated possible to recover from 1v and its only some manufacturers that aren’t saying this, I think it’s not a chemical composition issue and it’s a legal issue. Then again im assuming similar chemistries across manufacturers.
It could also have something to do with the actual material thickness of the jelly roll and how it reacts under a certain voltage, im sure some constructions are likely more robust than others.
I do believe that some chemistries are more prone to damage and degradation than others - seems like just looking at the different aging characteristics and proposed cycle life would indicate something different is going on inside.
When i get some more time this week ill start trying to outline a testing procedure for scrutinizing. And see about making a table of cell links
Sounds like you’re looking at the one page spec sheet, labeled “Datasheet” but just meant for public consumption. The full datasheet for engineers/pack assemblers is 14 pages long.
It’s important to note that the procedure for charging a cell that has been over-discharged down to as low as 1V for some, 1.9V-2.0V for others, says nothing about “recovery” and no one should ever think the cell has recovered to the way it was before.
Lots of cell/pack vendors say you can recharge (“recover”) over-discharged cells. Some even say it’s “safe”. But none of those companies have tested the safety or cycle life of those cells…it too huge a project. So they play the odds.
The cell was damaged when overdischarged…period. For every cell, every time. There’s not a single academic or industry research paper that will say otherwise. If there was no damage then there wouldn’t be a 2.5V limit, every manufacturer would take advantage of the chance to spec their cells with a slightly higher capacity by going down to 2V or 1V (whatever their safety limit was).
What happens next is determined by the degree of over-discharge (voltage), the amount of time it spent there, the temp while it was there, and the particular cell.
A cell that has been carefully recharged (per the procedure listed in some datasheets) has been recharged…that’s it. There was no recovery other than its voltage. It can seem fine (it didn’t explode) and be used but the risk is higher.
If one reads the datasheet for the cells with these charging procedures you’ll see the procedure listed in the pack design guidelines…that’s critical!
The manufacturer assumes that any cell that was over-discharged and recharged will be part of a pack that is being monitored by a full-featured and properly configured BMS. This is because the cell is not “back to normal” and needs to be carefully monitored for the life of the pack.
The manufacturer also assumes that any cell brought back from an over-discharged condition will be tested for IR, capacity, and self-discharge rate changes that can help determine if the cell if still usable.
The datasheet is written by engineers for engineers and these things are standard procedures.
Whats the point of investing all the time and effort to risk “recovering” a cell discharged to 1V? What, you invest all that time and effort to isolate a cell group, trickle charge it while monitoring it, repeat again for every other p group in the pack because chances are they’re all fucked, and for what? To end up with a pack with questionable wear and stability upon the next time you intend to use it as anything BUT a fire starter? Unless you consider your time to be worth jack shit and just really want to make a claim on your insurance for fire damage, just replace the pack.
It really doesn’t take that long to check on a pack regularly and see what is up with it, or to bring a pack back up to voltage. I’ve overdischarged a pack, though not to 1 V per cell, brought it back up to voltage, let it sit on the charger for a while to balance, and checked on it more than I otherwise would have, and there has been no noticeable difference from before the overdischarge. That was from forgetting a loop key for a bit, so they weren’t sitting low for very long either.
Packs are expensive, and seeing people just immediately throw out packs just because they’re slightly under 2.5 V or whatever the datasheet minimum is seems absurd to me, but I’m not going to try to change people’s minds on it or recommend they try to use it. Really, if we were using BMSes properly, it shouldn’t be a problem at all unless the BMS couldn’t keep up with rebalancing it every cycle. Bypassing the BMS for discharge does create potential issues, though.
If a group has considerable self-discharge, I’m not going to mess with it, and I’ll consider it trash. And if a group is getting way out of balance, that is an issue, but otherwise, keeping an eye on it and running it has worked fine for things most people on this forum would probably call for thowing away for me.
Lol, so you’re gonna suggest taking an entire 20S pack thats been excessively discharged down to 1V and just charging the entire lot? What happens if the group voltages drift more than the BMS can manage in the process and you take an already potentially damaged P group from 1V to 4.5V because you didn’t individually monitor the groups during the charging process?
This is like citing GM showing a 10k interval oil change on 0W20 as a good idea. Its asinine and the benefit is not worth the risk, as much as the OE may cite it as “possible”.
If you’re gonna do it right, its a lot of effort to do it safely, and the benefits are still questionable as you have no way of knowing how the cells have been affected internally without heavy monitoring. And if you do it the quick and dirty way… that one should be self explanatory. No manufacturer in their right mind is going to QA for a 1V discharge spec as perfectly safe, and thats for a good reason. Molicel cites it as possible, not a recommended practice. You saying “well they dont explicitly call it a bad idea” doesn’t make it a good one either.
, any chance you could ask them where they got this info as it seems kinda suspicious. They have a pretty significant conflict of interest but that doesn’t mean they don’t have a real justification for their stance. They seem like pretty solid dudes