Self-Discharge UPDATE On 30Q 141 Cells

[eMark]

From 1/2/21 thru 2/14/21 (44 days) 20 out of the 30 “141” cells had self-discharge no greater than 0.005V. Then reassembled again in the 30Q 10S3P experimental Vruzend pack--now being tested for p-group self-discharge ...

141--141--141--141--141.......141--141--141--141--141
.K.....K.....K.....K....141.........K.....K.....K.....K.....K
141--141--141--141--141.......141--141--141--141--141

From 7/22/21 thru 7/28/21 only three of the ten p-groups had self-discharge less than 0.005V after 7 days; while four p-groups had self-discharge no greater than 0.01V after 7 days. The other three p-groups (blue type) had self-discharge that ranged from 0.04V to 0.11V after just 7 days ...

4.03--4.03--4.03--4.03--4.03……...4.03--4.03--4.03--4.03--4.03
variance among 10 p-group voltages after seven days from 7/22 thru 7/28
4.03..4.02..4.02..3.99..4.03……...4.02--4.00--3.92--4.02--4.03

The “141” cell in the middle "K" row diagram had the least amount of self-discharge (Sub Pack 1 2S-2P 0.02V) of the ten cells with self-discharge from 1/2/21 to 1/15/21 (see ten high-lighted cells in the previous post at bottom of page 3). This "141" cell was used to replace the new/unused defective “KH1T” cell suffering from significant self-discharge possibly due to the can wall puncture as received and visible only after wrap removed to check can codes ...

 

[Darren2018]

From 1/2/21 thru 2/14/21 (44 days) 20 out of the 30 “141” cells had self-discharge no greater than 0.005V. Then reassembled again in the 30Q 10S3P experimental Vruzend pack--now being tested for p-group self-discharge ...

141--141--141--141--141.......141--141--141--141--141
.K.....K.....K.....K....141.........K.....K.....K.....K.....K
141--141--141--141--141.......141--141--141--141--141

From 7/22/21 thru 7/28/21 only three of the ten p-groups had self-discharge less than 0.005V after 7 days; while four p-groups had self-discharge no greater than 0.01V after 7 days. The other three p-groups (blue type) had self-discharge that ranged from 0.04V to 0.11V after just 7 days ...

4.03--4.03--4.03--4.03--4.03……...4.03--4.03--4.03--4.03--4.03
variance among 10 p-group voltages after seven days from 7/22 thru 7/28
4.03..4.02..4.02..3.99..4.03……...4.02--4.00--3.92--4.02--4.03

The “141” cell in the middle "K" row diagram had the least amount of self-discharge (Sub Pack 1 2S-2P 0.02V) of the ten cells with self-discharge from 1/2/21 to 1/15/21 (see ten high-lighted cells in the previous post at bottom of page 3). This "141" cell was used to replace the new/unused defective “KH1T” cell suffering from significant self-discharge possibly due to the can wall puncture as received and visible only after wrap removed to check can codes ...

That is unlikely to be the reason as I recently discovered those cells will be at 0V.

I only use Samsung cells when absolutely necessary and even though I have only used ~500 30Q I have seen this problem myself. It's also with mentioning that I have seen inconsistent self discharge on VTC6 and HG2 but nothing like 30Q. I don't really use enough of these 20-30A 18650 cells to say with absolute certainty but from the 1000 or so 30Q, VTC6 and HG2 I have used I would say that it is something to do with these cells in general. It is either that or I have been really unlucky with just those because I have used literally 1000's and 1000's of cells and have never seen this issue new out of the box, it has only been 30Q, VTC6 and HG2 with 30Q being the absolute worse.

Are you using a meter with a good amount of accuracy and resolution? I need to use mine on it's 500000 count mode because the last digit and therefore the following digit is useless. When I test for self discharge I balance all the cells against one another first, I don't use a balance charger. It makes it easier to get the data am looking for.

 

[eMark]

That is unlikely to be the reason as I recently discovered those cells will be at 0V.

Assume you're referring to at least three of those nine "141" cells in blue ...

141--141--141--141--141.......141--141--141--141--141
.K.....K.....K.....K....141.........K.....K.....K.....K.....K
141--141--141--141--141.......141--141--141--141--141

4.03--4.03--4.03--4.03--4.03……...4.03--4.03--4.03--4.03--4.03
variance among 10 p-group voltages after seven days from 7/22 thru 7/28
4.03..4.02..4.02..3.99..4.03……...4.02--4.00--3.92--4.02--4.03

The above voltages were measured to the nearest 0.001V, then rounded to the nearest 0.01V. I use two different digital voltage readouts for comparison. My DMM reads to 0.01V and other digital meter reads to 0.00001V.

Does ... "as I recently discovered those cells will be at 0V" also apply (IYO) to these ten highlighted 30Q cells (if left to fend for themselves) having suffered from self-discharge over 14 days from 1/2/21 to 1/15/21 after 150 c/d cycles. The other twenty cells were still at their resting voltage taken 14 days earlier on 1/2/21 (having disassembled the 10S3P pack in 12/20) ...

My experimenting and that of another ES member suggests it's possible to [partially] regenerate 30Q cells suffering from significant self-discharge so as to at least slow the degree of self-discharge.

Have you done any such experimenting or know of any such efforts that may offer some encouragement as to reversing or at least significantly slowing the extent of self-discharge among high energy cells. Particularly 30Q which seems more prone to self-discharge than other name brand energy dense cells (15A-20A continuous discharge rating) ?

Also could you offer some further insight into ... "I recently discovered those cells will be at 0V."

 

[Darren2018]

I wasn't really being specific with anything I was saying other than the cell with a hole in it is unlikely to have self discharge as it will probably just be at 0V. I also noticed that most of your records were at ~3.7V which makes any potential results from the experiment take much longer to acquire. What I was trying to explain about the multimeter was that they have a margin of error and this can potentially destroy your results. I use mine in its 500000 count mode to try and get as much accuracy as possible at .000 rather than .00000 because those extra digits are not very good for anything else other than stabilizing the digits to the left or perhaps as an indicator for increasing or decreasing voltage. It's just something that I thought I would mention because I wasn't sure if you were aware that multimeters do this. Most people think that the meter has an accuracy spec and that's it but both my Brymen 867s which is probably considered as a reasonably ok meter and my cheapo Uni-T UT89XD have an odd tendency to infrequently be off by more counts than they would typically and then very slowly reach the correct voltage. If you knew all of these quirks sorry but I didn't and I only learned these things when I got strange results doing the same testing as you.

You asked if I knew anything about 30Q regeneration and I don't. I didn't know that it was possible. Imo Samsung generally do not make quite as nice cells as LG, Murata and Panasonic/Sanyo and I just assumed that this was just another manufacturing issue or QC problem that they were having but I have also seen some self discharge with VTC6 and HG2.

 

[eMark]

I also noticed that most of your records were at ~3.7V which makes any potential results from the experiment take much longer to acquire.

Time ("taking longer") is on my side being retired from previous QC problem solving work experience with engineers at both Medtronic and Sci-Med. The Senior Production Manager at Sci-Med once slipped me a small hand-written note ... "We need more positive boat-rockers like you."

All thirty 30Q "141" p-group cell voltages were equalized (ABAP) at 3.75V (rounded to the nearest 0.01V) on 1/1/21. The next day removed the bus bars for testing individual cell voltages. All thirty individual cells measured either 3.75V or 3.74V (rounded to nearest 0.01V) on 1/2/21. After 14 days (1/15/21) the same 5 cells were still at 3.75V, and the same 15 cells at 3.74V. The other ten cells with self-discharge ranged from 3.73V to 3.43V (rounded to nearest 0.01V) as shown in the highlighted diagram. After 44 days these same 5 cells were still at 3.75V and the same 15 cells were still at 3.74V. The other ten cells continued to self-discharge at varying degrees.

The purpose of my experimenting was not to determine how "good" were the good cells "over two months" (as you suggested), but rather how "bad" were the not-so-good cells suffering from self-discharge ranging from the lessor of 3.73V to 3.43V (1/2/21--1/15/21). Two weeks was enuf to determine which cells suffered from unacceptable self-discharge (1/2/21 to 1/15/21) as 14 days was sufficient for recording degree of 30Q self-discharge (3.73V to 3.43V). The 3.73V cell with the least amount of discharge was substituted for the "K" cell with the can puncture when reassembling my 10S3P experimental pack.
___________________________

When you test your new 30Q cells (or other energy dense cells) do you first test their resting voltage upon receivng (e.g. 3.40_V) to the nearest mV to first determine mV variance? Do you then proceed to charge to say 4.100V (rounded to nearest mV) ... rest for how many hours and then test again to see what cells have a self-discharge of at least 7mV or greater to earmark as "bad" ?

Any guessimate of the number of 30Q cells out of 100 are "bad" with a self-discharge greater than 7mV being your benchmark of a "bad" cell (according to your PMs the past few days). Appreciate you sharing your testing criteria :thumb:

 

[eMark]

opps ... previous double post deleted

I also noticed that most of your records were at ~3.7V which makes any potential results from the experiment take much longer to acquire.

The possibility that some of the fifty new 30Q "141" cells received in 12/20 were already suffering from unacceptable self-discharge (+7mV and greater) had never been considered a possibility . Should have known better with 30Q's past history of unacceptable self-discharge ... presumably being a lack of manufacturing QC.

The idea that the fifty 30Q "141" cells i received would have any self-discharge from the time of manufacture plant packaging, to being unpackaged by me was never a consideration. All 50 cells were at the same voltage (3.40V) when checked the day of arrival on my doorstep . The idea that some of these new "141" cells had already self-discharged by +7mV or greater had never been mentoned before until your testing criteria of resolution accuracy.

If it's possible to determine which new 30Q cells (136, then 141, and now K) exhibit self-discharge to the point of being "bad" then self-discharge with a new spot-welded DIY pack should be so minimal (hopefully) that self-discharge is no longer a problem with a new 30Q battery pack (e.g. 14S7P) or at least no more of a problem than with a 25R pack or Panasonic/Sanyo pack.

Soooo ... do i ever wish i had tested my fifty 30Q "141" new cells upon arrival using your testing criteria and only used cells having less than 7mV of self-discharge. With fifty new cells it's possible there could have been at least 30 new cells with less than 5mV of self-discharge instead of 0.008V if the range of self-discharge was greater than from say 3.404V to 3.396V (3.40V to the nearest humdredth volt).

If i had incorporated your testing criteria it's possible that instead of 10 out of 30 "141" cells with varying self-discharge over only two weeks there would have only been one or two or none. And instead of 20 good "141" cells over 44 days there may have been as many as 28 good cells and the not-so-good cells (say only 2) may have had no more than 0.03V of self-discharge over 14 days instead of one cell with 0.31V of self-discharge (3.74V to 3.43V).

Bottomline: You've convinced me about the need to test new energy dense cells to the nearest mV so as to remove "bad" 30Q cells (+7mV self-discharge variance from "good" cells) before DIY pack make-ready and spot-welding.

 

[eMark]

This is a followup to the degree of self-discharge resolution accuracy of 7mV that Darren2018 uses to separate energy dense bad cells (+7mV) from energy dense good cells (less than 7mV) ... like Samsung 30Q cells. This degree of resolution accuracy (±7mV) doesn't come cheap.

Even moreso the resolution accuracy requied to reliably distinguish a self-discharge difference of only a little more than 3mV from a little less than 3mV that separates a good energy dense cell from a bad energy dense cell. Apparently possible by Samsung QC departments and other Li-ion manufactures. Test equipment with that degree of resolution accuracy is expensive, but affordable and available to Samsung and other cell manufactures. It's just that they decide how much self-discharge is permissable to pass on to the consumer :wink:

In the example ... the Delta-OCV due to self-discharge was 3 mV. Bad cells would measure above 3 mV and good cells would be 3 mV or less. This means that the measurement accuracy requirement isn’t only to accurately measure 3 mV, but to be able to accurately measure the difference between a little more than 3 mV and a little less than 3 mV. ... https://www.electronicdesign.com/technologies/test-measurement/article/21808344/keysight-technologies-measure-selfdischarge-using-ocv-on-lithiumion-cells

In order to achieve this degree of resolution accuracy an instrument the likes of a Keysight Technologies BT2152B Self-Discharge Analyzer starting at $32,538 is required ...

One becomes aware that if Samsung and other manufactures of energy dense cells (30Q, VTC6, HG2) used this degree of accuracy (not that they can't) they would reject more 30Q cells because of self-discharge than apparently was the QC benchmark with 30Q 136, 141 and possibly their latest K cell.

This is an interesting article providing insight into the degree of self-discharge accuracy that is possible. A degree of self-discharge accuracy that manufactures could incorporate into their QC test (zero tolerance for defects) ... https://www.electronicdesign.com/technologies/test-measurement/article/21808344/keysight-technologies-measure-selfdischarge-using-ocv-on-lithiumion-cells

Attached is photo of one technique i initially used (no longer) on my experimental 10s3p for bottom balancing p-groups within 4mV of each other before bulk charging. YES, it can be done even while connected as a 10s3p battery (see 12awg silicone blue connection). You could also connect two LVC cell monitors. If you had two 8s LVC cell monitors you could monitor the p-groups of a 16s battery using two 8s leads

The middle XT60 connection joiining each 5s3p Sub-Pack next connects to the Controller when in the Cargo Container. No BMS Allowed !

 

[Darren2018]

I was just trying to explain the variables which are important that you might have missed. Starting with an even voltage is important for me. I wasn't sure if you were aware that multimeters can drift by many many counts on their last digit. The 7mV that I use is just a loose figure that generally fits my schedule and methods. It's the method that is important.

I don't know much about multimeters but I think you could probably get ±7mV on something like this https://www.aliexpress.com/item/330....store_pc_groupList.8148356.35.e8af15bckwqPaq.
This was recommended to me by someone else.

Someone posted a Keysight document which explained how they measure self discharge. You could probably build it with accurate references, high precision resistors and components.

 

[eMark]

Someone posted a Keysight document which explained how they measure self discharge. You could probably build it with accurate references, high precision resistors and components.

Your benchmark of 7mV for separating good cells from bad before building your custom packs is only good practive on your part :thumb: Will disassemble and test individual cells of my experimental 10S3P 30Q pack (21- "141" cells and 9- "KH1T" cells) this winter. After 250 c/d cycles don't really need mV accuracy when tracking the delta OCV self-discharge over 5 days or 44 days (1/1/22 - 2/14/22).

After 250 c/d/cycles i'll be satisfied if twenty of the thirty 10S3P 30Q cells have self-discharge no more than 0.01V after 44 days. That's most likely too little self-discharge (only 0.01V) to expect this go around from 1/1/22 thru 2/14/22 after 100 more cycles.

Expensive exacting equipment like in that Keysight article is hopefully used by Samsung QC for their benchmark (3mV) when separating the good cells from the bad before shipping 30Qs to suppliers.

I don't know much about multimeters but I think you could probably get ±7mV on something like this https://www.aliexpress.com/item/33004463675.html?spm=a2g0o.store_pc_groupList.8148356.35.e8af15bckwqPaq .

Wish i had known about that DMM as i surely would've purchased it for testing the 30Q "141" cells before building the 10S3P 30Q experimental pack. Will be ordering one so it's here in time for my winter tracking of delta OCV self-discharge of 30 individual cells.

For this winter's test will also be using a stand alone hand held little Chinese USB DMM which will provide mV comparison readings for tracking self-discharge along with that aliexpress DMM. After 250 c/d cycles only need to know approximate mV readings of individual cells (delta OCV) after 5 days, 10 days, 15 days and 45 days for tracking unacceptable self-discharge out of the thirty 30Q cells. Probably wouldn't even need to report to nearest 0.01V, but to nearest mV is more impressive :wink:

Twenty of the "141" 30Q cells had no more than 0.01_V after 44 days (1/2/21 - 2/14/21). Will be interesting to see how they do this time around (1/1/22 - 2/14/22), as well as the other ten cells now that i'm able to take several readings of each cell to nearest mV. More than sufficient for measuring unacceptable delta OCV self-discharge over 5, 10, 15, 45 days after 250 c/d cycles since mid-March of 2020 (150 c/d cycles in 2020 and 100 c/d cycles in 2021. The research goal going forward is another 125 c/d cycles in 2022 and another 125 in 2023.

 

[eMark]

Forgot to mention there's no indicaton that p-group discharge voltages are more than 0.014V (0.01V) variance from each other over the past 97 cycles this year. So have decided to complete 125 c/d cycles before November before disassembling to test individual cells for unacceptable self-discharge over 5 days, 10 days, 15 days, 30 days, and 45 days probably beginning in December instead of waiting until January 1, 2022.

Normal charge since beginning in 2020 has been no greater than 41.0 volts 90% of time, several times 40.5V and no more than ten times at 42.0V and soon discharged. Average discharge is around 35.0 volts ±1.00 volts. Have only discharged it to Controller Cutoff of 32 volts five times since first c/d in 2020. Average amp draw has been between 4 to 8 amps with Controller 19 amp draw infrequently and for no more than 10-30 seconds..

So you ask why with such an average meager amp draw did you choose 30Q cells? Good guestion ... well for one thing it's only 3P which decided to do on purpose instead of 5P to accent any self-discharge tendency. Also my rationale was that with such TLC there would be less of a problem with unacceptable self-discharge. But apparently it's a QC problem so TLC doesn't help all that much.

Hopefully, my 10S3P experimental 30Q pack would be good for at least 500 cycles. The thinking being that with 30Q's low IR rating the pack would serve me well. Then to my dismay found 9 cells out of 30 with what i considered unacceptable self-discharge when testing individual cells last winter. Replaced with 9 new "KH1T" cells in late February of 2021.

Will be VERY INTERESTING to test these 9 "KH1T" cells and 21 "141" cells come Nov/Dec.

 

[eMark]

This is an UPDATE to how many of the thirty 30Q "141" cells are an **acceptable** Delta 'Open Circuit Voltage' (OCV) self-discharge. This is with respect to my experimental 10S3P Vruzend V2.1 DIY pack after the first 125 charge/discharge cycles in 2020. The imprressive Delta-OCV minimal self-discharge was no greater than -0.005V (from 3.750V to 3.745V) after dry 68 F degree storage for 45 days. The first 125 charge/discharge cycles during 2020 within 1-3 days of each other (usually just 1-2 days) between the next charge/discharge cycle.

Twenty of the 30Q '141' cells had **acceptable** Delta-OCV self-discharge of only -0.005V after 45 days. Nine of the thirty cells (including two at 3.70V after 45 days) were replaced with new 30Q6 "KH1T" cells. Another "141" cell at 3.73V after 45 days was used again for the next 125 cycles in 2021. This experimental Vruzend V2.1 10S3P 30Q "141" pack was only charged to 41.0V only after the ten p-groups were first bottom balanced within 0.01V of each other before bulk charging. The average discharge cycle voltage (after resting bounce back voltage) was 3.50V-3.60V.

After another 125 cycles in 2021 (250 total) were completed on 11.30.21. Six of the previously **acceptable** 30Q "141" cells were found to be suffering from high self-discharge after just 5 days (after 24 hr stablized rest at 3.980V) ranging from self-discharge of -0.010V to as great as -0.175V(cell w/severe cell can burn thru). The other with less severe can burn thru (but still severe) had self-discharge of -0.049V(see can burn thru photo) again after just 5 days. None of the 10 p-groups c/d cycles on 11.30.21 had an **acceptable** Delta-OVC self-discharge. The better p-group still had a self-discharge of -0.010V after 5 days and the worst of the ten p-groups (with severe cell can burn thru) had a p-group self-discharge of -0.027V.

Six of the remaining twenty-one good 2020 "141" cells suffered high self-discharge in 2021 having endured 125 more c/d cycles even though this 10S3P pack was only charged to 41.0V with average discharge amp drain between 4 to 10amp (avg close to 6amps). These six '141' cells will be replaced with slightly used 30Q "141" cells or new 30Q6T cells(IF within my budget). A high energy dense cell like 30Q will invariably suffer from high self-discharge beginning somewhere beginning after 125 cycles depending on the pack's TLC. With Raw Performance the cells in a 30Q pack will most likely suffer from high self discharge before 125 c/d cycles depending on the charge voltage, charge amperage, and discharge amperage.

Summarizing: Arrived at what i considered an **acceptable** Delta-OCV self-discharge of only -0.005V after 125 charge/discharge cycles after 45 days (dry storage at 65 F degrees). This finite parameter was based in part on contributing info by Darren2018 and the following professional Electronic Design article ... https://www.electronicdesign.com/technologies/test-measurement/article/21808344/keysight-technologies-measure-selfdischarge-using-ocv-on-lithiumion-cells

As far the nine 30Q6 "KH1T" cells (after 125 cycles in 2021) am tracking the cell storage voltages beginning on 12.1.21 at 3.600V, and the self-discharge after 5 days, 15 days and 30 days. Will report pack on degree of self-discharge below storage voltage of 3.60V on 1.2.22.

Any **acceptable** Delta-OCV self-discharge of these nine "6 KH1T" (with 125 c/d cycles in 2021) will undoubtedly be affected by the other "141" cells (with 250 c/d cycles) in each of the ten p-groups (2-141 cells w/250 c/d cycles) to only 1-KH1T cell with 125 c/d cycles). Presumably more adversely the two p-groups with "141" cells with severe cell can burn thru (see photo).

The Vruzend V2.1 design is reasonably priced with ease of assembly and disassembly for experimental testing of individual 30Q cell voltages after 125 cycles and again after 250 cycles. I'll probably carry a small fire extinquisher in the cargo container with this 10S3P 30Q battery next year. I'm as surprised as you guys that those two 30Q "141" cells with severe cell can burn thru didn't explode. Not only destroying the 10S3P pack as well as melting the LT cargo container (see photo of adult electric Liberty Trike w/mods)

 

[izeman]

@eMark: As I'm also suffering from a 2016' 30Q (136) pack (15s10p = 2 packs 15s5p) self discharging battery, which I'm trying to "repair", I'd like to ask some questions:

Tbh your last post has too much info for me to follow

I examined my pack, looking for p-packs that suffered higher discharged then the others, and after removing the nickel strip of the 5p packs it was easy to tell which cell was the culprit. I replaced that cell with a LG HG2 and was hoping that the problem was solved.

Now, just some month later other packs are showing self discharge.

So my question:

Have those cells that you have seen as "good" over the years shown sign of self discharge after some time? Or have they ALL remained good? I'm asking because I would ONCE AGAIN open my pack and "repair" it, but only if I can be sure that it will remain healthy for a while and not show some more "sleepers" after a month or so.

 

[izeman]

And still after reading all(?) threads about the self discharging 30Q cells, I'm pretty unsure how "desulfating" of the cells is done?! Discharge until they stay at 2.50V and then charge to 4.20V and see if something changed?
I will now charge some of the removed self-dischargers to 4.20V and let them sit and see how much they discharge over some days.
Then I will deep discharge them to 2.50V and recharge to 4.20V and check self-discharge again.
Is that how it's supposed to work? Would love to NOT have to take this pack apart again if this procedure could help a little with these f***** cellls. :lol:

 

[eMark]

And still after reading all(?) threads about the self discharging 30Q cells, I'm pretty unsure how "desulfating" of the cells is done?! Discharge until they stay at 2.50V and then charge to 4.20V and see if something changed?
I will now charge some of the removed self-dischargers to 4.20V and let them sit and see how much they discharge over some days.
Then I will deep discharge them to 2.50V and recharge to 4.20V and check self-discharge again.
Is that how it's supposed to work? Would love to NOT have to take this pack apart again if this procedure could help a little with these f***** cellls.

Will reply to your 2nd post first and then your previous post.

goatman changed it from "desulfating" to "regeneration" upon the suggestion of another ES member. My experimenting with discharging a cell suffering from high self-discharge to discharging a problematic cell to as low as 2.50V and recharging to 4.10V showed that there was still plenty of capacity (3294mAh). Further experimenting verified that high self-discharge is "leaking" capacity like a water bottle with a small hole. Thus a cell with unacceptable self-discharge can so-to-speak be refilled to its potential capacity (depending on its age ... number of charge/discharge cycles).

Whether a 30Q pack is used more for Raw Performance or Casual Cruising its just a matter of time before unacceptable self-discharge becomes more noticeable in at least a couple of the p-groups. The more c/d cycles the more noticeable will become a higher self-discharge in some 30Q cells of inferior quality to other 30Q cells. Thus as i said from the beginning it's a QC problem. It's a QC challenge with any high energy dense cell, but apparently more so with 30Q cells whether: 136, 138 or 141 cells. Time will tell if this QC challenge has been somewhat mitigated with the recent "new improved" Samsung 30Q6 "150" cells Made In China.

As far as "regenerating" 30Q cells suffering from high self-discharge (136, 138, 141) it's only possible short-term and even then the self-discharge IMO is unacceptable (-0.010V) as soon as a few days rest. The best way to counter a 30Q cell from "leaking" capacity (unacceptable self-discharge) is to recharge your pack and use it again within 1-2 days from its latest discharge. The problem whether a 3p, 5p or 8p pack the suspect p-group will show 4.1V (or 4.2V) after charge, but that doesn't mean a cell is at "leakng" weak cell is at 4.1V (or 4.2V) as you've discovered. And as you've discovered a "leaking" cell will lower the voltage of its p-group if the pack is left to rest for a few days. The degree of voltage loss more noticeable with 3p grouping and less noticeable with a 8p grouping.

 

[izeman]

Thanks for the long reply. I was expecting some answer like yours. So self discharge is not healable, and may/will sooner or later happen to all the cells as they are all from the same batch. Keeping the pack fully charged all the time is a "work around" at best, but no real solution.
If you leave it uncharged for some weeks the pack will be unbalanced by like 0.2V, and my poor little BMS with some mA balance current will never ever be able to balance that again.
So now I got 150 cells, most of them are still good, too good to be dumped, and some are junk.
And a new pack is like 500+ to build. Damn.

 

[eMark]

So my question:

Have those cells that you have seen as "good" over the years shown sign of self discharge after some time? Or have they ALL remained good? I'm asking because I would ONCE AGAIN open my pack and "repair" it, but only if I can be sure that it will remain healthy for a while and not show some more "sleepers" after a month or so.

After 125 cycles in 2020 on my experimental Vruzend V2.1 10S3P (using fresh 30Q 141 cells) was pleasantly surprised that 20 out of the 30 "141" 30Q cells had remarkably LOW self-discharge (less than -0.010V) after 45 days (67-70 F dry storage).

The Delta-OCV discharge after 45 days (as close as i could estimate) was as low as -0.005V to -0.008V. I reused one cell that had only leaked 0.020V (3.75V to 3.73V) after 45 days. Two other cells were still at 3.70V after 45 days, but chose not to reuse them. Having purchased 10 of the newer 30Q6 (KH1T) cells from IMR in 11/20, i decided to replace 9 of the "141" cells i considered suffering from **unacceptable** self-discharge replacing them with 9 of the supposedly latest new and "improved" 30Q6 (KH1T) cells.

After 125 more c/d cycles (250 total by 11/30/21 six of the remarkably performing "141" cells in 2020 were now suffering from **unacceptable** self-discharge when tested on 11/30/21. As far as 9 of the new 30Q6 (KH1T) cells none have suffered from **unacceptable** self-discharge after 125 cycles since 12/2.

All 250 discharge cycles over the past 2 years were what i'd consider "Casual Cruising" NOT "Raw Performance" use. Also the ten p-groups in the Vruzend V2.1 10S3P experimental pack were first bottom balanced within 0.01V of each other before bulk charging at 1.5A rate to 4.10V (pack voltage of 41.0V to 41.1V)

Bottomline: Sometime after 125 c/d cycles 20 "141" cells with previous **acceptable** self-discharge now suffered from varying degrees of **unacceptable** self-discharge after 250 c/d cycles. The dangerous cell can burn thru occuring somewhere between 125-250 mild-mannered 30Q "141" c/d cycles ... https://endless-sphere.com/forums/download/file.php?id=307395 ... is a concern Would you call it quits for my experimental Vruzend V2.1 10S3P 30Q pack after 250 c/d cycles even with "Casual Crusing" use going forward in 2022 ?

 

[izeman]

I had less than 50 cycles for sure. The pack was built in Feb 2018 though, and showed first signs of self discharge exactly 2 years after built.

 

[eMark]

I had less than 50 cycles for sure. The pack was built in Feb 2018 though, and showed first signs of self discharge exactly 2 years after built.

Showing signs of **unacceptable** cell self-discharge "exactly 2 years after built" is probably more typical than atypical for 30Q cells whether 136, 138 or 141 used by DIY builders. **unacceptable** Delta-OCV self-discharge happening with "less than 50 cycles" suggests you may have been using your pack(s) more for "Raw Performance" than "Casual Cruising and bulk charging to 4.20V and discharging close to or at Controller Cut-off (3.20V).

OF COURSE the number of **acceptable** c/d cycles depends to some extent on the builder's knowledge / experience / tools / craftsmanship, etc. It's not uncommon to put the blame on the BMS which with some el-cheapo BMS' is probably the culprit.

Whether or not your 30Q "136" cells were more prone to **unacceptable** self-discharge than the more recent 30Q "141" cells will never be known, but you'd hope the newer "141" cells would be good for at least 125 cycles whether "Raw Performance" use or "Casual Cruising" use before **unacceptable** Delta-OCV becomes so obvious. Guess if it's rate of self-discharge is **unacceptable** it no longer is referred to as "Delta-OCV" ... which i understand to be the rate of "acceptable" self-discharge.

Bottomline: Who's going to pay $8.99 for a 30Q "141" cell ... https://www.18650batterystore.com/collections/18650-batteries/products/samsung-30q ... or $5.51 per cell (plus shipping cost) via Voltaplex for what is supposedly a new "improved" 30Q6 "150" T cell (Made In China) or from EVVA TECHNOLOGY CO., LIMITED ... https://gm1.ggpht.com/HO6-Wj23RQGvBZNo1zSyrFeTKxZSByN30rRtnL5vF6v1zvHnUkiliSHB9-eQ33kuGBcBhaNNAE3dvcwaEMFdwd2jsSDRjcdZ70KjZbVfwDo4U7MykNarYsDGRBL2Z19fa1d0fQVkyyd24cBADDsXqEr0Fep-w1aHB7l8LUc_2wXOh8rivEpU1A6fzARBpvmFj8KoIwJ3Sucq97z9AlQxXZf5qUKLLSSRNUE3ntVIAhejsm9w_sy2xG3jB_KBhf_Aa_QUpplVKCFSZnDewXSVpORNUzE9YcKSzVpn6xto1pqySp1kIBl2g9Jkbkobsk1SJWk16vxWaHPpw70he1wGWAD4434SL0sNatZ-WMGP2jrtdywWuuEqGupUwqJEyu-teqFkpdDdCwvi0Pw1zP2OkxsUsa60Q2OTB0ygUmKzjOrQIbvLzTDgGIIqsRDLnNgsfmTlL7-aN-uUJ3Acfg7K8qBu68bbMsi-Lr9P7Fq339gKz4s7KB8jWlY-TBWqS18TT1jTk8IwwiIF2jJAKqPKiBmTsOGPW4kaUp9YtrPBCYhusNAnFHdB1nIaBrai4GqdlegfztufJ_xiQ3375vBnlH9MgNKQSKDPN8mfIm8zXKAsfZO9QHx5tfEUHJFipLWR6X6e8dZxuoI1j80ORtBavkBq4paTi6L-dKJSzlOERryYY_Tkc_KAmpWrN-wEBoNdY1HRv5zz-g4kO5eczvfvtVp4VPNpZZrEwpdbAGBi8w=s0-l75-ft-l75-ft . Apparently Battery Bro is a US distributor for Voltaplex batteries.

Maybe roll-the-dice and buy an 18650 25amp (Maximum Continuous Discharge) rated at 2,500mAh capacity for $2.45 via Aliexpress or whoever. You'd hope those "cheap" cells that are most likely Made In China are good for at least 50 c/d cycles (with TLC). :thumb:

 

[goatman]

izeman, why not just put an active balancer on the pack instead of a bms and call it good

mark
you build your packs without the wrappers on the cells
is it possible a piece of metal got into your pack and shorted out between the cans?

 

[izeman]

Yes maybe just install an active balancer. Discharge is pretty low, so no big deal at the moment. But high enough that the small balancer can not handle it.

But another questions that seems unanswered, or I didn't ask it that clear: Would you just replace the broken cells in the pack? Or would other good cells turn bad over time as well? It was perfectly fine over two years, and now like 10% of the cells are gone bad.

I have the two packs on my workbench now and measure voltage every day or two. I would need to replace some 6 or 7 cells. All other groups didn't loose a single mV over a week's time.

 

[eMark]

you build your packs without the wrappers on the cells
is it possible a piece of metal got into your pack and shorted out between the cans?

Just one Vruzend V2.1 kit (10S3P) **experimental** DIY build to date. Specifically for testing any significant 30Q self-discharge beyond what should be an **acceptable** Delta-OCV 30Q self-discharge over 30-45 days at end of 2020 and now doing again at end of 2021.

The Vruzend caps are so tight fitting is why i decided to remove the pink label wrap for closer inspecton of codes. Even so after 250 cycles three of the end caps (just positive end cap) has split open along its side (imagine how tight fitting with the pink label wrap). Don't have my UBS stick with me or would upload photo of end cap split failure ... even so it doesn't affect the secure contact with eight barrel bolts holding everything snug.

Your "piece of metal" isn't possible because the bare cans on all 18650 cells (as you know) are negative. The 10S pack is always protected by a couple towels covering it even when not in use. Only included this photo below to show how the pack fits in my Liberty Trike Cargo Container. Otherwise it is always covered by a couple towels ... https://endless-sphere.com/forums/download/file.php?id=286331

I've racked my brain trying to think of your scenario as a possibility, but again it's not possible being all 18650 bare cans are negative. So you could rub the sides of two bare 18650 cells together without any danger whatsoever because the cans are negative from bottom to top with a self-adhesive insulator ring at the top. Besides adding the adhesive insulator ring to the top of each bare can cell i also put the white insulator ring that came with the shrink wrapped cell in the positive end cap first before inserting the 30Q cell with its own adhesive insulator ring into the positive Vruzend V2.1 end cap.

It's baffling to me that those two cells (with burn thru metal can) didn't explode and start a chain reaction. Possibly because i treat that experimental pack with TLC (only rarely pulling 12-15amps and then for only 10-30 seconds). Even more baffling why those two cells suffered from can burn thru. GOT TO BE a QC manufacturing defect that didn't show up until somewhere between 125 and 250 c/d cycles.

Always bottom balance p-groups within 0.010V of eachother before bulk charging. Charging the 10S3P pack to 41.0V-41.1V at charge rate of 1.5A. Average discharge over the last 125 of 250 cycles between 6-10 amps (closer to 6) with average discharge about 35.0V (3.50V per p-group). Only three times out of the 125 cycles in 2021 did i discharge pack to 32.0V (Controller Cut-off).

 

[eMark]

So self discharge is not healable, and may/will sooner or later happen to all the cells as they are all from the same batch. Keeping the pack fully charged all the time is a "work around" at best, but no real solution.

My understanding although quite limited is that perhaps only every tenth 30Q cell (at best) is checked for "zero tolerance" for defect. Every manufacture has there own testing criteria for how they define "zero tolerance" and "defect".

Samsung's 30Q manufacturing plant(s) are under pressure to produce as many [good] cells as possible (business as usual) for passing on as many cells as possible from a manufacturing run to a potential customer. So there's the added pressure from supervisor/management to sometimes bend the rules and let more cells pass than an engineering "wirtten process" (good cells) would permit if strictly followed. If as a manger your salary depended on meeting and exceeding quoto you might look the other way. IMO corporate Samsung has looked the other way interested more in profits than consistent quality control considering the percentage of 30Q cells suffering from high self discharge with 136, 138 and 141 cells.

If you leave it uncharged for some weeks the pack will be unbalanced by like 0.2V, and my poor little BMS with some mA balance current will never ever be able to balance that again.
So now I got 150 cells, most of them are still good, too good to be dumped, and some are junk.

Such too is my dilemma .

I'm thinking of calling it quits with this **experimental** 30Q 10S3P pack. Possibly rebuild into a 10S4P pack using 25R cells. My nature is as problem solver and why i took on this 30Q self-discharge challenge which i still consider was worth my time because i've learned so much along the way. Going forward i probably use LG MJ1 if i could find 40 cells (at a reasonalbe price) that weren't five years old. For all i know the 25R cell inverntory at IMR may be at least three years old.

 

[goatman]

mark, the metal cans are negative til they are connected in series, draw it out, i could be wrong

izeman, trying taking the pack down to 2.5v then charge to 4.1v then back down to 2.5v and charge back to 4.1v and see what happens. i wouldnt try charging past 4.1v anymore.

 

[izeman]

izeman, trying taking the pack down to 2.5v then charge to 4.1v then back down to 2.5v and charge back to 4.1v and see what happens. i wouldnt try charging past 4.1v anymore.

I will do with the know bad cells I already removed from the pack the last time. They show different grades of self discharge. Some are down by almost 0.15V after 3 days. They now have been discharged to 2.8V.
Will monitor for some more days, then do a discharge to 2.5V and see if this makes any difference.

 

[eMark]

mark, the metal cans are negative til they are connected in series, draw it out, i could be wrong

goatman, the metal 18650 cans are always negative -- test it out. Doubt you'll ever hear of a cell having reverse polarity in an 18650 battery pack. All 30 of my 30Q cells have and always will have correct polarity as long as i'm in positive charge

The two cells with can burn thru were in two different 3P rows separated by a "good" 3P row. The self-discharge of the worse can burn thru was -0.175V (3.977V to 3.802V) after 5 days. The other with less can burn thru - 0.049V (3.984V to 3.935V) after 5 days.

The 10 p-groups were first bottom balanced and then bulk charged (as usual). This was after the 125th discharge cycle in 2021. The 10S3P pack was bulk charged at 1.5A (as usual) to 40.0V followed by removing all the bus bars and recording the voltages of all 30 cells. Six of the previously "good" "141" cells in 2020 now suffered from varying degree of **unacceptable** self-discharge after 5 days and had to be replaced with the pack now in storage intially at 36.50V until 1/1/22 and then all bus bars again removed and all 30 cells tested for amount of self-discharge.

The self-discharge of the nine 30Q6 KH1T cells after 125 c/d cycles in 2021 varied from -0.001V to 0.004V after 5 days. Time will tell by 1/2/22 if the self-discharge of these nine 30Q6 "KH1T" cells is **acceptable** (subjective?).