one cell group wont fully charge

[m3vuv]

when building the pack,first all cells were tested and marked for capacity and ir,then the data fed into reakkr program to match the groups,the ir of the cells were pretty much the same,they were cells brought for a power wall roject that got cancelled,just too clear things up.this is the site i used.https://www.repackr.com/#/pack-builder

 

[amberwolf]

Regarding actual mismatched-construction packs and their many problems, posted here on ES, if you're curious this is a bit of info (there is a lot more if you poke around).

I don't recall the details, but here's one recentish thread with pics about a pack built (or repaired) with mismatched cells:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=117112

Been a long time since I read this thread, but it's purpose was to help people build packs from scratch, and some sections about testing to use potentially mismatched cells
https://endless-sphere.com/forums/viewtopic.php?f=14&t=26383

I can't find the thread (from the last year or two) about a cheap battery from aliexpress I think, that arrived "DOA", and turned out to be at least a few different kinds of cylindrical (18650, I think) cells inside (visibly different, with obvious old spotwelds/etc where they'd been taken from other packs and reused in it. Some were essentially dead, none were "good".

I've seen pics on an aliexpress page linked by someone asking about the packs that site sold that showed "factory" images of packs made of visibly different cells (no way to know what they were, but if they were well-matched they shouldn't appear different either; all the shrinkwrap should be the same if they're from the same batch of cells that would have closest-matched properties, for instance).


Side note: Just before the OP clarified with the post above mine, I found the site the OP noted
https://www.repackr.com/
that is specifically designed to help use recycled cells of different capacities together in a "new" pack together.

Further side note: there's been quite a few people (experienced and not) over the years on ES that want to (and sometimes do, with varying results) parallel "new" cells to old ones (that are each of different origins, and characteristics), either to add capacity or to bolster an aging or failing pack.

Based on pack source/cost/age-when-failing, descriptions and problems reported, I expect there are many mismatched-build packs being troubleshot here on ES but most never post pics or pack details, so it's not possible to know for certain.

 

[eMark]

Side note: Just before the OP clarified with the post above mine, I found the site the OP noted
https://www.repackr.com/
that is specifically designed to help use recycled cells of different capacities together in a "new" pack together.

Believe m3vuv was as thorough as thorough can be in testing, sorting and deciding which cells to put into each of the 13 groups. So as to make all 13 10p-groups as similar as possible in capacity. IMO, a variance of 72mV between the 13 10p-groups (after charge) is to be expected with used cells having some variance in capacity; especially when relying only on a BMS for top balancing. Assume they were all name brand used cells (originally Grade A) with life yet to give.

Could get a lot of use out of his 13s10p DIY build with some occasional bottom balancing of p-groups before bulk charging as the battery ages. 10p should prolong the cycle life of his DIY build. m3vuv's DIY build with used cells is nothing new at ES. Expert builders have been doing the same for years. As long as the limitations are known and the application whether as low drain powerbank or ebike is reasonable

Even after bottom balancing and bulk charging isn't it possible there still could be a voltage variance as much as 30mV to 50mV ranging from 4.200V to 4.150V with only BMS top balancing? If there was NO bottom balancing before bulk charging couldn't the variance be even greater (e.g. 120mV) even with a reasonably good BMS?

Further side note: there's been quite a few people (experienced and not) over the years on ES that want to (and sometimes do, with varying results) parallel "new" cells to old ones (that are each of different origins, and characteristics), either to add capacity or to bolster an aging or failing pack.

Should note if your intention was to imply ... parallel "new" grade A cells with old(unused or slightly used Grade A cells) of similar capacity", but different brands. Just because they are "old" doesn't necessarily mean they are of no use for a DIY build ... depends on how old and the intended use.

Based on pack source/cost/age-when-failing, descriptions and problems reported, I expect there are many mismatched-build packs being troubleshot here on ES but most never post pics or pack details, so it's not possible to know for certain.

And probably more often are used as a reserve power bank with capacity draw at a minimum (e.g. 5amp drain). While others are junk, but nver-the-less was undoubtedly as worthwhile learning experience ... if only for what not to do.

 

[amberwolf]

h Should note if your intention was to imply ... parallel "new" grade A cells with old(unused or slightly used Grade A cells) of similar capacity", but different brands. Just because they are "old" doesn't necessarily mean they are of no use for a DIY build ... depends on how old and the intended use.

I was only providing the information that it has been done, in response to a statement by another poster that they hadn't seen some things that have been posted here over the years.

Judgements on the acts, processes, and results are left to each reader.

 

[eMark]

Following is relevant to those interested in tracking performance of a DIY build with used cells needing attention.

Thanks Mark. ... How often do you take your batteries apart and bottom balance the parallel cells?

Don't need to take apart when using my RC 6S Charger. But do need to be able to split the pack into two 5s3p. Can also parallel into a 5s6p with Y JST-Xh 5S cable and a Y Deans cable. My RC 6S Charger also has an IR function which is a must when doing experimental testing. My two DIY Vruzend builds (V.2 & V.1) serve as both experimental as well as many miles of enjoyable riding. I disassemble both builds every winter to check individual cells and replace any weak/problem cells with 30Q needing more attention because of 30Qs self-discharge tendency with 136, 138, 141. Will test newer 30Q 6-T cells for the first time this winter. Could do same thing with 6S Charger and 12s DIY build.

Do you typically do this with the alligator clip method on the sides of the pack, one parallel group at a time?...or through the BMS balancing leads?

Don't use a BMS, but do use balance sensing leads w/JST-Xh connector. Because i prefer bottom balancing and then bulk charging i decided not to use a BMS. One less thing to be concerned about when interested in tracking just cell performance and NOT trouble-shooting any BMS problem. Because of my meticulous nature and the importance of routine preventative maintenance no need for a BMS ... other than my 78yr ol' brain as a smart BMS :wink:

Do you find yourself having to discharge some of the parallel groups with the electronic load tester you show?...or do you simply sag the entire battery down before you balance charge and then select an elevated voltage target say, 3.5 volts for all parallel groups?

After a riding discharge rest (avg p-group bounceback voltage to 3.60V), then do Bottom Balancing usually p-group variance within 5mV then bulk charge at either 1.5amp rate or 2.0 amp rate until p-groups at 4.10V. Average p-group variance of 5mV after bulk charging. RC Charger is set on 1S with 1.5amp charge rate (22awg balance wires).

The TORCH 180W Load Tester (Discharger) is used primarily for experimental use, occasional Top Balancing and when determining overall capacity of my two experimental DIY builds as they age with more and more cycles. If i used Top Balancing then i would use this TORCH Load Tester instead of my RC 6S Charger for Bottom Balancing.

If Top Balancing the way to go is with discharge method like i suggested to m3evuv in previous reply. RC Hobby Chargers are such that they aren't able to affectively charge an individual p-group from say 4.00V (or even 3.95V) to 4.20V. For example charging all the lower p-group variances (previously shown) of the build by m3vuv to 4.20V.

If this was my DIY battery build i'd do the following discharge as much as a learning experiment and for narrowing the variances ...

• 1. Discharge p-group 1 (4.200V) to 4.130V resting volts

• 2. Discharge p-group 10 (4.200V) to 4.130V resting volts

• 3. Discharge p-group 6 (4.185V) to 4.130V resting volts

• 4. Discharge p-group 2 (4.171V) to 4.130V resting volts

My guess is the variance between the 13 parallel groups will then be no greater than 30mV to 40mV.

Then bulk charging (2amp) to 4.20V with p-group variance no more than 4.200V to 4.170V (30mV variance).

A further explanation of your technique would be appreciated. Thanks

(see photos) ... p-group numbering is wrong in first photo -- 5 is really 1 and 1 is 5. Also 0(10) is really 6 and 6 is 10. It was late that night (early morning an no coffee yet

The two wires (red & blk) at the top of the 2nd photo serve as just one wire (doubling up awg) connection between 5 (left side) and 6 (right side). The XT60 connector (connected to 1 & 10) is used for both charging and discharging.

The closeup photo of the Torch Discharger display gives one a better idea of all the informative data that is very useful whether testing an indiviual cell, a parallel group or the overall capacity of either my 30Q or 33G DIY 10s3p build. The bottom photo shows my Liberty Trike. There is plenty of room inside the Cargo Container for both the DIY 30Q & 33G experimental builds. There is also room under the Cargo Container for either of my 36V 10Ah UPP batteries. When on a long journey i take all 4 batteries with me.

 

[m3vuv]

seems to be going off topic.

 

[eMark]

If I wanted to follow similar suit and build a 14S 5P battery, how would you break up such a battery such that you could bottom balance it with an available RC charger like you do?

With used cells the more cells in p-groups the better (e.g. 13s10p). The two 8S mentioned at ES are ...

• https://www.amainhobbies.com/isdt-q8-max-dc-lithium-battery-charger-8s-30a-1000w-isd-q8max/p1253192?gclid=CjwKCAjw1ICZBhAzEiwAFfvFhNOq_fF8AF9xaE-ZUlX6Ao2QHQKLRz5TQ8Fw_BYv4y5EgXkepfxpUxoCBmMQAvD_BwE ... iSDT Q8 Max DC Lithium Battery Charger (8S/30A/1000W) - $89.99

• Junsi iCharger X8 Lilo/LiPo/Life/NiMH/NiCD DC Battery Charger (8S/30A/1100W) ... https://www.amainhobbies.com/junsi-icharger-x8-lilo-lipo-life-nimh-nicd-dc-battery-charger-8s-30a-1100w-jun-x8/p945383?gclid=CjwKCAjw1ICZBhAzEiwAFfvFhHiTjWmeVN9dqEjRhWfABqTZHh8ijKwln-LxmubtVg92QP79-XqKLRoCwu8QAvD_BwE - $145.99

Could also use for Bottom Balancing individual p-groups of a 16s DIY build comprised of used cells of similar capacities.

Like Amberwolf and others have previously posted over the years at ES it's better to just stick with a good BMS for Top Balancing a DIY build using new Grade A cells. With new name brand Grade A cells very little (if any) balancing is needed until the pack is around 80% of original rated capacity (unless abused).

Also remember that an "Active (equalizing) Balancer Board" only balances the parallel groups within a variance of 85mV to 100mV. I think that's what Chalo uses to balance his DIY pack of used (e.g. $2) cells. Beats Bottom Balancing for ease when a variance of 85 to 100mV is possibly the best balance to be expected with $2 cells.

Bottomline: IMO, Bottom Balancing should only be considered with DIY builds like that of 3Mvuv with used/older-new cells of similar capacity (hopefully originally Grade A name brand cells) of similar capacity rating.

seems to be going off topic.

Yes and No. Maybe ebuilder is considering building a pack of used cells (like your pack) that may need occasional Bottom Balancing. TOP Balancing isn't within the capability of a good BMS that could takes days to balance the parallel groups of used cells within 30mV of each other. If even possible, but is possible in less than an hour with Bottom Balancing.

 

[eMark]

there are 9x 15q of 1.5ah cells and one samsung 2.5ah cell per groupe,cant remember the part number tho,the pack only charges to 53.4v max for some reason.

That's sufficient reason to manually Top (discharge) Balance the thirteen 10p groups (via discharge as suggested) before again bulk charging to BMS 4.20V cut-off. Expecting the BMS to balance your unique 13s10p build isn't likely.

You may be the only one that's built a 13s ebike battery using 117 cells rated at only 1500mAh and another 13 cells rated at 2500mAh. It doesn't take any imagination to surmise the minimal cost of the 117 cells was your justification for your 13s10p DIY build.

By now you may or may not yet realize you'd been farther ahead using 78 25R cells (2500mAh) even costing more than your budget could afford. You would only need 78 25R cells for a 13s6p (15Ah) build compared to your present 16Ah build with 130 mismatched cells.

What is the result of the Top Balancing (discharge) suggestion ...

If this was my DIY battery build i'd do the following as much as a learning experiment and for solving the problem ...

1. Discharge p-group 1 (4.200V) to 4.130V resting volts
2. Discharge p-group 10 (4.200V) to 4.130V resting volts
3. Discharge p-group 6 (4.185V) to 4.130V resting volts
4. Discharge p-group 2 (4.171V) to 4.130V resting volts

Then charge to BMS 4.20V cut-off and report back to us the variance of the 13 p-groups. My guess is the variance between the 13 parallel groups will then be no greater than 30mV. This is a typical rebalancing procedure with any DIY build of used questionable cells. Doing so will reveal the overall condition of your battery parallel groups. Your battery may not be bad if all it needs is occasional balancing of the p-groups when more than 50-70mV out of balance. There's only so much a BMS can do with a DIY build using cells of questionable quality.

Please let us know if the above Top Balancing suggestion was helpful. You may decide that after the manual Top (discharge) Balancing the average SoC may be around 4.10V with p-group variance no more than 30mV to 50mV. Will prolong cycle life with a SoC of 4.10V (53.3V) than charging to 4.20V (54.6V).

Going forward you should use the above example for occasionally Top Balancing your 13s10p DIY build (as needed). You could still get many cycles from your 13s10p with occasional balancing as needed. Your 13s10p build could still serve you well with some manual Top (discharge) Balancing as needed :thumb:

(apologize for going off-topic with my bottom balancing thing for my experimental purposes)

 

[m3vuv]

firstly it wasnt the cost why i built the pack using a mix of cells,it was a rush job due to having my 18s pack go up in flames due to no bms and a bad charger,its my only transport so had to use what i had on hand so i had transport,when my litakalla li 500 gets here i will tear the pack apart,i expect to have it in a week,then will test the cells in the low groups individualy,i may need more nickel strip tho,will keep you posted when it arrives,this is the state of it at he moment,been on charge about 35hrs now.

 

[eMark]

That's a p-group variance of ONLY 0.035V (35mV). That's about the best you could expect to get from any BMS after 35 hrs considering the unknown condition of your 130 cells.

If it were me (while waiting for your litokalla lii500) i'd go for a ride discharging your 13s10p build to around 44V to 45V. Then give the pack a rest for 1-2 hours and post photo of the 13 p-group voltages.

Your pack is in reasonably good condition so discharge p-group variance shouldn't be greater than 50mV. If more than say 80mV variance after discharge an indication the capacity variance of the 15q cells is drifting from their original rating of 1500mAh. Were they fairly new cells or older stored unused cells? Any variance in IR (within reason) among the 117 15Q cells shouldn't have much affect on the discharge variance assuming your discharge ride is leanng more to casual/conservative than raw performance. What about the condition of other 13 cells (new or used) ?

My thirty 33G 10s3p $2 cells (Battery Hookup) of my DIY build have a higher IR with a range in IR. Still have only a 5-10mV p-group variance after a riding discharge from 41.0V to 33.0V. That's after the p-groups have been bottom balanced within 5mV before bulk charging at 2amp rate before discharge rides.

 

[m3vuv]

the 15q samsung cells were brought for a powerwall project that got cancelled,the others were from a pack that had bad cells due to having a bad bms draining them down,those are 2500mah samsung inr18650s 9wh cells,the i may be a one its not clear with my old eyes lol,they came out of a new old stock scooter pack they had no cycles on them.

 

[eMark]

this is the state of it at the moment,been on charge about 35hrs now.

So, the green charge light was on for over 30 hrs (35)? The purpose being that the BMS would slowly (ever so slowly) balance the parallel groups via discharge balancing.

How does one explain that p1 & p10 are still at 4.20V after 35 hrs? These are the same two parallel groups in your previous photo post before leaving your charger on for 35 hours to supposedly balance the parallel groups via discharge balancing.

Previous photo for comparison before 35 hours of suppposed BMS discharge balancing...

What's weird is that 12 of the 13 p-groups had same or lower voltage before your 35hr extended BMS discharge balancing. The only p-group out of the thirteen that indicates a discharge over 35 hrs of supposed discharge balancing of the 13 parallel groups is p6 going from 4.187V to 4.170V (17mV). The other 12 were either the same (4.20V) or actually showed an increase in voltage.

It appears that so-called 'smart' BMS is faulty when it comes to discharge balancing even after 35 hours. Or is it possible the 'smart' BMS is trying to balance the 13 p-groups (ever so slowiy by charging :wink: instead of discharging? Houston! We seem to have a problem

 

[m3vuv]

dont know if it matters but used bike to pop to the shops,about half a mile run then stuck it back on charge.

 

[eMark]

Hi all,i have a homebrew 13s 10p pack with a chineese smart bms over bt,i notice cell groupe 9 never charges more than 4.108v any ideas why this is? all other groups of cells seem fine,cheers.

In the first photo 11th10p is 1mV lower than 9th10p (groupe 9). One reason for 9th10p & 11th10p having lower voltage (4.124V & 4.123V) could be that the overall capacity in those two p-groups is of enuf difference than the capacity of the other eleven p-groups.

Yes, voltage does affect cell capacity and vice versa. Two identical capacity rated cells (name brand Grade A) with one at 4.20V has more mA capacity than a sister cell at 3.30V. Likewise a cell at 3.65V has slightly less mA capacity than a sister cell at 3.75V.

When the 1st10p & 10th10p hit 4.200V your 'smart' BMS detected HighVoltageLimit and no longer permitted continued charging. Even with continued charging (with green light on) any continued balancing is at a very low/slow rate taking hours just to narrow the p-group variance by 20mV with your 13th10p.

The mean/medium average voltage variance between your eleven 10 p-groupes and two p-groupes at 4.200V after 35 hours (at a very low/slow) balance charging rate was 0.034V (34mV). That's the best you can expect as the eleven p-groupes are already balanced at 4.165V Previously the mean/medium voltage variance between those same 11 p-groupes and two groupes at 4.200V was 0.053V (53mV).

Overall your 13th10p pack of cells just needs some occasional extra balancing with the help of some manual discharging (e.g. 1st10p & 10th10p). With the help of some manual discharge balancing after TOP charge cycle and/or some manual charge balancing after BOTTOM discharge cycle you could narrow the voltage variance of your thirteen 10 p-groupes to 15-20mV (or less) in no more than an hour of your time. Hopefully only bi-monthly with or without the help of some manual balancing.

Your pack isn't as bad-off as you may think (IMO). Just could use some occasional manual discharge balancing after TOP charge cycle and/or some occasional manual charge balancing after BOTTOM discharge cycle.

Using the litokalla lii500 probably isn't worth the effort of disassembling your pack at this time to test some or all of the 130 cells. Wait until seasonal weather when ebiking isn't that enjoyable to then do some labor intrensive time consuming testing.

dont know if it matters but used bike to pop to the shops,about half a mile run then stuck it back on charge.

You really don't need to balance the thirteen 10p groupes closer than a variance than 20-30mV (IMO). You may decide to do some extended hours and hours of 'smart' BMS TOP end charge balancing bi-monthly to keep the mean/medium 13s10p voltage variance within 20-30mV.

If you add balance sensing leads to your thirteen 10p groupes it shouldn't take more than an hour to discharge the high p-groupes (e.g. 1s10p & 10s10p) and/or charge the lower p-groupes (e.g. 5s10p, 9s10p, 11s10p, 13s10p) to narrow the variance within 20-30mV). With two patch cables you could be charging a low p-groupe at the same time discharging a high p-groupe (if not beside each other). Just depends on how much of a perfectionist, your ingenuity, your patience and available time IF nothing better to do.

 

[m3vuv]

i was just going to test the cells in the lower groups.may go for a 2 or 3 mile ride and look at the ballace then.

 

[eMark]

i was just going to test the cells in the lower groups.may go for a 2 or 3 mile ride and look at the ballace then.

Apparently the best (least variance) you can achieve with your 'smart' BMS has already been achieved after 35 hours. Seven of the p-groups were balance charged to 4.165V, three balance charged to 4.166V and the 6th10p groupe balance discharged to 4.170V from 4.187V.

Apparently your 'smart' BMS is smarter than thought as it is balancing eleven of the 10p groupes via both charge and discharge balancing. IF it was a true 'active' (equalizing) BMS it would have also discharged the two 10p groupes at 4.200V, so that after 35 hours the variance possibly would have been no more than 5mV, and you'd be ready for some ebiking even after 24 hrs.

It now makes more sense that a so-called 'smart' BMS would also balance via charge as well as discharge when the Charger is left plugged in with green light on for hours and hours, BUT only with a small trickle charge and discharge. The design circuitry of your 'smart' BMS is such that it leaves the p groupe(s) at 4.20V alone as is. Otherwise the Charger would again kick-in again at its amp setting (e.g. 2amp rate).

Could you post a link to the brand/make of your BMS?

 

[m3vuv]

its the 13s 40amp of this model.https://www.ebay.co.uk/itm/313332095639?hash=item48f40c5a97:g:Xu4AAOSweR9fzJ41&amdata=enc%3AAQAHAAAA4Mo7%2FLy%2BN2kDq9IqPpGAe1Dv%2BlcIZ1SkxXtGZaX18N%2BsXDyXFLvxtv8sgHB1Mp29EzNauR%2BBdUYlbFURZVzjRZRUk9hD%2FJdxusX2Tr%2FTWjpSIXhoF479YEwZkES9SAo64ibUaQkeIPM7CeNN0tmQDve0i6ssyGB%2BbdApcXYel%2FJ5mDEUG9GYcvQOjcQGC2f4i6IAFHwmKzLnDcgV7BLzIr04tu9k%2Fv4ZfnIOPDPVcRgqg%2F%2F7D7zCzp3E%2F39WNRpdih%2BO69FV5VGp3f7AgS8T7U5wn4OrxtKZFlcjE1lpSbCL%7Ctkp%3ABFBMvIDx0eNg

 

[m3vuv]

here it is now,looks ok to me?

 

[mickyd]

the cells were not new but supposedly unused,i used repakrr program on the net to match the cells when doing the build.

What's the repakrr program you mention? No Google results for the term.

 

[m3vuv]

its this.i spelt it wrong.https://www.repackr.com/

 

[mickyd]

its this.i spelt it wrong.https://www.repackr.com/

hmmmm...went to that site but not seeing how it works. Can you give an example of what to enter in steps 1 and 2 after clicking the "Packer" icon on the left.

 

[m3vuv]

you enter each cells capacity and tell it the series and paralell groups and it tels you what cells to put in each groupe to match the groupe capacitys,shame it doesent do the same with ir tho!.

 

[mickyd]

you enter each cells capacity and tell it the series and paralell groups and it tels you what cells to put in each groupe to match the groupe capacitys,shame it doesent do the same with ir tho!.

Ah, now I understand. Thanks.

 

[m3vuv]

first time i used it i spent over an hour inputting all the cell capacities then when i saved it most of the cells were missing from the list maybe a bug so best grab a screen shot just in case!.they should do an offline version imho!,regards Paul m3-vuv 73.

 

[mickyd]

first time i used it i spent over an hour inputting all the cell capacities then when i saved it most of the cells were missing from the list maybe a bug so best grab a screen shot just in case!.they should do an offline version imho!,regards Paul m3-vuv 73.

That's funny!! After you told me how the site worked, I made up 39 values, entered them all, then ACCIDENTLY hit the browser back button an BAM....lost all the data!! Re-entered made up values in Google docs (which autosaves) then copy / pasted into the websites data entry field.

I appreciate you sharing that site. I'm going to practice my first battery build using old cells and it will really help me make the best parallel combo with my used varying cells.