Charging voltage steps anomally

stevees

10 µW
Joined
Aug 3, 2022
Messages
6
HI
Have a 13s5p battery pack and its not charging or disharging.
The Pack was bought with an ebike 2 years ago and used twice.
No charging was done till now so i would say 18 months has gone by hence the problem.
I have measured the voltage at the BMS pins and i get
pin1 4v
p2 8v
p3 12v
p4 16v
p5 20v
p6 24v
p7 28v
p8 32v
p9 36v
p10 40v
p11 40v
p12 44v
p13 48v
i have measured voltage at p11 which is 0.

Does this mean 1 of the cells within the pack is totally dead?
Can i use a different manufacturer as i cant seem to source the exact same samsung 18650 26e cells?
Its an unusual layout see below. its the middle pack 3 thats the problem.
13s5p.jpeg
 
It means that the 5 cells in that parallel group is dead if that group is 0v.
The best way to get a balanced pack would probably be to take out one cell from every group and use 4 of these to repair the dead group. Then you can use 13 other cells (that dosent have to be the same as the ones they replace) to make the pack 5p again.
 
I noticed that if one cell or can is weak, it can take out a grouping, depending on how you connected it.

Way back when I paralleled tool Makita's 5 times on each brick 5s2p when making 10s4p to 10s8p.
Would kill groupings easy if weakness occured in just one 18650 can, stressing the other good neighbors that have to then take up the slack and take over, yet in time killing the good guys. I then switched to paralleling tool Makita's only on the + and - of each brick. Solid copper house wiring from Home Depot, stripped, tinned..... pool on tab....cool, then its game time press wire down firmly with pliers, reflow, inspect, done. I inspected those multiple times a year. Good for a cheap, ghetto diy build. Tip - due to vibrations, tabs can break and not keep the original flow of electricity, killing it. Lots of tape, lots and lots, I even used 1/4" wood to protect tabs.

The 0v, throw out.
The lower then min voltage (18650 - 3.20-3.33v), if its 3.00v then its up to you to slowly recharge (0.1-0.5c, depending on how low) them and reuse them. Dip to 2.50v, or say 2.00v is when you need to seriously think about things.

Edit
Yes, that is about the limits (2.00-2.50v) that I'd use without doing much researching. I bypassed a 2.50v on a 9ah 5s3p (3ah cans) tool pack brick, only because I had 13 other good voltage cans to use at 3.60v. It was a little more involved, isolating the cans via tabs.

That pack doesnt look as bad to take one out, mine are completely encased tool pack 18650's.

eMark said:
Dip to 2.50v, or say 2.00v is when you need to seriously think about things.
Depends on how many cycles. If newer pack with Grade A cells and few cycles it's possible to revive even if p11 is 2.5V to 2.0V (after disconnecting from BMS).
[/quote]
 
ebuilder said:
Can you measure the aggregate voltage of the pack outside the BMS and tell us what it is?
He can also take his two probes and go down the connector on each series connection measuring the voltage of each p-group with the BMS disconnected.

If the problematic p-group (p11) still has some voltage when taking reading (after disconnecting from BMS) he could try a slow 1.0amp charge on just p11 for a couple hours to see if it holds ... probably not :(
file.php


The good thing is 4.0V on each of the other 12 p-groups :D if possible check soldered connection on p11

p1 4v
p2 8v
p3 12v
p4 16v
p5 20v
p6 24v
p7 28v
p8 32v
p9 36v
p10 40v
p11 40v
p12 44v
p13 48v
calab said:
Dip to 2.50v, or say 2.00v is when you need to seriously think about things.
Depends on how many cycles. If newer pack with Grade A cells and few cycles it's possible to revive even if p11 is 2.5V to 2.0V (after disconnecting from BMS).
 
Thanks for the replies
I have dismantled the packs and measured the group of 5 as per picture.
How is this possible that all 5 cells are Zero?
As you can see the connecting strips are purpose made and rely on the tabs to interconnect.
Where would i source the same to repair as i would have to replace all 5 cells?
Aslo looks like ill need a mini spot welder unless anyone knows of another method?
 

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ebuilder said:
You ask the perfect question because it does seem anomalous that all 5 cells would go to 0V in a single parallel grouping...how could all 5 cells of a given cluster fail?

How can anything else happen than all 5 parallel cells go to 0v at the same time?

They are parallel and has to have the same voltage..
It can be a bms problem, or a self discharge problem with one of the cells.
If it is one of the cells, it will defiantly take the other parallel cells with it. There is no other possibility :roll:
If it is the bms, well then it discharges that parallel grop.
 
Thanks again.
Whats your opinion on a similar battery 2600mah.?
These are samsung 2600mah code 26E
i have found these which look the same but code 26f

https://www.ebay.co.uk/itm/394098581038?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338749386&toolid=20006&customid=GB_12576_394098581038.143909750104~1587019106638-g_CjwKCAjw3K2XBhAzEiwAmmgrAnzY5VtikzJJxrVGU9xokghjv7pQT4W8TCR_2OAdlORwJR1GteLUghoCi-EQAvD_BwE

seems the originals 26E are only available outside the uk.
 
stevees said:
Thanks again.
Whats your opinion on a similar battery 2600mah.?
These are samsung 2600mah code 26E
i have found these which look the same but code 26f

https://www.ebay.co.uk/itm/394098581038?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338749386&toolid=20006&customid=GB_12576_394098581038.143909750104~1587019106638-g_CjwKCAjw3K2XBhAzEiwAmmgrAnzY5VtikzJJxrVGU9xokghjv7pQT4W8TCR_2OAdlORwJR1GteLUghoCi-EQAvD_BwE

seems the originals 26E are only available outside the uk.

There are many cells that are like 26e. (26F was my first of the type and then I realized they had H, J F looking the same with about the same specs as well. That is how I see then)

My guess is there may be some kind of differece but they should all be the same mah to my knowledge.

Apart from getting the correct cells. There would be a big difference if the cells in your pack today is at for example an 80% capacity. But it will work.
 
Ebuilder - yes i am going to replace the BMS you are correct it makes sense.
I Have tried charging the whole pack on the B6 at 0.1a for half an hour and theres 0.5v gone in?.
I am at work so will try a longer charging time in the bunker at home see how we go
 
ebuilder said:
Bad cells...or trying to turn bad cells back into good 'may' have a consequence. Cells that degrade to unknown degree may never be the same and a threat to safety. I try to minimize any safety risk and bad cells can do very bad things aka heat and potential fire threat and why tempt fate?
We all are guilty of being so intent on doing something knowing the odds not favoring us. Listening to the advice of our elders based on their experiences and that of others didn't persuade us from proceeding anyway. Even though our gut instinct told us the odds were against us.
stevees said:
I am at work so will try a longer charging time in the bunker at home see how we go
At least he has a bunker. Hopefully he'll have good eye protection and protective fire resistant clothing should he venture too close ... :shock:

Remember when you picked up a firecracker that you thought the fuse had died out :bolt:

Maybe, he will prove us all wrong ... :wink:
 
ebuilder said:
You taught me, if a given cell is bad, it can wipe out the whole P-group, in this case 5 cells...and take them all to "0v" even with a healthy BMS. I didn't think that was possible because a healthy BMS would attempt to charge the entire group and the good cells would take the charge while the bad cell wouldn't.
There is no visibility possible to what is happening at the unit level, when there are multiple connected in parallel.

Best is to select cells that are the Ah capacity you desire for the pack as a whole.

So if a 250Ah pack is what you want, a 280Ah cell would be a good choice.

Building that from teeny units under 20Ah would not be sensible.
 
Just an update.
Removed the 5 cells and used a smart charger.
4 cells are charging but 1 is shorted
Anyhow i have ordered 5 new cells and bms so hopefully should be up an going soon
 
It earlier to read voltage like this

1. 4.12v
2. 3.95v
3. 4.01



13. Xxx volt
That's good to replace all in a parallel group
And yes I had a bms with one bad bleed resistor on one channel that stopped the pack.
 
ebuilder said:
Excellent. Can you tell us what cells you ordered and from where? Also about what BMS you decided on?
Do you have the other supplies like nickel strips, spot welder and Kapton tape?...or did you order this stuff too?

Hi
Finally got sorted
Bike works great
I ordered a BMS but would not fit so i bought https://www.ebay.co.uk/itm/284917545667
Fits great and although it doesnt balance it offers protection
Replaced all 5 although only 1 was shorted through and i managed to trickle charge the others up to 4.2v with an 18650 4 port balance charger
Bought 6 of these https://www.ebay.co.uk/itm/394098581038
Bought a spot welder from amazon with nickel strip included (takes a bit to get used to as blew a hole in one of the new cells when on power 4 of 10?) something to do with not seating the electrode properly?

Used masking tape covered with parcel tape

Now my next project is my water damaged Pixel 4a 5g
Fault finding - Micro soldering Ill start a new thread see if anyone on here can help
Thanks All
 
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