Top balancing and charging

[c3auto]

Hi
I ordered 16x 320ah cells liitokala from AliExpress

I'm in the process of trying to charge them. I plan on doing 2x 8s 24v banks but I'm charging them with a 12v charger first in 4s with a JBD BMS. Here are the voltages so far before they got cut off from the BMS.

When they arrived they were all 3.29v.

This was the voltages after I had noticed the charger had terminated the charge. (Probably from the BMS cutting off the charge)
Batch 1
1. 3.365
2. 3.575
3. 3.373
4. 3.491
Batch 2
5. 3.372
6. 3.397
7. 3.573
8. 3.377

I'm in the process of charging the rest. It seems there's a high voltage or low capacity cell in each batch that's affecting the others.

The voltages for the cells have now dropped to 3.34v besides one that is 3.37 which was the 3.575 cell.

Batch 3 which is in the process of charging also shows a 0.2v difference between the highest and lowest cells.

Is this typical for AliExpress cells? Are they repackaged used cells?

So what should I do now?
I will charge up the third and 4th batch.

Do I recombine the cells to exclude the low capacity ones and charge them in 4S?

Do I then put 16 cells in parallel and set the voltage for 3.55v? Or do I seperate them into 2 sets of 8 cells each in parallel with the low voltage cells in one and the high voltage cells in the other.

 

[time2roll]

If you have two chargers I would be taking the lowest group to continue in series and the top group to start the parallel journey to 3.55-3.65

Yes fairly common for Liitokala. These are unmatched cells. May still work fine, don't get discouraged yet.

 

[c3auto]

Thanks. I've put them all into parallel now. Sitting at about 3.40v. I've set my DC bench supply to 3.6v and it's drawing about 8A.
What do I do once they've all reached 3.55-3.65v? Do I disconnect them all? Then measure voltage after a day or so

 

[time2roll]

You can test them all you like or can simply assemble your battery and get on with business. If you suspect some bad cells you may want to do a capacity test but I will leave that to others.

 

[c3auto]

Is there a way I should pack the 8s cells? Should I put low ones together and high ones together?
If I ordered them 1-16 in terms of the initial voltage I got when each batch of 4s cut out from the BMS should I put battery 1-8 together and then 9-16 or does it not matter that much

 

[time2roll]

See how high is high and how low is low. But yes I would tend to mix them to hopefully even things out. Not sure resting voltage is necessarily an indicator of capacity unless there is a real outlier.

 

[MisterSandals]

What do I do once they've all reached 3.55-3.65v? Do I disconnect them all?

First label them. I suggest using letters (A, B, C...).
Then put a big piece of red tape or something next to the + terminal.

After top balancing, disconnect them. Take voltage readings of all of them after about 15 minutes and then an hour and then a day.

I am working on a theory that the cells that discharge the quickest (lose their surface voltage) are the weak ones. I have 3 out of 19 280Ah cells that dropped within 30 minutes to 3.48-ish while the others stayed right around 3.52.
After a few days, they all settled down to around 3.45. Without my notes, these would all appear the same.

But, that's my theory. If you want to potentially identify some laggards in the first 15 minutes, this is a good way.

I am still waiting on equipment where i can stress a big high voltage battery but with just a BMS running, these 3 cells look suspiciously low.

Take good notes.