Does this look like a bad cell?

[NCblueridge]

Hi everyone. I've posted a few times regarding a battery pack I am building and also have a build thread here:

My lightweight portable power station build

I am building a small portable power station that will be used as a power source for my kayak's trolling motor and fish finder as well as a small backup system for power outages. For my kayak uses, this will plug into a single outlet on my Slayer Propel 10 kayak and suppy power for a 12 volt...

diysolarforum.com

The batteries I am using are 105 Ah Shenzhen Luyuan 3.2 Volt packs in a 4s configuration. Some may be familiar with these since Will did a battery build with them a while back. I sourced the batteries from Power BLS on aliexpress and they were sent from the US distribution center with free shipping.
However, when I received these batterys they weren't even close in terms of voltage, here are the initial numbers:

3.298
3.288
3.248
3.184

None of the numbers on the label were close either so this appears to just be some bin batteries packed into a box and sent. I sent these numbers to the vendor and she said they don't top balance them before shipping.

So I did a top balance and they were closer but still some variance. Then I hooked them up in series using an overkill BMS (which I like very much). I then hooked up a small inverter and did a run down on the batteries to @22%. At that point, the cell voltages were pretty close (see image).

I then hooked up a Victron 12V/17A charger and began charging, The balance cells when charging feature was enabled on the BMS and it began charging. I let this continue for a few hours but when I checked back on things, charging had been stopped and I had (2) cell overprotection alerts, it looks like cell 1 went rogue or something for lack of a better term..(see image)

So now charging has stopped at 13.84v because of this individual cell. In my opinion this is a bad cell and needs to go back to the distributor for replacement. Would you folks agree?

Any comments greatly appreciated.

 

[NCblueridge]

My BMS config's protection settings, standard settings.

 

[MisterSandals]

So now charging has stopped at 13.84v because of this individual cell.

For some reason, its always cell #1 that is odd for me too.
Can you swap cells 1 & 4 and cells 2 & 3 to see if it behaves differently?

What is your setup? Maybe something with your wiring or connections can be seen if you post a photo.

What model is your "Victron 12V/17A charger" ?

 

[NCblueridge]

i could swap the cells to confirm it is that particular cell. Everything is setup with the wiring per the Overkill BMS instructions. I've included a picture. The charger is a Victron IP67 12 volt/17amp charger. It seems to be fine, it's the BMS that shutdown the charging process, there were (2) cell over voltage warnings that forced the stop.

 

[MisterSandals]

i could swap the cells to confirm it is that particular cell.

Well, what are the odds that cell #1 is the weakest, cell #2 second weakest, cell #3 3rd weakest and cell #4 the strongest?

I'm a gambling kind of guy but that would be a remarkable coincidence if done randomly.

Wiring looks fine. Not sure how you are connecting charger but i do not see that making a difference.

 

[NCblueridge]

I sent a message to the supplier, he is on a different time zone so it may take a while before he responds. I also gave him a link here to the post here so he can see the images and where these cells are. I had already alerted him to my concerns when I first saw these cell voltage variances upon arrival, and that I did try top balancing. Basically I feel these are bad cells. I have asked to return these and have a different set sent. They have a distribution site in CA. We will see what the response is and what if any charges I may incur with shipping. Hopefully I can switch them out since I paid a very fair price for what were to be brand new cells.

 

[MisterSandals]

Just out of curiosity, which cells in your initial voltage list matched with the screenshot voltages?
You did label your batteries and keep track right?

 

[Ampster]

Would you folks agree?

Not enough information yet for me to reach a conclusion. Have you tried discharging your pack to see if the same cells are runners in the opposite direction? If so that is a sign that they may have less capacity. Otherwise you may have a top balance that was not perfect.

 

[NCblueridge]

I didn't label the initial cells, I probably should have. The out of the box voltages were:

3.298
3.288
3.248
3.184

As long as I have some spare time while I'm waiting to hear back from the suplier, I think I'm going to discharge them a bit with my inverter and then top balance them again to 3.65 individually - then I will set them back up in series, do a deeper discharge and see how it does when charging again as it gets closeer to the level seen today. I have a feeling though one of more cells will bounce over though and the overcurrent protection setting on the BMS will completely stop the charging process early again.

 

[NCblueridge]

Not enough information yet for me to reach a conclusion. Have you tried discharging your pack to see if the same cells are runners in the opposite direction? If so that is a sign that they may have less capacity. Otherwise you may have a top balance that was not perfect.

I'm going to do that and see what happens. I'll post the results.

 

[NCblueridge]

I decided to point a camera on the BMS app and start a Zoom meeting since it is in my office and runs on an iPad and I don't really want to sit there watching it, I'd rather have a window back in my den.

If you want to view the discharge test that I'm getting ready to start, you can use this link if you have Zoom and see the BMS data in realtime also.

Zoom Meeting:

https://zoom.us/j/99883995581?pwd=c3VqTzJBbEpadUIrckJUanRMRzVlZz09

Meeting ID: 998 8399 5581
Passcode: 0P6dwm

 

[NCblueridge]

Once I started discharging, that 1st cell dropped right down in line...hmmm.

10:19pm, zoom session ended. I have the problem cell below the limit now so I'm going to try charging again and will see if it shutdown as it gets close again. We'll see what happens this time.

 

[NCblueridge]

Ok - so I discharged to get the cell that caused the shutdown voltage lower than the BMS cell protection settings. Then I started charging with my Victron at 17amps. All went ok for a while but as the cells inched up and one got closer to the limit - I hit record right before that limit was reached and the BMS shutdown the whole charging process:

 

[Ampster]

That will tell you i

.........I have the problem cell below the limit now so I'm going to try charging again and will see if it shutdown as it gets close again. We'll see what happens this time.

I now have more facts to suggest that the cell you suspected has less capacity. No matter what you do it will limit the capacity of your pack. Did you happen to note the Amphours it took to go from the top to the bottom? That was an artificial capacity created by that one cell.

 

[tictag]

Does this look like a bad cell?

Yes.

 

[NCblueridge]

Some follow up on this bank. I did talk to the vendor and he was very responsive. They made some suggestions and I individually balanced each cell to @3.7 and then did a rundown with it reconnected to the BMS. WAH was close when the OK BMS cell under voltage kicked in on one. I also adjusted my cell over voltage settings slightly upward in the BMS since 3500 seems a little too low and then did a charge and they were pretty close at the top end.

For my needs with the kayak pack I think these will be ok. Next order I do though will be A plus cells since at some of the discount prices, even with good original cell manufacturers, you can end up with mismatches with discount pricing and even if it's only a few amp hours it can be a real hassle. I think I'd rather pay a little more and know I am getting new/matched cells produced together with low resistance tolerences right off the bat.

The seller also offered to send me some extra bus bars because of the mismatched cell voltages and fact they may have been bin pulls with little supply left in the US distribution center. They also were willing to replace one or more cells if they turn out to be an issue with use.

 

[Ampster]

Thanks for letting us know. It is a good lesson for future readers.

 

[NCblueridge]

Final follup, the seller is sending me a new cell to replace the main one that has poor IR, there is no charge for this other than shipping and it's not very heavy as a single cell.