Bulged and slightly damaged CATLs

[Gould]

Hey everyone,
Thought I’d post yet another “received my cells” thread because I have a question about balancing. Cells arrived in undamaged boxes and at first glance looked darn good. I got to planning the build out the other day and noticed two things, slight bulging with all cells and a slight indentation. I hope it comes through in the pictures.

I understanding the bulging is a regular occurrence with many reporting the same thing on arrival. The first question I have is about balancing. Do I compress and top balance or do I top balance, drain them through a capacity test to remove the bulges, compress then top balance again? Not sure if compressing with the bulge will damage them.

Second question is about the dent. Voltage checks out perfectly aligned to the other cells at 3.27. Just looking for some moral support to proceed amd not let the OCD overwhelm me.

 

[jwelter99]

If you are top-balancing to 3.65V you should compress them prior.

The dent looks like the outcome of bulging in that it caused the short side to buckle a bit and wrinkle the blue film.

I think you will be ok; just work to ensure to limit bulging in the future.

 

[Gould]

Appreciate the response. My intent is to stay within the 80% range and no extreme, extended power demands so hoping that will reduce the risk of bulging in the future.

 

[mikefitz]

My intent is to stay within the 80% range

For interest, how do you intend to ensure the cell does not charge beyond the chosen limit, for example 90% capacity?
This is often discussed but I cannot determine a reliable and consistent technique to do this.

Mike

 

[NMNeil]

One day, we may be able go into a store, take a cell from the shelf, and if it looks like it's been hit by a truck or has teeth marks, you can just put it back and find a good undamaged one.
Much like sorting through the pile of 2x4's at a hardware store trying to find one that is straighter than a dogs hind leg.
Until then we can only rely on the honesty of the seller and good luck.

 

[jwelter99]

For interest, how do you intend to ensure the cell does not charge beyond the chosen limit, for example 90% capacity?
This is often discussed but I cannot determine a reliable and consistent technique to do this.

Mike

Use a BMS with charge cutoff set to 3.45V or so per cell.

 

[Gould]

One day, we may be able go into a store, take a cell from the shelf, and if it looks like it's been hit by a truck or has teeth marks, you can just put it back and find a good undamaged one.
Much like sorting through the pile of 2x4's at a hardware store trying to find one that is straighter than a dogs hind leg.
Until then we can only rely on the honesty of the seller and good luck.

Isn‘t that the truth. I went through Micheal (funny how that’s all you have to say here and everyone understands) so I know I’m in good hands if it turns out the cell is bad. I’ll run it through it’s paces, top balance and capacity test and take it from there.

In terms of setting upper and lower limits yes, I’ll be setting extreme upper and lower limits via the the BMS but that will be the safety net. My inverter and solar charge controllers can be configured with limits as well - that will be the primary means of setting the 10% discharge and 90% charge limits. I’ve also way overshot what I think my daily usage requirements will be. 580ah is at least on paper 3 times what I expect to be using on an average day.

 

[MisterSandals]

Use a BMS with charge cutoff set to 3.45V or so per cell.

No!
Your BMS is NOT for controlling charging voltage. It’s a safety disconnect.

Your SCC is designed to control the charging.