Spot weld cell puncture - how 'catastrophic' is this?

[Hot Toddy]

Hi guys,

I'd appreciate your wealth of experience on this one ...

I'm building a 13S5P li-ion ebike pack using a DIY spot welder built from a car battery (630A cold start), 500A solenoid switch, and digital timer (10ms resolution running at 80ms bursts). Having completed welding the first side of the pack with no issues, I was half way through the second half and had had a small cell puncture when the welder arc'd for some reason. Rather than have to tear the pack apart to replace the affected cell, I immediately applied some epoxy resin over the puncture hole to avoid electrolyte loss and hopefully salvage the damaged cell.

How 'catastrophic' is this cell damage to the overall pack if I continue the build without replacing the offending cell, with the epoxy 'patch' in place? Is it even possible to salvage a damaged cell with an epoxy patch? If not, what is the likely outcome of leaving the damaged cell in the pack? Will it simply die and refuse to take charge? Will it take the rest of the cells in its parallel group with it and kill them? Are there far more serious implications to be considered? Could the damaged cell go into meltdown? And affect neighbouring cells?

The ideal solution would be to tear the pack down and replace the damaged cell. But I've expended a lot of time and effort so far and tearing the pack down could easily damage other good cells. I would just like to know if there are other possible (*safe*) alternatives. Best case scenario: the epoxy patch holds and all is well. But I need to understand the likely and worst case scenarios to make a judgement as to whether that risk is worth taking.

Thoughts and recommendations?

Many thanks.

 

[j bjork]

I guess it is in the negative side?
If it is the positive, no problem. Then you have not penatrated the cell.
Hopefully you will get answers from people that know, but I think if you penetrated the negative side that cell is lost.
I only have experience from taking some small packs apart, but when I removed the welds a few cells got punctured.
Those cells died, after a few days there was 0v.

 

[Hwy89]

Replace the cell or look forward to many sleepless nights worrying about it and facing a constant struggle trying to keep the pack balanced. Your choice.

 

[spinningmagnets]

Its "probably" OK, but...if it's a problem, the worst-case scenario is a battery fire. The downside is steep, so...I wouldnt risk it.

 

[DogDipstick]

What would I do?
I'd weld it shut with lead, and monitor it for the next year to know the answer definitively. In a drawr in a fireproof safe in a bank vault under Fort Knox. Datalogged from baseline every week for a year.

I would not use it in a pack that you will rely upon or be complacent with in any regard, , or sell, or store indoors / whatnot. No longer reliable.

Dont be macho. Dont be complacent. You are not invulnerable. Do not resign to "Well I cant do anything about this, so thats that. " Do not work on impulse. Listen to the authority. Do not subscrivbe to any of these, well known, "Hazardous attitudes."

You are playing with fire.