“PSA: Do not weld on/near the bottom venting ring of a Lishen or other cell”
Be sure to mention that not all Lishens have the ring and, IMO it would be great to show photos of the ring and link to the video I just posted for those who have no idea what the post is referring to. 
watching that video I’m learning that vent rings can be added from the inside of the can, are there examples of this? are there any instances of an internal venting ring being added with no external marking for it?
If the center disc pops open to vent, perhaps bottom vented cells could use nickel strips with a slightly larger diameter hole punched through. Center the hole with the vent disc and weld around the outside.
Not that I know of.
The stamping process for creating the internal ring seems to always leave a mark on the outside too.
That’s what I was thinking too. Seems to be the only way to use these cells without hugely interfering with the vent. The vent will still be blocked, possibly, by fishpaper, Kapton, and/or filament tape but at least it wouldn’t be blocked by metal too.
We just have to realize that we do not build packs nearly as safe as we think we do. Not with the top vent being forced to blow all the blazingly hot thermal runaway ejecta directly onto adjacent cells by nickel strip and/or the bottom vent being completely blocked.
If you were to stack a fishpaper ring (or 2) on top of the hole-punched nickel strip, you may be able to create just enough height to allow the vent to freely open, and still build the pack per normal methods.
Once that vent cracks, I imagine there’s no stopping the pressure release. And anything in the way will get pushed/melted aside.
You would need extra wide nickel for this of course.
Or ten.
We just don’t know how far they have to open to reduce the pressure enough to help prevent thermal runaway as designed.
Top vents can get blocked enough during runaway to force a side-wall rupture though. One of the reasons why bottom vents are added to high capacity cells.
Forgive me if i’m wrong, but the vent is only there as a catastrophic safety measure right?
Meaning that in the event of a catastrophic circumstance, these cells could potentially be a little safer than cells without a vent?
If we cover the vent, the cells are essentially gonna have the same damage potential as most other cells we use?
Arguably more.
If the cell is designed to use the bottom vent then not having that available can mean the chance of the cell going into thermal runaway (versus just mechanically venting hot electrolyte) is higher. Cells designed to just use a top vent, or only need a top vent, would be arguably safer in that circumstance.
Thankyou for clarifying.
I cannot think of a way we could use these cells without either severely blocking the bottom vent, or having a very elaborate configuration.
Laser cut nickels, but it’s not worth the hassle I reckon
Yeah but even with laser cut nickel, most builds will have that bottom vent pretty much firmly pushed up against another cell, or firmly against whatever enclosure you are using.
It seems like it would take some clever design to use these cells in a way that the vent could actually be utilised safely.
And even if you did go to all that effort, if one or more of the cells vented, you probably still gonna have a hell of a mess to clean up 
Ah yeah, hadn’t thought of that. Fuck that.
I thought u shouldn’t be welding the the center bottom of all these cylindrical cells. I don’t have the pic anymore but the center most millimeter or two is where the can attaches and that connection can be damaged increasing resistance
I mean at the end of the day we pretty much cover vents in all of our cells anyway
Also… Have you ever seen an esk8 fire that would have been better off if the vent wasn’t covered?
Are we sure this makes any difference at all?
This is the easiest and most simple safety measure I feel like we should all take if you aren’t already
A123 26650s also have this vent on the bottom side but it’s the positive.
Buy my cells for a buck each!
What if we welded only on the venting lid? 
Anyway, thank you Mooch for sharing that video! It was unclear to me before which part actually opened up to let out gas. I guess cells that use a bottom vent shouldn’t be used in modular cell-holder style packs like NESE or Trampa’s explody box. Heck, the vent might even squeeze inwards! 
That ignores the primary function of the vent though…to release the pressure and lower internal cell temps. Vents that are allowed to do their job can help prevent that runaway from ever happening in the first place.
Once runaway occurs though then the venting really can’t do much more than direct the flames and ejecta and, hopefully, prevent bursting of the top of the cells or a side-wall rupture.
Hmm…actually, that’s frakkin’ important too and perhaps addresses what I quoted above…properly used (not covered) vents allow the flames and ejecta be directed away from the cells. This significantly lowers the odds of the entire pack going up in flames.
If we cover the vents then we increase the odds of more damage occurring because of the heating of the cells adjacent to the one in runaway.
Thanks for posting that. Their safety workshops provide some incredible info on how to make packs safer. Unfortunately there is a slight difference between the budgets we have and what NASA can spend on making a pack safer. 
We can still pull good info from their testing though.
