Battery Post replacement/repair?

[Kauai Jim]

I'm building my 1st battery bank of 40, 3.2v, 25Ah LiFePO re-purposed aluminum cased cells. Yesterday as I was checking the cells for their voltages I accidentally bumped a loose buss-bar. This shorted a line of 8 cells, one of which caught fire and mostly burned up one of the battery post. I was able to quickly put the small fire out and checked all the shorted cells, including the burnt cell. Fortunately they all were still holding the 3.3v's they had before the short/fire, but it left one cell with only one fully functional threaded post. I was able to use my probe and place it against what was left of the burnt post to check it.
I have been looking for a way to repair or replace this cell's one loose post, but haven't had much luck. While cleaning the area I tried to solder a wire to what was left of the 2 little metal pieces that ended up flush with the aluminum case , but had no luck. I then tried to drill the middle of these pieces, but it just pushed them further into the aluminium case. There is enough left of the partially destroyed post that I could possibly use it if I could figure out how to solder it back on, but the solder just won't stick and I really don't know much about soldering.

These are unusually small aluminum cell batteries and I can't find any similar 10mm #8+- threaded battery post for sale on-line. Does anyone have any other ideas on how to save my cell???

 

[Supervstech]

Lead/tin solder doesn’t stick to aluminum. At all.
There are some aluminum welding/braising solders... easiest would likely be to drill and tap to the terminal, but yeah... pictures might help us make better suggestions.

 

[John Frum]

This shorted a line of 8 cells, one of which caught fire and mostly burned up one of the battery post.

Do you mean lifepo4 or some other chemistry?

 

[Kauai Jim]

I'm not sure that the almost hidden stubs of what's left of the post are aluminum. They aren't attached to the aluminum shell of the cell, but poke through the hole in the aluminum case and attach to both sides of the base of the threaded post. In the photo you can see a drop of the tin/lead solder I tried to attach on the far stub, which has since fallen off. I don't know if the stub is the same metal as the post piece, but it appeared to not have the same coloration as the post material when I filed the top of the stubs to try and drill a hole for a way to attach something that would work. As I noted before, the stubs moved lower when I tried this, and are not attached to the aluminum case.
To clarify, these are LiFePO4 3.2 cells, 25000mAh.

 

[Supervstech]

Ahh... yeah, I have no idea how you could repair that, sorry.

 

[Ped]

Tig weld

 

[Supervstech]

It looks like the positive post is carbon... I don’t think tig can attach to it.

 

[Ped]

I thinks thats surface carbon from the fire....lol

 

[Kauai Jim]

When I filed the stub it was a silver color once the carbon was removed

 

[KG6S]

Good it is till working.

Clean up ports, post and surface area as best as possible then see how much metal there is left inside for hold-ability of screws/bolts...then purchase some high strength conductive epoxy put er in the port, on screw/bolt threads and under the post(s) then seat screw/bolts and let er set.

Don't be miserly on the epoxy or too liberal.

Thats what i would do.

For example: "High Impact Absorption Silver Epoxy, High Strength Adhesive, Electrically Conductive, Heat & Stress Resistance Applications, Cure Only, 1 Part 2979, 2.5gm" -- "Newegg"

You may find another of your liking.

I have seen some low temperature brazing rod on Harbor Freight/Northern tools that looks like a small butane torch could be used as heat source.
Or Amazon. Not sure of use with steel:

Robot Check

 

[MisterSandals]

Didn't someone do a teardown of these cells? How is that top plate attached?
If this could be accessed from the bottom, and the broken/melted posts removed, i wonder if a threaded rod could be put in there.

 

[tictag]

Imho, any process involving heat is going to make matters worse. Additionally, aluminium welding is very difficult and best left to experts. I'd be thinking of drilling into the studs, thread the new holes and secure the existing terminal with bolts into the new thread. This very much depends on how deep the studs go - you don't want to be drilling into the battery material itself!

 

[KG6S]

Just ran across this video tonight on the U-Tube. The Money Shot starts around 24 Minutes in. YMMV.

 

[tictag]

Just ran across this video tonight on the U-Tube.

I that is a different cell.

 

[Kauai Jim]

Thank you all for the suggestions. I tried the conductive epoxy. It didn't hold for more than a couple of days. I tried not to over or under torque the nut on the battery post, but it eventually pulled up. Well, it was worth a try!

PS: I did originally try to drill the post but the whole post pushed in with the pressure from the drill. Stopped after that.