Replacing bad battery cells

[snydes]

Just want to mention if anyone is rebuilding a pack we can help furnish the factory VTC6 cells.

The pack Cyrus David is working on has the Panasonics, which you might also still have. Sounds like he may very well need some.

 

[snydes]

I am sure you guys are aware, but I will post it anyway.
What you guys are planning to do is extremely dangerous without the proper equipment and training. Please be very careful.

Yes, this is definitely not for anyone without the skill set for working with energized equipment, and even still comes with extreme hazards of accidental electrocution and/or fire. @Cyrus David or @Philip , could you please edit the first post in this thread and head it off with a bit of a disclaimer for anyone reading this in the future? Thank you.

 

[bluefxstc]

You might be able to use something like this to replace the Alta cell honeycomb. This may not be exactly correct, but there may be something similar that will work.

 

[snydes]

You might be able to use something like this to replace the Alta cell honeycomb. This may not be exactly correct, but there may be something similar that will work.

There are a few of them now that have slipped out from the Alta liquidation. In another post, AltaWest also claims they are working on a reproduction that could be 3D printed. It would need to be an exact replacement for the PCB to line up properly (among other things).

 

[Mark911]

Alta probably spent bank on the molds for the cell supports (aka honeycomb, eggcrate, thermal shield). The only pack that I've seen that comes close to the cell density of the Alta pack is from NASA's LLB2 project. Of course, one could simply stack cells side-to-side in a staggered configuration without ANY intermediate support for MAX density but the pack wouldn't be very safe. The NASA pack wouldn't work with the "one sided" wiring layout that Alta uses, however. Which is why the Alta component is not electrically conductive.

 

[privateer703]

There is another maker of honeycomb cell holders:

vruzend holders

 

[Cyrus David]

Ok so can anyone actually prove that the soldered aluminum connections are actually fuseable links by design? I’ve got some similar gauge aluminum mig wire that i’m Going to test for it’s current threshold. Just looking to see if anyone has more specifics on this or have seen a link between the cell and board burnt from current.

 

[AltaWest]

There are a few of them now that have slipped out from the Alta liquidation. In another post, AltaWest also claims they are working on a reproduction that could be 3D printed. It would need to be an exact replacement for the PCB to line up properly (among other things).

We have a parts scanner here in house, if we could get one of the honeycombs we can scan it and share the file for those with 3D printers (or we can print parts in house).

 

[Mark911]

There is another maker of honeycomb cell holders:

vruzend holders

Closer, but still not as dense as Alta. Plus, you really need some barrier between cells to reduce the chances of a cell going thermal and then propagating to the adjacent cell(s) creating a thermal runaway situation (lots of fireworks). The material and design (air space) Alta used for their cell supports was reportedly designed to prevent or at least minimize this possibility.

 

[privateer703]

Closer, but still not as dense as Alta. Plus, you really need some barrier between cells to reduce the chances of a cell going thermal and then propagating to the adjacent cell(s) creating a thermal runaway situation (lots of fireworks). The material and design (air space) Alta used for their cell supports was reportedly designed to prevent or at least minimize this possibility.

Really? By the dimensions shown on that page, center to center distance of those holders is 19.4, that is only 1.4mm in between cells. That looked as tight if not tighter than the pic on page 1 of this thread. I wonder how much bigger the completed honeycomb would be, maybe it's possible it would still fit within the Alta battery case? If we need to make all new battery packs, these may work. I get your point about having something in between the cells, which if you wanted you could make a mold with dummy cells in the honeycomb then pour foam around them. Then you'd have insulated, closed cell foam completely around the cells. But that may not be heat resistant enough, which is why they used epoxy. It would be nice if we could pull individual cells out if they lose capacity though.

 

[snydes]

Ok so can anyone actually prove that the soldered aluminum connections are actually fuseable links by design? I’ve got some similar gauge aluminum mig wire that i’m Going to test for it’s current threshold. Just looking to see if anyone has more specifics on this or have seen a link between the cell and board burnt from current.

There is a ton of info on tinned copper wire used as cell level fusing on youtube on DIY powerwall batteries, and yes, (for everyone else) I'm aware this is much more critical than DIY powerwall batteries. Also, the Alta fuse wire is sonic welded, it can not be soldered, which at the end of the day is the dead end we face here.

 

[Cyrus David]

There is a ton of info on tinned copper wire used as cell level fusing on youtube on DIY powerwall batteries, and yes, (for everyone else) I'm aware this is much more critical than DIY powerwall batteries. Also, the Alta fuse wire is sonic welded, it can not be soldered, which at the end of the day is the dead end we face here.

Good info.. ok so i’m Going to try it. I’ve successfully both soldered and spot welded to lithium cells in the past rebuilding cordless tool packs and such. I feel I could remove the Alta fused wire, burnish the tiny plated contact point on the PCB and solder it back with a piece of single strand copper wire. Yes I know i’ll probably make a bit of a mess destroying and boring the old cell out of there (yes I know to deplete it first).
I’m good with my hands, good with a bunch of great tools I have access to and have @Cody129 battery in my garage that is only two cells away from being balanced to spec.
Two!! Just Two!! Yup I know I may face balance issues with those same two cells if I pull it off but still going to try.
Everybody is telling me a million reasons why it can’t be done but I have not seen any pics of any failed attempts or heard of any attempts for that matter.
DM me pics of anyone actually has successfully got a single cell out..

 

[Redwolf]

 

[Mark911]

I think you have a good plan and wouldn't hesitate to do it if it were my pack. I suspect getting the cell(s) out will be much easier than expected and soldering to positive end and gold plated PCB pads will be easy. Soldering to the EDGE of the cell housing (- end) is risky. If there's room, I'd at least consider soldering a tab on the typical negative end and route that conductor up to the top and then to the PCB pad. A longer and slightly higher resistance path but much less chance of cell heat damage.

You could flip the cell as you suggested, but the MAIN heat path is through the negative end to the plate and out to the housing. The positive end simply cannot transfer the required heat energy and those cells will run hotter and get out of balance quickly as the electro chemistry is heat dependent (among other things). That's also why using the proper (same) adhesive(s) is a very good idea.

Do it, you can be the first!

 

[snydes]

We all want to see you repair this pack, and you would be attempting this with or without us, so it makes no sense to not share what we know with you to give you the best chance of a success. But we also have to convey all the negatives as it would be irresponsible not to, especially since we are talking on an open forum.

You can solder to the edge of the cell for the negative connection but it’s SKETCHY and I WOULD NOT recommend it! Only as a last resort and it’s a dangerous proposition. You have to be fast, use as big of a tip as you can and try and get as little heat in the cell as possible. Even then you will likely cause some damage to that insulting ring of the cell. Coming up with a spot weld solution is a better bet, problem is there is not enough room to get two electrodes in there at the slot in the PCB.

First problem is getting those cells out. If you are able to do that then we can start thinking our way through the rest.

 

[Happy Neighbors]

There's probably three or four of us out in Alta land working on a cell replacement process with the common theme being we're all looking for bad modules to experiment with. Of course, if the battery is bad enough that it'll only charge 50% you've got almost nothing to lose.

My approach would be to map out the bad cells and using a counterbore with a mechanical stop carefully cut the bottom plate to expose the negative end of the cell. There'll be some cured film adhesive (blue) between the two so you'll get some warning before you go too far. Then snip the fuse wires and push the bad cell(s) out through the bottom.
Pre weld the +/- leads to the new cell(s) and balance the new cell(s) to match the module. Align and position the new cell(s) into the corresponding bores and finalize the terminations to the PCB however you desire. Do whatever electrical tests you think is appropriate at this stage.

Using a hole saw with no pilot, cut out preplacement "disks" for the bottom plate. Here's the first big unknown, what did Alta use to bond the cells to the plate? Not sure, but I guess some kind of thermally conductive electrically insulating pressure sensitive room cure film adhesive. There's quite a few choices in the aerospace industry so take your pick and cross your fingers. Select the proper thickness film adhesive and bond the "disks" over the negative cell ends using a flat plate to ensure co-planarity of the bottom plate interface surface.

Final electrical test and re-assembly into pack. That's it!

I found an older article that some may have not seen, it might be worth reading for those that are working with their batteries
https://chargedevs.com/features/alt...ric-dirt-bike-has-world-class-energy-density/

 

[OneLapper]

I think Mark911 had taken a correct guess on the the blue adhesive in the modules.......

"Passive cooling means that the thermal conductivity of the materials that surround the cells is very important. After some testing, we found that a two-part polyurethane from Wevo-Chemie (a German company for tailormade casting, bonding and sealing resin solutions) had the highest thermal performance, so it became a critical component in our system as an adhesive."

And

"Rob Sweney: The Wevo mixture we chose contains special inorganic fillers. Many thermally conductive adhesives have slivers of aluminum filler, however aluminum works against the dielectric barrier. A thermally conductive ceramic, on the other hand, can help achieve both goals. So we found a great material, but then ran into some challenges working with it in a production environment.
Kevin Kim: Basically, the resin has the consistency of peanut butter – it’s extremely viscous or thick. Also, the hardener component of the two-part mixture has a very low viscosity, about the consistency of water. That, [together with the challenging 100:8 mixing ratio of the material] makes it difficult to dispense.
So it was a pretty unique material that we wanted to use and, thankfully, Scheugenpflug was able to help by customizing its dispensing equipment specifically for this material. In fact, they were the only company we found that had successfully dispensed this material before. And they were the only company that was willing to tackle trying to build up a production machine for us to dispense it."