BAK N18650CP - aluminum can, spot welding difficulty

[From-A-To-B]

I have an extra case of 100 BAK N18650CP cells that I am trying to utilize to rebuild a battery for a Juiced bike. I'm struggling with spot welding these cells because they, apparently, have aluminum cans instead of the more common nickle-plated-steel cans used by most manufacturers. I've spot-welded many, many batteries from cylindrical cells in the past, so these issues are not so much the struggles of a first-time builder. I'm looking to see if others have found any tricks to working with these cells because I'm about to recycle or sell the whole case.

Using a KWeld, I find that 25-30J is normally appropriate for getting a good weld to most battery cans with 0.15 nickel strip. This power setting does great to afix nickel strip to the BAK cell's positive terminal, which I assume is steel. However, I'm struggling with welds to the negative terminal. At power settings between 25-50J, the nickel strip does not create a good weld. When "pull tested", the strip merely pulls off, revealing indents in the case where a bond did not occur. At 60J, I can get a satisfactory weld, with nickel tearing. Unfortunately, 60J is also enough power to blow a hole right through the thin cell can about 25% of the time.

60J is quite a bit of power for 0.15 strip, and it seems to me that getting enough heat into the weld to create a proper bond rides right on the edge of puncturing the can. My difficulty with these cells is not helped by the fact that the cell has a large safety vent etched into the negative terminal. Welding on top of that vent almost guarantees a punctured cell, and there is little material around the edge of the can that's suitable for welding. And even on that thin suitable diameter of the can, I've punctured cells.

Any advice is welcome regarding spot welding these cells.

Cells: BAK 18650 3050mAh 6.1A Battery (N18650CK)
This listing details that the case is made of aluminum: Cell Li-Ion 3000mAh 3.6V BAK N18650CK



BELOW: my first test cell showing welds between 25-40J, where mostly none of the welds stuck, and I popped the cell by welding on top of the vent.



BELOW: My second test cell, showing 8 welds at power levels between 40-60J, about half of the welds stuck properly. No punctured case.




BELOW: I began assembling a block of cells at 60J, and punctured a cell on the 4th weld (circled in orange). Not much to see this morning, but I certainly punctured through because that cell spat electrolyte last night. It's toast. Look past all the sharpie.




BELOW: Review/Rant: These tube-style batteries are downright awful to rebuild in the first place. The little tabs sticking out are not only for balance connections, they also complete the series connections with the groups above. The OEM aligned and soldered all those little connections together, along with balance wires. There are between 2 and 4 of these soldered connections on each face of each block of cells, or 24 soldered tabs on the whole 13s battery - half of which carry series current. It's tedious to put together and, IMO, a poor showing for electrical work. The bike is rated at 500W / 48V / 10A and the OEM nickel strip is 4mm of 0.15mm strip. I've worked on other Juiced batteries that were plainly laid out and easily serviced. This style of battery is a disaster to work on, even without my cell welding issues.



Thanks, y'all!

 

[scianiac]

It seems that the issues with spot welding aluminum are from the oxide layer and there are a few ways to improve this that revolve around disrupting the oxide layer. First I would just try sanding the end of the cells right before spot welding at a lower energy level and see if that helps, I've heard of other methods involving specially shaped electrodes too.

 

[From-A-To-B]

It seems that the issues with spot welding aluminum are from the oxide layer and there are a few ways to improve this that revolve around disrupting the oxide layer. First I would just try sanding the end of the cells right before spot welding at a lower energy level and see if that helps, I've heard of other methods involving specially shaped electrodes too.

Thanks for the tips and ideas, Scianiac!

 

[999zip999]

Wild I never thought to think of that before buying a cell. Aluminum. I have the Bak 18650 30amp not knowing what case it's made with aluminum. I bought 120 of those cells. But put them in the N.E.S.E. modules.
I still have five left over I was going to put in a tool pack but if they have an aluminum case ? I can't spot-weld.
Oh there's one downstairs in Tupperware outside in the weather and it's Rusty. So it must be steal.
But something else about BAK it cel is bigger in circumference than other 18650 cells as they wouldn't fit in the 18650 N.E.S.E. kit. He told me to take the wrappers off and they fit and reminded me that be okay because they're all in parallel then in the plastic N.E.S.E. module.
So that manufacture has more than one trick. For us to learn.
Have you found any progress with that aluminum case ?

 

[From-A-To-B]

It seems that the issues with spot welding aluminum are from the oxide layer and there are a few ways to improve this that revolve around disrupting the oxide layer. First I would just try sanding the end of the cells right before spot welding at a lower energy level and see if that helps, I've heard of other methods involving specially shaped electrodes too.

Thanks again, so much, for the tip-off. You helped me pull this project out of the scrap bin. I used a grinding stone tool in a dremel to scuff up the aluminum can. I was thorough about removing material in the desired welding area, but was also careful about not removing too much material. After that, the cell welded up just fine. A wire wheel attachment didn't cut the cheese -- erm... satisfactorily scuff the cell can. Pictured: scuffed negative terminals in cell holders.




Here's a photo of a 0.15mm nickel tear-off after scuffing. One set of welds was 30J and the other was 35J on a Kweld - they both worked well.

Wild I never thought to think of that before buying a cell. Aluminum. I have the Bak 18650 30amp not knowing what case it's made with aluminum. I bought 120 of those cells. But put them in the N.E.S.E. modules.
I still have five left over I was going to put in a tool pack but if they have an aluminum case ? I can't spot-weld.
Oh there's one downstairs in Tupperware outside in the weather and it's Rusty. So it must be steal.
But something else about BAK it cel is bigger in circumference than other 18650 cells as they wouldn't fit in the 18650 N.E.S.E. kit. He told me to take the wrappers off and they fit and reminded me that be okay because they're all in parallel then in the plastic N.E.S.E. module.
So that manufacture has more than one trick. For us to learn.
Have you found any progress with that aluminum case ?

Zip - incidentally, I also had a half-case of BAK 2500mah cells, and just used some to rebuild a tool battery. My guess is that their cans are steel - they welded up just fine in a nickel-copper sandwich. Give it a rip and let me know how it goes!

These 2500mah BAK cells slotted just fine into the cell holders that previously contained Samsung 15E cells. I think the 3050mah cells are larger in diameter than the 2500mah cells, but haven't measured.

 

[999zip999]

I'm thinking they only used the aluminum case on certain chemistries. I also wonder what other cells are made with aluminum case ? I also wonder which brands and what cells are slightly bigger or smaller. Because they wouldn't fit with the rapper on. It was okay to use with the NESE kit in parallel. Cuz I think but you couldn't take the rapper off in a 5S 1p or 2p tool pack. I would sure hate to have to buy a hundred to 140 cells for a pack and find out they're a slightly larger size or a smaller can size. Are now I also have to think about if it's aluminum or steel can. I'm glad you're welder is strong enough to weld the aluminum. There are some pouch cells that have one copper tab and one aluminum tab. More to think about more to know.

 

[From-A-To-B]

I'm glad you're welder is strong enough to weld the aluminum. There are some pouch cells that have one copper tab and one aluminum tab. More to think about more to know.

Just to be clear- I've tried spot welding aluminum pouch cell tabs in the past and had no luck. Those tests included using 0.1mm nickel strip to facilitate the weld. I've never tried with abrading the aluminum tab as was done with the aluminum cell cases, above. But I imagine that, much like nickel-copper sandwiching projects -- the trick is to use another metal (nickel / nickel-plated-steel) to facilitate the weld because aluminum is too conductive to allow for spot welding on its own.

 

[999zip999]

They sell A123 with one cut aluminum tab and laser welded a copper tab. They say their new cells but anytime the welded tab tabs I think of the recalled recalled car batteries that they rip the cells out of a laser welded package and they try to reweld tabs on them so when you buy cells you got to make sure that they don't pull the okie dokie on you but one manufacturer thinks he should cut the aluminum tabs on a new cell and laser weld a copper one on for you. I don't worry about it I just bolt them together.
But back to spot welding yeah I was going to buy one of those little two capacitor welders for under 100 bucks because I'm cheap but that b welder sure looks good I guess it'll cost at least 300 bucks.