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Model 3 battery bond wire fuseable link size
- Thread starter spaceballs
- Start date
EV-Tech Exp
Member
I'm going to guess nickel or palladium plated copper. Aluminum wire, although technically usable, has dissimilar metal adhesion issues. Unless the battery cases and the busbars are aluminum, I'd be concerned with reliability issues. Plus they're higher resistance than copper.
darth_vad3r
Well-Known Sith
Roadster??
AlanSubie4Life
Efficiency Obsessed Member
I want to know why there are red circles around some of the cells.
Where are these fusible links located? I see thin wires connecting to each battery terminal in the complete battery, but what you have pictured in the original post doesn’t look like it is lifted from those locations. Maybe the edges been snipped away so the shape does not match? Or...?
A single fusible link just removes one 2170 cell from the pack, right? Or more? I know it is 96s46p, but don’t know exactly how failures are dealt with, or how a single cell could be removed from the pack...etc. Is it literally just a fuse and blows if too much current flows in the cell? (I assume so.) Or is it blown by an external circuit on command?
What other methods exist in the pack to bypass defective elements? Can a single block of 46p elements be entirely bypassed somehow? But that would lower the maximum pack voltage - I guess that is ok?
Really? is this a tesla battery module?
Came marked from Tesla, the ones circled are ones that failed QA I believe, as there are two ultrasonic weld marks present vs the normal one.
The red circles indicate a visual check that identifies a potentially weak wire bond. Typically if there is just one, it can be plucked and isolated, and no effect on safety or range. If there are multiple, there module is placed offline for further checks, and then wire bonded again to ensure enough cells are connected to the IC (interconnected) plate.
AlanSubie4Life
Efficiency Obsessed Member
Wait, what? Occasionally 2170 cells (I guess the picture above was not 2170, but I'm referring to a Model 3 pack) are just left disconnected in the pack and it's ok? I guess you said "potentially weak". What if the wire bond is obviously weak or disconnected? Is the wire bond redone in that case, even if it's just a single cell? What's the maximum number of cells out of 4416 that can be left disconnected? (It sounds like there are also separate requirements on the number allowed within a parallel group of 46?)
Is this the reason for the TSB/Recall of a small set of AWD batteries in late-summer 2018?
darth_vad3r
Well-Known Sith
I’m guessing you wouldn’t be able to notice until there were 2 dozen cells randomly disconnected.
22/4416 is 0.5%, it doesn’t surprise me if they let them out the door with a few disconnected.
This is the wrong way to do the math because it assumes the disconnected cells are evenly distributed among the 96 cell groups. The thing that actually matters is that the cell groups have equal Ah capacity so that they can remain balanced. A high speed probing station could actually find bad bond wires pretty quickly.
darth_vad3r
Well-Known Sith
darth_vad3r
Well-Known Sith
We could probably use the Birthday Problem as an analogy, to figure this out exactly
[EDIT: Yes we can. Birthday problem - Wikipedia ... it appears for 83-99 days, you need only 12 people, so I'd say for 96 bricks, with 12 disconnected cells there is a 50% chance two are in the same brick (same "birthday").]
Anyways, even a random failure could concentrate them in one brick, yes, so by "random" I guess I really meant what a human would look at and think is random, since if we see tails flipped 4 times in a row on a coin we think it's non-random for some reason, even though it is
Modules for M3 use adhesive to hold it all together essentially. Once cells are glued to tubes, and bandoliers placed together between clamshells, its kinda hard to remove a cell...so if there is a bad bond that can't be resolved, or a bad cell (short from human error), a cell can be capped and isolated. Removed from a brick, it has little to no effect. Obvi the goal is to balance. There are tests done inline at various stations to ensure there is a minimum being met to ensure that you don't get an uneven module in a pack, causing an issue.
The TSB/recall was related to potential of weak wire bonds within a certain time frame and their likelihood of becoming disconnected. Happened to affect AWD, but no difference in modules from an AWD to RWD pack...
The TSB/recall was related to potential of weak wire bonds within a certain time frame and their likelihood of becoming disconnected. Happened to affect AWD, but no difference in modules from an AWD to RWD pack...
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