hwy17
Anti-Solar Enthusiast
This is just one that's been in my mind for a while. I have seen posts of people who have had m6 studs fail despite what they believed to be reasonable torque application. The stud material itself could be substandard, and as far as I can see these studs are only held down by a maybe 4-5mm deep aluminum collar, which is the part that gets actually welded onto the cell.
So say that you tightened a whizz nut down, unknowingly right to the very point of failure, the steel stud or nut threads being just past their max stretch and beginning to separate, but not to the point that you could detect it giving away. Then say, over time, the thermal cycling of the battery even just by the diurnal ambient temperature pulled and pushes at the stud and the hold gets weaker and weaker.
What is the failure mode as that bus bar connection goes high resistance while under load, and do we have a common mechanism in place to stop it?
I'm thinking heating is how the failure progresses, at the connection but also that terminal starts sinking the heat into the cell.
Does any common mechanism stop this here? Do the cell taps definitely start seeing a voltage drop on the cell or an adjacent cell as connection resistance rises? I hope so, because then the standard monitoring for low cell would catch that, and interrupt the load current. What if it was charging? Would the bad connection look like high voltage to the cell taps then, and trigger charging disable protection? Or would it still appear as a low cell?
I guess the same questions all apply to a fluke internal short in a cell. Do we have a common mechanism that does catch internal shorts or are we all just sort of betting we won't have one? This question might have an obvious answer that I'm just naïve about.
So say that you tightened a whizz nut down, unknowingly right to the very point of failure, the steel stud or nut threads being just past their max stretch and beginning to separate, but not to the point that you could detect it giving away. Then say, over time, the thermal cycling of the battery even just by the diurnal ambient temperature pulled and pushes at the stud and the hold gets weaker and weaker.
What is the failure mode as that bus bar connection goes high resistance while under load, and do we have a common mechanism in place to stop it?
I'm thinking heating is how the failure progresses, at the connection but also that terminal starts sinking the heat into the cell.
Does any common mechanism stop this here? Do the cell taps definitely start seeing a voltage drop on the cell or an adjacent cell as connection resistance rises? I hope so, because then the standard monitoring for low cell would catch that, and interrupt the load current. What if it was charging? Would the bad connection look like high voltage to the cell taps then, and trigger charging disable protection? Or would it still appear as a low cell?
I guess the same questions all apply to a fluke internal short in a cell. Do we have a common mechanism that does catch internal shorts or are we all just sort of betting we won't have one? This question might have an obvious answer that I'm just naïve about.
