Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Spot Welding nickel strip as a fuse
#1
This is NOT a place to debate Welding vs. Soldering.  Please start a new thread for that.  I've done both and have personally found that they both can be dangerous if one isn't careful.

I've seen the videos of folks talking about their preferences between soldering and spot welding.  I've also seen some video evidence that fuses perform well in some cases but not others.  what I haven't seen is catastrophic effects (besides manufacturing defects, Note 7 ect...) of spot welding.  The packs we open have 6 or 9 cells mostly and are all spot welded.  I've measured from .1-.25 thickness of the nickel strips used.  Some pure nickel, some nickel plated (really easier to weld and cheaper but not my style) and obviously rely on the bms for safety.  There are millions of them out there that haven't failed and I've seen with my own eyes .15 nickel wire literally glow red hot and vaporize from a huge short in a failed experiment with magnets on a 56P pack.

My theory is:
.15 nickel may retain integrity and burn up the cells of a 6 cell laptop pack but not a higher Amp 56P pack.  The nickel will be burned up and act as a fuse 

My question is:
Has anyone tested this?

Thanks.
Reply
#2
0.15x7mm nickel strip, say 25mm long between centers of 2 cells, would have a resistance of 62.5 micro ohms per side at room temperature, so to this extent its a fart in the breeze compared to the esr of a cell,

now in your 56P case, i will assume 8 rows, 7 columns, with all the strips being joined at one edge, with the strip on both sides, so each of the 8 columns would be ~880 micro ohms to the busbars, so effectively at the busbar 110 micro ohms + whatever the ESR of the batteries. and i'll assume each cell able to produce a peak short current of atleast 20A per cell before the chemistry limits them, so even though the esr is lower, lets say an effective ESR under short of 0.2 ohms per cell.

so 110 micro ohms for the strip, 3600 micro ohms for the batteries. and all charged up to 4.1V (worst case), roughly 1100A short current, and if that went through a piece of that nickel stripping 650mm long, (enough to short between the 2 busbars, he would be giving off only 2W of heat, which would make him hot, but likely never fuse unless he had a poor connection at one or both sides, which welding is meant to prevent.
7Bigjohn likes this post
Reply
#3
I've seen Nickel strip in power tool batteries that has been notched to crate a narrower section that acts as a fuse. About 2/3rds of the width cut away.
Some have said it works, I've not been game to try with something that easily pumps 60A into wire.
7Bigjohn likes this post
Reply
#4
Thank you all for the feedback.  I have some 96P prototype packs that I ruined by running 200Amps through a series of 4 for 19 seconds.  They ranged from 1.3-1.7Ah so it's not a big loss.  I think I'm going to do some testing with them.  I will post the results here and make sure I have pictures and video.
Reply
#5
I'm curious to see the results of that. For my first project, I'll be recharging off the grid. Kinda want to see about how fast I can charge a 4s bank. Smile
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)