The Need for Fusing Individual Lithium Cells

[GijsW]

Hi everyone,

I'd like to discuss the need for fusing individual cells within a pack.
The idea behind fusing cells is that when one cell fails (shorts), the fuse burns, the failed cell is isolated, and the rest of the pack continues to function.
Tesla does this by using small wires to connect each cells (search for "wire bonding lithium battery").
Most DIY'ers do not fuse individual cells, though some individuals do.

What are your thoughts on wheter or not to fuse? Does anybody have an idea what the chance is an individual cell will fail (does this happen often?), Should all (commercial) packs be fused individually?, Are smaller commercial packs built with fuses (like ebikes etc.)?

Also, would you fuse a LiFePo4 pack? (a shorted cell wouldn't easily result in fire, but could result in the pack seizing to work).

I'd love to hear your thoughts on this topic!

 

[john61ct]

Why not do some googling first.

Have been dozens of threads on this exact topic, some quite recent.

You're asking the community to waste so much time repeating the same discussions.

Just resurrect an existing thread, after educating yourself on the issues already covered.

 

[flippy]

Hi everyone,

I'd like to discuss the need for fusing individual cells within a pack.
The idea behind fusing cells is that when one cell fails (shorts), the fuse burns, the failed cell is isolated, and the rest of the pack continues to function.
Tesla does this by using small wires to connect each cells (search for "wire bonding lithium battery").
Most DIY'ers do not fuse individual cells, though some individuals do.

What are your thoughts on wheter or not to fuse? Does anybody have an idea what the chance is an individual cell will fail (does this happen often?), Should all (commercial) packs be fused individually?, Are smaller commercial packs built with fuses (like ebikes etc.)?

Also, would you fuse a LiFePo4 pack? (a shorted cell wouldn't easily result in fire, but could result in the pack seizing to work).

I'd love to hear your thoughts on this topic!

first off: tesla does not use fuse wire. they use wire. their way of using wire and welding it with ultrasonic heads is simply a result of solving the problem of how you automate welding millions of cells together every day perfectly. its simple speed of manufacuring as a robot can do this REALLY fast. (if you bolt a quarter million dollar weld head on it)

second: it has nothing to do with actual safety. its a theoretical nice bonus but i have not seen a blown wire in a tesla pack EVER and i dont know anyone that ever has. the only time i have seen broken wires was simply because the car crashed into a concrete pillar at 170kph at wich point the "fuse" wire was kinda redundant as the battery pack was smashed in a dozen pieces and ended up in a field 200 meters away along with what was left of the car. pretty sure the owner of that car was really worried about his cells being individually "fused" during that event.

your basic premise is flawed. you battery does not need any cell fusing. every cell already has a protection plug built into the top.

 

[spinningmagnets]

Nothing wrong with fusing cells with individually. The positive end is very robust and isolated from the jelly-roll inside. However the negative end of 18650 cells is sensitive to heat. So if you use soldering to attach fuse-wire, I strongly recommend you do so on the positive end.

Many believe that its un-necessary for an ebike, but...its your time and money.

 

[amberwolf]

Some existing threads that may have useful info
https://endless-sphere.com/forums/search.php?keywords=cell*+level*+fus*&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

https://endless-sphere.com/forums/search.php?keywords=cell*+fuse*&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search (not all of these are relevant, but you can typically tell by title)