evb wrote: deVries wrote:
Do you think replacing a failed cell is possible?
Yes. When I assembled this battery, one cell (4th) was bad and I changed it for 30 mins.
unfolded tabs by screwdriver difficult
I guess if change one of cells more 3-5 times, tabs can break
I agree, it is very hard to unfold the tabs once they have been crimped, but it is doable at least once.
I am so glad to see other people demonstrating success with the crimping method. I pioneered the crimping method for these cells in 2010: http://endless-sphere.com/forums/viewtopic.php?f=6&t=12461&start=60#p281360
But my implementation was met with criticism and skepticism, and I was really frustrated by comments from certain "experts" that such a join was resistive enough to heat up when loaded with an "ebike-significant" load, and the tabs would quickly come loose. I proved to myself that a crimped joint could handle the load without heating up - I mean heck both sides of the entire tab is in contact - and two years later those packs are still going strong, so in-your-face to my critics
. If you are building an ebike pack, you don't need a fancy heavy rig to hold it all together, save yourself a ton of hassle and just crimp the cells together.
If you want to put 600a through the cell, a little spot-weld will help:http://endless-sphere.com/forums/viewto ... 14&t=29959
I like the cotter pin idea for spot-welding (unnecessary for crimping), because it makes the external clamps I used unnecessary. I can see putting a cotter pin over the end of a pair of tabs instead of the steel strips I used, spot welding through the cotter pin to melt the tabs together, then roll it up and crimp it together. The crimp would carry the load, and the cotter-pin weld would guarantee a weld no matter what happens to the crimp. If you have to replace a cell, unroll the crimp, cut off the cotter pin, and there will still be plenty of tab to spot-weld a new cotter pin.
liveforphysics wrote:You do not want any conduction through the pin itself. For long-term function it would be best to even put a little layer of kapton where the pin sits just to avoid the chance of carrying any current through the pin itself.
Luke, you always seem to see an angle I miss, but I don't understand this issue. Since this pin is external to the interface between the tabs, isolated from the pack and outside air with heatshrink, what is the risk here?