Building your own 18650 / 21700 pack: what you need and whether you should
Should you: only if you will build more than one, or need a shape nobody sells. A quality prebuilt 48V 15Ah pack is $350 to $500; building one costs $250 to $350 in cells plus a $150+ spot welder plus the BMS, nickel, fish paper, cell holders and shrink wrap. The first one is not cheaper.
If you do: new matched cells from a reputable supplier (not "recycled laptop cells" for a traction pack), a real spot welder with pure nickel strip (test with the magnet-and-sand test; plated steel strip gets hot), fish paper rings on every positive, a BMS with balance leads landed in the right order (series tap 0, 1, 2… or you fry it), kapton over everything, a hard case. Charge the first time outside, on concrete, watching it.
Read the Endless Sphere battery stickies twice. Then decide.
#battery-pack#18650#spot-weld#bms#nickel-strip#ebike
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The "what went wrong" section is the most useful part of this. More people should do that.
Unplug it. Always. Takes two seconds and the worst case otherwise is a trip to the ER.
Followed along, got it done in about twice the time quoted, but it is done and it works.
Can confirm, the cheap part is the one that fails. Replaced mine twice before reading this.
Would this work on the older model? Mine is about ten years older than the one shown.
Question: do you need to disconnect power for this or is it safe to leave it plugged in?
Bookmarking. I have exactly this problem and was about to pay someone.
Glad it helped.