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18650 Pinholes

Ianmac52

Ianmac52
Joined
Jun 14, 2020
Messages
3
Location
London U.K.
Hi
Started building battery packs with harvested 18650's. I think I know where I am going wrong but would like some like minded person(s) to comment.
The basic problem is that when I spot weld the packs I have ended up with a number of pinholes in the negative end of some cells.
This is the first time I have harvested cells so I figure mistake 1 was to use a dremel with a fine grinding wheel to remove previous spot weld tags. I can see that they would work on having a minimal amount of metal thickness for the casing so I have probably shaved a bit off thus making them prone to holing.
The second thing is the welder, it is a d.I.y. one (groan) using a 12 volt battery etc. My original intention was to fit a timer to limit the number of milliseconds of power to each weld, but I managed to brick the timer going through all the permutations of connections as there is no manual available. So the weld time is governed by the user and on occasions was probably a couple of milliseconds too long. I have another timer on order but it is weeks away and I had to scratch that itch so to speak.
I am guessing that the pin holed cells would be deemed potentially dangerous so these are being removed.
Would the consensus be that I am right or is there something I have not considered.
 
I would definitely scrap the pinholes cells. Some of them will actually leak some kind of (electrolyte?) fluid. Most likely, your time is too long. I also wouldn’t grind on the cells. Your best bet is to peel the old contacts off and snip the old welds with some tiny side cutters. That way the base is still at original thickness
 
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