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How much damage to a cell is too much?
#1
I started putting my first 18650 pack together today and my spot welding solution can be finnicky and stick on, burning a hole in the ends of my cells sometimes. However, only one cell seemed to actually be punctured as I could smell the fruity electrolyte, and I'm getting rid of that one. I'm going to test the voltage of all the cells again tomorrow and see if any dropped.
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#2
No damage is allowed.
Hole=bin
Sent=bin

Why gamble. You are unsure you bin. You dont even ask.

Voltage is not an indicator of IF the cell survived.
Jim Jr., OffGridInTheCity, Korishan like this post
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#3
Yup, holes means the containment device is now compromised and can leak electrolyte. If not caught soon enough, this goo can wreak havoc on a pack as it accelerates the oxidation process rapidly. You could go from shiny silver cells to a brick of rusty cells in a matter of weeks.
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#4
(07-26-2020, 08:01 AM)daromer Wrote: No damage is allowed.
Hole=bin
Sent=bin

Why gamble. You are unsure you bin. You dont even ask.

Voltage is not an indicator of IF the cell survived.

Well, because my spot welder is not 100% consistent, I know this will always happen during welding an entire pack together, and I'll probably end up re-buying cells forever at this point. Even the cells I didn't damage can hardly be removed from the nickel without damaging them, it seems. 

I kind of just wanted to try this once and I don't plan on making a hobby out of it, so I avoided buying hundreds of dollars of specialized equipment.

I'm not really sure what to do now short of just quitting while I still can. For anyone who wants to help me debug my spot welder, it's basically a foot pedal controlling a 555 timer in a pulse-shortener configuration, connected to a SSR, connected to a truck solenoid, connected to a car battery. I tuned it to turn on for the right amount of time when I press the foot pedal, and when it works it works perfectly, but then maybe 10% of the time it just makes a big spark and the solenoid clicks 4 or more times instead of 2 like it's supposed to.

For what it's worth, I noticed that most of the time, I damaged the positive side of cells, which seems to be hollow. (I'd guess ~2mm of air underneath) Maybe it's more prone to making the spot welder act up. It also seems like not as much of an issue as damaging the negative side. Any suggestions on what to do now?
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#5
Big sparks can be caused by not holding the electrodes firmly in contact with the nickel strip. I now use a welding wand only have to hold one object firmly instead of 2.
Later floyd
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#6
(07-26-2020, 02:54 PM)floydR Wrote: Big sparks can be caused by not holding the electrodes firmly in contact with the nickel strip. I now use a welding wand only have to hold one object firmly instead of 2.
Later floyd

I was always pressing firmly but it was dark and maybe I wasn't doing it right sometimes. I'm doing this outside but with lights at night because it's oppressively hot during the day.

What does a welding wand do?
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#7
Another thing to do is to do all your testing on dud cells. That way you don't have to worry about destroying good cells in the process of learning. This helps you zero in the welders settings and also hone your own skills to be more consistent.
You state that the welder isn't 100% consistent. It's possible that you aren't always applying the same amount of pressure on "both" electrodes with sufficient pressure. There's also the issue of possible contaminants on the strip that hinders contact. So you might also want to do a quick wipe with an alcohol cotton ball. This will help remove any residual oils during the manufacturing process.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
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#8
(07-26-2020, 03:22 PM)Korishan Wrote: Another thing to do is to do all your testing on dud cells. That way you don't have to worry about destroying good cells in the process of learning. This helps you zero in the welders settings and also hone your own skills to be more consistent.
You state that the welder isn't 100% consistent. It's possible that you aren't always applying the same amount of pressure on "both" electrodes with sufficient pressure. There's also the issue of possible contaminants on the strip that hinders contact. So you might also want to do a quick wipe with an alcohol cotton ball. This will help remove any residual oils during the manufacturing process.

I'll try that, thanks. Do you have any recommendations about removing the damaged cells from the pack, trying to preserve the undamaged ones? I think whatever I do is going to break the nickel strips, so this is going to get pretty janky looking with multiple layers of nickel patched together. Different thicknesses too, since I was experimenting with which worked best.
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#9
Both electrodes are in one unit so you just have to old one thing not two. if both electrodes aren't in firm contact you get the hole in the nickel strip and big sparks. get a couple pieces of nickel strip and practice welding them together. All it takes is for one of the electrodes to be a fraction of a mm off the surface of the nickel strip to create big sparks, You may jerk when pressing the foot peddle expecting a spark involuntarily but it can and has happened. I use a wand and auto weld pulse, welds when both electrodes are in contact with the nickel strip. and I still occasionally get sparks. but no more holes in nickel strips or welding holes in cells. practice on a scrap piece of nickel strip. Took a bit for me to get the technique down. I am no expert on welding others here have welded many hundreds/ thousands more cells than me.
Later Floyd
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#10
(07-26-2020, 03:41 PM)floydR Wrote: Both electrodes are in one unit so you just have to old one thing not two. if both electrodes aren't in firm contact you get the hole in the nickel strip and big sparks. get a couple pieces of nickel strip and practice welding them together. All it takes is for one of the electrodes to be a fraction of a mm off the surface of the nickel strip to create big sparks,  You may jerk when pressing the foot peddle  expecting a spark involuntarily but it can and has happened. I use a wand and auto  weld pulse, welds when both electrodes are in contact with the nickel strip. and I still occasionally get sparks.  but no more holes in nickel strips or welding holes in cells. practice on a scrap piece of nickel strip. Took a bit for me to get the technique down. I am no expert on welding others here have welded many hundreds/ thousands more cells than me.
Later Floyd

I practiced on maybe 20 cells but then I ran out of clean ones. I might need to clean up some dud cells specifically to practice on, but the noises my spot welder makes are making me suspect that something is happening that's out of my control.
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