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18650 best soldering technique?
#31
And another thing....
#32
Maybe we could grab a dead 0V cell or two, slice in half long ways & solder away with some different temps/techniques & see what looks like melting inside at either end?
Anyone got a good band saw with a narrow blade?

Update:
PS will need chemical gloves due to the electrolyte.
Looks like could just cut a panel out of the side with a knife/sidecutters.
Will try & report back....
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#33
(07-20-2020, 12:28 PM)Redpacket Wrote: Maybe we could grab a dead 0V cell or two, slice in half long ways & solder away with some different temps/techniques & see what looks like melting inside at either end?
Anyone got a good band saw with a narrow blade?
Hmm even that would cause some heat maybe a very thin waterjet cutter?
Don't know what kind of contamination that would cause in the water tray though.
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#34
You wont see anything by eyes to be honest. You would need some kind of x-ray system to dig into it. Thats basically how they test when spotwelding cells to make sure it works.

Note that when opening the cell you contaminate the inside and therefore that most likely affect as well.

Looking into the heat on the inside is the only thing you can do but that also depends on having the cell as a whole since the heat traverses on the side.
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#35
(07-14-2020, 12:04 AM)Korishan Wrote: [...] As far as videos go [...] DIY Tech & Repair's video: https://www.youtube.com/watch?v=G9WNutq6PV0

The thermal test in that youtube was not properly performed, e.g. see Olavi's comments on the video about emissivity etc. The video author replied admitting he has little experience with thermal testing ("Olavi yeah i only went for the sleve. The inside i didnt care about as such. Good points. I have not much experience with thermal as such").

Below are some thermal images from a Flir A325sc that compare various types of welding to soldering with low temperature alloys (from a study on the feasibility of soldering using low temperature bismuch and cadmium alloys Bi52Pb40Cd8, Bi55.5Pb44.5, Sn50Pb32Cd18 with melting points 90°C,124°C,145°C). Take note that the temp scales differ in each image.

Compare spot-welding (upper left) vs. soldering (lower right) using Sn50Pb32Cd18 (145°C melting point). Notice spot-welding yields much lower temperatures and has much more localized heating, whereas soldering is much less localized and already close to the dangerous 80°C decomposition temp (they wrote "the electrochemically active materials start to decompose at about 80°C. That is why cell manufacturers mostly define 60°C the maximal temperature of a lithium-ion battery cell"). The common Sn60Pb40 alloy has a much higher melting point of 190°C (e.g. popular Kester 24-6040-0027) so it will be even worse. Indeed, if it follows the trend below it would be 93°C-101°C at 6s after solder, well above the dangerous point.
[Image: 3RNlC.jpg]

Excerpted from: Brand et al. Electrical resistances of soldered battery cell connections. Journal of Energy Storage, Vol. 12, August 2017, Pages 45-54
#36
Yeah all that is nicely said and done. We agree it's not optimal to solder to 18650s. That's why we're discussing how you can solder and not to leave a huge thermal spot. My take has always been high heat (> 150 wattage) small chisel tip. Quick and localized. My solder spots are no more than 1/8" or 2-3mm. But that being said, unless there's a high risk of explosion it's really not a big deal. Yes there's a possibility of degradation of the cells but for god's sake we're used repurposed cells to begin with! 

So the bottom line is it's not a big deal. Just solder on dude...
#37
(07-25-2020, 11:22 PM)not2bme Wrote: [...] But that being said, unless there's a high risk of explosion it's really not a big deal [...] just solder on dude

It really is a big deal to anyone who seriously values safety, viz. soldering may greatly increase the risk of explosion, since - as all top-tier Li-ion cell manufacturers warn - it may damage crucial safety mechanisms (CID(vent), separator, etc).  Ignore it at your own risk.
#38
Topic title: "Best soldering technique?"

gauss: Please create a new thread discussing the comparison between soldering and other methods including dangers and suggested alternative techniques. This thread was created to discuss "soldering" techniques. Not if it was good/bad/fine.

Please stay on topic.
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#39
^^^ Imo, safety is always on topic in a thread like this. To imply otherwise is extremely irresponsible. I happen to personally know folks who have serious injuries from Li-ion explosions (which could have been avoided if they were properly informed of the risks). Do you?
#40
(07-26-2020, 12:01 AM)gauss163 Wrote: ^^^ Imo, safety is always on topic in a thread like this. To imply otherwise is extremely irresponsible. I happen to personally know folks who have serious injuries from Li-ion explosions (which could have been avoided if they were properly informed of the risks). Do you?
Safety is great & yes we need to keep it in mind. 
But there's a huge number of folk on this forum with a combined soldered cell count that'd have to be well over 1,000,000 cells, most soldered, some spot welded.
Daromer alone has 10's of thousands.
So far the fire thing has not proven to be a problem from soldering.

IMHO, a process on the outside of the case is different to heating the core of the cell. 
There are several layers before the electrolyte sees heat especially at the + end.
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