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18650 best soldering technique?
#1
I've tried several soldering irons and all sorts of soldering techniques.  I've developed my own, which I believe is superior to anything I have seen on YouTube.  It's certainly not how I learned to solder "properly", but it seems to work best for 18650s. And no, the solder is not "balled" - the contact is solid and cannot be simply scraped off.

See video in link
https://drive.google.com/file/d/1l7_27rw...LoX0V/view

Soldering iron: 70W Taiyo Electric PX-401, set to ~390C, with 5mm diameter "large tip for high thermal-storage", but cut at an angle to allow pointed contact.
 
 
 

Solder: Standard 60/40 rosin core, 1mm diameter

I think this technique works well, because:
1) The rosin has no time to boil away and gets to work immediately, maximizing its effectiveness
2) While the iron is fairly massive, the actual contact area is small at perhaps just 3mm diameter, thus heating all the area I need and not more.
3) The molten solder ensures maximum heat transfer to the cell surface in the shortest time, as opposed to pre-heating with a "dry" tip and then applying solder



The negative side is a bit more challenging, because some of the heat gets drawn into the cell. But it's basically the same procedure.  Just a little steeper angle to make the contact area smaller, and perhaps 2 seconds of contact.  Hopefully ending with something like this:
 
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
#2
The most important part of it is contact time. Quick contact and you're safe.

See my old article about it here:
https://xaeus.wordpress.com/2014/04/20/s...damage-en/
#3
The "best soldering technique" for Li-ion cells is: never solder to cells - it may greatly compromise safety. Instead you should use a spot welder like the pros do (they're cheap nowadays).  Soldering directly to a cell can make them much more dangerous by possibly compromising basic safety mechanisms such as the CID (which uses a penetration weld), or the separator, etc.  Every reputable cell manufacturer warns pack manufacturers not to use soldering, e.g. see the excepts below from datasheets:

LG
Do not solder on battery directly

Samsung
Don't heat partial area of the battery with heated objects such as soldering iron.
6.1.1 The cell should not be soldered directly with other cells. Namely, the cell should be welded with leads on its terminal and then be soldered with wire or leads to solder.
6.1.2 Otherwise, it may cause damage of component, such as separator and insulator, by heat generation

Sanyo/Panasonic
11) Soldering
Do not directly solder the battery.
The insulator could melt or the gas release vent might get damaged from the heat.
Additionally, the battery may catch fire, smoke, heat generation or explode.

Sony
Do not disassemble, remodel, or solder.
Do not solder lead directly to the battery body.
Do not apply solder directly to cells.
Under no circumstances should wires be soldered to battery terminals to enable use with other equipment
Do not puncture batteries with nails, strike them with hammers, step on them, or apply solder to them
khauser likes this post
#4
The required amount of heat to make the CID fail would be a *lot* for a soldering iron, considering the POS connection end is held up off from the rest of the cell.

If using a high enough massed iron and at least 60W, the time the iron is on the cell is not long enough to melt any of the plastic if the iron doesn't touch the shrink wrap in the first place.

The time that an iron should be allowed to make contact with a cell is NO LONGER than 3 seconds. Even 2 seconds is approaching the limit. This why it is imperative to have an iron with sufficient mass and heating wattage to transfer the required heat to melt the solder to flow. Place the solder wire on the cell, then apply the iron tip. The solder should flow almost immediately. Once it does, pull the iron off.

On the Pos end, you have a little more time, 4 seconds max. On the NEG end, 3 seconds is absolutely max time allowed.

Spot welding can be just as dangerous, if not MORE so, than soldering. A spot welder can burns holes straight through the casing. It is possible to cause holes and not even know it if there is a piece of nickel strip on top. It doesn't take much of a hole for electrolyte to get through.

For beginners, I would recommend soldering first. Then later on graduate to a welder. You can go straight to spot welding if you have plenty of bad/dead cells to test with to get the proper feel for it. And it's not weld 10 cells and you're a pro. More like 100's before you get the proper feel for it.
Proceed with caution. Knowledge is Power! Literally! Cool 
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Certified 18650 Cell Reclamation Technician

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#5
(07-13-2020, 07:26 PM)Korishan Wrote: Spot welding can be just as dangerous, if not MORE so, than soldering. A spot welder can burns holes straight through the casing. It is possible to cause holes and not even know it if there is a piece of nickel strip on top. It doesn't take much of a hole for electrolyte to get through.

For beginners, I would recommend soldering first. Then later on graduate to a welder. You can go straight to spot welding if you have plenty of bad/dead cells to test with to get the proper feel for it. And it's not weld 10 cells and you're a pro. More like 100's before you get the proper feel for it.
I won't disagree ... it took me a bit of effort to learn spot welding. I did indeed practice on throwaway cells, and I started with a value I knew would be too little and slowly worked my way up.

I recently tore apart a pack I made (the first pack I made, actually) and I'm happy to say that the attachments were quite solid without burning through, and the cells have not appeared to suffer any damage (including to capacity).

I use the Malectrics spot welder, driven by a LiPo pack (selected just for that purpose).
#6
(07-13-2020, 07:26 PM)Korishan Wrote: [...] For beginners, I would recommend soldering first [...]

That's very dangerous advice, I strongly encourage anyone who values safety to follow the prior posted warnings of top-tier cell manufacturers, viz. never solder directly to Li-ion cells.

(07-13-2020, 07:26 PM)Korishan Wrote: The required amount of heat to make the CID fail would be a *lot* for a soldering iron, considering the POS connection end is held up off from the rest of the cell [...]

On the Pos end, you have a little more time, 4 seconds max. On the NEG end, 3 seconds is absolutely max time allowed.

What is the basis for your belief in these claims?   Do you seriously think you know better than the scientists and engineers who design and manufacture the cells?
#7
Considering that there have been literally 10's of thousands of cells that have been "soldered" on in this forum, and only a handful of cells failed, AND those cells failed because of lazy or improper soldering, then I think the "forum experience" speaks for itself.

As for spot welding, I have seen a LOT of people on this forum that have punctured holes in their good cells even after a few 100 spot welds have been done. So again, I say the forum's experience speaks for itself.

And, considering several members of this forum have done extensive tests of varying degrees as to how much heat, how much solder, how big of an iron, etc, etc, again, the forum speaks for itself.

Many knowledgeable people here, "including" (with actual legal degrees) Electrical Engineers, Space Engineers, Electrical Chemical Engineers, and many other types of very knowledgeable individuals. I don't recall all their names, but you can go through the "Introduce yourself" section to find them.

I know that both of you "khauser" and "gauss163" are new to the forum, not even a month here. Maybe a little bit of history reading would recommended of past experiences.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
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#8
I think all i did was relate my experience. I have not offered much of an opinion on the safety side of this debate because I don't know. I do know heat kills, and I personally am more comfortable spot welding.
I certainly didn't mean to offend you or anyone else.
#9
No offense taken.

I agree that heat kills. And so can a spot welder. Not everyone is as experienced with a spot welder as another. That is why I recommend a "newbie" start off with soldering. Or at least test spot welding on lots of bad cells.

In a recent video by Lithium Solar, he shows that one of his cells developed an electrolyte leak. It destroyed 2 of his cells. They were almost brand new cells. He spot welded those cells. It is possible that perhaps he poked a small hole in the cell while spot welding. I don't know. I don't have the cell to inspect it, and I don't know if he has the equipment to inspect it.
However, I am just noting that even an experienced spot welder (he's done 1000's of welds if not 10's of thousands himself) can poke holes in a cell with a spot welder. At least with a cell that has gotten a little hot from soldering will just slowly deteriorate over time and can be replaced w/o damaging other cells. A leaker will damage other cells around it. Something to watch out for
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)
#10
(07-13-2020, 09:35 PM)Korishan Wrote: Considering that there have been literally 10's of thousands of cells that have been "soldered" on in this forum, and only a handful of cells failed, AND those cells failed because of lazy or improper soldering, then I think the "forum experience" speaks for itself [...]

How do you know that some haven't failed?  It is quite common that folks are too embarrassed to publicly admit their mistakes. 

Unfortunately it is likely the case that some soldered powerwalls are ticking bombs and will fail down the road, since the effects of such cell damage may take many cycles to rear its ugly head. 

Of course it's a very personal choice just how much risk one is willing to take. But, relatively speaking, likely this is not far from playing Russian roulette.

To those who may not know: while it is easy to extinguish small pack fires with water (it's the recommended way), you'll have no hope of doing likewise with a huge pack like a powerwall (you may have heard reports about Telsa packs reigniting days and even weeks later in junkyards). Huge pack fires are difficult to control even by professionals - not to mention the extremely toxic fumes from Li-ion fires - which can cause serious permanent damage from even a single whiff.

I wouldn't let my loved ones anywhere near a soldered powerwall. Far, far too risky.

(07-13-2020, 09:53 PM)Korishan Wrote: In a recent video by Lithium Solar, he shows that one of his cells developed an electrolyte leak. It destroyed 2 of his cells. They were almost brand new cells. He spot welded those cells. It is possible that perhaps he poked a small hole in the cell while spot welding. I don't know [...]

Do you have a link?  Such leaks can be caused by many factors, most having nothing to do with spot welding.


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