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18650 best soldering technique?
#11
We highly recommend that no powerwall be put anywhere near a home, vehicles, or where property damage to yourself or others could occur. We always advocate putting the power bank in some sort of external building. This is regardless if using new or used cells.
So yes, we agree to not put any of these near our loved ones.

Even spot welded pack could fail. We also don't know if the failure was due to the welding, the soldering, or the failure of the cell itself for some other reason. So you cannot say with 100% certainty that a soldered cell will fail "because" it was soldered. There is absolutely no way to know for sure.

We also know that using high volumes of water is how to "contain" these fires. There is no way to "put them out" as they provide their own oxygen. Only thing we can hope is to contain the blaze until it becomes cool enough that the chemical reactions cease.
These fire can happen with spot welded packs just as easily as it can happen with soldered packs. Again, we don't know 100% sure if the cell went rogue and short circuited itself, if there was a solder ball under the cap, if there as a spot weld that actually blew a hole in the casing and caused corrosion to the point of self igniting. We just don't know.

As far as videos go, here's Lithium Solar's Pack: https://youtu.be/fber6bUvzuE?t=324
Also, just for added bonus material there is also DIY Tech & Repair's video: https://www.youtube.com/watch?v=G9WNutq6PV0


And something to take to note, just because the "casing" got up to 60C does not mean the internal part of the cell reached that temperature. I have not seen a video those shows how much heat goes "into" the cell rather just along the casing.
I reviewed about 10 random cell datasheets to see what their temp ratings were. Every one of them was 60*C. If the "casing" only reaches 60C for a few seconds, that is no where near the "operating" temperature of the internal of the cell. And I would consider operating cell in an environment longer than a few seconds.
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#12
(07-14-2020, 12:04 AM)Korishan Wrote: [...] These fire can happen with spot welded packs just as easily as it can happen with soldered packs. Again, we don't know 100% sure if the cell went rogue and short circuited itself, if there was a solder ball under the cap, if there as a spot weld that actually blew a hole in the casing and caused corrosion to the point of self igniting. We just don't know [...]

And something to take to note, just because the "casing" got up to 60C does not mean the internal part of the cell reached that temperature. 

Yes, of course, fires can happen in any pack for motley reasons, but that implies little about the matter at hand. All reputable manufacturers strongly recommend against soldering (cf. post #3) because it is inherently much more dangerous than spot-welding due to the much higher risk of internal damage due to the much greater thermal load while soldering. Understanding precisely why that is true requires a fair amount of expertise - so it's better to defer to expert knowledge on such rather than instead rely on anecdotal evidence (such as "I've done it a lot and nothing bad happened yet"). 

As for making guesses about the temperatures that cell components may reach during soldering, and what consequences that may have on safety, that is probably difficult even for experts. When it comes to matters of safety, it is best not to rely on guesses. Better to be safe than sorry.
#13
Manufactures also state that the cell should *never* be used outside of its original design/pack. Which means, "we" are using them against the manufactures recommendations as we are using them in a way that they were not meant to be used for.

And, they probably only state that to cover their own butt. It cuts drastically down on manufacturing accidents. Mass production "obviously" requires spot welding. It would be stupid to do soldering on an industrial scale.

Also, for making guesses that spot welding is the "only" way to go because it "might" cause damage to the cell is just as blind as saying soldering causes damage to the internal structure of the cell. As you yourself noted, "that is probably difficult even for experts". So therefore, your anecdotal dogmatic approach about stating that spot welding is the "only" acceptable method is not solid enough.

Perhaps after doing loads of tests you can come back with the results with videos and graphs and maths to back up your claim.
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#14
(07-14-2020, 01:23 AM)Korishan Wrote: Manufactures also state that the cell should *never* be used outside of its original design/pack. Which means, "we" are using them against the manufactures recommendations as we are using them in a way that they were not meant to be used for.

And, they probably only state that to cover their own butt. It cuts drastically down on manufacturing accidents. Mass production "obviously" requires spot welding. It would be stupid to do soldering on an industrial scale.

Apples vs. oranges. The "never solder to cells" warning is in datasheets, which are targeted at battery professionals (engineers, pack manufacturers, etc) who are presumed to already have requisite expertise on design and manufacture of battery packs, but who may well lack the lower-level expertise yielding intuition that soldering may internally damage cells, making them less safe. Iirc in the old days there were some incidents due to cell soldering before the dangers became common knowledge among such professionals (long before consumer use of Li-ion cells became common). There would be no reason for such soldering warnings if it were merely inefficient ("stupid on industrial scale"). Rather, the warning exists because soldering to a cell may make it less safe - not only in end use, but also in pack assembly, storage, and transportation.

OTOH, the recent warnings on cell labels are targeted at consumers - spurred primarily by the widespread adoption of cells in vaping. As the many recent vaping accidents show, Li-ion cells generally are unsafe for use by a layperson without any special Li-ion knowledge, since they typically wrongly assume that they are just as safe as other common consumer-level cells.

While it is possible to remedy the latter problem by better educating consumers on Li-ion safety (as some of us attempt to do in various hobby forums), there is no analogous workaround for the soldering problem because the deficiency is an inherent property of current cell design. They simply are not designed to handle the much larger thermal load imposed by soldering. That may be fixable with new designs, but there is little motivation to do so since there is no demand for such by professionals.

(07-14-2020, 01:23 AM)Korishan Wrote: Also, for making guesses that spot welding is the "only" way to go because it "might" cause damage to the cell is just as blind as saying soldering causes damage to the internal structure of the cell. As you yourself noted, "that is probably difficult even for experts".  So therefore, your anecdotal dogmatic approach about stating that spot welding is the "only" acceptable method is not solid enough.

My point was simply that what's difficult (but doable) for experts may well be hopelessly impossible for novices. You are questioning advice of experts based on what? Do you have their deep knowledge of battery electrochemistry and cell design and manufacture? If not then why do you think it is wise to ignore such sage advice, esp. when it comes to matters of safety - where wrong guesses could wreak havoc?

It seems you presume that the experts recommendations against soldering are "blind guesses". But that's not typically how we scientists make logical inferences. I don't know offhand if they ever did rigorous studies on such, but if they did they were probably so long ago that they are unlikely to be accessible online now (and probably only available to OEM partners - like much data from manufacturers). If there is interest I could elaborate on possible reasons that may be behind such inferences, but I'd rather not waste my time doing so if it will simply be (wrongly) quickly dismissed as "dogmatic", seemingly without careful consideration.
#15
(07-14-2020, 03:10 AM)gauss163 Wrote: OTOH, the recent warnings on cell labels are targeted at consumers - spurred primarily by the widespread adoption of cells in vaping. As the many recent vaping accidents show, Li-ion cells generally are unsafe for use by a layperson without any special Li-ion knowledge, since they typically wrongly assume that they are just as safe as other common consumer-level cells.
Like the warning label on a hairdryer, "Don't operate in the shower"

(07-14-2020, 03:10 AM)gauss163 Wrote: They simply are not designed to handle the much larger thermal load imposed by soldering. That may be fixable with new designs, but there is little motivation to do so since there is no demand for such by professionals.
As in the current technologies, or the ones that were in effect "in the old days"?

(07-14-2020, 03:10 AM)gauss163 Wrote: You are questioning advice of experts based on what?
I'm not questioning "experts". I'm questing what you have proposed as being from experts. The link you posted above it to more of your viewpoint in another forum, not a tech document or datasheet that backs up what you are starting. At this point, what you have said is basically here-say.

(07-14-2020, 03:10 AM)gauss163 Wrote: Do you have their deep knowledge of battery electrochemistry and cell design and manufacture? If not then why do you think it is wise to ignore such sage advice, esp. when it comes to matters of safety - where wrong guesses could wreak havoc?
No I do not have "deep" knowledge of the designs. But what I do know is that there are companies that still solder their cells. I know that there are people who are capable of applying the proper amount of heat to a cell during solder so as to not damage the cell. In several videos there have been thermal recordings of soldering and spot welding. In both instances, the cell never got over 50C. Even the spot welding ones reached close to 45C. Even spot welding incurs heat into the cell. However, spot welding also "can" damage the cells physically in a way that is not noticeable to novice just as soldering can. So for a "novice", both methods can not be compared or one made better than the other. It only takes a pin prick of a hole from spot welding to make the cell super dangerous. At least soldering you know relatively immediately if you got some solder inside the Pos cap. There is no ticking time bomb

(07-14-2020, 03:10 AM)gauss163 Wrote: It seems you presume that the experts recommendations against soldering are "blind guesses". But that's not typically how we scientists make logical inferences. I don't know offhand if they ever did rigorous studies on such, but if they did they were probably so long ago that they are unlikely to be accessible online now (and probably only available to OEM partners - like much data from manufacturers). If there is interest I could elaborate on possible reasons that may be behind such inferences, but I'd rather not waste my time doing so if it will simply be (wrongly) quickly dismissed as "dogmatic", seemingly without careful consideration.

I do not presume it's "blind guesses". Again, I haven't seen any articles pointed out by your previous comments as to your backings. Currently, you have only said what "you think" to be accurate. Please back up your claims with accurate information, not links to other forum posts.
It is only made dogmatic when there is no evidence to the information presented. Please share your information with relevant data referrals (in its own thread though, please).
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#16
(07-14-2020, 04:21 AM)Korishan Wrote: I'm not questioning "experts".  I'm questing what you have proposed as being from experts. The link you posted above it to more of your viewpoint in another forum, not a tech document or datasheet that backs up what you are starting. At this point, what you have said is basically here-say.

But you do appear to be questioning experts, since above I posted in this forum excerpts of datasheets from all top-tier cell manufacturers that explicitly warn not to solder on cells. That's not "here-say" [sic].

(07-14-2020, 04:21 AM)Korishan Wrote: No I do not have "deep" knowledge of the designs. But what I do know is that there are companies that still solder their cells [...]

Please give some evidence supporting that claim. I don't recall ever seeing such soldering by any reputable company.
#17
I have yet to see a post about soldering vs spot welding.
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#18
I have soldered all my packs with no issues.  Over 8,000 cells and counting....

Oldest batteries (3,300 cells) are 2 yrs old with 730 charge/discharge cycles with average 40% DOD.

The proof is that there has been 
1) no loss of pack ah from pre-solder (adding up the ah of individual cells) to post solder (discharge test)
2) no noticeable degradation on the 2 yr old packs
3) no balance required between the 2 yr old (3,000 cells) batteries and the newest battery (~1,400 cells) with 30 cycles.
which indicates a healthy set of packs!

I use/used 100w Weller - https://www.amazon.com/gp/product/B002I7...UTF8&psc=1
and (self fluxing) solder - https://www.amazon.com/gp/product/B07KWD...UTF8&psc=1 
which allows for quick soldering.

I do agree that spot-weld can be faster - but you have to get proper spot welder / technique all lined up Smile
#19
(07-14-2020, 02:24 PM)OffGridInTheCity Wrote: I have soldered all my packs with no issues.  Over 8,000 cells and counting....

Oldest batteries (3,300 cells) are 2 yrs old with 730 charge/discharge cycles with average 40% DOD.

The proof is that there has been 
1) no loss of pack ah from pre-solder (adding up the ah of individual cells) to post solder (discharge test)
2) no noticeable degradation on the 2 yr old packs
3) no balance required between the 2 yr old (3,000 cells) batteries and the newest battery (~1,400 cells) with 30 cycles.
which indicates a healthy set of packs! [...]

Such anecdotal observations don't "prove" anything other than you are very lucky that nothing bad has happened yet.

We don't know how much soldering on cells increases the risk of future dangerous events. It may well be hundreds or thousands of times more risky. If you choose to ignore the manufacturers' warnings and expose yourself to such risks than that's your prerogative. But if you seriously value safety matters then you should heed the warnings of all top-tier manufacturers to never solder directly to Li-ion cells.  

Also worth emphasis: such risks are likely compounded by other highly risky practices, e.g. some hobbyists attempt to use cells that have been severely overdischarged - which is also prohibited by manufacturers (most datasheets warn not to charge cells that are below 1.5 to 2.0V, though iirc one goes down to 1.0V). The damages caused by both this and soldering likely interact in ways that may increase the risks even further. And many of the cheap BMS used are very low quality and further compound the risks. 

As always, it's better to be safe than sorry. But the best I can do is guide you to knowledge that may help you to make wise decisions. The rest is in your hands. I sincerely hope that you don't lose them due to unsafe practices.
#20
Will respectfully disagree.   My results are consistent with many battery packs/powerwalls built over the last 4 years as evidenced by many youtubes + the experience shared on this forum.     I would not call this history of success 'anecdotal'.      Here's an interesting youtube investigating solder/heat in practical terms - https://youtu.be/G9WNutq6PV0

Remember that warnings are not the same as actionable facts in DIY powerwall terms.   For example, these Ring batteries have a 'severe warning' 
 
but they absolutely perfect for DIY powerwalls Smile


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