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18650 best soldering technique part2
#21
(08-13-2020, 08:20 PM)gauss163 Wrote: ^^ I see nothing misread. My critique is with the (ill-founded) method of inference you employ to attempt to deduce that soldering is a "viable option".  As you can see from the analogy, that's not a wise to make deductions.

I have yet to see any concrete information from you on the damage that soldering cells actually does though. For someone who loves science and research papers as much as you do, I'd figure you could find or perhaps create such a study.

It sure seems like with how fervently you are pushing this agenda that "soldering cells is evil", you're an agent of a big cell manufacturer trying to discourage us from making DIY powerwalls  Wink
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#22
^^^ Damn, you got me. Soon orange men will come to confiscate your "fake packs" and I will be a hero for making Li-ion batteries great again!

But, more seriously, part of the goal of keeping people safe is ensuring that something like that never happens. Because if enough accidents do occur we will have to suffer even more draconian restrictions on consumer use of Li-ion cells.
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#23
So where is the in-the-field proof that this theoretical damage path is occurring?
Theories have to be proven. So far this one hasn't been.

re the wrappers stopping thermal runaway domino effect, I don't think it's going to be any practical use at all.
Like you said the wrapper is for electrical insulation, agreed there. 
Once there's a fire, it's melted & useless.

For science I heated the wrapper from the cell I opened above with a cigarette lighter.
It shriveled immediately with only slight heat at the edge of the flame & melted badly in sustained flame.
Before:

After:

It did fair better when still on the cell as "normal" due to the metal can of the cell
a) sinking heat away &
b) holding it's shape
but it went very soft & melted like this at the cell top in only a few seconds of flame:

I could poke it & it yielded immediately.
Running off solar, DIY & electronics fan :-)
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#24
^^^ As I said above, there are many type of wrappers in use. Some have high melting point (in fact I have seen them specified on various projects on which I consulted for the reasons I mentioned above). Whether or not they occur on the OP's cell or any other cell is not really relevant to the point I made, i.e. that generally (without specific wrapper info) we can't deduce that the cell didn't get hot simply because the wrapper didn't melt.

In any case, it's a small amount of work to replace the neighbors to be on the safe side, and the OP already did that, so it's a moot point by now.
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#25
(08-14-2020, 12:24 AM)gauss163 Wrote: ^^^ As I said above, there are many type of wrappers in use. Some have high melting point (in fact I have seen them specified on various projects on which I consulted). Whether or not they occur on the OP's cell or any other cell is not really relevant to the general point I was making (i.e. that generally you can't deduce that the cell didn't get hot simply because the wrapper didn't melt).

I would be interested in finding out about these high temp wrappers if you can find a link/info. I know they make kapton cell insulators for the top of cells which are nice, but harder to find. A kapton sleeve would be interesting, though you couldn't shrink it.
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#26
(08-13-2020, 11:32 PM)Redpacket Wrote: re the wrappers stopping thermal runaway domino effect, I don't think it's going to be any practical use at all.
Like you said the wrapper is for electrical insulation, agreed there. 
Once there's a fire, it's melted & useless.

In sidewall rupturing shorts like the OP's there needn't be a direct flame on other parts of the cell, but there may be a great deal of heat conducted through the can. If the wrapper doesn't melt then - as in the OP - the short may be controlled through internal safety mechanisms (e.g. ceramic/fusing separator) and eventually die down with little global effect. Otoh, as I explained in a prior post, if the wrapper melts and the can swells a bit then this may cause neighboring cans to touch, which can yield a short in the neighbor (in some pack topologies), which might lead to a chain reaction that causes the entire pack to go thermal.

In demanding contexts (not only for batteries) it is not unusual to require the use of insulators with high melting points to help protect against anomalies like the above.

@rev0: Re: links. I don't recall the particular material that was used on the projects I was involved in, but it's probably easy to locate material on insulators with higher melting points (including PVC) by obvious keyword searches.

Btw, in this or the prior thread someone touted the advantage of spacing between cells in parallel packs. But NASA (Darcy 2018) has shown that even 4mm spacing doesn't suffice to prevent (full) thermal runaway from damaging (shorting) neighbors. Notice that it only took a rise to 100°C to short the neighbors #2 and #8.

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#27
The lawn-tool brand "Ego" made by Chervon (not Chevron), uses double wrapped cells with a phase change wax-like material that will melt when a cell gets too hot. It's not exactly high-temperature wrap, but it's another solution.

Gauss163, I took a 240 watt soldering iron and held it on 30 high discharge 18650 cells for probably 30 seconds each time (I was soldering the caps to 10 gauge copper with 35 year old rosin core-solder), and on both ends of the cells, when I was making a 3S10P pack a few years ago. On one cell, either solder fused the negative to the positive, or it just got so hot that some separator probably melted, but either way, the CID tripped. I measured the temperature of the cell shortly after hearing the hiss and puff of smoke and I think it was 240*F if I remember correctly. Anyway, I replaced that cell and kept building the rest of the pack. I used that pack for a while, but vibrations rattled the solder joints so bad that the pack just went out of balance from loose contacts. So a month ago, I retested all of the cells and they didn't show any real capacity loss. So, I spot welded that pack back together and have been using it ever since. This is a perfect example of what you are saying not to do.

Don't get me wrong, I'm not saying what I did was safe by any means. I'm not even saying that anyone should solder their packs. What I am saying is that your efforts on this forum and others (you use the same username everywhere) to push safety above all else with countless cites, while dismissing anything anyone says to the contrary, is hurting your message. If you really want to protect the public and educate everyone on using Lithium-Ion safely, why not do so in a constructive way where people will listen? You get shot down everywhere you go, Candlepower, BudgetLight, SLS! You are obviously well read and have first-hand experience in the field, which I think we all respect (and honestly I'm happy you are here to share your knowledge). But you don't have people skills. I'm not attacking you. I'm trying to help you. Honestly, when I first started seeing your posts, I thought you were an AI Bot, considering you edit your posts 10 times on average and link so many cites. Just understand that people are going to disagree with you, no matter how much evidence you bring to the table, and just leave it at that. People will be much more receptive of your message if the have a positive opinion of you. You have the same number of posts as me with 0 reputation points, despite you contributing a lot more information than I have in my posts. Share something positive about Lithium-Ion; after all, there are two sides to every cell.
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Check out my long-term capacity test of 18650s: https://secondlifestorage.com/showthread.php?tid=6868
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#28
gauss, the example you quoted show thermal damage/runaway happened WITH wrappers AND extra space!

I agree measures certainly could be taken to improve thermal runaway results by fitting extra sleeves of higher temp material.
Has anyone noticed which cells might have the higher temp sleeves? Eg maybe the LG high current cells?

The NASA report was an interesting read.
Of the actions forum DIY pack builders might reasonably adopt (exotic solutions, while effective, will obviously not suit DIY'ers),
a) A clear stand out was individual cell fusing as a must have.
b) Kapton sleeves (or other high temp material) is one.
c) Using the cell holder/spacer plastic parts vs packing the cells tightly is another (noted DIY blocks might not be 4mm).
Fortunately a) & c) seem common practice already.

Weather or not DIY'ers do adopt to add another sleeve, that'll be seen with time I guess.
Anyone got a source of Kapton (or other high temp) sleeve?
Kapton tape is readily available but right sized sleeve?

It's interesting that Tesla battery banks don't appear to have sleeves at all, they are all bare metal cans.
It seems they have deliberately done this for heat dissipation reasons?

Just a reminder as mentioned earlier most of the DIY'ers build large "1s" blocks so if cans touch nothing happens electrically

The primary point(s) remain:
Do we have an active problem causing issues now or only a theoretical risk to consider & think about?
(on two fronts now it seems: soldering & thermal runaway).
Apparently it's the later: No Problem
Running off solar, DIY & electronics fan :-)
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#29
(08-14-2020, 08:07 AM)Redpacket Wrote: It's interesting that Tesla battery banks don't appear to have sleeves at all, they are all bare metal cans.
It seems they have deliberately done this for heat dissipation reasons?

I'm not as familiar with the way it was done on the Model S/X packs, I believe for those there was an electrically insulated aluminum "wavy" channel running through the cells to moderate temperature. For the newer Model 3 pack, the wavy aluminum channel is actually one of the electrical conductors (negative) while the other is the positive cap. Model 3 packs are potted also, making disassembly and harvesting of cells extremely difficult for most people. It seems the BatteryClearingHouse guy has been able to do it fairly well, and sells individual re-wrapped and laser welded (added button top, since the bare cell has an odd indented top) Model 3 cells.
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#30
The problem with gauss163 is that he/she doesn't offer any practicality to his posts. More often than not he post with no solutions to the problem other than do not do it. Sometimes he posts solutions based on a perfect world, like a perfectly balanced powerwall that would never exists. It's like the adage, those that can do, do; those that can't, teach. The thing is that if everything was done to perfection, there will be nothing done in this world. Imagine telling someone that the recipe calls for 1/2 inch slices and have someone measuring your slices with a caliper.

Don't get me wrong, I like his posts, it brings information to the table that I wouldn't know existed, but his insistence on hammering down his message, getting that last word in, so it drowns you that pisses everyone off.
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