Experiment: Soldering 18650 = Capacity Fade?


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drbacke

Member
Joined
Apr 3, 2019
Messages
60
Hey, guys,
I did a test to find out if soldering 18650 cells leads to a loss of capacity or not.
I tested 4 cells and used the following procedure:
1. Each cell measured 4x (capacity). So 16 tests overall
2. 2x soldered, (one solder point)and then again soldereda piece of virtual wire.
3. let it cool down
4. 4x capacity measured.

In my opinion there happens absolutly nothing.

Here are the results (blue is before soldering an red after). The error bars describes the deviation of the 4 tests:

image_mifgar.jpg


I also documented this on YouTube (german):

 

Korishan

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Jan 7, 2017
Messages
6,943
There are a few videos that used thermal cameras to show the process of what happens when soldering. The heat from the iron travels very quickly down the shell of the cell, even in a couple seconds (which about 2-3 seconds is the longest contact should be made). Unfortunately, it's hard to tell what happens on the inside of the cell and what happens chemically.

drbacke: I do appreciate the testing done (haven't yet watched the video at this time). However, I would recommend revisiting those cells in a few months time and see what happens. I would gather that any capacity degradation shouldn't happen in a few hours/days, but over a longer period. Perhaps even do a test where you specifically heat the cell up (with the iron) for longer durations, say 10 seconds or so. Maybe that will have an adverse effect in a few months.

Any time we deal with these types of things, how long is the determining factor of failure.
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
2,125
Annecdotally, I've soldered all my cells (over 5,000 to date). The actual ah of each pack after soldering them up vs the total of cell tests via OPUS has been within 1% - in other words, any 'immediate' damage is not detectable within looseness of using OPUS etc.

My longest (soldered) pack has been running for 18months with 458 daily charge/discharge cycles with average 35% DOD - and have not detected loss of capacity yet. But again, my measurement info is not that rigorous.

However, so far, I'm not concerned about soldering and plan to continue.

I'm more concerned about 13.6% loss of power due to my inverter efficiency . I've generated 9300kwh but only been able to consume 8,031 due to inverter losses. That's 1,268kwh left on the table - sigh, I definitely have SOCD (Solar Obsessive Compulsive Disorder) to some degree :)
 

jdeadman

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Joined
Mar 28, 2017
Messages
967
Lol SOCD (Solar Obsessive Compulsive Disorder) Didn't know it was a thing but that being said I have it too. - and Yes I had to steal that
 

drbacke

Member
Joined
Apr 3, 2019
Messages
60
Korishan said:
There are a few videos that used thermal cameras to show the process of what happens when soldering. The heat from the iron travels very quickly down the shell of the cell, even in a couple seconds (which about 2-3 seconds is the longest contact should be made). Unfortunately, it's hard to tell what happens on the inside of the cell and what happens chemically.

drbacke: I do appreciate the testing done (haven't yet watched the video at this time). However, I would recommend revisiting those cells in a few months time and see what happens. I would gather that any capacity degradation shouldn't happen in a few hours/days, but over a longer period. Perhaps even do a test where you specifically heat the cell up (with the iron) for longer durations, say 10 seconds or so. Maybe that will have an adverse effect in a few months.

Any time we deal with these types of things, how long is the determining factor of failure.

That would actually be very interesting, unfortunately these specialcellsare my servants for everything ;) I'm afraid but these cells won't live for a few months.
In addition, there would be no comparison cells, how is that possible with used ones? So I would have no statement after a few months.

But I also measured the internal resistance (before and after) and could share the results with you. If you're interested in.
However, they are clearly more contradictory, but perhaps this is very interesting.
 

100kwh-hunter

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Joined
Mar 2, 2019
Messages
816
@drbacke,
Why don't you get a (ONE)defective ebike battery.
The bms is usually demolishing/ignoring(thus not charging) the first group, but the other two groups are usually very good.
Those two last groups are (mis) treated the same, so consistent results?
Of Course do a ir test on all those cells first.
Then charge and discharge them equally at the same amount and time.
This will give you very consistent and reliable data, in my opinion that is.
 

drbacke

Member
Joined
Apr 3, 2019
Messages
60
100kwh-hunter said:
@drbacke,
Why don't you get a (ONE)defective ebike battery.
The bms is usually demolishing/ignoring(thus not charging) the first group, but the other two groups are usually very good.
Those two last groups are (mis) treated the same, so consistent results?
Of Course do a ir test on all those cells first.
Then charge and discharge them equally at the same amount and time.
This will give you very consistent and reliable data, in my opinion that is.

I'll admit that's a possibility. To be honest, it's just too expensive for me.
I also think that if you can't see a change in capacity and resistance, then the probability of a change after a few months is relatively low. But maybe there is one.

Another possibility would be to take 4 new and identical cells:
1. Soldering a cell
2. To heat a cell strongly (so that something should happen)
3. And leave one alone.
4. Then to unload them and cut them open and look inside the cells


But what do you think about the measured IR, there is an increase in at least 3/4 cells:

image_bkbfqz.jpg
 

100kwh-hunter

Member
Joined
Mar 2, 2019
Messages
816
I think you did not measure at the soldering point, i think due to heating up the metal, the metal physically changes.
So my best guess would be that this is the origin for a ir increasement.
With heating a metal you alter the molecular structure.

In my endeavors i also find out that the translucent paint is sometimes thicker at one cell or spot

To get consistent results 4 cells is a bit to low, i would aim for ten
What i would also do is test them every two weeks on a full scale capacity test.


Also like Korishan said.
Heat up one or two cells extra long, like 10 seconds.
I think just like him 2-3 seconds is the most a cell can handle, 4 is max.
One other word of advice, despite all the tests with heatguns and ect.
I would do the 10 second contact outside, just to be save.
A heatgun is 500-600?C a paintstripper is rougfhly 800-900C
A 100w soldering iron can get up to 450C, but it makes direct contact instead first thru the air.
 

BatteryMooch

New member
Joined
Sep 26, 2019
Messages
18
Any data on changes in the leakage current rate, pre- and post-soldering? I can see that as being the primary indicator of damage. Except for thermal runaway, of course. ?
 
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