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Locating Self Discharging Cell(s) in Packs
#21
At Wolf.
After harvest, i segregate them to my specs, between 20 and 80 mohm, higher then 2.0v, no rust damage ect.
I charge/discharge them cell allone.(you know my charging board.)
After charging, i leave them in a separate box for 30 days.
After 30 days, everything below 4.05 is out.
Then the capacity test at 1Ah, minimum keepers 90%soh, rest is out
Charge them back up to 3.4v for storage and check ir more seriously, meaning max deviation 10%(if i say this correct?)
If the cells manufacturer ir, is 25 mohm, and i have one with 65 mohm, he is out, or the other way around.

Then i assemble packs with the winners, charge them up to 4.2, desolder the neg side and leave them again for 2 weeks, just to make sure.
After two weeks i check for ir and volt(and fuses), this morning i found a sd.
He could have a heart attack that he is going to be used again.
Ir starts at 80 mohm and climbs very rapidly to infinity.

The cell spec what i wrote down on the cell it self: second ir test was 24 mohm, first capacity test 2772 mah, second 2793 mah.
Third ir and voltige test 80 to infinity and 0.78 volt.
Inr18650-29E, in my cell database it must have a ir from 20-30 mohm(22.5-27.5 oke,)

What could have happened? It was leaking oil ish substance with no smell.

All the measuring is done with the yr3035 and my zb's are all the same, tested with the same (one) resistor and on voltige.

After the last check they are soldered together again, and discharged to ~3.4v, the discharger 180 watt i have now, does not yet what i want: cut off at 2.8v, it only gives a alarm sound.

Best.

@ohmgrown.
you wrote:
In any case, I think I'll take the advice here and make a back up pack or two to swap in and out as I'm sure another will undoubtedly crap the bed after I fix this one. Ya know, I thought that would be the fun part for me, putting packs together and welding/soldering everything up while listening to a podcast and clearing my mind with just rote muscle memory but, so far, it has been the most annoying and monotonous portion of this whole process. Dah well, time to clear off all the hand tools on the work desk.

That's why the most of us make a "special" table for it, cous you will be spending a lot of hours over there....
In my case i want a minimum of 140 packs, 100 cells each, to reach 100 kwh, i am on a third right now.



As you can see, i sit on a bar stool and not on a regular stool.
My soldering wire is running thru a hole, so muscle memory in action, you can get it blind.
And a lot saver, trust me, you dont want a hot soldering wire in your hand.
Also my packs are elevated, to give them more stability when you do the other side, or must desolder.
The fuses have there own tray, easy to pick and no flying around.
My wire is also on a trolley, works perfect, no more catching it or winding it up when it falls from the table or what ever irritating event.
Also very happy, i can pick it up to make room or all in one go and solder in the garden.

For your back up packs...i am no real expert, just beginning: but i think its important to have your "back up pack" equal in capacity, i hope someone here can give more clearance on this one.

My two cents, Best
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
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#22
Question 
(08-21-2019, 03:23 PM)100kwh-hunter Wrote: At Wolf.
After harvest, i segregate them to my specs, between 20 and 80 mohm, higher then 2.0v, no rust damage ect.....................................................He could have a heart attack that he is going to be used again..................................................................................

What could have happened? It was leaking oil ish substance with no smell.
100kwh-hunter,

LOL heart attack  yea I guess that is a possibility or maybe a heat attack from soldering.
As you know I am not a fan of mixing INR and ICR chemistries as the cell interaction is quite dramatic during charging and discharging.


Does that mean it is wrong I don't know yet more study needed. I do know though the closer the IR is matched the better the discharge interaction is between the cells.


What could have happened to your cell? IDN. Is it possible the soldering caused a "good" cell to weaken enough to fail?
The combination of being in a pack with unfamiliar cells the only one with low IR and the rest high IR?
No clue on the oil-ish substance other than a possible vent but then it should have the smell of lithium I would imagen.


Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 8/7/2019
Total Number of Cells Recorded and processed                 6149
Total Cells required for PowIRwall                                   2856
Total Cells ≥2200mAh, ≥80%, ≥35mΩ, ≤75mΩ, ≥4.12V   2760
For Info Google Drive
Not your average Wolf       
            Cool
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#23
>. Is it possible the soldering caused a "good" cell to weaken enough to fail?
I've soldered almost 6,000 cells and have not detected any loss from original OPUS discharge tests (pre-solder) and battery-bank AH delivery (post solder). Of course you need to solder quickly etc... - I use 100w iron.
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#24
@offgrid,
I personally don't think that soldering will "weaken" them, if you know there internal structure, probably a shortcut between layers due to heating like wolf was saying.

We pull the strips off while harvesting, remember jing jang?
What you push in must come out.
Sometimes i use the cells base as the lever to pull.
At one side we pull, at a other side if the strips are reluctant, we push and damage the inner layers.
Some cells need more heat to let the tin flow due to there transparent paint or thicker metal.
Due to there internal structure and build up i think we short circuit two or three layers.
So i stick indeed to "heat attack" of the soldering iron, every metal reacts different on heat.
Paper will smulder with a soldering iron, there goes the insulation.

With smulder i dont mean burn like a cigarette, more like turning wood into gas, apply heat but no oxygen.
You can put 1m3 of wood into a 3l gas cylinder, without oxygen to burn the wood and your leftovers are pure ases(lye)
But still the same amount of energy is stored in the gas cylinder that the wood would have in there cellular based body.
Well almost kinda~.

Paper has a lower burning temperature, so also a lower disintegration temperature.
But gasifying wood or wood products is a whole different/other story.

Your soldering iron will go to what? 400c. Lithium gets unstable at what? 120c? Also possible.

When the cid chip heats up to much, the cell will be a instant zero volt.
This is my guessing, also swinging with a baseball bat in the dark.

Best

@ Wolf,
The story of different ir makes sense.
But the low ir (high drain cells) can be easy used with high ir cells(low drain cells)
We use the cells at really low drain, so i think there is no issue/problem here.
The other way around, if i would use the average laptop cell in my power tools, things might get to go sparky.
I found cells in laptop batteries that where the same as in my hilti power tool batteries, yes the one you don't like....begins with a S.
So that can be done, high drain in laptop = low drain application; other way around, no go!
Our powerwalls are basically low drain applications.(mine is down to 150mah a cell and will get lower with extension).
Charging up is a different story, on this one you are correct.
Cloudy day, and then a full sun on your 10kwh array....and no consumers used at that time, only charging!?!?

What do you think about those thoughts/hypotheses? about high and low drain cells mixed, suited for the application?
If i am wrong just say it, i am in the learning process also.

Thanks in advance.
Still learning English. Learning Li ion and solar technology.

4200 cells in packs Exclamation above 2500mah and 90%soh.
1500 waiting for testing.

Saving for 3 times phoenix inverter 48/3000 230v to gain also 380v
3 chargers?

Time is our enemy, must work to, the sun is our friend, must relax to.
With best regards
Reply
#25
Yeah Wolf, I agree, IR I do think is pretty important factor in making packs with reclaimed cells. I wish I had a quick and reliable way to check that. I've been using a type of manual method learned from YouTube with basically a multimeter (specifically from the channel Tom Donnelly) which I think is pretty reliable for the most part for a room temp sitting cell. Started doing that soon as I realized the opus and liitokalas are basically crap at it. But the manual method can take a bit of time, especially when you're looking down the barrel of 500 cells. How do you measure it? Tester/device or just with a formula and readings?

100kwh-hunter,

"That's why the most of us make a "special" table for it..."

That's quite a nice setup there. I have customized my tables a bit to allow an easier time of it but I definitely need to make a dedicated workstation like that. Getting a permanently placed soldering "hood" alone would probably be worth it. I think a lot of my wasted time is just setting up all the crap I need and then storing it away when done to allow for extra workspace. But having stations like that would be much better. Now I just need to clear out my living room for a larger space than the office offers. Not like I sit and watch TV in there anyway.

Oh and yes, all my packs, back up or not for this particular project will indeed be the same capacity. Luckily I have enough varied cells that I can pretty much match anything with the use of Repackr. I think right now they're in theory supposed to be around 250Ah (though likely lower than that in reality)

(08-21-2019, 04:50 PM)OffGridInTheCity Wrote: >. Is it possible the soldering caused a "good" cell to weaken enough to fail?
I've soldered almost 6,000 cells and have not detected any loss from original OPUS discharge tests (pre-solder) and battery-bank AH delivery (post solder). Of course you need to solder quickly etc... - I use 100w iron.

So I've seen videos on YouTube (which I'm pretty makes me a certified master on the subject) where they test and open cells that were soldered vs welded. From what I remember, the soldered ones definitely showed more stress than the welded versions but honestly it didn't look like anything too significant or major. So, I think if you do like you did and are quick and focused with the heat, it's really not that terrible and shouldn't cause failures left and right. With that said, I still spot welded mine but that was mainly because I wanted to make and use a spot welder.
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#26
Holy shit, went with your guys idea and desoldered the usual suspects... The very FIRST cell I undid was 2.056V and dropping a mv per second about. I can't believe that I actually found it that quick.

Now I wouldn't be surprised if there's more than one with my luck but the other 12 I desoldered are holding steady at 4.1V so far. Man that was lucky. Thanks for the suggestions guys
100kwh-hunter, ajw22, Korishan like this post
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#27
That's what we're here for Smile

Glad you found the rogue so soon.
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

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#28
(08-23-2019, 11:10 AM)OhmGrown Wrote: ..............went with your guys idea and desoldered the usual suspects... The very FIRST cell I undid was 2.056V and dropping a mv per second about. I can't believe that I actually found it that quick.

Now I wouldn't be surprised if there's more than one with my luck but the other 12 I desoldered are holding steady at 4.1V so far. Man that was lucky. Thanks for the suggestions guys

Congrats on finding the offending cell so quickly.

Now in all your excitement don't forget to measure IR and compare it to what it was before.
Also what kind of cell it was and the stats on it.

Thanks
Wolf
Korishan likes this post
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 8/7/2019
Total Number of Cells Recorded and processed                 6149
Total Cells required for PowIRwall                                   2856
Total Cells ≥2200mAh, ≥80%, ≥35mΩ, ≤75mΩ, ≥4.12V   2760
For Info Google Drive
Not your average Wolf       
            Cool
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#29
Glad you got that sorted. But where there is 1 there may be more. Whenever I find a couple cells that SD I generally leave the pack for a while to make sure there are none others that still SD but slower.
100kwh-hunter and Korishan like this post
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