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Locating Self Discharging Cell(s) in Packs
#11
[quote pid='53554' dateline='1566348939']


(08-21-2019, 12:22 AM)Korishan Wrote: What I would do is charge the pack back up to 4.2V, then disconnect 1/2 the pack. Watch what happens. Then the half that went low again, split it half, or there abouts. Depends on how you have it wired up.

That's not a bad idea at all. So just kinda whittle it down in halves basically, trying to find the correct part with the drainer in it instead of taking the whole thing apart? And I could add cells back in one at a time or so if it the part I left connected doesn't self discharge again. Better than ripping the whole thing apart definitely.
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Sounds like a good idea based on the pictures.   You could sever the bus at the far end and always reconnect it when your done.
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#12
They were going out of balance with very little use. 2 cells were significantly higher after about 6 months of use and the Balancer I was using was too low of a current balance (80mA) that it could not keep up. After the Swap and re-balance of capacities of those cells and now they stay within 10mV during charge and discharge even without the balancer connected.
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#13
I would say the cells with self discharge will now be heaters. Good chance if you charge it up you will be able to spot it with a cheap IR thermometer, or even just by touch.

Hopefully it doesn't pop a CID before you find it. A cell that can self discharge a pack of that size, is probably self discharging rather quickly.

Also you could try the 'educated guess' given Sanyo cells are famous heaters, you could just disconnect those first - which is about half the pack. Also those green and black topped Sony cells have given me a bit of strife too.
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#14
Another Thing I have been doing is to keep the capacity of all my packs within 1Ah of each other when I build them (repackr to the rescue) so I can have a couple spare packs incase there is an issue or the Pack times out.

Times out = a pack has a limited time in the system before being tested. For my starter packs I set it at 6 months but now that it is soo stable I will be increasing that to 1yr. then that pack comes out and temp one goes in it's place.
ajw22 and 100kwh-hunter like this post
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#15
Sorry to say, but i agree with others.
Charge up the pack to 4.2v disconnect one side(i would cut thestrips at the neg side)
Let it sit for 2-3 weeks, then check on v and ir.
Usually the ones with a high ir or sd or any other problem, will show itself in v drop.

For the late night testing, we all bin there i guess, i am no exception.
To tackle this kind of errors, i adopted a other test for my packs.
First the regular normal cell testing.
Assemble the packs, solder only wire to connect the whole pack, charge it up to 4.2v.
Let it settle for 24-48 hours, desolder one side, put it away for 4 weeks.
Test with a yr3035 meter on v and ir.
Bad cells/mistakes are easy to be found this way(for me, for sure).
This way you make sure that all the cells are top notch and healthy, before you put them in your wall.

With so many cells around it is easy to make a mistake.
I also think, but a second opinion would be nice:
Some cells are in "storage/sleeping mode" for years, we wake them up.
So the first test rounds are good, then they had it and sink back to "not for work anymore".

Good luck with tracking down the bad ones, best.
OhmGrown likes this post
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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#16
(08-21-2019, 02:57 AM)Wolf Wrote: Not trying to be a pain in the butt here but where these cells checked for IR before the pack was assembled?
If they were and there still was such a failure then it would be good to know which cell(s) causes this issue once you find them and recheck the IR to see how different it is now from when the cells were assembled.
Certainly looks like something odd has happened. 

Best of luck finding the bad cells and hope you get the pack up and together quickly.

Wolf

So, yes, I did record the IR for the cells though did not factor that in nearly as much as mAh & other stats when assembling the packs with Repackr. Also, halfway thru the testing phase I realized that the testers do not give a very accurate IR reading and only then switched over to a more manual method. So, admittedly, that is one area of info that I didn't very good on at all. I have a number for each cell but I'm not willing to bet much on its accuracy. I'll recheck em once I unassemble the cells and try to see if there's any corresponding factor to any of the bad ones. Thanks for the tip!

Yep I knew you guys would all have good info for me. I'm gonna take a closer look at the usual suspects (read Sanyo heaters) first but either way I think there's no way around disassembling this piece o' crap. I thought I was doing pretty good selecting cells, using Repackr, but I may have just gotten lucky with the other 3 packs. It is very disconcerting that this guy is draining so quickly and so far down though none of my fuses have popped so I think that could point to multiple cells self discharging instead of just one bad apple dropping REALLY fast?

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.
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#17
This morning i was checking a pack that i left alone for 2 weeks.
Tested cell per cell, and i found a sd, 0.78v, the rest was still above 4.1....oke 2 x 4.05
To bad i have to replace him, but at the other hand, what if i did not find this sd?

The ir and everything was good when i was assembling the pack.
jdeadman likes this post
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
#18
(08-21-2019, 11:20 AM)100kwh-hunter Wrote: This morning i was checking a pack that i left alone for 2 weeks.
Tested cell per cell, and i found a sd, 0.78v, the rest was still above 4.1....oke 2 x 4.05
To bad i have to replace him, but at the other hand, what if i did not find this sd?

The ir and everything was good when i was assembling the pack.
100kwh-hunter,
How long did you let the cells sit before testing them again for IR and for SD?
I let mine sit for at least 30 days before the second IR and V test.
When I checked IR and V for the second time I found some that had risen in IR, some that had below 4.12 V and some that were below 1V.

I am still 96 cells shy of my 2856 cell goal.  As I am waiting the 30 days to retest the missing cells. So most of the cells that I will put into my powerwall will be checked again for IR and V a third time and a lot of them will have sat at least 5 months. Better to find them now than when the whole pack is assembled.
Does that mean we will find every one ? Probably not but I for one am going to give them a good chance to show their true colors before I  assemble them in a pack.

Wolf
100kwh-hunter 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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#19
I'm on the fence over IR. If I had a really good tester I might do it more often but I Look more at the Capacity measured vs Rated. But until we use brand new cells we always be in the test, check, Check, CHECK method.
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#20
(08-21-2019, 12:41 PM)jdeadman Wrote: I'm on the fence over IR.  If I had a really good tester I might do it more often but I Look more at the Capacity measured vs Rated.    But until we use brand new cells we always be in the test, check, Check, CHECK method.

Jdeadman,


Hm, Slightly off topic but still relevant to the OPs post.
I agree on the capacity VS rated criteria as it is a good indicator of SOH of the cell.
On the other hand if you have 500 cells you are about to test and just by measuring IR you can eliminate 300 of those as you know by there IR that their capacity VS rated will be insufficient then first of it has saved you a lot of time and you have eliminated some very poor cells.
Second the cells that do pass the IR test will still have to be tested and some of those will not be great either but you have eliminated the majority of non performers. For a $50.00 investment in a very good tester that is not much of money to spend to speed things up considerably and have at least some peace of mind knowing that you have eliminated 95% of potential heaters and SDs.
Yes as we are using reclaimed cells there will always be a check ,check and check again but to have IR in your toolkit is as far as I am concerned an imperative measurement to have.
Wolf
jdeadman 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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