Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Using low capacity cells for powerwall?
#1
Hello guys, 

I have crosschecked a lot of threads here, starting my first harvest. I have got around 140 notebook packs. 

From first 30 pack, I have got mostly Samsung (the blue one, rated 2800mAh - I am not home and will edit the post with specs). I have got those packs in average for around 1.2E/pack - that I already consider too much, but in a future I hope to get better source.

Now my question is, has anyone of you ever tried to build a pack from 1500mAh batteries/or in general from batteries with less than 60% of original capacity? Most of my Samsungs has around 1500-1700mAh and IR=120-160mOhm. I try to cycle them and they looks solid, not much change in the capacity, it does not go down, but neither much up. They also do not heat. Everywhere we can find a charts, how the li-ion batteries behaves when you cycle them to 80% capacity, then they are considered 'dead', but around those 80% the curve does usually look 'almost flat (linear)', isn't it that some chemistry will be still working just fine and handle another hundreds of cycles with much smaller capacity loss?

I know, that some of you has a problems with old Sanyo or Sony, that heats up, or dying fast with every cycle, but those Samsungs looks solid and stable at this point, does someone of you have tried to use them in your power walls with such a 'small' cap? What is your opinion?
winny likes this post
Reply
#2
You can use the lower capacity cells. There's nothing wrong with that as long as the packs in the series all have the same capacities. The IR is a bit high, but expected, and usually not an issue at the sub-C amp draw these will experience.

The big issue is the current capacity compared to original capacity. If you're aware that they have 60% of their original ratings, and you keep an eye on them, that's fine. I would recommend putting them in packs that would be easy(easier) to replace them. Unless, you build two strings. One has all your high value cells, the other with all the lows. Then as you collect high value cells, you replace the lower strings (as a whole, not individual packs).

Example: You have enough 80+% cells to make a 14s80p, or 1120 cells. And you have enough subPar cells to do 14s40p, or 560 cells. Then you could have two strings that are connected in parallel, either at the ends (requiring two bms strings) or each pack in parallel with the other string (using 1 bms string). Then you get another batch of 1120 80+% cells, you make another 14s80p and pull the 14s40p out and drop the 80p set in.
ibikunle likes this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)

Kickstarter: Honest STM32F103 based dev Boards
Patreon: Korishan
Reply
#3
(02-12-2019, 12:03 PM)Korishan Wrote: You can use the lower capacity cells. There's nothing wrong with that as long as the packs in the series all have the same capacities. The IR is a bit high, but expected, and usually not an issue at the sub-C amp draw these will experience.

The big issue is the current capacity compared to original capacity. If you're aware that they have 60% of their original ratings, and you keep an eye on them, that's fine. I would recommend putting them in packs that would be easy(easier) to replace them. Unless, you build two strings. One has all your high value cells, the other with all the lows. Then as you collect high value cells, you replace the lower strings (as a whole, not individual packs).

Example: You have enough 80+% cells to make a 14s80p, or 1120 cells. And you have enough subPar cells to do 14s40p, or 560 cells. Then you could have two strings that are connected in parallel, either at the ends (requiring two bms strings) or each pack in parallel with the other string (using 1 bms string). Then you get another batch of 1120 80+% cells, you make another 14s80p and pull the 14s40p out and drop the 80p set in.

Thanks for your answer, yeah it makes sense, something like that I wanted to make. I was thinking about having two invertors - one lowpower (1500W/48V) with 'bad' cells like mentioned above and use it to power lights in the house and second (3500W/48V) with a good cells for powering plugs. I have gas heating. 

I need about 15kwh (with reserve, willing to use pack only between 3.3v-4.1v), so I was thinking to have 2 independent strings (one will be 5kwh pack with separate BMS, second will be 10kwh pack). Of course I still need to collect much more cells, I was just curious about those Samsungs, I have a lot of those, so it would be a pitty to just throw it away. Does it makes sense?

I have another question, also considering the Samsung cells, I have already seen leaked, or burned all other cells - Sony, Sanyo, Panasonic, Chinese nonames, but I have not seen leaked Samsungs and LG cells yet. I know I still have very bad statistics with just about 140 packs, so that cannot be objectively said, that is why I am asking what is your experience in that case? Have you seen leaked Samsung/LG cells?
Reply
#4
I have only harvested about 700 Cells, but there was no Samsung or LG which leaked. Only Sony and Sanyo's.
Reply
#5
Since when cells actually leak?

The only way they can leak is by physical damage.
The power of lithium ion is in our hands!
We'll show them what we're made of!
Reply
#6
I've harvested also around 700 cells so far, and found a few Samsung's also corroded and leaking , but I think they're initiated from a scratch, nick, and then just when I took off the nickel strips, one cell casing tore a bit, and the rest had residue, so I just dumped them. There were quite a few Samsung's as well that had leakage from the top of the cell, between the positive and casing.
Reply
#7
I use a lot of packs with low capacity cells, even with 10% capacity remaining. LED systems can do with these too.
I just make sure not to have damaged/rusted cells and I keep an eye on their health over time.
Reply
#8
(02-13-2019, 01:06 AM)BlueSwordM Wrote: Since when cells actually leak?

The only way they can leak is by physical damage.
No, they actually leak sometimes between the plus and the minus pole, as beserker786 described.

Here, fer example are some leaked NCR20700A from Sanyo:


Sometimes it's just a little, then you have to remove the shrink and insulator ring to see it.
Reply
#9
If a cell leaks for any reason, toss it. Don't even use it for a flashlight. If you open a pack and get that destination smell, find out which one(s) are compromised and get rid of them.
Electrolyte is very corrosive to steel/iron. Nasty stuff
LEDSchlucker likes this post
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Certified 18650 Cell Reclamation Technician

Please come join in general chit-chat and randomness at Discord Chat (channels: general, 3d-printing, linux&coding, 18650, humor, ...)
(this chat is not directly affiliated with SecondLifeStorage; VALID email req'd)

Kickstarter: Honest STM32F103 based dev Boards
Patreon: Korishan
Reply
#10
(02-13-2019, 03:14 PM)Korishan Wrote: If a cell leaks for any reason, toss it. Don't even use it for a flashlight. If you open a pack and get that destination smell, find out which one(s) are compromised and get rid of them.
Electrolyte is very corrosive to steel/iron. Nasty stuff

Yeah I usually get rid of those and dont even test when I see just a bit of corrosion/leak... 

To BlueSword: hehe it seems that you did not open much packs, I had a lot of pack without single mechanical damage with leaked cells. From my recent delivery it was about 10% of pack with leaked cells...
LEDSchlucker likes this post
Reply


Who read this thread?
77 User(s) read this thread:
daromer, Majorphill, Korishan, PAF, Mike C, wim, watts-on, Hanssing, Stefaan De Ridder, BlueSwordM, Mazlem, Geek, Menno, David Arnshelm, DCkiwi, ChrisD5710, Oz18650, bogptrsn, Ste Collister, Charly144, djuro, drchips, mbrunton, Dala, ARLISS, Ibiza, Onizuka, Zvonko000, Jonas Vanbeveren, Bubba, Cherry67, Riplash, 100fuegos, bukvaahmed@gmail.com, Katarn_89, Sammm, chuckp, emuland-metroman, clupton, Wolf, Bastler_Ro, Wardy, ibikunle, camthecam, Dallski, Solardad, Speicher, stevelectric, richie241, kevinjaye, kennyfk2, mart1nn, nickydw, OffGridInTheCity, Maniac_Powerwall, LEDSchlucker, nathan173, zoookii, Satiriasis, tsmurray, kurt13r, Richard, Iker138, Overmind, mskip, Church1182, bournevexed, beserker786, intra, rhedbatt, winny, Edster, Lucan, Havskum, cowboyrolo, planepilot, WimVsan

Forum Jump:


Users browsing this thread: 1 Guest(s)