Thread Rating:
  • 0 Vote(s) - 0 Average
  • 1
  • 2
  • 3
  • 4
  • 5
Discharge after capacity testing?
#1
I am still in the beginning throws of testing capacity of ~650 cells and growing daily with a single Opus C3100 charger, and working on an extreme budget. After testing the cells and letting them rest for about a week I have been discharging them to ~3.40 - 3.5 volts and placing them in the bin according to capacity. So my question is, it is worth the time and effort to discharge them? It will be awhile before I am ready to start assembling the packs (either 24v or 36v at this time, long term plan is to replace the sealed lead acid batteries in either an APC or Tripp-Lite with a BMS).
Reply
#2
After charging them, are you letting them sit at full charge for a few weeks to weed out most of the self dischargers?

Discharging to 3.5V (which 3.7V would be sufficient) and letting them sit is fine for long term storage, like 6 months to a year or longer.
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)
Reply
#3
Not yet, mostly looking at capacity at this time, however I have been keeping track of the cells, noting the voltage as it was salvaged from the pack, the voltage before testing, and the resting voltage after the capacity test with the date. Maybe a little overkill on what all I am keeping track of on a per-cell basis, but it may prove useful in the future. It will be a good 6 months before I will have any free funding to start building the packs.
Reply
#4
Nope, not overkill. Good records. However, you need to do the resting voltage with full charge. If you drop the voltage down to 3.6V, you will have a hard time finding those SD cells. Might as well get them out of the way now.

And actually, the order should be:

1) Full charge cell
2) Sit for 2 - 3 weeks to check for SD
3) Drops more than .02V/day, considered SD cell and put in separate bins
* If they stabilize around 4.0V or even 3.9V, they could be used in small applications, like flashlights and such
4) Remaining cells get recharged to full, then discharge capacity tested. If they are within spec, keep. If they are quite short, toss
5) Recharge to full charge and let cells sit for another 2 - 3 weeks, repeating step 3
6) Cells that pass step 5 then can be discharged to storage voltage (about 3.7V) if going to store for many months to a year or longer. Store in cool dry place if possible. At least in a sealed container if humidity is an issue.

This is how I would do the steps. There may be some other steps that could be added as well to get even better results on good cells

If you focus on capacity test "first", then you could potentially be wasting a lot of time, energy and effort on cells that are SD's. Why waste that on the ones you are going to toss anyways?
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)
Reply
#5
I know I should do the SD charge, but like I said I got a lot of time at the moment while planning on the packs. Having a ton of kids certainly does not help on the funds at the moment, and the next one will be here in over a month from now. I would like to have as much data at the moment on the cells to possibly assist with issues with the packs down the road. It's a learning experience for sure.

I would like to follow up with a IR test as well in the near future and test those that have already been put in the spreadsheet, will need to do some searching for the resistances (maybe suggest putting in the proper resistances in the cell database for ease). Looking at the YR1030 from vapecell, reasonably priced for what I need.
Reply
#6
Plus one on Korisan.
Charge them up to 4.20, wait 4 weeks(very important), then a discharge test....
After 4 weeks:
The time saving bonus after the four weeks, if there is a cell that dropped below 3.9 or lower is a sd'dr.
Trow them out
So you don't have to take them into further testing.
With the discharge test after the four weeks, you will weed out every bad cell.
Everything that is below 80% from there original capacity, is not worth the effort anymore!

I would also recommend to buy a ir tester, the yr1030 is the best for this, and dive into the world of ir.
It saves more time when you test your cells first on ir, then charge, wiat 4 weeks then discharge.
Then you will have the best cells for your pw and NO dubble work!

Voltage for long term storage: 3.3-3.4v, cous on this point that there is nothing that can harm the cell anymore.
For short term storage it is best to have them at 3.6v at this point the cells chemistry is at there best balance.

First learn to walk, then learn to run, meaning: forget your 6 months goal, spend more time in the beginning with your cells, to save a lot of time in the end, and create better packs.

Search on this forum for Wolf, The Wolfman did not reinvent the wheel he invented it.

My testing way(remember that there are more ways to rome!) after getting my cells.
1 with the ir meter, test for v and ir, odd ir and below 2 volts are out.
2 charge to 4.2 volt.
3 wait 4 weeks.
4 check for v, every cell below 3.9 is out
5 discharge to 2.8v and calculate the remaining capacity,below 80% soh is out.
6 charge them up to 3.35v for storage.
7 sort them into 100mah trays to build your packs.
8 solder
9 enjoy
10 sit back and relax
Reply
#7
For my first 1000-2000 Cells i have pre tested them for voltage drop. The ones who dropped (3,9-4,05) got marked with a "V". I tested them und let them sit for at least a Month, but half the cells have no more voltage sagging after that. There are even ones who have 4,15V after 8-9 months. So i dont pre test them any more. Charge, discharge, store (1-2 months) voltage test.
Reply
#8
@nickydw.
You will want to know the SOH in %
Especially for the "german punktlighet" (sorry if it was grundligheid).
You can get away with that, but if you have one cell in a pack of 100 you will not be able to tell what is going on.
So it is a waste of work.
I have a "secret test setup" that only contains cells that are not dropping below 4.00.
Not looking good, especially in the balancing akt and ir, there are some sd also.
test cells: icr18650 26h, 25 cells a pack x 14...
Again you can get away with that for the next two years....just saying
Reply
#9
what is the difference between checking the voltage loss before or after the capacity measurement? of course the cell will be fully charged after test.
Reply
#10
Checking the voltage right after charge gives you your starting point. If you pull the cell off and just assume it's 4.2V, you could be wrong. Also, some cells start SD immediately after coming off the charger. I've seen some drop almost 0.1V within minutes of pulling off the charger. That cell gets binned and not even further tested, at least for powerwall applications.
Also, some chargers will stop at 4.18, 4.21, 4.2, 4.22. These are all safe voltages and can vary from charger to charger and from slot to slot. So a baseline voltage reading is needed to know how much the cell voltage dropped after resting.

On average, a cell that drops 0.01V/day is a good cell. 0.05V/day is too much. And you don't want to loose more than about 0.1V - 0.15V overall after a month of resting. If it's more than that, it's on its way to dieing
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)
Reply


Forum Jump:


Users browsing this thread: 1 Guest(s)