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Discharge after capacity testing?
#11
Also to add: if a cell take to long to charge it could also be a potential sd.
If you charge a 2000mah cell with 1amp a hour and it takes 4 hour to complete then there is something wrong with that cell.
Inlc also heating up.
Those cells must be discharged immediately to 0 volt and in the bin for the recycler.

Now most diy chargers like the tc40xx can charge 1ah but they must have the proper power supply for it also.
So if the max is 500mah that the charger is getting, then a 2000mah cell must have 5 hours to complete full state.
Make sure you got power enough to spare, when charging cells

Before you consider a sd after the cell comes from the charger, give the chemistry some rest so it can settle, usually it takes one hour.
To make sure just wait 4 weeks.
To make it more complicated on the charging part: its not only from charger to charger or from slot to slot.
Some cells simply dont want to be charged to 4.15v and the other will take charges up to 4.25 without pain.

Arnt we having fun? Huh Angry Confused
Selling everything at marketplace.
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#12
Even though I didn't do it this way, I would recommend charging and testing for voltage drop FIRST before capacity testing for 2 reasons: (1) It will help you weed out self draining cells and save you the time you would spend testing those cells; and (2) keeping cells at full charge for extended periods of time WILL damage your cells. So why test twice? I made that mistake and let cells sit at full charge for between 8 months and 1 year before testing AGAIN and found out I lost like 3% of my good cells and a whole bunch of time retesting. So after you test for self-dischargers, do a capacity test, and then bring those cells to a uniform storage voltage (I would do 3.4V but most would do 3.7V). Keeping the voltage low and uniform will aid in pack building. You don't want to solder/spot weld a fully charged cell in case you make a mistake (it happens).
BatteryMooch likes this post
Formerly known as Dallski
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#13
But doing that way includes more moments to work with it manually.

For me doing it with Opus its just one moment and then 2 weeks later i know if self discharge is ok.,

Ie
1. Put into opus let it run capacity test and also tell me if IR is ok (heat)
2. Let it sit and then meassure for self discharge

The other way would be
1. Charge it up
2. Let it sit and then test for self discharge
3. Do capacity test in opus or even worst charge them up adn then put them into another tester...

For me the manual labour is more costly than anything else Wink
100kwh-hunter likes this post
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#14
interesting i have built a 11kw powerwall.i have been reading the messageboard and maybe i have made a mistake on cell selection.The method you use will result in a very high quality battery bank,but with a lot of waistage.What i did was set up a bank of 14 TP4054 chargers and used 5v computer supply charged cells untill modual said full charge(this is automatic as light changes colour).Any cells that is warm is discarded.This is were i differ i leave for 24 hours any cell under 4v is discarded as it is a SD CELL.I then immedily discharge test to 2.8v and write on cell capacity.For discharge i use these chines discharge moduals that are resonably accurate for my needs.i have some weak banks on my powerwall so add some batteries to balance out.It seems your way is a good one to increase the quality of power bank with probably some small cost but i think might be way forward to increase life of the battery bank overall.Any comments will be read as i want to increase bank life .
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#15
To increase battery bank life = get more cells and dont stress them as much

For having a battery bank that will last from start make sure to weed out ALL cells questionable. If they cant sustain sitting fully charged for several months they will for sure not last in a powerwall being abused Wink

Thats how easy it is. If they dont pass first test they are out.
BatteryMooch, 100kwh-hunter, Ibiza like this post
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#16
@Korishan that's my usual way to do it, except 6) . I don't discharge them.
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#17
For my process:
I am using tp4056 to charge and zb206 to capacity test.
The tp4056 are much cheaper (from memory around AU$0.45) than the zb206 (about AU$11.50)
I will have more tp4056 and do the charging/self discharge test first and only capacity test the cells which pass the self discharge test.
This saves the more expensive capacity testers from being used on cells which may fail SD testing.
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#18
(10-15-2019, 05:12 AM)Generic Wrote: Even though I didn't do it this way, I would recommend charging and testing for voltage drop FIRST before capacity testing for 2 reasons: (1) It will help you weed out self draining cells and save you the time you would spend testing those cells; and (2) keeping cells at full charge for extended periods of time WILL damage your cells. So why test twice? I made that mistake and let cells sit at full charge for between 8 months and 1 year before testing AGAIN and found out I lost like 3% of my good cells and a whole bunch of time retesting. So after you test for self-dischargers, do a capacity test, and then bring those cells to a uniform storage voltage (I would do 3.4V but most would do 3.7V). Keeping the voltage low and uniform will aid in pack building. You don't want to solder/spot weld a fully charged cell in case you make a mistake (it happens).

I'm in a similar position, I'm pretty new to this I salvaged 600 x 18650 cells from old laptop batteries, fully charged removing heaters and leaving the rest for 2-3 weeks to weed out the any that SD then capacity tested using the NOR test on my LiitoKala Lii-500's

Now I've realised I wont get to build all of these in to packs for a while and I have 600 cells at 4.2v Why doesn't the NOR test charge to a storage voltage rather than a full charge surely that would be more useful and quicker?

Any advice on how best to get this many cells down to 3.7v to store for a while
Ibiza likes this post
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#19
I'm surprised at the amount of people that leave their cells charged at full voltage for month(s).  There is quite a body of work out there that says don't do it as you are needlessly losing capacity.  Besides the many articles at BatteryUniversity.com (including this and this)there is this white paper that has done quite a bit of empirical work -

https://www.researchgate.net/publication...Assessment
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#20
Diggsut... Yeah you can loose up to couple of % per year doing it BUT.... Most bigger solar installs you will also have the powerwall fully charged for up to 8 hours a day.

So if we look at the numbers. Lets say you have used cells and you let them sit at 15c that I do... Lets say I leave them for 3 months. If you look at that white paper you will see that I loose a whopping 1% or so.

So if we take this further and if you read that white paper you send you will see that sitting at lower SoC does not save you that much in terms of degradation during those 3 months. If you add how much you actually degrade using the cells later on especially for those pushing cells harder you degrade ALOT faster doing that

If you pull all those numbers on the table this is the result:
* Sitting at full charge some month does not kill the cells
* Spending that extra time discharging and wasting that capacity in the cells cost MORE in time and energy wasted than actually just buying some extra cells to compensate the minimal loss
* Sitting att full charge during that time you can even better weed out self dischargers. That self discharging cells actually saves you more energy than what you have lost letting them sit there comparing using the batteries over some years.
* If a cell actually wont be able to sit at full charge for lets say 3 months... Its not even worth having in a powerwall. Because 3 months full there equals 9 summer months sitting full in my powerwall... And this I cannot do anything about unless i want the battery bank to sit half charged and loose valuable DoD capacity.

Do I have numbers of this? Yes i calculated and tested this. Im not going to write all numbers here because thats a white paper it self Smile

Yes - Leaving them fully charge degrades the batteries slightly faster than middle/close to empty.
BUT just lowering the temperature where they sits do ALOT and really... If thats your biggest concern loosing energy you should consider buiing better wiring or inverter/charger. Thats where you save alot more energy.

Would letting them sitting fully charge cause a "fire" -> NO.

We have a couple of side-tracks here becaue LiPo on other hand are more sensitive and thats because of the case. If LiPo would sit in hard-case its not a problem there either. I have done my fair share of RC last 10+ years and I have many cells sitting for all winter fully charged for testing. Some brands doesnt like it as much when using soft cases since they do wanna puff a bit but so far not problem.
I have killed more cells due to abusing them when in use than leaving them as is Tongue


Lastly: If you dont know when you will use them or its a very long time like half a year or years then of course discharge them down to 40-50%. its just better. But for a month or 3 during the build its ok
Frenno likes this post
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