The joys of testing.

[J_Mack58]

I’m adding on or possibly replacing a nice 14s80p battery made with 18650’s cells. I never tested not one cell. Matter of fact up into last week I never owned a tester. Now I own two. With my limited experience I learned there are four type of bad cells. 1. Shorted or Heaters, they get hot when you try to charge them. They don’t charge and could damage your charging source so you stop charging them and mark them as bad. 2. Open, the CID has popped from cell over pressure and I‘m not brave enough to reset it. (Seen it done on YouTube though) Risk not worth getting the cell to work again only to have the capacity suck because it was damaged in the process of being over pressured due to overcharge or too heavy discharge. 3. Self-Dischargers, they charge, they don‘t get hot but the charge drops like a Jamaican Bobsled team coming down the Swiss Apps. 4. Low Capacity, they charge, don’t get hot. Discharge a little worst than a good cell but using our great “Battery Tools” on this site the cell suppose to be a 2900 mAh and you get less than 1000 mAh. Usable but not worth it.

So with this batch of 280, 26650 cells I plan to test every one of them. Notice I wrote “plan to”. I’m not close to half way and I‘m already tired. The tiredness comes from waiting. These cells come from a 4s5p battery…20 cells.

Inserting $50,000 question here.

if I bulk charge the 20 cells, and they all charge to 3.6v, (CID good)I get no heat, (Non-Heater) I pulled them off the bulk charger one at a time and they hold a solid 3.59xx volts for a minute (Non-self discharger) and the next day still at 3.592x volts…. Capacity test a random 4 cells from the 20 with my Opus and they range 30xx mAh to 32xx mAh can I call the 20 good?

Somebody pleeeeeeaaaaase say “yes”.

 

[Korishan]

First off, you didn't mention if these cells are new or reclaimed or from new-old stock.
Secondly, you state that you charge to 3.6V. I'm assuming these are LiFePO4 cells, correct?

And to answer your question a little more direct, it all depends.
Firstly, to do what you want to accomplish, you would need relatively new cells, new-old stock for example. Reclaimed cells, nope. Test them all.
Secondly, you would want to IR test "every" cell at least (do this anyways regardless of cell condition). This will help weed out any possible SD's.

And then, after that, you could possibly pull random cells to check. Altho, waiting a day or two would be too soon. You would want to wait at least a week, and 2 weeks would be more like it. If you could put them on hold for a month, even better. Most cells will have the most drop within the first day or two. But they could continue to drop over the next weeks. Some slow down to only a few mV per day. Others could maintain 10's or 100 of mV each day.

 

[J_Mack58]

First off, you didn't mention if these cells are new or reclaimed or from new-old stock.
Secondly, you state that you charge to 3.6V. I'm assuming these are LiFePO4 cells, correct?

And to answer your question a little more direct, it all depends.
Firstly, to do what you want to accomplish, you would need relatively new cells, new-old stock for example. Reclaimed cells, nope. Test them all.
Secondly, you would want to IR test "every" cell at least (do this anyways regardless of cell condition). This will help weed out any possible SD's.

And then, after that, you could possibly pull random cells to check. Altho, waiting a day or two would be too soon. You would want to wait at least a week, and 2 weeks would be more like it. If you could put them on hold for a month, even better. Most cells will have the most drop within the first day or two. But they could continue to drop over the next weeks. Some slow down to only a few mV per day. Others could maintain 10's or 100 of mV each day.

Yep the cells are LiFePO4 cells, reclaimed. I agree with you I should test them all.... I just was hoping you would say something different.

 

[100kwh-hunter]

Test them all on:
Appearance: Rust, dents ect
IR
Heaters
Self dischargers(give m 4 weeks)
Charging (incl time) ( a bit odd if a cell of 3000mah isnt full after 8 hours with charging with 1Ah
Discharging.
( i keep forgetting two ?important? factors that i was also testing, sorry)
Make your packs as even as possible so not 15 packs @ 20A and one at 18A, then the whole string is 18A

keep only the ones if you have the luxury: above 90%soh.
If not divide them into two strings or three strings 70-80%, 80-90% and 90 to 100%SOH
This way it will be easier to swap them in the future, without testing the whole pack on cell level

Some advice from a "coekoek locowako" tester...built your own tester(charge/discharge), match your psu according to it.
Some people on the forum just test on charge and discharge--->minimal 80% SOH they go into there powerwall, BUT they have a powerwall above 100kwh!

Find topics from a forum member named @Wolf, he did a lot of testing on testers, if you want to buy a ready to go one.
His advice for IR testing is the yr1035....did not thank him enough for this...No i don't think after every tested cell: thank you wolf.

My advice for building your own tester, get simulair, so for your lifepo4 that is, this is for li ion! some zb2l3 and some TP4056.
If you order 10 tp you must have a psu over 10A and a timer(per tp 1A+)
zb will take per piece 70mah per 10( i never understood!) just 150mah.
My topic on building a tester is ~2 years old somewhere.
Good luck and keep us posted please.

With best regards Igor.

 

[floydR]

Charging the cells in bulk to 3.6v will really shorten your turn around time. Charge them then place in your Opus's on test mode. 3.6v to 3.7v happens fast. Even faster if you remove the cells after they finish the discharge portion of the test mode. Then Bulk charge the cells back up to 3.65v. I am not sure how hard of life the cells have had. Self discharge is different in LiFePO4 cells, They tend to rest at 3.34v-3.5v , my 26650 A123 cells rest around 3.375v- 3.45v. It has been my experience that all LiFePO4 cells will self discharge and come to a resting voltage where they settle to.
later floyd

 

[Redpacket]

+1 LiFePo4's seem to settle to a lower voltage after disconnecting the charger & this is normal behavior.
+1 IR testing them is a good idea.
My 2 cents: the less you charge them to 3.65V the better for long term, only charge to about 3.45V & hold there until current drops, then = full.
3.65 shortens the cell life.

 

[J_Mack58]

+1 LiFePo4's seem to settle to a lower voltage after disconnecting the charger & this is normal behavior.
+1 IR testing them is a good idea.
My 2 cents: the less you charge them to 3.65V the better for long term, only charge to about 3.45V & hold there until current drops, then = full.
3.65 shortens the cell life

You right Redpacket, looks like OPUS consider 3.47 and above “Full”. No need to pre-charge to 3.6volts. IR tests is fairly quick, do you believe the numbers? I read people writing about a 4 wire for a more accurate measurement.

 

[J_Mack58]

You right Redpacket, looks like OPUS consider 3.47 and above “Full”. No need to pre-charge to 3.6volts. IR tests is fairly quick, do you believe the numbers? I read people writing about a 4 wire for a more accurate measurement.

 

[J_Mack58]

3.46 volts full… l’m waiting on that last joker to start discharging them all at once.

 

[floydR]

If in "test" mode The OPUS will charge them then discharge them then charge them. all automatically

No need to use the "charge" mode then change the mode to "discharge" The OPUS quick test (IR) is not really usable inconsistent results
Later floyd

 

[Redpacket]

The OPUS quick test (IR) is not really usable inconsistent results

Like floyd suggests, the Opus IR readings seem to be more of an indication than an accurate reading.
For any accuracy you need a proper 4 wire IR tester like a YR1035 or similar.