EVE cell issue-retest or reject?

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
New 8s EVE LF280K build. I top balanced using multiple steps. My first screenshot is what I got when first connected to the BMS. Delta Volts .002 a good day plus after balancing I ran my discharge test at approx 100 watts. Took days of course, but the delta remained nice and low. Under load cell 7 was always a touch higher and cell 1 always a touch lower. The delta stayed very low but as the test went on the delta climbed with #1 dropping faster than the rest. The bulk of my testing was with balancing off. I did experiment with brief periods of balancing on especially towards the end, but it could not correct it. As the average cell voltage hit 3.150 the delta was up to .064 and continued to climb At 3.125 it was at .084 and at 3.012 it was at .159. The test stopped (screen shot 5) when cell #1 hit 2.5v with a delta of .374. All of the rest of the cells were reasonably well balanced at 2.8-2.9v The BMS scored my cycle capacity at 254.5ah although I don't think the the BMS is finished calculating until I'm back to full charge. My tester said 278ah but of course there was seemingly a good bit left in the other 7 cells.

I am presently charging back up at 10a constant current and should be finished in a few hours. My question is do I perform another test on cell 1 and maybe one other cell? Do I reject cell 1? Or do I just accept what I have as "good enough for who it's for"?

My OCD says reject. They are from a US warehouse.
 

Attachments

  • Screenshot_20220105-112319.png
    Screenshot_20220105-112319.png
    282.7 KB · Views: 31
  • Screenshot_20220108-080600.png
    Screenshot_20220108-080600.png
    275 KB · Views: 29
  • Screenshot_20220108-083317.png
    Screenshot_20220108-083317.png
    269.9 KB · Views: 22
  • Screenshot_20220108-101105.png
    Screenshot_20220108-101105.png
    280.8 KB · Views: 25
  • Screenshot_20220108-115344.png
    Screenshot_20220108-115344.png
    282.8 KB · Views: 31
Last edited:

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Upon charge the delta came right back in line quite quickly and is doing well throughout. I'm approaching 80% capacity and it's still down in the thousandths.
 

Attachments

  • Screenshot_20220108-151047.png
    Screenshot_20220108-151047.png
    269.1 KB · Views: 15

Wibla

Engineer
Joined
Jun 6, 2021
Messages
262
Did you properly top balance these cells before putting them into service?
 

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Did you properly top balance these cells before putting them into service?
First line of post and screenshot 1. Can't get much better than that. For final step I ran all 8 individually with my power supply set to 2.65v which produced an actual 2.644 volts output and I pulled them off after then VERY slowly crept up to 2.640v At this point the amperage/wattage was down to next to nothing.
 

Wibla

Engineer
Joined
Jun 6, 2021
Messages
262
Ok, based on that info, I'd reject the weak cell. 30 Ah capacity lost across the whole pack because of a bad cell is not acceptable.
 
Joined
Nov 30, 2019
Messages
12,127
Ambient temperature should be 25C for the test.
Be sure to note how well the pack re-converges at 100% SOC.
 

DJSmiley

Solar Addict
Joined
Aug 13, 2020
Messages
551
Did you properly clean/sand/check the terminals?

you might swap cells and see if this issue 'moves along'. Swap cell 1 and eg cell 3 and see if the issues persists on the same cell (3 in that case).
If you have, do a seperate capacity test on the suspicious cell.
 

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Ambient temperature should be 25C for the test.
Be sure to note how well the pack re-converges at 100% SOC.

Yeah winter time sub zero °f it's not practical to heat the shop that warm especially with radiant floor. 62°f vs 77°f isn't a huge difference.

Active balance off I assume and just see what it does? Right now my delta is running around .006v and capacity around 80% according to the BMS.
 

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Did you properly clean/sand/check the terminals?

you might swap cells and see if this issue 'moves along'. Swap cell 1 and eg cell 3 and see if the issues persists on the same cell (3 in that case).
If you have, do a seperate capacity test on the suspicious cell.

I actually filed a couple quick strokes on them.

I suppose I got ahead of myself in that I grouped and taped them together, but I have them in 2 groups of 4 so I could just rearrange the busbars.

I figure I'll charge up as a pack and then re-top and retest cell #1 and maybe one other for comparison. Test will definitely go much faster with 100 watts at 3.x volts versus full pack.
 
Joined
Nov 30, 2019
Messages
12,127
Yeah winter time sub zero °f it's not practical to heat the shop that warm especially with radiant floor. 62°f vs 77°f isn't a huge difference.

Active balance off I assume and just see what it does? Right now my delta is running around .006v and capacity around 80% according to the BMS.
Yes leave the balance off for this charge cycle.
 

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Recommendations on a good compact, reasonably priced portable inverter that operates selectable between 12v and 24v inputs?

I've been wanting one for 12v to say 1500-3000watts, but having 24v input option would save me running my little 100 watt load tester for 3+ days.
 

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Latest screenshot
 

Attachments

  • Screenshot_20220109-094741.png
    Screenshot_20220109-094741.png
    273.1 KB · Views: 31

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Delta remained very steady and low across 27v and started to climb above 27.25. By 28v my high cell shut down at 2.64v while the delta was across .241. I changed my numbering and resumed charging with the active balance on. Plan is to get all of the cells balanced a second time and test the entire group again.
 

Attachments

  • Screenshot_20220109-165433.png
    Screenshot_20220109-165433.png
    277.8 KB · Views: 10
  • Screenshot_20220109-170809.png
    Screenshot_20220109-170809.png
    278.6 KB · Views: 10
Joined
Nov 30, 2019
Messages
12,127
Delta remained very steady and low across 27v and started to climb above 27.25. By 28v my high cell shut down at 2.64v while the delta was across .241. I changed my numbering and resumed charging with the active balance on. Plan is to get all of the cells balanced a second time and test the entire group again.
Was it the weak cell that popped high?
If yes then I suggest to test it individually.
Probably should test the penultimate cell as well.
 

Just John

Photon Sorcerer
Joined
Aug 15, 2020
Messages
2,664
Yeah winter time sub zero °f it's not practical to heat the shop that warm especially with radiant floor. 62°f vs 77°f isn't a huge difference.

Active balance off I assume and just see what it does? Right now my delta is running around .006v and capacity around 80% according to the BMS.
I would get them back top balanced like you had, turn off the active balance portion of the BMS and run another capacity test. You could even swap cell position to verify the problem follows the cell. If it does, yes I would exchange it.
 

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
I ended up re-topping using active balance then changed order of the cells and re-tested. The hi and low did not follow the cells in question. When I got below the bottom knee things did deviate again but on different cells. I charged them up to 50% +/- and assembled into the box. I changed my orientation a bit so I ended up short by one 51.5mm busbar and had to use a solid one. I still may add rubber caps to the other 14 exposed terminals. Battery T1 is inside the case between the cells that had been kept warm in truck. T2 I put just outside the case so it was reading room temp which was just a touch low because I had the overhead door open to bring the battery inside.
 

Attachments

  • PXL_20220115_180329173.jpg
    PXL_20220115_180329173.jpg
    971.7 KB · Views: 10
  • Screenshot_20220115-121650.png
    Screenshot_20220115-121650.png
    284.8 KB · Views: 10
Last edited:

Diesel Pro

Solar Enthusiast
Joined
Jul 21, 2021
Messages
107
Did not have enough time to get them fully topped that day. Next day was very overcast and gray. Went back next day and saw that the Classic had produced only .4kwh It's been hit and miss weather so far this week. This and cook off is what killed my lead acid batteries. I'm much more at ease knowing that my lithium pack does not much care if its 20% or 90% and no need to try to crowd 98%+ for battery life.
 
Top