Left cell pack at 3.55v for over 4weeks

[Berseker]

So i have a nearly 2month old pack working ok.partially offgrid. With 3600w of solar supporting charging.inverter was set to charge cells to 3.55v
So owner moved it to a new location with stable grid and pack ended up cycling very light and staying at fully charged state for extended periods of time.

So observed 3 cells voltage dropping to 3.35v while other cells are 3.51v.
Attempted to top balance the "low" 3 cells and they took about 5ah before getting filled up and voltage spiking to 3.6v....and dropping quickly to 3.45v and then 3.37v after about 4minutes
So my question is, my theory is that the 3 cells may have suffered some damage from the 3.55v charge voltage and staying at 100% soc for extended period of time.

Is this theory correct, if yes..is it permanent.
Have reduced the pack voltage to 55.6v/3.48v . Set trigger balance voltage to 3.34v and 0.02 delta and is observing the pack further.

Any tips or thoughts is welcome

 

[BentleyJ]

3.35V per cell is the normal resting voltage for LFP chemistry a couple of hours after a full charge.

 

[Berseker]

3.35V per cell is the normal resting voltage for LFP chemistry a couple of hours after a full charge.

Yes, but the other 13 cells are 3.45v, pack is full and inverter has throttled charging . delta between the cells is high as seen on the bms screenshot

 

[BentleyJ]

Let the battery float at 55.6V for several hours and verify the balancer is working. If so, the voltages will all even out eventually.
In your screenshot balance is turned off so you turned it on and reset the trigger voltage after posting the screen shot I assume?

 

[Q-Dog]

Loose connections after moving it around?

 

[Berseker]

Let the battery float at 55.6V for several hours and verify the balancer is working. If so, the voltages will all even out eventually.
In your screenshot balance is turned off so you turned it on and reset the trigger voltage after posting the screen shot I assume?

the daly bms inbuilt balancer is wimpy (100mA) and a bit glitchy..balance light on app barely stays on for more than 60secs...then it goes off. hard to tell if its actually balancing or not.

Loose connections after moving it around?

wasn't moved around, so likely not loose connection.


longterm, I intend to slap on a 1a daily balancer permanently on the pack. my major issue is knowing if the cells have been damaged somehow... guess I may have to capacity check the individual cells to be sure of this

 

[Lt.Dan]

the daly bms inbuilt balancer is wimpy (100mA) and a bit glitchy..balance light on app barely stays on for more than 60secs...then it goes off. hard to tell if its actually balancing or not.


wasn't moved around, so likely not loose connection.


longterm, I intend to slap on a 1a daily balancer permanently on the pack. my major issue is knowing if the cells have been damaged somehow... guess I may have to capacity check the individual cells to be sure of this

Typical Daly BMS is only 20mA in my research and experience.

To answer the OP, each sell with have a slightly different "resting voltage" unless they are perfectly binned/matched etc. The spread you have is pretty extreme though.

Do a capacity test and IR test and see if they pull capacity or not.

 

[Q-Dog]

So i have a nearly 2month old pack working ok.partially offgrid. With 3600w of solar supporting charging.inverter was set to charge cells to 3.55v
So owner moved it to a new location with stable grid and pack ended up cycling very light and staying at fully charged state for extended periods of time.

So observed 3 cells voltage dropping to 3.35v while other cells are 3.51v.
Attempted to top balance the "low" 3 cells and they took about 5ah before getting filled up and voltage spiking to 3.6v....and dropping quickly to 3.45v and then 3.37v after about 4minutes
So my question is, my theory is that the 3 cells may have suffered some damage from the 3.55v charge voltage and staying at 100% soc for extended period of time.

Is this theory correct, if yes..is it permanent.
Have reduced the pack voltage to 55.6v/3.48v . Set trigger balance voltage to 3.34v and 0.02 delta and is observing the pack further.

Any tips or thoughts is welcome

I guess I misunderstood?

 

[Berseker]

Yeah, the spread wasnt like this before.
It developed after it stayed at 3.55v for weeks with shallow cycling.

Oh daly is 20mA, i thought twas 50mA.
Ok would def throw on a 1A daly balancer when i can take the pack apart. And if possible a capacity test.

I guess I misunderstood?

Yeah, my bad. I typed wrong.
Used a torque meter to recheck the busbars, all rock solid at 6nM