I purchased 8x280AH cells from Docan Tech in July of 2022 for a 24v pack, but due to family emergencies I wasn't able to build this battery until almost a full year later.
Fast forward, I pulled the cells out in June of this year, and every cell was at 3.29V except for one (we will call this cell #5 as that's where it ended up) which was at 3.22V. I thought it was odd so I kept note. I top balanced them all in parallel at 3.65v and held them there for over 24 hours. I don't remember exactly but I seem to recall cell #5 voltage settling much faster than the others after disconnecting.
After I assembled the battery, cell #5 was always 40-60 mV lower than every other cell. This is part of a larger project (including a second battery built from a different batch of 280AH cells - those are working fine), so I figured I'd wait to get it into the system to do some real testing as far as charging/discharging. Well today was that day, the two batteries are connected in parallel to a Multiplus. I let this 'trouble' pack charge fully from 85% (with a cell delta of 0.044V) and this was what I ended up with:
Damn cell #5...
I double checked the connections (will triple check again though), and verified the cells voltage with a multimeter.
So at this point, I need to do a capacity test, which I hope to do tomorrow.
I'm sure I'm past the date for asking for a replacement cell, which I understand. The task of ripping the pack apart is more painful than spending the money to replace the cell if it comes to that. Depending on how the capacity test goes, would you even consider adding an active balancer to this pack? I'm using the 100A JBD BMS with passive balancing only.
Fast forward, I pulled the cells out in June of this year, and every cell was at 3.29V except for one (we will call this cell #5 as that's where it ended up) which was at 3.22V. I thought it was odd so I kept note. I top balanced them all in parallel at 3.65v and held them there for over 24 hours. I don't remember exactly but I seem to recall cell #5 voltage settling much faster than the others after disconnecting.
After I assembled the battery, cell #5 was always 40-60 mV lower than every other cell. This is part of a larger project (including a second battery built from a different batch of 280AH cells - those are working fine), so I figured I'd wait to get it into the system to do some real testing as far as charging/discharging. Well today was that day, the two batteries are connected in parallel to a Multiplus. I let this 'trouble' pack charge fully from 85% (with a cell delta of 0.044V) and this was what I ended up with:
Damn cell #5...
I double checked the connections (will triple check again though), and verified the cells voltage with a multimeter.
So at this point, I need to do a capacity test, which I hope to do tomorrow.
I'm sure I'm past the date for asking for a replacement cell, which I understand. The task of ripping the pack apart is more painful than spending the money to replace the cell if it comes to that. Depending on how the capacity test goes, would you even consider adding an active balancer to this pack? I'm using the 100A JBD BMS with passive balancing only.
