I really wish I had an experienced LiFePO4 battery builder able to help me out with this, I'm very confused.
What I have:
8 304 AH EVE cells from Docanpower
JK 8s BMS
LV2424 Hybrid inverter charger
Multimeter
What I noticed when I received the cells:
They looked great, no bloating or scratches.
QR codes in tact. Looked brand new.
What I did initially.
Connected them all in series with the bus bars that came with.
Installed the Balance leads for the BMS
Connected the BMS and jump started it.
Hooked up the inverter charger to the battery and AC power.
Charged the cells at 30A
Set bulk charge to 28.8v and float to 28.6v
What I noticed during first charge:
As they charged up, slowly I noticed some slight bloating, but it was wavy. As I felt the sides of the cells, the middle was concave while the left and right side were slightly bloated.
It took several hours to charge the cells at 30A (expected this)
I charged them up this way, and my BMS was reporting about 0.16v cell differential at some points, and sometimes the BMS would cutoff charging due to over voltage.
Then the BMS would attempt to balance the cells.
once cell voltage differential dropped, it would continue charging.
Eventually all cells read the same voltage again and the inverter stopped charging.
Voltage readings from the inverter and my multimeter seemed to match up with the total battery bank voltage so I figured they were essentially top balanced and charged.
I then disconnected the inverter charger from AC power and let the batteries run the inverter.
Load according to the BMS was between 12-24 watts. It ran for 5 or 6 days as I monitored voltage.
Voltage started dropping very quickly day 4 and 5. BMS was claiming I had used about 80 AH and should be at 74% or something. But I was around 26v and every chart I read stated that I was about 30% capacity. I continued to run it to see what it would do. Eventually I dropped down to 24.8v after using roughly 100 AH (according to my BMS at least). This places it about 12% SOC while my BMS was still claiming something close to a 70% SOC.
At the end, when I turned the inverter off, the voltage increased a little bit, but still pretty low. I still notice the cell walls being a little wavy with the middle being lower than the sides despite low SOC (according to voltage charts anyways).
When I do the math, this large of a bank should be able to supply 20w continuous to run the inverter for at least double the number of days that it ran it for.
It almost seems like I'm only getting 120-130 AH out of the full system.
I can't think of anything that I may have done to hurt the cells, but that capacity has me seriously concerned that there is something very wrong with the cells.
I now have a compression box on them that is lightly compressing them in hopes to prevent too much further bloating.
I am taking a trip to attempt to finish my bus conversion this next week so I wanted a compression box for safe shipping of the cells and wanted them around 30% SOC for the trip just in case. I connected the inverter back into AC power to again charge the cells at 30A. I disconnected the AC and turned off the inverter when the overall battery voltage while charging hit 27v. It has now leveled to about 26.4v.
I noticed it only took about 1.5 hours of charging at 30A to bring the batteries up from 24.9v to 26.4v resting... Which has me concerned as well since it should have taken longer to bring it from 10% SOC to 70% SOC (all SOC's are based off of a 24v voltage chart I found on here).
After writing all of this out, I'm even more concerned about the cells than I was before... It all seems to be pointing to something being very wrong. I really wanted to avoid needing to spend an additional $100 on a variable voltage power supply for top balancing and anything to run a legitimate capacity test and thought that my method would work just fine. After all I wasn't charging any of the cells above 3.6v so they shouldn't be damaged in any way.
Can I please get some input from you guys about what I'm seeing? What are some things I can do with what I have to figure out the condition of the cells and solve these problems? I'm hoping that its just the BMS was drastically underestimating the power that the battery was supplying to the inverter to run it, but then the charging being so quick at 30A makes me still believe that the capacity is literally less than half of what it should be.
What I have:
8 304 AH EVE cells from Docanpower
JK 8s BMS
LV2424 Hybrid inverter charger
Multimeter
What I noticed when I received the cells:
They looked great, no bloating or scratches.
QR codes in tact. Looked brand new.
What I did initially.
Connected them all in series with the bus bars that came with.
Installed the Balance leads for the BMS
Connected the BMS and jump started it.
Hooked up the inverter charger to the battery and AC power.
Charged the cells at 30A
Set bulk charge to 28.8v and float to 28.6v
What I noticed during first charge:
As they charged up, slowly I noticed some slight bloating, but it was wavy. As I felt the sides of the cells, the middle was concave while the left and right side were slightly bloated.
It took several hours to charge the cells at 30A (expected this)
I charged them up this way, and my BMS was reporting about 0.16v cell differential at some points, and sometimes the BMS would cutoff charging due to over voltage.
Then the BMS would attempt to balance the cells.
once cell voltage differential dropped, it would continue charging.
Eventually all cells read the same voltage again and the inverter stopped charging.
Voltage readings from the inverter and my multimeter seemed to match up with the total battery bank voltage so I figured they were essentially top balanced and charged.
I then disconnected the inverter charger from AC power and let the batteries run the inverter.
Load according to the BMS was between 12-24 watts. It ran for 5 or 6 days as I monitored voltage.
Voltage started dropping very quickly day 4 and 5. BMS was claiming I had used about 80 AH and should be at 74% or something. But I was around 26v and every chart I read stated that I was about 30% capacity. I continued to run it to see what it would do. Eventually I dropped down to 24.8v after using roughly 100 AH (according to my BMS at least). This places it about 12% SOC while my BMS was still claiming something close to a 70% SOC.
At the end, when I turned the inverter off, the voltage increased a little bit, but still pretty low. I still notice the cell walls being a little wavy with the middle being lower than the sides despite low SOC (according to voltage charts anyways).
When I do the math, this large of a bank should be able to supply 20w continuous to run the inverter for at least double the number of days that it ran it for.
It almost seems like I'm only getting 120-130 AH out of the full system.
I can't think of anything that I may have done to hurt the cells, but that capacity has me seriously concerned that there is something very wrong with the cells.
I now have a compression box on them that is lightly compressing them in hopes to prevent too much further bloating.
I am taking a trip to attempt to finish my bus conversion this next week so I wanted a compression box for safe shipping of the cells and wanted them around 30% SOC for the trip just in case. I connected the inverter back into AC power to again charge the cells at 30A. I disconnected the AC and turned off the inverter when the overall battery voltage while charging hit 27v. It has now leveled to about 26.4v.
I noticed it only took about 1.5 hours of charging at 30A to bring the batteries up from 24.9v to 26.4v resting... Which has me concerned as well since it should have taken longer to bring it from 10% SOC to 70% SOC (all SOC's are based off of a 24v voltage chart I found on here).
After writing all of this out, I'm even more concerned about the cells than I was before... It all seems to be pointing to something being very wrong. I really wanted to avoid needing to spend an additional $100 on a variable voltage power supply for top balancing and anything to run a legitimate capacity test and thought that my method would work just fine. After all I wasn't charging any of the cells above 3.6v so they shouldn't be damaged in any way.
Can I please get some input from you guys about what I'm seeing? What are some things I can do with what I have to figure out the condition of the cells and solve these problems? I'm hoping that its just the BMS was drastically underestimating the power that the battery was supplying to the inverter to run it, but then the charging being so quick at 30A makes me still believe that the capacity is literally less than half of what it should be.