So recently I finished by 10P 4S LiFePo4 battery back. Each cell is 3.2v and four in series make 12.8v. I have a bms which seems to be working well (It is designed for LiFePo4 cells). When I am finished charging the battery each cell is about 3.3 volts. I was testing it today when my BMS cut off the load. After checking the voltage of each cell I realized something was wrong. The first cell was about 3.05v, the second was 2.8v, the third was 3.04v and the final cell was 2.6v. This is the first battery I have ever made and I am very confused right now. I made sure all of the cells are connected but this problem still persists even after recharging and trying the test again. Here is a picture of my battery, let me know if you need any more information.

 

So recently I finished by 10P 4S LiFePo4 battery back. Each cell is 3.2v and four in series make 12.8v. I have a bms which seems to be working well (It is designed for LiFePo4 cells). When I am finished charging the battery each cell is about 3.3 volts. I was testing it today when my BMS cut off the load. After checking the voltage of each cell I realized something was wrong. The first cell was about 3.05v, the second was 2.8v, the third was 3.04v and the final cell was 2.6v. This is the first battery I have ever made and I am very confused right now. I made sure all of the cells are connected but this problem still persists even after recharging and trying the test again. Here is a picture of my battery, let me know if you need any more information.View attachment 188055

You need to start with each parallel section separately fully charged to 3.3 volts. During discharge, each section will discharge the same amount of power as the other two but the voltage across each section will be slightly different from the others because of small differences between the cells.When they are re-charged, they will all reach 3.3 volts at the same time unless you have faulty cells in the sections.

 

You need to start with each parallel section separately fully charged to 3.3 volts. During discharge, each section will discharge the same amount of power as the other two but the voltage across each section will be slightly different from the others because of small differences between the cells.When they are re-charged, they will all reach 3.3 volts at the same time unless you have faulty cells in the sections.

The BMS automatically charges each cell to 3.3v. The issue is discharging. The bms cuts off the power when the cell voltages differ too much and this happens only after a few hours of use.

 

IIRC a fully charged LiFe cell should be 3.6 volts. 3.3 volts is their nominal voltage. I would suspect a wiring error somewhere.

 

My advice is to ditch the BMS .... Looks like your cells are new , there is no reason the 4 parallel blocks should get out of sync with one another , I have a larger battery I have put a small $2 voltmeter on each parallel block and have found they all stay very close ... when the voltage of the whole battery reaches max , a circuit cuts of charging ...

 

My advice is to ditch the BMS .... Looks like your cells are new , there is no reason the 4 parallel blocks should get out of sync with one another , I have a larger battery I have put a small $2 voltmeter on each parallel block and have found they all stay very close ... when the voltage of the whole battery reaches max , a circuit cuts of charging ...

So you think that the BMS is causing the cells to have different voltages? Is there a safe way to test this?

 

IIRC a fully charged LiFe cell should be 3.6 volts. 3.3 volts is their nominal voltage. I would suspect a wiring error somewhere.

I used an IMAX B6 to charge the battery on the 12v Pb setting. I checked a few hours after it had finished charging and each cell was 3.3v.

 

Well there's your problem! You're using the lead-acid setting on your charger to charge LiFe cells. Big No-No.