Part Number: BQ78350-R1
Other Parts Discussed in Thread: BQ78350
Hello,
I have SOC issue during development and testing.
Background:
- Battery include 14 NMC cells in series
- BMS include BQ78350 & MCU
- BQ78350 detect current, cell voltage; MCU detect temperature, battery voltage (48V), control MOS.
- The cell is from 2.5V to 4.2V in cell spec. and capacity is 60Ah
- MCU limit the voltage from 2.9V to 4.1V and the design capacity is 48Ah in Golden file
- Test the cell for ChemID based on 2.5V to 4.2V test at first
- Set the ChemID into BMS, then start the charge & discharge test at high, RT, low temperature
- Upload test data and got the Golden file from TI system
- Put EDV0,1,2 value based on battery discharge test data with 0.2C from 2.9V to 4.1V
Situation after golden file learning,
- SOC can be correct to 100% at end of charge
- SOC can be correct to 7% when trigger EDV2
- The SOC performance is strange. When wakeup from shutdown, the SOC is not as expected everytime. The deviation is high (up to >15%) when Battery real SOC is low. The deviation is small (~4% = 100% - 96%) when full charged battery and reactive.
Question
- How to deal with the ChemID when MCU limit the voltage range from [2.5V, 4.2V] to [2.9V, 4.1V]. Am I correct, or should redo the test based on [2.9V, 4.1V] on cell level for ChemID?
- Why the SOC value is so strange after wakeup from shutdown, this SOC is calculated based on OCV table inside ChemID?
This is hte Golden file file.
Looking forward to your reply. Thank you so much!
