I have a custom PCB where I implemented BMS system based on TP4056 from a 5V regulated solar power source. Everything works as expected regarding battery charging and output but I am encountering a special case when if power source isnt connected before the battery, for some reason, battery (-)ve drops to less than ground (ie -2.8 volts currently) and battery (+) has remaining 0.5-1v. Soon as Power is connected from either solar/bench supply battery negative reference becomes the same as ground reference of PCB.
I compared the voltages to before and after power is connected and have them shown is the attached schematic as yellow and blue fonts. In the TP4056 with protection circuit I have from Aliexpress/amazon, battery negative is always the same has Circuit Ground, and irrepective of when the power is applied.
What I can see based on voltages is :
- on DW01, pin 1(OC), and pin 3(OD) somehow split the total voltage of the battery between them, compared to when power is connected, and both have the same potential.
Right now I am clueless as to how to ensure battery negative reference is the same as ground reference of the PCB.