Common bad analysis of BMS lithium battery protection board
1. No display, low output voltage, no load
For such defects, first eliminate the bad battery (the battery has no voltage or the voltage is low). If the battery is bad, the self-consumption of the protection board should be tested to see if the self-consumption of the protection board is too large and the battery voltage is low. If the cell voltage is normal, it is because the entire circuit of the protection board is blocked (components are soldered, false soldered, FUSE is poor, the internal circuit of the PCB board is blocked, the via is blocked, MOS, IC is damaged, etc.).
2. No short circuit protection
There is a problem with the resistance of the VM terminal: use a multimeter to connect one test pen to IC2 pin, and one test pen to the MOS pin connected to the VM terminal resistor to confirm the resistance value. Check whether the resistance and IC, MOS pins are soldered.
IC and MOS abnormality: Since the over-discharge protection and over-current and short-circuit protection share a MOS tube, if the short-circuit abnormality is due to a problem with the MOS, the board should have no over-discharge protection function.
The above are defects under normal conditions, and short-circuit abnormalities caused by poor IC and MOS configurations may also occur. For example, in the BK-901 that appeared in the previous period, the delay time in the IC with the model of ‘312D’ was too long, which caused the MOS or other components to be damaged before the IC took the corresponding action control.
Note: The easiest and direct way to determine whether an IC or MOS is abnormal is to replace the suspected components.
3. Short circuit protection without self-recovery
The IC used in the design has no self-recovery function, such as G2J, G2Z, etc.
The short-circuit recovery time of the instrument is too short, or the load is not removed during the short-circuit test. For example, the test leads are not removed from the test end after the short-circuit test leads are short-circuited with the multimeter voltage file (the multimeter is equivalent to a load of several megabytes).
Leakage between P+ and P-, such as impurity rosin between the pads, impurity yellow glue or P+, P- capacitance breakdown, IC Vdd to Vss breakdown. (The resistance is only a few K to Several hundred K).
If none of the above is a problem, the IC may be broken down, and the resistance between the pins of the IC can be tested.
4. The protection board BMS has large internal resistance
Since the MOS internal resistance is relatively stable and the internal resistance is large, the first thing to suspect should be the components whose internal resistance is relatively easy to change such as FUSE or PTC.
If the resistance value of FUSE or PTC is normal, the resistance value of the via hole between the P+, P- pad and the component surface may be detected according to the structure of the protection board.
If there is no problem with the above, it is necessary to suspect whether the MOS is abnormal: first determine whether there is a problem with the welding; secondly, the thickness of the board (whether it is easy to bend), because the bending may cause abnormal soldering of the pins; then put the MOS tube in Observe whether it is broken under a microscope; finally, use a multimeter to test the resistance of the MOS pin to see if it is broken down.
5. ID exception
The ID resistor itself is abnormal due to virtual welding, fracture, or because the resistance material is not closed. You can re-weld both ends of the resistor. If the ID is normal after re-welding, it is a virtual resistance welding. If it is broken, the resistor will crack after re-welding.
The ID via does not conduct, and a multimeter can be used to test both ends of the via.
If there is a problem with the internal circuit, you can scrape the solder mask to see if the internal circuit is disconnected or short-circuited.