Analysis of the reasons for the widespread poor performance of 18650 lithium battery protection boards.
1、 No floating, low output voltage, unable to carry load
This type of deficiency mainly eliminates the deficiency of lithium battery cells (which originally have no working voltage or low working voltage). Assuming that the lithium battery cells are deficient, the self consumption of the lithium battery protection board should be checked to see if it is due to excessive self consumption of the lithium battery protection board causing low working voltage of the lithium battery cells. Assuming that the working voltage of the lithium battery cell is normal, it is due to the blockage of all control circuits of the lithium battery protection board (electronic device empty soldering, false soldering, poor FUSE, internal power circuit blockage of the PCB board, via blockage, MOS, IC damage, etc.).
In depth analysis of the entire process is as follows:
（1） Using a digital multimeter, connect the black DC ammeter to the negative stage of the lithium battery cell, and then connect the red DC ammeter to both sides of the FUSE and R1 resistors, as well as the Vdd, Dout, Cout terminals, and P+terminals of the IC (assuming the working voltage of the lithium battery cell is 3.8V). Analyze each section, and all of these detection points should be 3.8V. If not, what is the problem with the power circuit in that section.
1. The two DC voltages of FUSE have been modified: check whether FUSE is on or off, if it is conductive, it is due to a blockage in the internal power circuit of the PCB board; If there are any issues with the FUSE (such as poor incoming inspection report, damage caused by overcurrent (ineffective MOS or IC manipulation), or material problems (FUSE burned out before MOS or IC positioning), then connect the FUSE with power lines and continue to analyze it further.
2. The two DC voltages of R1 resistor have been modified: check the resistance value of R1. If the resistance value is disordered, it may be due to air soldering or the resistor itself cracking. If there is no disorder in the resistance value, it may be a problem with the internal resistors of the IC.
3. The DC voltage detected by the IC has been modified: the VDD terminal is connected to the R1 resistor. If the Dout and Cout ends are disordered, it is due to empty soldering or damage to the IC.
4. If the previous operating voltage has not been modified and the operating voltage between B - and P+is detected to be disordered, it is due to the blockage of the positive via of the lithium battery protection board.
（2） The red DC ammeter of the digital multimeter is connected to the positive pole of the lithium battery cell, and the MOS tube is pulled out. The black DC ammeter is connected to pins 2 and 3 of the MOS tube, pins 6 and 7, and the P-terminal.
If there is a modification in the operating voltage of pins 2 and 3, and pins 6 and 7 of the MOS transistor, it indicates that the MOS transistor is in disorder.
If the operating voltage of the MOS transistor is not modified and the P-DC voltage is disrupted, it is due to the blockage of the negative via on the lithium battery protection board.
2、 Short circuit fault without maintenance
1. Difficulty with VM end resistor: It is possible to use a digital multimeter with a DC ammeter connected to pin IC2 and a DC ammeter connected to the MOS pin connected to the VM end resistor, acknowledging their resistance values. Check if the resistor is soldered to the IC and MOS pins.
2. IC and MOS disorder: Due to the use of the same MOS transistor for power loss maintenance, overcurrent, and overcurrent protection, if the short circuit fault disorder is caused by MOS problems, then this board should not have maintenance function.
3. The above refers to the shortcomings under normal conditions, and there may also be short circuit faults caused by inadequate IC and MOS weapon equipment. As early as BK-901, the IC with the model specification of '313D' had a long time delay, causing MOS or other electronic devices to be damaged before the IC could make relative posture manipulation. Note: The simplest and most immediate way to acknowledge whether an IC or MOS is malfunctioning during this period is to replace suspected electronic devices.
3、 Overcurrent protection without self repair
1. The commonly used ICs in overall planning do not have self-healing functions, such as G2J, G2Z, etc.
2. The short-circuit fault repair time set for the instrument equipment is too short, or the load is not removed during short-circuit fault detection. For example, if a digital multimeter is used to connect the short-circuit fault DC ammeter in the working voltage range, the DC ammeter is not removed from the detection end (a digital multimeter is equivalent to a load of several megabytes).
3. Between P+and P -, if there is residual resin in the middle of the solder layer, yellow glue with residue or capacitors between P+and P - are penetrated, and between ICVDD and VSS are penetrated. The resistance value is only a few K to several hundred K.
4. Assuming there are no issues with the above, perhaps the IC has been penetrated and the resistance value between each pin of the IC can be detected.
4、 High internal resistance
1. Due to the relatively stable internal resistance of MOS, the occurrence of high internal resistance is mainly suspected to be caused by electronic devices such as FUSE or PTC, which have very simple modifications to their internal resistance.
2. Assuming that the resistance values of FUSE or PTC are normal, the resistance values of the pads between the P+and P-solder layers and the electronic device surface during the maintenance board structure inspection may be high due to micro breakage in the via.
3. Assuming there are no issues with the above, it is necessary to suspect whether there is disorder in MOS: mainly acknowledging that there are difficulties in electric welding; Secondly, the thickness of the management board (whether it is easy to bend) may cause disorder at the welding points of the pins during bending; Place the MOS transistor under a microscope again to observe if it has cracked; Finally, use a digital multimeter to check the resistance value of the MOS pin and see if it has been penetrated.
5、 ID disorder
1. The ID resistor itself may become disordered due to empty soldering, cracking, or unqualified resistor material: the resistor can be welded on both sides from scratch. If everything is normal after re soldering, it is considered as empty soldering of the resistor. If it cracks, the resistor will crack from within after re soldering.
2. ID pad not disconnected: can be checked on both sides of the via using a digital multimeter.
3. Internal route problems: Apply scratch solder mask paint to check if the internal power circuit is broken or short circuited.
