The role of lithium battery and PCM board, BMS board.
The role of lithium battery and PCM board
1. The composition of lithium battery
The lithium battery is mainly composed of two blocks, the battery cell and the protection board PCM (power battery is generally called the battery management system BMS). The battery cell is equivalent to the heart of the lithium battery, and the management system is equivalent to the brain of the lithium battery. The battery core is mainly composed of positive electrode material, negative electrode material, electrolyte, diaphragm and shell; while the protection board is mainly composed of protection chip (or management chip), MOS tube, resistor, capacitor and PCB board.
2. the advantages and disadvantages of lithium batteries
Lithium batteries have many advantages, high voltage platform, high energy density (light weight, small size), long service life, and environmental protection.
The disadvantage of lithium batteries is that the price is relatively high, the temperature range is relatively narrow, and a protection system is required.
3. lithium battery classification
Lithium batteries can be divided into two categories: non-rechargeable batteries and secondary rechargeable batteries (also known as batteries). Non-rechargeable batteries such as lithium manganese dioxide batteries, lithium-thionamide batteries.
4. Comparison of various power batteries
Power batteries are mainly considered based on their application, and are mainly used in electric electric vehicles, electric bicycles, and electric tools. Power batteries are different from ordinary batteries and have certain particularities:
1. Series and parallel of batteries
2. The battery has a larger capacity
3. The discharge rate of the battery is larger (hybrid and electric tools)
4. Higher battery safety requirements
5. The battery has a wide operating temperature range
6. The battery has a long service life, generally requiring 5~10 years
5. BMS function introduction and analysis
1. Battery protection, similar to PCM, overcharge, overdischarge, overtemperature, overcurrent, and short circuit protection. Like ordinary lithium manganese batteries and ternary lithium batteries, once the voltage of any battery exceeds 4.2V or the voltage of any battery is lower than 3.0V, the system will automatically cut off the charging or discharging circuit. If the battery temperature exceeds the battery operating temperature or the current is greater than the battery discharge current, the system will automatically cut off the current path to ensure the safety of the battery and the system.
2. Energy balance, the entire battery pack, because many batteries are connected in series, after a certain period of work, due to the inconsistency of the battery cell itself, the inconsistency of the working temperature and other reasons, it will eventually show a big difference, which will affect the battery. The life of the battery and the use of the system have a huge impact. Energy balance is to make up for the differences between individual battery cells to do some active or passive charging or discharging management to ensure the consistency of the battery and extend the life of the battery. There are generally two types of passive balancing and active balancing in the industry. Passive balancing is mainly to balance the power with more power through resistance consumption, and active balancing is mainly to transfer the power of the battery with more power to the less power through capacitor, inductance or transformer. The battery reaches equilibrium. Because the active balancing system is relatively complex and the cost is relatively high, the mainstream is still passive balancing.
3. SOC calculation, battery power calculation is a very important part of BMS, many systems need to know the remaining power situation more accurately. Due to the development of technology, many methods have been accumulated for SOC calculation. The remaining power can be judged according to the battery voltage if the accuracy is not high. The main accurate method is the current integration method (also called Ah method), Q = ∫i dt, and There are internal resistance method, neural network method, Kalman filter method and so on. The mainstream in the industry is still the current integration method.
4. Communication. Different systems have different requirements for communication interfaces. The mainstream communication interfaces include SPI, I2C, CAN, RS485, etc. Among them, the automobile and energy storage systems are mainly CAN and RS485.
6. the protection board failure analysis
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, PCB internal circuit is blocked, vias are blocked, MOS, IC is damaged, etc.). Specific analysis
Proceed as follows:
(1) Connect the black test lead of a multimeter to the negative pole of the battery cell, and connect the red test lead to the FUSE, R1 resistor terminals, the Vdd, Dout, and Cout terminals of the IC, and the P+ terminal (assuming the battery cell voltage is 3.8V), and analyze it section by section. These test points should all be 3.8V. If not, there is a problem with this section of the circuit.
1). The voltage at both ends of the FUSE changes: test whether the FUSE is turned on, if it is turned on, the internal circuit of the PCB board is not turned on; if it is not turned on, there is a problem with the FUSE (bad incoming material, overcurrent damage (MOS or IC control failure) , There is a problem with the material (the FUSE is burned out before the MOS or IC is activated), then use a wire to short the FUSE, and continue to analyze.
2). There is a change in the voltage across the R1 resistor: test the resistance value of R1. If the resistance value is abnormal, it may be a virtual weld and the resistor itself is broken. If the resistance value is not abnormal, there may be a problem with the internal resistance of the IC.
3). The voltage of the IC test terminal changes: the Vdd terminal is connected to the R1 resistor. Dout, Cout end abnormal, it is due to the IC weak welding or damage.
4). If there is no change in the previous voltage: the voltage between test B- and P+ is abnormal, it is because the positive via of the protection plate is blocked.
(2) Connect the red test lead of the multimeter to the positive electrode of the battery. After activating the MOS tube, the black test lead is connected to the MOS tube 2, 3, 6, 7 and P- terminal in turn.
1). If the voltage of MOS tube 2, 3, 6 and 7 has changed, it means the MOS tube is abnormal.
2). If there is no change in the MOS tube voltage and the P- terminal voltage is abnormal, it is because the negative via of the protection plate is blocked.
7. short circuit without protection
1. There is a problem with the VM terminal resistance: 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.
2. IC, MOS abnormality: Since over-discharge protection and over-current, short-circuit protection share a MOS tube, if the short-circuit abnormality is due to MOS problems, the board should have no over-discharge protection function.
3. 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.
8. Short-circuit protection without self-recovery
1. The IC used in the design has no self-recovery function, such as G2J, G2Z, etc.
2. 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).
3. 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 value is only a few K to several hundred K).
4. 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.
9. large internal resistance
1. Since the internal resistance of MOS is relatively stable and large internal resistance appears, the first thing to suspect should be the components that are relatively easy to change such as FUSE or PTC.
2. If the resistance of FUSE or PTC is normal, check the resistance of the via hole between the P+, P- pad and the component surface depending on the structure of the protection board, and the via may have micro-breaks and the resistance value is relatively large.
3. If there are no problems with the above, it is necessary to doubt whether the MOS is abnormal: first determine whether there is a problem with the welding; secondly, the thickness of the billboard (whether it is easy to bend), because the bending may cause abnormal pin welding; then the MOS tube Put it under a microscope to observe whether it is broken; finally, use a multimeter to test the resistance of the MOS pin to see if it is broken down.
10. ID is abnormal
1. The ID resistance itself is abnormal due to virtual welding, fracture or because the resistance material is not closed: you can re-weld the two ends of the electric resistance. If the ID is normal after the re-welding, it will be the resistance welding. If it is broken, the resistance will be after the re-welding. Split from it.
2. ID via is non-conducting: use a multimeter to test both ends of the via.
3. 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.