What is charge equalization? Lithium battery pack equalization charging principle

　　Charge balancing, referred to as equalizing charge, is charging that balances battery characteristics. It means that during the use of the battery, the battery terminal voltage is unbalanced due to individual differences, temperature differences, etc. of the battery. In order to avoid the worsening of this imbalance trend, It is necessary to increase the charging voltage of the battery pack and activate the battery to achieve a maintenance method that balances the characteristics of each battery in the lithium battery pack and extends the battery life.

　　A lithium battery pack is composed of multiple single lithium batteries connected in series. Due to the differences in the cells, inconsistent rise in terminal voltage during series charging will cause some cells to be overcharged and some cells to be undercharged. All batteries are connected in parallel during equalizing charging and in series during normal charging and power use. During balanced charging, the parallel voltages of all batteries are equal, achieving forced balancing of each battery.

　　Lithium battery pack equalization charging method

　　When the lithium battery pack is produced and stored for a long time, due to the different static power consumption of each channel of the protection board and the different self-discharge rate of each cell, the voltage of each battery string in the entire battery pack is inconsistent. Balance has the function of equalizing the voltage of the lithium battery pack, so that the battery pack capacity can be fully charged and discharged, so that the battery pack can exert its maximum effect.

　　Commonly used lithium battery pack balancing charging technologies include constant shunt resistance balancing charging, on-off shunt resistor balancing charging, average battery voltage balancing charging, switched capacitor balancing charging, buck converter balancing charging, inductor balancing charging, etc. When a set of lithium batteries is charged in series, each battery should be charged evenly, otherwise the performance and life of the entire set of batteries will be affected during use.

　　1. Attach a parallel balancing circuit to each single cell of the lithium battery pack to achieve a shunt function. In this mode, when a battery reaches full charge first, the balancing device can prevent it from overcharging and convert the excess energy into heat energy to continue charging the under-charged battery. This method is simple, but it will cause energy loss and is not suitable for fast charging systems.

　　2. Before charging, discharge each cell one by one through the same load to the same level, and then perform constant current charging to ensure a more accurate equilibrium state between each cell. However, for battery packs, due to physical differences between individuals, it is difficult for each cell to achieve completely consistent ideal effects after deep discharge. Even if the same effect is achieved after discharging, new imbalances will appear during the charging process.

　　3. Timing, sequencing, and individually detecting and evenly charging the single cells in the lithium battery pack. When charging the lithium battery pack, it can be ensured that each lithium battery in the battery pack will not be overcharged or overdischarged, thus ensuring that each battery in the lithium battery pack is in normal working condition.

　　4. Using the time-sharing principle, through the control and switching of switch components, additional current flows into the battery with a relatively low voltage to achieve the purpose of balanced charging. This method is more efficient, but the control is more complicated.

　　5. Use the voltage parameters of each battery as the balancing object to restore the voltage of each battery to be consistent. During equalization charging, the capacitor is alternately connected to two adjacent batteries through a control switch, receives charge from the high-voltage battery, and then discharges to the low-voltage battery until the voltages of the two batteries become consistent. This balancing method can better solve the problem of battery pack voltage imbalance, but this method is mainly used in situations where the number of batteries is small.

　　6. The entire system is controlled by a single-chip microcomputer, and each battery has an independent set of modules. The module performs charge management on each single battery according to the set program, and automatically disconnects after charging is completed. This method is relatively simple, but it will greatly increase the cost when the number of single cells is large, and is not conducive to reducing the system volume.

　　Lithium battery pack parallel equalization charging method

　　1. Diode isolation parallel charging equalization method

　　Taking 6 single batteries connected in series as an example, turn off the switches S1-S5 and then connect the charging power supply. The diode is 1N5401-5408. The measured forward voltage drop of the diode is 0.8V at the rated current of 3A. When the forward voltage drop is 0.7V, the current flowing through the diode is very small. Lithium iron phosphate battery has a maximum charging voltage of 3.65V. In fact, in order to extend the battery life, the maximum charging voltage is set to 3.5V. The charging voltage = 3.5+0.7+0.7=4.9V plus the line voltage drop is very suitable to use a 5V power supply.

　　2. Direct parallel charging equalization method

　　The charging voltage for lithium iron phosphate batteries is 3.5-3.6V, and the charging voltage for ternary and polymer batteries is 4.1-4.2V. The red alligator clip leads are welded together and connected to the positive pole of the charging power supply; the black alligator clip leads are welded together and connected to the negative pole of the charging power supply. When balancing charging, first disconnect S1-S5, and the red alligator clips clamp the positive electrode of each single battery respectively; the black alligator clips clamp the negative electrode of each single battery respectively, and all batteries are connected in parallel.

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