Lithium Battery Pack Series and Parallel Charging Caution

October 10, 2020

Lithium Battery Pack Series and Parallel Charging Caution


Lithium battery series charging


At present, the charging of lithium battery packs generally adopts series charging, which is mainly because the series charging method has a simple structure, low cost, and easy realization. However, due to the differences in capacity, internal resistance, attenuation characteristics, self-discharge and other performance between single lithium batteries, when charging lithium battery packs in series, the single lithium battery with the smallest capacity in the battery pack will be charged first At this time, other batteries are not fully charged. If you continue to charge in series, the fully charged single lithium battery may be overcharged.


The overcharging of the lithium battery will seriously damage the performance of the battery, and may even cause an explosion to cause personal injury. Therefore, in order to prevent the overcharging of the single lithium battery, the lithium battery pack is generally equipped with a battery management system (Battery Management System, referred to as BMS), through the battery management system to protect each single lithium battery from overcharging. When charging in series, if the voltage of a single lithium battery reaches the overcharge protection voltage, the battery management system will cut off the entire series charging circuit and stop charging to prevent this single battery from being overcharged, which will cause other lithium The battery cannot be fully charged.


Parallel charging of lithium batteries


When lithium batteries are charged in parallel, each lithium battery should be balanced, otherwise the performance and life of the entire group of lithium batteries will be affected during use. Commonly used equalization charging techniques include: constant shunt resistance equalization charging, on-off shunt resistance equalization charging, average battery voltage equalization charging, switched capacitor equalization charging, step-down converter equalization charging, inductance equalization charging, etc.


Several issues need to be paid attention to when charging lithium batteries in parallel:


1. Lithium batteries with and without protection board cannot be charged in parallel. A battery without a protective plate is easily damaged by overcharge.


2. Batteries charged in parallel usually need to remove the protective board that comes with the battery and use a battery protection board uniformly.


3. If the battery charged in parallel does not have a lithium battery protection board, the charging voltage must be limited to 4.2V, and 5V chargers cannot be used.


After the lithium battery is connected in parallel, there will be a charging protection chip to protect the lithium battery. When making the lithium battery in parallel, the lithium battery manufacturer has fully considered the change characteristics of the lithium battery after the parallel connection, and the current design and cell selection are also carried out according to the above requirements Yes, users need to charge step by step according to the instructions of parallel lithium batteries to avoid possible damage to the battery caused by incorrect charging.


Precautions for Lithium Battery Charging


1. Lithium batteries must use special chargers, otherwise they may not reach saturation and affect their performance.


2. The lithium battery does not need to be fully discharged before charging.


3. Do not plug the charger into the socket for a long time, and take out the charger as soon as possible after the battery is fully charged;


4. The battery should be removed from the electrical appliances that have not been used for a long time, and the battery should be emptied and stored;


5. Do not insert the positive and negative poles of the battery in reverse, otherwise it will cause the battery to swell or rupture;


6. Nickel charger and lithium charger cannot be mixed.