In the field of batteries, there are batteries with and without monitoring circuits. Lithium batteries are considered smart because they contain a printed circuit board that manages their performance. In contrast, standard sealed lead-acid batteries lack circuit board controls to enhance functionality.
Smart lithium batteries have three basic levels of control. The first level is simple balancing that optimizes cell voltage. The second level involves a Protection Circuit Module (PCM) that protects the battery from high/low voltages and currents during charging and discharging. The third level is the Battery Management System (BMS). the BMS contains all the functions of the balancing circuitry and the PCM and adds features to optimize performance over the battery’s life, such as monitoring the state of charge and health.
The Keheng Li-ion Bluetooth series has an intelligent Battery Management System (BMS).
Li-ion Balancing Circuit
In batteries with a balancing chip, the chip balances the voltage of each battery cell only during charging. The battery is considered balanced when the voltages of all battery cells are within a small tolerance range.
There are two types of battery balancing: active balancing and passive balancing. Active balancing utilizes the high voltage cells to charge the low voltage cells, thus reducing the voltage difference until all cells have similar voltage and are fully charged. Kaiheng lithium batteries all use passive balancing, i.e., a resistor is connected in parallel with each cell, and the resistor is activated when the cell voltage exceeds the threshold value. This reduces the charging current of the higher-voltage cells and allows the other cells to catch up.
Why is cell balancing critical? In lithium batteries, as soon as the cell with the lowest voltage reaches the discharge voltage cut-off point, the entire battery pack shuts down, resulting in some of the energy in the cells not being utilized. Similarly, if the cells are not balanced during the charging process, the charging process stops when the cell with the highest voltage reaches the cut-off point, resulting in some cells not being fully charged.
What’s the downside? Continuously charging and discharging an unbalanced battery will reduce its capacity over time. It also means that some batteries may never reach a 100% state of charge. A balanced battery will discharge at the same rate and cut off at the same voltage. However, a balanced chip ensures a perfect match when charging, thus maintaining battery capacity and enabling full recharge.
Lithium Protection Circuit Module
The Protection Circuit Module consists of a balancing circuit and additional components that control battery parameters by preventing overcharging and over-discharging. It does this by monitoring current, voltage, and temperature during charging and discharging and comparing them to preset limits. If any battery reaches these limits, the battery will stop charging or discharging until the release method is met.
After protection has been initiated, there are several ways to resume charging or discharging. The first is time-based, where a timer counts down (e.g., 30 seconds) and then releases the protection. The timer may be different for each protection and is of a single level of protection.
The second is value-based and requires a value below a threshold to release. For example, the voltage must be below 3.6 volts per cell to release the overcharge protection. Once the release conditions are met, it is immediately discharged.
Check out our golf cart lithium battery selection guide for a more in-depth look.
Lithium Battery Management System
There are multiple levels of control and protection to consider when it comes to lithium battery management. At the basic level, a balancing circuit ensures that all cells in the battery are balanced to prevent overcharging and overdischarging. This is ideal for simple applications such as motorcycle batteries.
The Protection Circuit Module (PCM) provides enhanced safety features for more complex needs. It provides a single level of protection that activates when specific conditions are met, such as voltage or temperature thresholds. For example, overcharge protection may be activated if the battery voltage exceeds 3.6 volts for over 6 seconds. Similarly, over-discharge protection may require the battery voltage to drop below a specific voltage to reset.
The most advanced is the Battery Management System (BMS ), which includes all PCM functions but adds multiple levels of protection. This is critical for handling high-demand applications with inrush currents. For example, the Keheng PSL-SC-1290 battery can cope with inrush by implementing graded protection, which is activated at different current levels and durations, ensuring that the battery operates without damage.
The battery management system also provides valuable information about the battery’s status, such as state of charge, health status, and cycle count. Communication protocols must be used to access this data. Keheng offers a variety of solutions, such as Bluetooth connectivity for real-time monitoring via smartphone apps or wired protocols for more specialized applications such as medical equipment.
In summary, choosing the right Li-ion battery management system depends on the complexity and needs of the application. For basic needs, balanced circuits are sufficient. For moderate protection, PCM is appropriate. For comprehensive monitoring and advanced protection, a BMS is the best choice.
At Keheng, we understand the importance of multiple protection, and a Battery Management System (BMS) is the key to achieving this. There are many factors to consider when choosing the ideal lithium battery, and our team of experts is ready to help you. To learn more about finding the perfect battery for your specific needs, consult our experts today.