Do I need a battery management system when using Li-ion?
Battery management system(BMS) is an essential part of lithium-ion battery. Lithium ion battery is very sensitive to overcharge, short circuit and over discharge. The management system constantly monitors each battery and controls the charging system to ensure that these conditions do not occur or cause damage or overheating.
All kinds of lithium batteries over charged or discharged will cause irreversible damage to the cell, and lithium batteries are also extremely sensitive to temperature: if used at a high temperature, it may cause electrolyte decomposition, combustion and even explosion; if the temperature is too low, the performance of lithium batteries will be significantly deteriorated, affecting the normal use of equipment.
Due to the limitation of battery manufacturing process, the internal resistance and capacity of each cell will be different. When multiple battery cells are used in series, the charge and discharge rate of each cell is inconsistent, which leads to the low utilization rate of battery capacity. In view of this, lithium battery in the actual use process usually needs a special protection system to monitor the health status of the battery, so as to manage the use process of lithium battery.
The capacity attenuation and power consumption of lithium battery at low temperature can not be accurately predicted, which makes the maintainability of the equipment poor. The long-term on-line instrument needs to replace the battery regularly, but the remote monitoring equipment work site is scattered, the distance between each station is far, so the battery replacement workload is huge and the cost is high. In order to reduce the workload of maintenance and reduce the maintenance cost, it is necessary for the battery management system to have accurate charge state estimation function to accurately grasp the charge state of the battery, and to replace the battery more purposefully. At the same time, the battery management system should have low power consumption to reduce maintenance frequency and prolong battery life. Therefore, it is very important to design the battery management system reasonably for the remote monitoring instrument with long-term continuous power supply.
However, the characteristics of remote monitoring instruments and the inherent characteristics of lithium batteries make it very difficult to develop a battery management system to meet the requirements of such applications. The main factors are as follows: first of all, in order to reduce the power consumption, the remote measuring instrument will sleep and wake up periodically. Its working current is dynamic. The working current of the wake-up phase is much higher than that of the dormant state, but the working time of the wake-up phase is far less than that of the sleep stage.
Secondly, the discharge curve of lithium battery is very gentle, and the main power is concentrated above 3.6V voltage. Then, with the further decrease of voltage, the battery power begins to drop sharply, and the remote instrument can not send out low power alarm according to the battery voltage. Finally, the self discharge rate of lithium battery fluctuates greatly with temperature. For the instruments working in the field, the temperature condition is very extreme, which further increases the difficulty of battery power prediction.
SCU BMS battery management system is three-level design, includes module, cabinet, system. Two-way active equalization, equalization accuracy less than 2%, equalization capacity up to 10% of the rated output. Single cell capacity change does not affect the system capacity, to ensure the safety of the battery system. It can effectively protect the overcharge, over discharge and over-current of the battery, and avoid the imbalance of single cell and uneven temperature distribution caused by long-time and high-rate charging and discharging of the battery, so as to ensure the safe, reliable and efficient operation of the whole system.