Views: 0 Author: Site Editor Publish Time: 2024-04-13 Origin: Site
Connecting several lithium batteries in series can form a battery pack, which can supply power to various loads and can also be charged normally with a matching charger. Lithium batteries do not require any battery management system (BMS) to charge and discharge. So why are all lithium batteries on the market equipped with BMS? The answer is safety and lifespan.
The Battery Management System (BMS) is used to monitor and control the charging and discharging of rechargeable batteries. The most important function of the lithium battery management system BMS is to ensure that the battery remains within a safe operating range and takes immediate action when any individual battery begins to exceed its limit. If the BMS detects a voltage that is too low, it will disconnect the load. If the voltage is too high, it will disconnect the charger. It will also check if the voltage of each battery in the battery pack is the same and reduce any voltage higher than other batteries. This ensures that the battery does not reach dangerously high or low voltage - which is usually the reason why lithium batteries catch fire as we see in the news. It can even monitor the temperature of the battery and disconnect the battery pack before it becomes too hot to catch fire. So, the battery management system BMS is designed to protect the battery, rather than relying solely on a good charger or proper user operation.
Why do lead-acid batteries (AGM, gel batteries, deep cycle batteries, etc.) not need a battery management system? The components of lead-acid batteries are less flammable, and if there are problems with charging or discharging, the likelihood of them catching fire is much lower. But the main reason is related to the behavior of the battery after being fully charged. Lead acid batteries are also composed of battery cells connected in series; If a battery cell has a slightly higher charging capacity than other cells, it will only allow current to pass through before the other cells are fully charged, while maintaining a reasonable voltage for the other cells to catch up. Through this method, lead-acid batteries will "self balance" during charging.
Lithium batteries are different. The positive electrode of rechargeable lithium battery is mostly made of lithium-ion materials, and its working principle determines that during the charging and discharging process, lithium electrons will repeatedly run to both sides of the positive and negative electrodes. If the voltage of a single battery cell is allowed to exceed 4.25V (excluding high-voltage lithium batteries), the anode microporous structure may collapse, hard crystal materials may grow and cause short circuits, and then the temperature will rapidly rise, ultimately leading to a fire. When the lithium battery cell is fully charged, the voltage will suddenly increase and quickly reach a dangerous level. If the voltage of one battery cell in a battery pack is higher than that of other cells, this cell will first reach the dangerous voltage during the charging process, and at this time, the overall voltage of the battery pack has not reached the full charge value, and the charger will not stop charging. Therefore, the battery cells that reach the dangerous voltage first can pose a safety risk. So, controlling and monitoring the total voltage of the battery pack is not enough for lithium-based chemicals, and it is necessary for the BMS to check the voltage of each individual cell that makes up the battery pack.
Narrowly speaking, the Battery Management System (BMS) is used for the protection of large battery packs, with typical applications being lithium iron phosphate power batteries, which have protective functions such as overcharging, over discharging, overcurrent, short circuit, and battery cell balance.
Broadly speaking, Protection Circuit Board (PCB), sometimes also known as PCM (Protection Circuit Module), is a simplified battery management system BMS. Usually used for small battery packs. Typical use for digital batteries, such as mobile phone batteries, camera batteries, GPS batteries, heated clothing batteries, etc. Most of the time, it is used for 3.7V or 7.4V battery packs and has four basic functions: overcharging, over discharging, overcurrent, and short circuit. Some batteries may also require PTC and NTC.
Therefore, to ensure the safety and long service life of lithium battery packs, a reliable battery management system BMS is indeed needed.
