Several lithium batteries can be connected in series to 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 do all lithium batteries on the market add BMS? The answer is safety and longevity.
The battery management system BMS (Battery Management System) is used to monitor and control the charging and discharging of rechargeable batteries. The most important function of a lithium battery management system (BMS) is to ensure that batteries remain within safe operating limits and to take immediate action if any individual battery begins to exceed limits. If the BMS detects that the voltage is too low, it will disconnect the load, and if the voltage is too high, it will disconnect the charger. It will also check that each cell in the pack is at the same voltage and reduce any voltage that is higher than the other cells. This ensures that the battery does not reach dangerously high or low voltages – which is often the cause of the lithium battery fires we see in the news. It can even monitor the battery's temperature and disconnect the battery pack before it gets too hot to catch fire. Therefore, the battery management system BMS allows the battery to be protected rather than purely relying on a good charger or correct user operation.
Why don’t lead-acid batteries need a battery management system? The composition of lead-acid batteries is less flammable, making them much less likely to catch fire if there is a problem with charging or discharging. But the main reason has to do with how the battery behaves when it's fully charged. Lead-acid batteries are also made up of cells connected in series; if one cell has slightly more charge than the other cells, it will only let the current pass until the other cells are fully charged, while maintaining a reasonable voltage, etc. Cells catch up. In this way, lead-acid batteries "balance themselves" as they charge.
Lithium batteries are different. The positive electrode of rechargeable lithium batteries is mostly lithium ion material. Its working principle determines that during the charging and discharging process, lithium electrons will run to both sides of the positive and negative electrodes again and again. If the voltage of a single cell is allowed to be higher than 4.25v (except for high-voltage lithium batteries), the anode microporous structure may collapse, the hard crystal material may grow and cause a short circuit, and then the temperature will rise rapidly, eventually leading to a fire. When a lithium battery is fully charged, the voltage rises suddenly and can quickly reach dangerous levels. If the voltage of a certain cell in a battery pack is higher than that of other cells, this cell will reach the dangerous voltage first during the charging process. At this time, the overall voltage of the battery pack has not yet reached the full value, and the charger will not stop charging. . Therefore, the cells that reach dangerous voltages first will cause safety risks. Therefore, controlling and monitoring the total voltage of the battery pack is not enough for lithium-based chemistries. The BMS must check the voltage of each individual cell that makes up the battery pack.
Therefore, to ensure the safety and long service life of lithium battery packs, a quality and reliable battery management system BMS is indeed needed.
Post time: Oct-25-2023
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