Lithium battery protection.NiMH No.7 batteries

　　When designing a battery system, there must be at least two safety lines. A common misconception is to use a charger (adapter) directly to charge the battery pack. This will completely transfer the responsibility of overcharging protection to the protective plate on the battery pack. Although the failure rate of the protection board is not high, even if the failure rate is as low as one in a million, the probability of explosion accidents occurring globally is still daily.

　　If the battery system can provide two separate safety protections for overcharging, discharging, and overcurrent, and if the failure rate of each protection is one in ten thousand, the two protections can reduce the failure rate to one in one hundred million. The block diagram of a common battery charging system is shown below, which includes two main parts: charger and battery pack. The charger also includes two parts: an adapter and a charging controller. The adapter converts AC power into DC power, while the charging controller limits the maximum current and maximum voltage of DC power. The battery pack consists of two main parts: a protective plate and battery cells, as well as a PTC to limit the maximum current.

　　Text box: adapter AC to DC text box: charging controller current and voltage limit text box: charger text box: protective board for overcharging, discharging, overcurrent, etc. Text box: battery pack text box: current limit plate text box: battery cell

　　Taking the mobile phone battery system as an example, overcharging protection is achieved by setting the output voltage of the charger at around 4.2V to achieve the first layer of protection. This way, even if the protective board on the battery pack fails, the battery will not be overcharged and pose a danger. The second protection is the overcharge protection function on the protection board, usually set to 4.3V. In this way, the protection board usually does not need to be responsible for cutting off the charging current, and only needs to be activated when the charger voltage is abnormally high. Overcurrent protection is handled by protective plates and current limiting plates, which are also two protective measures to prevent overcurrent and external short circuits. Due to over discharge, it only occurs during the use of electronic products. Therefore, the general design is to provide first to second protection by the circuit board of the electronic product, while the protective board on the battery pack provides second protection. When electronic products detect a supply voltage below 3.0V, they should automatically shut down. If this feature is not designed during the design of the product, the protection board will close the discharge circuit when the voltage drops to 2.4V. In summary, when designing a battery system, it is necessary to provide two separate electronic protections for overcharging, discharging, and overcurrent. The protective plate is the second layer of protection. Remove the protective board and charge it. If the battery explodes, it indicates poor design.

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