Design Specification For Lithium Batteries

Due to the hundreds of millions of mobile phones worldwide, in order to achieve security, the failure rate of security protection must be less than one in 100 million. Due to the fact that the failure rate of circuit boards is generally much higher than 1 in 100 million. Therefore, 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.
A common battery charging system includes two parts: a charger and a 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. Adaptor AC to DC function: Electric controller limiting current and voltage. Charger function: Protection board for overcharging, discharging, overcurrent, etc.
Battery pack function: current limiting plate. Taking the mobile phone battery system as an example, the overcharge protection system uses the output voltage of the charger to be set at around 4.2V to achieve the first layer of protection. This way, even if the protective plate on the battery pack fails, the battery will not be overcharged and cause 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 the first layer of protection by the circuit board of the electronic product, while the protective board on the battery pack provides the second layer of 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.
Summary: When designing a battery system, it is necessary to provide two separate electronic protections for overcharging, discharging, and overcurrent. Remove the protective board and charge it. If the battery explodes, it indicates poor design. Although the above methods provide two protections, consumers often purchase non original chargers to charge after the charger breaks down. Charger manufacturers, based on cost considerations, often remove the charging controller to reduce costs. As a result, bad currency drove out good currency, and many low-quality chargers appeared on the market. This makes overcharging protection lose its first and most important line of defense. And overcharging is the most important factor causing battery explosions, therefore, low-quality chargers can be called the culprits of battery explosions. Of course, not all battery systems adopt the aforementioned solution.