1. Serial and parallel composition:
The battery is formed by single cells passing through and connected in series. Parallel connection increases the capacity, and the voltage remains unchanged. After the series connection, the voltage doubles and the capacity remains unchanged. Parallel to serial: Parallel connection due to the difference in internal resistance and uneven heat dissipation will affect the battery cycle life after parallel connection. However, when a single battery fails, it will automatically exit. Except that the capacity is reduced, it will not affect the use after parallel connection, and the parallel process is strict. When a unit battery is short-circuited in parallel, the current of the parallel circuit is very large, which is usually avoided by adding a fuse protection technology. Series first and then parallel: According to the capacity of the entire group of batteries, the series is first connected in series, such as 1/3 of the entire group, and finally connected in parallel, which reduces the probability of failure of large-capacity battery packs.
2. Battery requirements:
Select the corresponding batteries according to your own design requirements. The parallel and series batteries require the same type and model, and the difference in capacity, internal resistance, and voltage value is not more than 2%. Under normal circumstances, after the batteries are connected in parallel and in series, the capacity loss is 2% ~5%. The more the number of batteries, the greater the capacity loss. Regardless of whether it is a flexible battery or a cylindrical battery, multiple string combinations are required. If the consistency is poor, affecting the battery capacity, the battery with the lowest capacity in a group determines the capacity of the entire group of batteries. High current discharge performance is required. The starting current of the motor is 3 times the normal working current, and the high current discharge can improve the power performance of the motor. Requires good battery cooling. The number of batteries is large, and the temperature rise of the battery inside the battery box is not easy to dissipate, resulting in uneven temperature among the batteries, different discharge characteristics, and a long-term decline in battery performance. High level of production technology. The battery must be able to withstand the vibration and shock of bumpy roads. High requirements on the production process, especially the spot welding process. After the welding is completed, the test is carried out to prevent the virtual welding and de-soldering.
3. The process of PACK:
PACK of the battery is realized by two ways, one is by laser welding or ultrasonic welding or pulse welding, which is a commonly used welding method, the advantage is better reliability, but it is not easy to replace. The second is the contact through the elastic metal sheet. The advantage is that no welding is needed, and the battery is easy to replace. The disadvantage is that it may cause poor contact.