The battery consists of a single cell connected in series by parallel. Parallel connection increases the capacity, the voltage remains the same, series connection multiplies the voltage, the capacity remains the same. First and then series: parallel connection due to the difference in internal resistance, uneven heat dissipation, etc. will affect the cycle life of the battery after parallel connection. But a single battery failure automatically exit, except for capacity reduction, does not affect the use after parallel connection, parallel process is more strict. When a unit of battery short-circuit in parallel connection, resulting in a very high parallel circuit current, usually add fuse protection technology to avoid. First series and then parallel: according to the whole group of battery capacity first in series, and finally in parallel, reducing the probability of failure of large-capacity battery pack.
According to their own design requirements to select the corresponding cells, parallel and series connection of batteries require the same type, the same model, capacity, internal resistance, voltage value difference is not more than 2%. Whether it is a flexible packaging battery or cylindrical battery, it needs to be combined with multiple strings, if the consistency is poor, affecting the battery capacity, the lowest capacity in a group determines the capacity of the whole group of batteries. Require high current discharge performance. Motor starting current is three times the normal operating current, high current discharge to improve motor power performance. Require good battery heat dissipation. The number of lithium battery module cells is large, and the temperature rise of the battery inside the battery box is not easy to dissipate, resulting in uneven temperature between the cells and different discharge characteristics, which will cause the battery performance to decline for a long time. High level of production technology is required. The battery should be able to withstand the vibration impact of bumpy roads, the production process, especially the high requirements of spot welding process.
Lithium battery module is realized in two ways, one is through laser welding or ultrasonic welding or pulse welding, which is a commonly used welding method, with better reliability. The second is through the elastic metal sheet contact, no welding, battery replacement is easy.