1
pACK composition
A battery pack consists of several components, including the battery pack, busbar, flexible connection, protection board, outer packaging, output (including connectors), and auxiliary materials such as barley paper and plastic brackets.
2
pACK characteristics
① Battery packs require batteries to have a high degree of consistency (capacity, internal resistance, voltage, discharge curve, lifespan).
②The cycle life of the battery pack is lower than that of a single battery.
③ Use under specified conditions (including charging and discharging current, charging method, temperature, etc.)
④ After the lithium-ion battery pack is formed, the battery voltage and capacity are greatly improved, so it is necessary to protect it and monitor its charging balance, temperature, voltage and overcurrent.
⑤ The battery pack must meet the design requirements for voltage and capacity.
3
pACK method
① Series-Parallel Composition: Batteries are composed of individual cells connected in parallel and series. Parallel connection increases capacity without changing the voltage, while series connection doubles the voltage without changing the capacity. For example, a 3.6V/10Ah battery is composed of 5 N18650/2Ah cells connected in parallel. ② Parallel-then-Series: Parallel connections can affect the cycle life of the batteries due to differences in internal resistance and uneven heat dissipation. However, if a single cell fails, it automatically disconnects, and the only impact is reduced capacity; it does not affect the overall use of the parallel connection. Parallel connection processes are more stringent. A short circuit in a single cell during parallel connection can cause a very large current in the parallel circuit, which is usually prevented by adding fuse protection. ③ Series-then-Parallel: Batteries are first connected in series according to the overall capacity of the group, such as 1/3 of the total capacity, and then paralleled last. This reduces the probability of failure in large-capacity battery groups.
② Cell Requirements: Select appropriate cells according to your design requirements. The batteries connected in parallel and series must be of the same type and model, and the difference in capacity, internal resistance, and voltage should not exceed 2%. Generally, the capacity loss is 2%-5% after batteries are combined in parallel and series. The more batteries there are, the greater the capacity loss.
Whether it's a pouch cell or a cylindrical cell, multiple cells need to be connected in series. Poor consistency will affect the battery capacity, and the lowest capacity cell in a group determines the overall capacity of the group. High current discharge performance is required.
The starting current of a motor is three times its normal operating current; high-current discharge is necessary to improve motor power performance. Good battery heat dissipation is also required. With a large number of batteries, the temperature rise inside the battery box is difficult to dissipate, resulting in uneven temperature distribution among the batteries and inconsistent discharge characteristics, ultimately leading to a decline in battery performance over time.
The manufacturing process is highly sophisticated. The batteries must be able to withstand the vibrations and impacts of bumpy roads. High standards are required for the manufacturing process, especially the spot welding process. Testing is conducted after welding to prevent incomplete welds or detachment.
③ Pack Manufacturing Process: Battery packs are manufactured using two methods. One is through laser welding, ultrasonic welding, or pulse welding, which are commonly used methods with the advantage of good reliability but are difficult to replace. The second method uses flexible metal contacts, which eliminates the need for welding and makes battery replacement easy, but may lead to poor contact.
pack example
4
Charge and discharge time
Charging time (hours) = (Battery capacity Ah x Charging coefficient) / Charging current A
Discharge rate: The discharge rate of a battery is expressed as the discharge time, or in other words, the number of hours required to discharge the rated capacity at a given discharge current. Specifically, discharge rate = rated capacity / discharge current.
5
Assembly of bus flexible connectors
The pACK process utilizes components such as nickel strips, copper-aluminum composite busbars, copper busbars, main positive and main negative busbars, and aluminum busbars. It also employs copper flexible connectors, aluminum flexible connectors, and copper foil flexible connectors. The processing quality of busbars and flexible connectors needs to be evaluated from these aspects.
① Check whether the material meets the requirements. If the busbar material does not meet the standards, it will increase the resistivity. In particular, it is necessary to confirm whether it meets the relevant RoHS requirements.
② Whether the critical dimensions are machined in place. Excessive tolerance in critical dimensions may result in insufficient safety distance between high-voltage components during assembly, causing serious safety hazards.
③ The bonding force of the hard zone of the soft connection and the stress absorption status of the soft zone.
④ Whether the current-carrying capacity of the actual processed flexible connection and busbar meets the design standards, and whether there is any damage to the insulated thermoplastic sleeve.
