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• Time of issue:2020-04-21
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(Summary description)The process of assembling the lithium battery cells into a group is called PACK, which can be a single battery or a battery module in series and parallel connection. Under the background of the new national standard, the demand for lithium batteries is increasing, and many lead-acid battery companies have also launched lithium battery products. In fact, the lithium battery PACK process is not difficult. The role of "battery porter", profit and after-sales are no longer controlled by others; mastering a technology, there are "lithium" everywhere.



PACK composition



PACK includes battery packs, bus bars, flexible connections, protective plates, outer packaging, output (including connectors), barley paper, plastic brackets and other auxiliary materials to form PACK.



Lithium battery PACK example

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Features of PACK



① The battery pack requires that the battery has a high degree of consistency (capacity, internal resistance, voltage, discharge curve, life).

② The cycle life of the battery pack PACK is lower than that of a single battery.

③Use under limited conditions (including charging, discharging current, charging method, temperature, etc.)

④ After the lithium battery pack is formed, the battery voltage and capacity have been greatly improved, and it must be protected to charge balance, temperature, voltage and overcurrent monitoring.

⑤ The battery pack PACK must meet the voltage and capacity requirements of the design.



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PACK method



①Serial and parallel composition: The battery is formed by single batteries passing through and connected in series. The capacity is increased in parallel, the voltage is unchanged, and the voltage is doubled in series, and the capacity is unchanged. For example, a 3.6V / 10Ah battery is composed of a single N18650 / 2Ah through 5 and. 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 for the reduced capacity, it will not affect the use after parallel connection. The parallel process is strict. When a unit battery is short-circuited in parallel, the current in the parallel circuit is very large, which is usually avoided by adding fuse protection technology. Series first and then parallel: According to the capacity of the whole group of batteries, the series is first connected in series, such as 1/3 of the whole 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 the same model, and the difference in capacity, internal resistance and voltage value is not more than 2%. Under normal circumstances, after the batteries are combined 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 battery. High current discharge performance is required. The starting current of the motor is 3 times of 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 should be able to withstand the vibration and shock of bumpy roads. High requirements on production process, especially spot welding process. After the welding is completed, the test is carried out to prevent the virtual welding and de-soldering.



③PACK process: The 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.



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pack instance



Charge and discharge time



Charging time (hours) = (battery capacity Ah x charging coefficient) / charging current A

Discharge rate: The discharge rate of the battery is expressed by the discharge time or the hour factor required to discharge the rated capacity with a certain discharge current. Among them, discharge rate = rated capacity / disc