Battery protection board sampling line welding

Due to fluctuations in the actual production process, even if the cells used in the same battery pack are consistently grouped, the difference between the individual cells is still objective. The power battery pack is large in size, and the environment in which the batteries are used in different positions is also different. After the individual cells are serially grouped, these differences will further increase due to the inconsistency of the individual cell cores, so it is necessary to carefully measure the voltage of the cells.

Voltage sampling directly determines the state of the battery, making this function of voltage collection one of the most important aspects of the entire safety assurance system.

The sampling line diameter needs to consider the following operating currents. Under the following operating currents, let us consider the following basic parameters:

• Quiescent current (Ipara): This current value is the parasitic current in the entire acquisition loop and the internal ASIC

• Working current (Iwork): This is applied according to the operating current at the time of acquisition of the selected ASIC.

• Balanced current (Iblance): The designed equalization current, the general limitation is the equalization resistance, which is also very important for the entire acquisition design.

• Fuse current (Ifuse): Whether using fuses designed by FPC's own circuit or purchased chip fuses, the designed fuse current and design need to be carefully considered.

• Soft & Hard Short Circuit Current (Ishort): refers to the corresponding impedance current in the case of a hard short circuit in the real circuit.

The connection between copper wire and aluminum Busbar needs to consider the combination of two substances.

a) The potential difference between the elements of copper and aluminum causes electrochemical corrosion

b) At high temperatures, the two elements may form intermediate compounds, and the interface resistance rises and becomes brittle.

c) During the treatment here, the coating is carried out on the aluminum Busbar, and after the welding, the joint is sealed (forming the airtight condition to block the electrochemical corrosion)

d) The expansion coefficient of aluminum is as high as 39% larger than copper. When two metal conductors are connected and pass current, the connection point generates heat due to the contact resistance, and both conductors expand. Here, if the temperature rise control is unreasonable, it may cause some potential problems

Some problems are relatively minor if copper-aluminum Busbar is used. If no transfer is used, there is a new challenge in how to ensure the long-term reliability of the contact without the seal.