How does the inconsistency of the battery cause it?

There are two important aspects: one is the inconsistency caused by battery production and processing, and the other is the inconsistency caused by the battery usage environment. The reasons for inconsistent production come from factors such as processing technology and materials. I said this is relatively simple, but the actual things inside are very complicated; the inconsistency of the environment is easy to understand. Because the location of each battery in the PACK is different, the environment will also be different. For example, the temperature will be slightly different, and long-term accumulation will cause the battery to be inconsistent. As mentioned earlier, equalization is used to eliminate battery SOC differences. In an ideal state, it always keeps the SOC of each battery unchanged, so that all batteries can reach the upper and lower limits of charging and discharging voltage simultaneously, thereby increasing the usable capacity of the battery pack. There are two cases of SOC difference. One is that the battery capacity is the same, but the SOC is different; the second is that the SOC changes with the battery capacity. The battery capacity is the same, but the SOC is different; among them, the battery with the smallest SOC reaches the lower limit of discharge first (assuming 25% SOC is the lower limit), and the battery with the largest SOC reaches the upper limit of charge first; in a balanced application, all batteries maintain the same SOC. Discharge. It is more troublesome to balance batteries of different capacities (scene 2). The battery capacity is different, the SOC is different; in this way, the battery with the smallest capacity is fully charged and then discharged; in a balanced use, all batteries maintain the same SOC for charging and discharging. Therefore, equalization is a very important function of current batteries. There are two ways to realize the equalization function, active equalization and passive equalization. Passive balance is discharge with resistance, and active balance is to allow charge to flow between batteries. In fact, the two names are somewhat controversial and will not be expanded; among them, passive equilibrium is used more in reality, and active equilibrium is less. Regarding passive balance, how should the balance current of the BMS be determined? Irresponsibly, the bigger the better, but considering the cost, heat dissipation, space, etc. We have to make compromises. Before selecting the equalization current, it is necessary to find out whether the SOC difference belongs to scenario 1 or scenario 2. At present, many situations are closer to scenario 1: The capacity and SOC of the battery are almost the same at the beginning, but with use, especially the difference in battery self-discharge, the SOC of each battery gradually differs, and the ability to balance should at least eliminate the influence of the difference in self-discharge . Therefore, the following is a simple formula for calculating the balance current. If the self-discharge of all batteries is the same, then do not balance; but if they are inconsistent, the difference in self-discharge current will cause a difference in SOC, and the balance is to make up for this difference in self-discharge current. In addition, since the average equilibrium time is limited every day and self-discharge continues every day, the time factor must also be considered. The above figure is a graph of the difference between the balance current and the self-discharge current according to the balance time of each day. Therefore, if the self-discharge rate of the battery cell is known, the required equalization current can be calculated, but the calculation result is a lower limit, and the actual equalization capacity must be greater than this value. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous: Do you know what a battery pack is?