Therefore, when two sets of batteries with equal capacity but different internal resistances are connected in parallel for low-voltage constant-voltage charging, it is impossible for the two sets of batteries connected in parallel to reach true saturation at the same time.
(1) Several sets of batteries of equal capacity should not be used in parallel for a long time.
When two sets of batteries are connected in parallel and charged with a low-voltage constant voltage, the battery with the larger internal resistance experiences negative charging. After the charging is supposedly complete, the two sets of batteries have unequal electromotive forces, i.e., U'01 and U'02. If the batteries are discharged in parallel after charging stops, when r01>r02 and U02'>U01', then Z2-Z1>0. This proves that when two sets of batteries with equal capacity but unequal internal resistance discharge, the battery with smaller internal resistance not only discharges to the load but also charges the battery with larger internal resistance. Undoubtedly, the battery with smaller internal resistance bears a heavier burden in the initial stage of discharge. On the other hand, when the terminal voltages of the two sets of batteries are equal, the battery with larger internal resistance also consumes the capacity of the battery with smaller internal resistance. Therefore, it can be seen that the utilization rate of the battery with larger internal resistance is far lower than that of the battery with smaller internal resistance.
(2) Parallel-connected batteries may experience increased internal energy loss if left unused for extended periods. If two or more groups of batteries are connected in parallel and left unused for a long time, these batteries will consume energy in two ways: self-discharge and the formation of an internal discharge circuit when two groups are connected in parallel. Long-term parallel connection of two or more groups of batteries will not only cause insufficient charging but also increase internal energy loss. When a UPS power supply battery encounters one of the following situations during use, equalization charging should be used to restore the battery's chargeability. Equalization charging involves connecting each battery cell in parallel and charging them with a uniform charging voltage. The aforementioned dedicated charger has this function. Situations requiring equalization charging of batteries include:
Excessive discharge causes the battery's terminal voltage to fall below its permissible discharge termination voltage. For a 12V M-type lead-acid battery, its discharge termination voltage is approximately 10.5V; in an UPS battery pack, the terminal voltage between individual battery cells exceeds approximately 1V; batteries that have been stored for a long time (including newly purchased batteries); and new batteries that have been replaced in a battery pack due to performance degradation before being connected to the pack.
To ensure good charge and discharge characteristics of the battery, for UPS power supplies that have been idle for a long time (UPS power supply shut down for more than 10 days), it is best not to apply a load before restarting. Let the UPS power supply use its internal charging circuit to float charge the battery for 10-12 hours before use. For users of standby UPS power supplies, if the UPS power supply has been operating in standby mode for a long time, it is recommended to run the UPS power supply in inverter mode for at least 2-3 minutes every month to activate the battery. Currently, for postal service rooms throughout the province, we require that the UPS power supply be manually discharged at least once every quarter to activate the battery.
Ensure the working environment temperature of the battery pack. In daily maintenance, the working environment temperature of the battery pack is often overlooked. In fact, the ambient temperature is closely related to the service life of the battery pack. Theoretical studies show that between 20 and 50 degrees Celsius, the service life decreases by nearly half for every 10-degree increase in ambient temperature. In July 2001, the UPS battery pack in the Green Card Provincial Center computer room was scrapped. The power room did not have air conditioning, and the temperature in the power room even reached over 40 degrees Celsius in the summer, which caused great concern. Therefore, for some computer rooms that did not have air conditioning in the power room during the design, it is necessary to consider adding air conditioning facilities. (3) Equalization charging: Under normal operating conditions, the battery pack should not be equalized charged. However, if it is found that the voltage between individual cells in the battery pack is unbalanced, the battery pack should be equalized charged.
