Tips for maximizing the life of battery packs in UPS

　　introduction

　　Through statistics of various failures in UPS maintenance work, we can draw the following conclusion: For backup UPS power supply , failures caused by batteries account for more than 50% of the total failures. For online UPS power supply, because of its reasonable circuit design and large margin of driving power component capacity, the failure rate of power circuit is very low. In contrast, the failure rate caused by battery packs rises to more than 60%. It can be seen that the correct use and maintenance of batteries is one of the key factors to extend the life of battery packs and reduce the total failure rate of UPS power supply.

　　1. Regular inspection

　　Check the terminal voltage and internal resistance of each unit battery regularly. For 12V unit batteries, if the terminal voltage difference between each unit battery is found to be more than 0.4V or the internal resistance of the battery is more than 80mΩ, each unit battery should be balanced charged to restore the internal resistance of the battery and eliminate the terminal voltage imbalance between each unit battery. The charging voltage during balanced charging can be 13.5~13.8V. Most batteries that have been well balanced charged can restore their internal resistance to less than 30mΩ.

　　During the operation of the UPS power supply, the above-mentioned imbalance caused by the change of the characteristics of each unit battery over time cannot be eliminated by relying on the charging circuit inside the UPS power supply. Therefore, for the battery pack with obvious imbalance in characteristics, if offline equalization charging is not adopted in time, the imbalance will become more and more serious.

　　2. Re-float charge

　　If the UPS power supply has been shut down for more than 10 days, before restarting it, you should start the UPS power supply without adding load to use the charging circuit inside the machine to float charge the battery for more than 10 to 12 hours before running it under load.

　　The UPS power supply is in a floating charge state for a long time without a discharge process, which is equivalent to being in a "storage standby" state. If this state lasts too long, the battery will fail and be scrapped due to "too long storage", which is mainly manifested in an increase in the internal resistance of the battery, which can reach several Ω in severe cases.

　　We found that after one month of storage at room temperature (20°C), the battery's available capacity is about 97% of its rated capacity. If it is stored for six months without use, its available capacity becomes 80% of its rated capacity. If the storage temperature rises, its available capacity will decrease.

　　Therefore, it is recommended that users intentionally unplug the mains input every 20°C months to allow the UPS to operate in a state where the battery provides energy to the inverter . However, this operation should not be too long. When the load is about 30% of the rated output, it can be discharged for about 10 minutes.

　　3. Reduce deep discharge

　　The service life of the battery is closely related to the depth of its discharge. The lighter the load carried by the UPS power supply, the greater the ratio of its available capacity to its rated capacity when the mains power supply is interrupted. In this case, when the UPS power supply automatically shuts down due to low battery voltage, the depth of battery discharge is relatively deep.

　　How to reduce the occurrence of deep discharge of batteries in actual process? The method is very simple: when the UPS power supply is in the state of being interrupted by the mains power supply and the battery supplies power to the inverter, most UPS power supplies will periodically sound an alarm with an interval of about 4 seconds to inform the user that the battery is now providing energy. When the alarm sound becomes rapid, it means that the power supply is in deep discharge, and emergency treatment should be carried out immediately to shut down the UPS power supply. Unless it is absolutely necessary, generally do not let the UPS power supply work until it automatically shuts down due to low battery voltage.

　　4. Use peak power supply to charge

　　For users whose UPS power supply is in a low voltage supply of the mains for a long time or has frequent power outages, in order to prevent the battery from being damaged prematurely due to long-term insufficient charging, the battery should be charged at peak power supply times (such as late at night) to ensure that the battery has enough charging time after each discharge. Generally, after a battery is deeply discharged, it takes at least 10 to 12 hours to charge it to 90% of the rated capacity.

　　5. Pay attention to the selection of charger

　　Maintenance-free sealed batteries used in UPS power supplies cannot be charged with thyristor -type "fast chargers". This is because this type of charger will cause the battery to be in a bad charging state of both "instantaneous overcurrent charging" and "instantaneous overvoltage charging". This state will greatly reduce the battery's available capacity, and in severe cases, the battery will be scrapped. When using a UPS power supply with a constant voltage cutoff charging circuit, be careful not to adjust the battery voltage under-voltage protection operating point too low, otherwise, it is easy to produce overcurrent charging in the initial charging period.

　　Of course, it is best to use a charger with both constant current and constant voltage to charge it.

　　6. Ensure the power supply ambient temperature

　　The available capacity of the battery is closely related to the ambient temperature. In general, the performance parameters of the battery are calibrated at room temperature of 20°C. When the temperature is below 20°C, the available capacity of the battery will decrease, and when the temperature is above 20°C, the available capacity will increase slightly. Batteries of different manufacturers and models are affected by temperature to different degrees. According to statistics, at -20°C, the available capacity of the battery can only reach about 60% of the nominal capacity. It can be seen that the impact of temperature cannot be ignored.

　　7. Conclusion

　　Of course, to extend the service life of the battery pack, you must not only pay attention to maintenance and use, but also fully consider the load characteristics (resistance, inductance , capacitance) and size when selecting. Do not run the battery under excessive light load for a long time, so as to avoid the battery being scrapped due to too small discharge current.