What is battery deep discharge and how to prevent over-discharge?

Time of issue:2022-12-14


1. What is the meaning of deep discharge and over discharge of UPS battery?

Deep discharge generally refers to the discharge of about 80% of the rated capacity of the battery. After the battery of UPS power supply has been used for a period of time, some active substances will inevitably sink. If the active substances are not activated in time, it will inevitably have some impact on the capacity of the battery. Therefore, it is best to perform a deep discharge on the battery every few months. This helps extend battery life. But avoid excessive deep discharge, otherwise it will cause damage to the battery.

During the discharge process of the UPS power battery, lead dioxide and sponge lead form small crystals of lead sulfate in the chemical reaction. After excessive discharge, lead sulfate will form many larger crystals, and when the crystals are unevenly distributed , causing irreversible warping of the plate, and at the same time increasing the internal resistance of the plate. When charging, the lead sulfate crystal block is difficult to restore, which hinders the charging process.


2. What are the causes of excessive deep discharge of UPS power battery?

Most UPS power supplies have the highest efficiency when the load is 50% to 100%. When the load is lower than 50%, the efficiency drops sharply. Therefore, when the UPS is excessively light-loaded, it is not economical. In addition, some users always think that the lighter the load, the higher the reliability of the machine operation and the lower the failure rate. In fact, this concept is not comprehensive, because the light load can reduce the probability of damage to the final power tube. , but it is extremely harmful to the battery. Because of excessive light load operation, once the mains power fails, if the UPS power supply battery does not have a deep discharge protection system, it may cause excessive deep discharge of the battery, resulting in permanent damage to the battery.


1) Long time low current discharge. We all know that the capacity used by the UPS battery is closely related to the discharge current. The smaller the discharge current is, the more capacity is actually released. Generally speaking, the discharge capacity of the battery must be controlled within 80% of the rated capacity. That is to say, when the battery discharges 80% of its rated capacity, it is not allowed to continue discharging. If the discharge continues, it will cause deep discharge of the UPS battery. If remedial measures are not taken in time, it may cause permanent damage to the battery.


2) Frequent discharge for a long time. In some units and regions, due to frequent power outages, UPS power batteries may be frequently discharged. If after the battery is fully discharged, there is not enough time to charge it, and it is discharged immediately for the second time. If this happens too many times, it may cause deep discharge of the battery.


UPS has the minimum voltage protection value of the battery, but the terminal voltage of the battery is closely related to the magnitude of the discharge current, the discharge current is small, the terminal voltage is high, and the actual capacity released when the minimum protection value is reached is more. Therefore, for a UPS operating at a light load, try to avoid the phenomenon that the UPS is discharged to the lowest protection value before shutting down. For long-delay UPS, the protection value of the discharge lower limit voltage should be appropriately increased.


3. How to prevent the damage of excessive discharge of UPS battery?

1) The battery that has been discharged to a low-power state with load must be recharged within 72 hours after the battery is discharged to avoid battery damage;


2) When the UPS power supply is not in use, the connected battery should be disconnected, otherwise the connected UPS battery will be damaged due to over-discharge within a few days to a week, so when the UPS uninterruptible power supply is not used, the battery and UPS should be disconnected The connection line of the power host;


3) We recommend that the UPS power battery should be charged immediately after discharge. Recharging the UPS power battery within 72 hours after discharge will completely restore the capacity and life of the battery. The UPS power battery does not allow the voltage of each unit to be lower than 1V after the battery is discharged, and it is 6V for a 12V battery;


4) UPS will generally design an alarm. When the voltage drops to close to the end-of-discharge voltage (when the voltage of a single 12 volt is close to 10.8 volts), an alarm will sound. At this time, the electrical appliances should be turned off immediately, and the UPS should be turned off. However, when the end-of-discharge voltage is reached, it will automatically stop to prevent over-discharge;


5) The UPS power supply battery does not have high requirements for cold and heat, as long as it is at room temperature. If it is too high, it will easily cause the temperature of the battery to rise and damage the performance of the battery. Indirectly shorten the service life of electric vehicle batteries.


The above is the reason for the excessive discharge of the UPS power supply battery. During the daily use of UPS power supply, short-circuit discharge or excessive deep discharge of UPS battery should be avoided. Only by using UPS correctly can the service life of UPS power supply be extended.