Light load operation of UPS

The efficiency of most UPS power supply is the highest when the load is 50% - 100%. When the load is lower than 50%, the efficiency drops sharply. Therefore, when the UPS is operated under excessive light load, 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. If the ups does not have a deep discharge protection system, it may cause excessive deep discharge of the battery and permanent damage of the battery.

The causes of excessive deep discharge of battery are generally as follows:

1. Long time small current discharge. As we all know, the capacity used by the battery is closely related to the discharge current. The smaller the discharge current is, the more capacity is actually discharged. Generally speaking, the discharge capacity of the battery must be controlled within 80% of the rated capacity. In other words, when the battery discharges 80% of the rated capacity, it is not allowed to continue discharging. If the battery continues to discharge, it will cause deep discharge of the battery. If remedial measures are not taken in time, it may cause permanent damage to the battery.

2. Long time frequent discharge. Some units and regions, due to the frequent power outage, may cause frequent battery discharge. If there is not enough time (generally more than 10h) for charging after the battery is discharged, and the second time is discharged immediately, more times like this may cause deep discharge of the battery.

UPS has the minimum protection value of battery voltage, but the relationship between the terminal voltage and discharge current is fundamental. If the discharge current is small, the terminal voltage will be high, and the actual capacity will be more when the minimum protection value is reached. Therefore, light load operation of UPS, should try to avoid discharging to the lowest protection value before shutdown. For long time delay UPS, the protection value of lower discharge limit voltage should be increased properly.