The Necessity And Suggestion Of UPS Battery Maintenance(1)

With market demand, UPS has been widely used in various industries, and batteries have become the power supply guarantee for uninterrupted power supply systems. A UPS without a battery can only be called a stable frequency power supply. When the utility power source is abnormal, the battery converts chemical energy into electric energy, and the inverter converts the AC power source into a load through the inverter, thereby ensuring the uninterrupted continuous operation of the load.

Valve-regulated, maintenance-free sealed lead-acid batteries are widely used in large, medium and small UPS, accounting for 1/4 ~ 1/2 of the total cost of UPS. According to the survey, the life of a battery in normal use is generally about 5 years, and about 50% of UPS failures at the end of use are related to the battery. Battery failure is mainly manifested as the single battery backward or low battery floating voltage, short backup time (insufficient capacity), and the UPS that needs battery startup after the mains is abnormal cannot start. In order to ensure the normal operation of the UPS system, it is necessary to establish a reasonable maintenance plan, especially the status of the battery.

1. Battery float voltage monitoring

(1) Medium and large UPS are generally equipped with monitors. By monitoring the upper and lower limits of the floating voltage, the health of the battery can be monitored at any time, and abnormalities can be found in time.

(2) Use a multimeter to measure the floating voltage of the battery.

Through the above method and referring to the YD/T799-2002 "Valve-Regulated Sealed Lead Acid Battery for Communication" standard, the floating charging voltage deviation of the battery in the floating state does not exceed 480mV (12V battery). If the test voltage deviation is large, observe and test After the average charging method, if there is no change after switching to floating charging, you need to consider the following methods for testing and verification.

2. Battery capacity test

Under normal circumstances, when carrying out periodic capacity tests on batteries, you can choose the following capacity test methods.

2.1 Offline measurement (when conditions permit)

(1) After the battery is fully charged, it is excluded for 1 hour, the use of UPS and the ambient temperature under external (smart) dummy load conditions are 25°C±5°C, and the discharge test is performed for 10 hours using the discharge rate.

(2) Before starting to discharge, the terminal voltage, ambient temperature and time of the battery should be measured.

(3) Record the terminal voltage, discharge current and room temperature of the battery when it is discharged. The measurement interval is 1h, and the discharge current fluctuation shall not exceed 1% of the specified value.

(4) Record the terminal voltage and room temperature when the battery is discharged, and the measurement interval is 1h. It should be measured at the end of the discharge cycle to accurately determine the time to reach the discharge termination voltage.

(5) The discharge current multiplied by the discharge time is the battery pack capacity. When the battery is discharged for 10 hours, when the temperature is not 25°C, the actual measured capacity should be converted to the capacity Ce at 25°C according to the following formula:

Ce = Cr / (1 + K (t-25°C)) (1)

Among them: t-ambient temperature during discharge

K-temperature coefficient (when discharging at a rate of 10 hours, K=0.006/°C;

When the discharge rate is 3 hours, K=0.008/°C; when the discharge rate is 1 hour, K=0.01/°C)

(6) After the discharging is completed, charge the battery pack, and the charging capacity is more than 1.2 times the discharged capacity.

2.2 Online measurement

(1) In the DC power supply system, adjust the UPS output voltage to the protection voltage, and the battery will supply power according to the actual load. When discharging, find the battery with the lowest voltage and the worst capacity in the battery pack as the capacity test object.