With the demand of the market, UPS is widely used in various industries, and the battery has become the power guarantee for the uninterruptible power supply system. When the mains are abnormal, the battery converts chemical energy into electrical energy, which is converted into AC electrical energy through the inverter in the UPS and delivered to the load to ensure uninterrupted and continuous operation of the load.

Valve-regulated maintenance-free sealed lead-acid batterieshttps://www.everexceed.com/lead-acid-battery_c1 have been widely used in large, medium and small UPS, accounting for 1/4 to 1/2 of the total cost of UPS. According to the survey, the life of the normal use of the battery is generally about 5 years, and about 50% of the UPS failures at the end of the use are related to the battery. The failure of the battery is mainly manifested in the backwardness of individual batteries or the low floating charge voltage of the battery, the short backup time (insufficient capacity), and the UPS that needs to be started by the battery cannot be started with load when the mains is abnormal. In order to ensure the normal operation of the UPS system, it is necessary to formulate a reasonable maintenance plan especially for the condition of the battery.

1 Battery float voltage monitoring

(1) Medium and large UPS is generally equipped with a monitor. By monitoring and setting the upper and lower limits of the float voltage, the health status of the battery can be monitored at any time, and abnormalities can be dealt with in a timely manner.

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

Through the above method, referring to the standard of YD/T799-2002 "Valve-regulated sealed lead-acid battery for communication", the floating voltage deviation of the battery in the floating state is not more than 480mV (12V battery). If the test voltage deviation is large, it is necessary to consider changing the Observation and testing are carried out after switching to the homogeneous charging mode. If there is no improvement after switching to the floating charging mode, the following methods should be considered for testing and verification.

2 Capacity test

of battery In general, the following capacity test methods can be selected when conducting regular capacity test of battery.

2.1 Off-line measurement method (if conditions permit)

(1) After the battery pack is fully charged, leave the UPS for 1 hour, and connect an external (intelligent) dummy load at an ambient temperature of 25°C±5°C. 10-hour discharge rate for discharge test.

(2) The terminal voltage, ambient temperature and time of the battery should be measured before the discharge starts.

(3) During the discharge period, the terminal voltage, discharge current and indoor temperature of the battery should be measured and recorded. The measurement time interval is 1h, and the discharge current fluctuation should not exceed 1% of the specified value.

(4) During the discharge period, the terminal voltage and room temperature of the battery should be measured and recorded, and the measurement time interval is 1h. To be measured at any time at the end of the discharge period, in order to accurately determine the time to reach the discharge termination voltage.

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

Ce=Cr/[1+K(t-25°C)] ( 1)

In the formula: t—ambient temperature during discharge

K—temperature coefficient (10-hour rate discharge, K=0.006/℃;

3-hour rate discharge, K=0.008/℃; 1-hour rate discharge, K=0.01 /℃)

(6) After the discharge, the battery pack should be charged, and the charged power should be more than 1.2 times of the discharged power.

2.2 On-line measurement method

(1) In the DC power supply system, adjust the output voltage of the UPS to the protection voltage, supply power to the actual load from the battery, and find the battery with the lowest voltage and the worst capacity in the battery pack during discharge as a capacity test object.

(2) Turn on the UPS to charge the battery pack, and wait for the battery pack to be fully charged for more than 1 hour.

(3) Carry out a 10-hour rate discharge test on the battery with the worst discharge in (1). Measure and record the terminal voltage, temperature, discharge time and room temperature of the battery before and after discharge. In the future, measure and record every 1h. When the discharge is approaching the termination voltage, it should be measured and recorded at any time in order to accurately record the discharge time.

(4) The discharge current multiplied by the discharge time is the capacity of the battery pack. If the room temperature is not 25°C, it should be converted into the capacity at 25°C according to formula (1).

(5) After the discharge test, use the charger to supplement the battery to restore its capacity.

(6) Draw the discharge curve according to the measurement record data.

2.3 Checking discharge test method

In order to know the approximate capacity of the battery pack at any time, it is necessary to carry out a checking discharge test load power supply. Before and after the battery pack is discharged, the terminal voltage, temperature, room temperature and discharge time of each battery should be measured and recorded. Release 30% to 40% of the rated capacity.

(2) After the discharge, the battery should be charged, and the charged power should be more than 1.2 times the discharged power.

(3) Draw the discharge curve according to the data recorded by the measurement, and reserves it for comparison when measuring again in the future.

Note:

(1) For the battery pack of the UPS power supply system, it is not recommended to use the offline measurement method for capacity testing.

(2) When conducting the online measurement method and the check capacity test, for the UPS equipment with the battery discharge test function, it is necessary to turn on the battery discharge detection function to conduct the battery discharge test. For a UPS without this function, it is necessary to turn off its AC input power supply and conduct a discharge test.

2.4 Precautions

(1) It is very important to ensure the operation of the system during the capacity test. Therefore, during the capacity test, it is necessary to know in advance whether there is a planned power outage in the mains, and the standby generator set should be in good condition.

(2) Before carrying out the battery capacity discharge test, use a multimeter, an internal resistance meter, and a conductivity meter to conduct a preventive test on the performance of the battery.

(3) In order to ensure the accuracy of the capacity test, professional battery capacity online test instruments and dummy loads should be used for the test.

3 Test of high current output at the moment of battery startup

In the actual use process, the switching time of the backup UPS from the mains power supply to the inverter power supply is required to be less than 7ms, and it is generally designed to be 4 to 5ms. When the mains power supply is abnormal, the battery must output what the load needs in less than 4-5ms.