Check discharge method, that is, 100%C deep discharge, has the advantage of accurate and reliable capacity test, so it is still the most reliable method to test battery performance in the world at present. Check discharge method, that is, full discharge capacity test, is the most direct and reliable method to detect battery capacity. Whether online or offline, standby power supply must be set as a preventive measure to ensure the safety of the system. However, the current accuracy, voltage accuracy and timing accuracy of discharge are all paid attention to.
2 Conductivity (internal resistance) measurement method (for general maintenance only)
It is the main daily maintenance instrument at present. From the testing technology, it can be divided into AC method and DC method, and more than 95% of the conductance (internal resistance) measuring instruments in use belong to AC method.
Ac conductance measurement is to add an AC voltage signal with known frequency and amplitude at both ends of the battery to measure the AC current in phase with the voltage. The ratio of AC current component to AC voltage is the conductance of the battery. Conductivity is a function of frequency, and there are different conductance values at different test frequencies. The smaller the battery capacity, the greater the battery resistance and the smaller the conductance. Conductivity method can accurately detect completely failed batteries. According to a large number of experimental analysis and research results, it is proved that the internal resistance or conductance of the battery will only change when the capacity is reduced to 50%, and it will change obviously after it is reduced to 40%. Therefore, the performance of the battery can be determined according to the conductivity or internal resistance of the battery to a certain extent. Testing the internal resistance or conductance of the battery by conductance method is a valuable reference idea to judge the quality of the battery, but there are some problems:
(1) However, accurate data cannot be provided for the quality of the battery. It is not enough to accurately measure the actual performance index of the battery, especially the capacity index. If the SOC exceeds 50%, it is impossible to judge the quality of the battery [2]. Can not meet the requirements of national standards. According to the relevant national power supply maintenance regulations and battery maintenance effect requirements, if the battery capacity is less than 80%, it should be eliminated as a whole.
(2) The measurement results of different types of electric meters are quite different because of the measurement frequency (15hz- 1000hz) and measurement methods (phase difference method, effective value method, modulation and demodulation method, comparison method, etc.). ) is quite different from the measured current of various AC meters (1A- 10a). It makes it difficult for users to choose instruments and doubt the reliability of instrument measurement results.
At present, the detection level of conductance (internal resistance) measuring instrument based on DC method has not exceeded that of AC method.
Although the conductivity measurement technology is simple, because the internal resistance and capacity are nonlinear, the test results can not well reflect the real health status of the battery.