The introduction of sealed lead-acid batteries, which do not need refills of water, greatly reduced the amount of maintenance required. However, it is difficult to estimate the battery's deterioration because they are sealed.A useful battery test system for estimating the battery deterioration was developed in NIT and NIT Power and Wlilding Facilities Inc. It can measure the battery's capacity in less than 1 m without affecting telecomnunications equipnent or power equipment, is accurate to within lo%, and is compact, light, and easy to handle.In this system, the battery's internal resistance which is calculated from the transient voltage change at the battery's terminal, and current which flows through the circuit, is used to determine the extent of deterioration in the battery. The pulse width of the transient voltage was set to some hundreds microseconds from the mutual relationship between the voltage drop and the battery's capacity.A regression expression was developed using batteries with artificially accelerated deterioration, and a total of 250 sets of 200-Ah sealed lead acid batteries now in use were applied for field experiments. Then, this system was confirmed to be accurate at estimating the batteries' capacity within an error of lo%, according to the regression expression applied after analyzing the relationship between the internal resistance and the battery's capacity. Errors of less than 10% were achieved for every brand of battery.We also verified that neither telecmications equipment nor power equipment was affected by this measurement.The system has been introduced in our battery's maintenance operation and has shown its usefulness to find out deteriorated batteries with ease.
The business activities of NTT Power and Building Facilities Inc. (NTT-F) consists of engineering and management for NTTs telecommunications system. A maintenance work related to batteries occupies about 1/4 of the entire telecommunications power system maintenance work. Moreover, a large number of valve regulated lead acid (VRLA) batteries have been installed and maintenance work of these batteries will increase in the future. To reduce this maintenance work, NTT-F has developed technology to evaluate the condition of a battery by discharging under a real load condition and to measure deterioration simply by measuring internal resistance of a single cell. NTT-F is scheduled to improve the efficiency of battery maintenance work by systematically using this technology.
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