Tsutomu Ogata

A deterioration estimating system for 200-Ah sealed lead-acid batteries

The introduction of sealed lead-acid batteries, which do not need refills of water, greatly reduces the amount of maintenance required. However, it is difficult to estimate the batterys deterioration because they are sealed. A useful battery test system for estimating the battery deterioration was developed in NTT and NTT Power and Building Facilities Inc. It can measure the batterys capacity in less than 1 ms without affecting telecommunications equipment or power equipment, is accurate to within 10%, and is compact, light, and easy to handle. In this system, the batterys internal resistance which is calculated from the transient voltage change at the batterys 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 batterys 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. Errors of less than 10% were achieved for every brand of battery. We also verified that neither telecommunications equipment nor power equipment was affected by this measurement.<<ETX>>

Multi-fuel cell energy system for telecommunications co-generation system

NTT is developing a highly efficient fuel cell energy system for telecommunications equipment that can run on various fuels, and is suitable for a telecommunications co-generation system. In this system, electrical power supplants the mains power and heat energy is used for the air-conditioners. Using this fuel cell power plant as an emergency generator and ensuring the reliability of telecommunications requires alternate fuels. This plant can run on liquefied petroleum gas (LPG) if the pipeline gas supply is stopped. The system configuration is described, along with a fuel substitution technology, an energy utilization technology, and demonstration test results using a 200-kW phosphoric acid fuel cell power plant.

Establishment of the relationship between capacity and impedance of trickle-charge nickel/cadmium cells by using electrolyte-deficient model cells

Abstract A relationship is established between the capacity and the impedance of trickle-charged nickel/cadmium cells by using electrolyte-deficient model cells. Loss of capacity is strongly related to cell weight and the logarithm of the impedance. Since the decrease in cell weight is thought to be caused by electrolyte loss, an electrolyte-deficient model cell has been prepared to simulate the deterioration conditions. The model cell and deteriorated cells exhibit linear relationships between cell capacity and the logarithm of impedance where its imaginary part is zero on a Cole-Cole plot. Furthermore, a linear relationship is obtained that follows closely the relationship obtained from measured data by modifying the relationship for the model cells by substituting for the capacity of the fresh (non-deteriorated) cell. This method provides an effective and time-saving way for obtaining the relationship because is not necessary to test many deteriorated cells or to carry out accelerated tests.

New Power Feed Techniques for Telephone Subscribers

This paper describes power feed techniques for telephone subscribers in a metallic two-wire digital subscriber loop system and optical fiber subscriber loop systems. In a metallic two-wire digital subscriber loop system, Digital Service Unit (DSU) and Digital Telephone (DTEL) are installed on the subscriber premises. Since the equipment has additional new service functions compared with the conventional analog telephone, the power consumption of the equipment is increased. Therefore, it is difficult to feed the equipment sufficiently using a conventional 48V constant-voltage power supply. A constant current supply method from the central office is suitable because constant power can be supplied with little energy loss, even if subscribers line distance varies. It is also possible to simplify the DC-DC converter circuit in DSU. A high conversion frequency (150kHz) multi-output constant current converter has been developed for power feeding in NTT. The converter can feed eight subscribers and has good constant current output characteristics. In optical fiber subscriber loop systems, it is difficult to feed the customers equipment with power from the central office. Therefore, an uninterruptible DC power supply, which includes batteries, has to be installed on the subscribers premises. The power supply is composed of sealed lead-acid batteries and a multi-input converter which has rectifier and DC-DC converter functions. This low-cost converter is very small compared with the conventional rectifier and DC-DC converter. Sealed lead-acid batteries are used in the power supply due to low cost and easy maintenance.

Battery research for telecommunications power supply systems at NTT

With the development of multimedia systems, batteries are becoming increasingly important for use in telecommunications systems. High energy density, safe batteries have been studied for use in portable telecommunications equipment. At NTT, lithium batteries have been studied in order to achieve a high energy density battery. The relatively large capacity of valve regulated lead-acid (VRLA) batteries makes them suitable for backup power. To ensure the reliability of power supply systems the deterioration of batteries for back-up power should be periodically measured. However, it is difficult to measure the deterioration of VRLA batteries because they are sealed. Therefore, NTT has developed a simple method for measuring deterioration. On the other hand, since the power consumption of telecommunications for multimedia systems will increase, power saving will become much more important. For example, cogeneration systems using fuel cells will produce much residual heat energy, so it will be important to transform thermal energy into electrical energy to save power. The authors explain the following: the main uses and requirements of batteries at NTT and battery trends in Japan; a method of measuring deterioration of VRLAs; new types of cells, which are a high energy density battery and a thermocell that can be simultaneously discharged and thermocharged.

High-capacity thin sealed lead-acid battery

The authors have developed a battery structure to achieve an ultra-thin sealed lead-acid battery with nondegrading performance. A thin and high-capacity sealed lead-acid battery utilizing the developed battery structure is described. To develop high-capacity batteries, several problems must be overcome. They include the establishment of a printing method to print thick lead paste layers precisely, and a technique to improve the bonding force between the active material and the collector. Consequently, the capacity of the batteries is 700 mAh, and its thickness is, respectively, 1.0 mm and 2.2 mm. In addition, these batteries have a life of over 400 cycles, and have achieved an energy density over 100 Wh/L.<<ETX>>

Portable fuel cell systems

Three types of portable fuel-cell systems were developed. These systems consist of a small fuel-cell stack, two hydrogen cylinders, and a power converter. Each system is complete in one cabinet. Each system supplies 200-250 W of power for more than 6 hours using the two 6.7-liter hydrogen cylinders. These systems generate power quietly and cleanly, and are thus suitable as indoor emergency power sources for various types of equipment.

Using a pulse-current technique and measured resistance to evaluate the capacity of trickle-charged nickel/cadmium cells

Abstract The use of a pulse-current technique to evaluate the capacity of trickle-charged nickel/cadmium (Ni/Cd) cells is investigated. A current pulse is applied to the cells in the charging mode and the resistance is estimated from the change in voltage. A linear relationship between the capacity and the logarithm of the resistance is observed. The combination of a pulse current of 0.1–1.0 C and a pulse width of 10 ms or less displays a high correlation coefficient for deteriorated cells. The error between the evaluated and the measured capacity is less than 10%, on average, under these conditions in the capacity range of greater than 50% nominal capacity.

Development of a 200kW multi-fuel type PAFC power plant

Nippon Telegraph and Telephone Corporation (NFT) has been developing a 200 kW multi-fuel type PAFC power plant which can generate AC 200 kW of constant power by switching fuel from pipeline town gas to liquefied propane gas (LPG) and vice versa. This paper describes the outline of the demonstration test plant and test results of its fundamental characteristics.