Fig. 13. Durability of the test bed. terminal voltage as a function of discharge time when the temperature of coolant into the cell stack is shifted from a standard operating temperature of 80 °C is illustrated in Fig. 11. According to this test result, it is concluded that such variation of temperature of the cell stack and the condenser does not influence the terminal voltage. On the other hand, it is expected that the electrodes will be drowned and then the terminal voltage will drop, when the temperature of the cell stack drops and the temperature of the condenser rises. The test results substantiate this expectation, as shown in Fig. 12; that is, the terminal voltage drops, when the temperature of coolant into the cell stack is shifted from a standard operating temperature of 80 °C to an operating temperature of 78 °C, and the temperature of gaseous hydrogen leaving the condenser was shifted from a standard operating temperature of 70.5 °C to an operating temperature of 72°C. A remarkable wetness of the electrodes was found upon disassembling the cell stack. 3.6 DURABILITY In order to confirm the durability of the test bed, an intermittent mission duty test was carried out during a cumulative time of 86 h, including a continuous running test for 29 h under the standard operating condition. In the mission duty test, as shown in Fig. 13, the terminal voltage drops little by little after an operation of 31 h, and then a drop of the terminal voltage of approximately 0.9% is found at the completion of the mission duty test. 4. CONCLUSIONS An alkaline-matrix-type fuel cell system with a standard power of 80 W was tested. It put out a power of 90 W at a standard load current of 20 A and a power of 147.7 W at a maximum load current of 35 A under an operating pressure of 0.4 MPa. The terminal voltage followed quickly the sudden change of load current, and the reactant supply system and the control unit were operated satisfactorily, when the load current was changed suddenly.
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