Patent ID: 7794889

Claim:
An abnormality detecting method for a fuel cell stack comprising a plurality of unit cells that generate power by supplying reaction gases to an anode and a cathode of each unit cell, the method comprising: stopping supply of the reaction gases to the fuel cell stack; determining a speed of cell voltage decrease of each of the unit cells after stopping supply of the reaction gases; determining that the fuel cell stack is abnormal when the speed of cell voltage decrease of any of the unit cells exceeds a warning value set for determination of abnormality of said fuel cell; when an abnormality of the fuel cell stack is detected, operating the fuel cell stack in an output limiting mode during a subsequent power generation by limiting the operational pressure of the reaction gases to a level lower than before the abnormality is detected; and determining a pressure difference between the anode and the cathode before stopping supply of the reaction gases, wherein the warning value is increased as the pressure difference is increased.