Patent ID: 7687167

Claim:
A power supply unit comprising: a fuel cell that uses methanol as fuel and air to output a power; a secondary battery that supplies power to a load; fuel cell control means for establishing at least three different power generation modes based at least in part on a residual capacity of the secondary battery and controlling introduction of a different and predetermined amount of fuel to the fuel cell in each of the power generation modes to achieve a desired output power corresponding to each of the power generation modes, wherein the fuel cell outputs electric power in each of the three power generation modes; controller means for determining a target value of current or voltage of the fuel cell based on the amount of fuel supplied to the fuel cell, the target value falling within a predetermined range including the value at which an amount of methanol discharged from the fuel cell is minimized; a power converter that converts the power output from the fuel cell to a voltage or current, controls the converted voltage or current based on the target value, and supplies the load and/or the secondary battery with a power based on the controlled voltage or current of the fuel cell; and a secondary battery residual capacity detector that detects the residual capacity of said secondary battery; wherein the fuel cell control means comprises: means for switching the amount of fuel supplied to said fuel cell from a first value to a second value that is greater than the first value in response to the residual capacity of said secondary battery decreasing to a first residual capacity, and means for switching the amount of fuel supplied to said fuel cell from the second value to the first value in response to the residual capacity of said secondary battery increasing and reaching a second residual capacity that is greater than said first residual capacity.