Patent ID: 8575940

Claim:
A power supply device, comprising: a battery that includes rechargeable battery cells and supplies electric power to a load; a positive terminal contactor that is serially connected to a positive side of the battery; a negative terminal contactor that is serially connected to a negative side of the battery; and a control portion that determines whether the load is electrically in a connected state or a non-contact state to output sides of the positive terminal contactor and the negative terminal contactor, wherein the control portion comprises: a voltage detecting circuit that detects a capacitor voltage of a capacitor of the load, the voltage detecting circuit being connected to the capacitor at the output sides of the positive terminal contactor and the negative terminal contactor, a contactor controlling circuit that controls opening and closing of the positive terminal contactor and the negative terminal contactor, respectively, and a determination circuit that compares the capacitor voltage detected by the voltage detecting circuit with a first predetermined voltage to determine the connected state of the load to the power supply device, wherein the voltage detecting circuit is configured to detect the capacitor voltage with the negative terminal contractor being controlled in a closed state and the positive terminal contactor being controlled in an open state by the contactor controlling circuit at a time a start switch is turned ON, and the determination circuit is configured to determine that the load is in a normal connected state to the power supply device when the capacitor voltage is not smaller than the first predetermined voltage.