Power supply device for vehicles

A power source device for a vehicle comprising:

• a first power storage portion configured to store power generated by a generator in a vehicle, and to supply power to a motor for starting an engine and an electric device in the vehicle;
• a second power storage portion connected to the first power storage portion in parallel, and configured to store power generated by the generator, and to supply power to the electric device in the vehicle;
• a switch inserted in a path between the first power storage portion and the second power storage portion;
• a diode directly connected in parallel with the switch such that (i) an anode side of the diode is directly connected to a first end of the switch on the first power storage portion side of the switch and (ii) a cathode side of the diode is directly connected to a second end of the switch on the second power storage portion side of the switch;
• and
• a controlling portion configured control the switch,
• wherein the controlling portion monitors a voltage of the first power storage portion and a voltage of the second power storage portion, and detects an abnormal state of the switch by comparing a voltage difference therebetween with a forward voltage drop of the diode,
• wherein the second storage battery comprises plural storage battery cells connected in series, and
• wherein a voltage of each of the plural storage battery cells corresponds to the forward voltage drop of the diode.