Apparatus for preventing over-discharge of batteries used in an electric

Abstract

To provide an electric vehicle in which a low voltage power, obtained by conversion from a high voltage power of a main battery by a DC--DC convertor, is supplied to an operation control unit and electric equipment loads such as a lamp and is also used to charge a low voltage secondary battery, in which the main battery and the low voltage secondary battery are prevented from being over-discharged even when a main switch is left in the on-state. A low voltage power VR outputted from a DC--DC convertor is supplied to an exciting winding of a relay and is also supplied to a low voltage secondary battery through a diode. The low voltage power VR is supplied to low voltage loads through a contact of the relay. The DC--DC convertor is so constructed that the output of the low voltage power therefrom is stopped when the output voltage of the DC--DC convertor is reduced to a value less than a specified range due to the reduction in the battery capacity of the main battery. In the case where the battery capacity of the main battery is reduced when the main switch is left in the on-state, the output of the DC--DC convertor is stopped, and the contact of the relay is opened for preventing over-discharge of the low voltage secondary battery.