Patent attributes
An electric power source for a motor vehicle is equipped with a welded state discriminator, and while a positive-side contactor and negative-side contactor are controlled to be switched off, the welded state discriminator detects a voltage of a positive-side contactor or negative-side contactor on its loading side with respect to a connecting point of a battery unit on a positive side and a battery unit on a negative side. Accordingly, when in a plus voltage where the detected voltage thus obtained is larger than a predetermined voltage, the positive-side contactor is judged to be in a welded state, and when in a minus voltage where the detected voltage is larger than the predetermined voltage, the negative-side contactor is judged to be in a welded state.
