Abstract: A vehicle electrical system includes an alternator, a rectifier connected to the alternator, a battery which is connectable to the output connections of the rectifier, and a reverse polarization detector connected to the battery. The reverse polarization detector includes a diode. In addition, the reverse polarization detector has a threshold-value element connected in series with the diode.

Abstract: A switch means (3) consisting of plural switching elements, which switches the connection relationship, is provided between a pair of power generating terminals (g1, g2) of a power generator (10) and a pair of output terminals (e1, e2), to apply the output voltage to a load means (2) so as to utilize the generated power, at the same time voltage of the output terminals is measured with a switch-output measuring means (4), and a controller (5) controls the connection relationship between input and output terminals of the switch means (3) in response to the measured result to output the voltage having polarity required by the load means (2) from the output terminals (e1, e2) continually.