Patent ID: 8773080

Claim:
A system for exciting a field coil of an alternator in order to produce a magnetic field that induces electricity in an alternator output coil assembly, the system comprising: an engine with a shaft that is rotatably driven; a magnet generating a magnetic field; an excitation output coil assembly disposed on the shaft within the magnetic field for producing alternating electricity, the excitation output coil assembly having an inductance; a rectifier having an input coupled to the excitation output coil assembly and having an output, the rectifier converting the alternating electricity into an output current with an output voltage and providing the output current at the output; a capacitor connected to the output of the rectifier and having a capacitance; a resonant circuit including the capacitor and the excitation output coil assembly, wherein the resonant circuit causes the output voltage and output current to vary cyclically based on the capacitance of the capacitor and the inductance of the excitation output coil assembly; a switch connected in series with the field coil and having a conductive state and a non-conductive state, the switch operable to control application of the output current to the field coil; a minimum current detector coupled to the output of the rectifier and operable to determine when the magnitude of the output current is at a minimum level and in response thereto producing an indication, the minimum current detector including: a voltage sensor, a voltage averaging circuit, and a comparator; and a controller coupled to a control terminal of the switch and an output of the minimum current detector, the controller, in response to an excitation control signal, places the switch in a conductive state in which the output current is applied to the field coil, and, in response to the indication received from the output of the minimum current detector, places the switch in a non-conductive state.