A portable backup starting device for a vehicle includes an internal power source, a switching circuit, a first voltage detecting circuit, a first electrode clip, and a second electrode clip. The first electrode clip and the second electrode clip are configured to connect to a first end and a second end of a vehicle load; the internal power source has a first electrode and a second electrode. The first electrode is coupled to the first electrode clip, and the second electrode is coupled to the switching circuit; and the switching circuit is coupled to the second electrode clip. The first voltage detecting circuit is coupled to the switching circuit, the first electrode, and the second electrode.

A power supply system is installed in a vehicle. The power supply system includes a first load circuit configured to operate using electric power from a main battery, the first load circuit being connected to a first load; a second load circuit configured to operate using electric power from the main battery or an additional battery, the second load circuit being connected to a second load; a first relay provided on a power supply line for electrically connecting the first load and the second load, the first relay that electrically connects or disconnects the first load circuit to or from the second load circuit; a second relay that electrically connects or disconnects the second load to or from the additional battery; and a controller that determines a state of a start switch for starting the vehicle. The first relay is in an on state when the start switch is off. The second relay is in an off state when the start switch is off. When determining that the start switch has been switched from off to on, the controller is configured to turn on the second relay and then turn off the first relay. A failure diagnosis for the first relay is performed with the first relay being off and the second relay being on.

A handheld jump starter device includes a rechargeable lithium battery pack comprising at least three lithium battery cells, a housing for enclosing the rechargeable lithium battery pack, and a jumper cable assembly removably attachable to the housing, the jumper cable assembly comprising a plug and a pair of cables, wherein the plug is configured to attach to the housing in a specific orientation.

Methods for switching the power source supplying an alternating current (AC) electrical load from a first AC power supply to a second AC power supply comprising: (a) determining, during a time period, the zero voltage crossings of at the first and second AC power supplies; (b) estimating for a future time period, based on information obtained in said determining step (a), the times at which a series of future current zero-crossings of said AC load and at least the current zero-crossing of the second power supply; (c) based on said estimating step (b), determining whether during said future time period the time of said zero-crossing of said load current and the zero-crossing of the second power supply are within about 0.1 microseconds of each other; and (d) for a time period during which said zero crossings are estimated to be within 0.1 microseconds of each other, switching said load to said second power supply at said time at which said zero crossings are estimated to be within 0.1 microseconds of each other, wherein said switching: (i) uses a solid-state switching system and microprocessor-based control system for actuating said solid-state switching circuit; and (ii) accounts for any known actuation delay between the actuation signal from said microprocessor and the occurrence of said switching.

A three-phase synchronous rectifier for charging a battery on board the vehicle, comprising a first and a second input which are independent of each other and each connectable to a respective first and second three-phase output branch of a generator, two independent negative and positive outputs each connectable to the respective poles of the battery, a first group of three rectification units configured to be connected to the first output branch of the generator via said first input, a second group of three rectification units configured to be connected to the second output branch of said generator via the second input. Advantageously, the rectification units are configured to be simultaneously connected to the battery of the vehicle.