A relay welding detector is adapted for detecting welding fault of a relay. The relay has a first electrical contact coupled to a neutral terminal of an alternating current (AC) power source through a first power line, and a second electrical contact coupled to a load through a second power line. The relay welding detector includes a signal generator generating a test signal, a current transformer wound with a portion of one of the power lines and generating an induced signal based on the test signal, and a determining unit determining, based on the induced signal, whether the electrical contacts of the relay are welded to each other.

In relay weld diagnostic device, a threshold value determination unit (104) determines a threshold value on the basis of a resistance value that is set for each of a P-pole-side resistor (24) and an N-pole-side resistor (23) provided to charging equipment. A peak value measuring unit (110) measures the peak value of a voltage supplied to a voltage line by an alternating-current signal output circuit (112). A comparison diagnosis unit (111) assesses the state of a relay (14) on the P-pole side and a relay (15) on the N-pole side by comparing the peak value and the threshold value, and makes a diagnosis as to whether the relays (14), (15) are welded on the basis of the assessed state of the relays (14), (15) and the state in which the relays (14), (15) are controlled.

A solenoid driver circuit for a circuit breaker is provided. The circuit breaker includes a control circuit, a solenoid and secondary contacts and is structured to be coupled between a power source and a load. The solenoid driver circuit includes a first switch coupled to a solenoid and a first resistor structured to sense solenoid current; a second switch coupled to a second resistor, the second switch structured to be turned on based on a switch drive signal from the control circuit; one pulse width modulation (PWM) current controller coupled to the control circuit, the first switch, the second switch and the first resistor, the one PWM current controller structured to adjust the solenoid current and drive the solenoid to open or close the secondary contacts using a plurality of peak solenoid current limits including a first peak solenoid current limit and a second peak solenoid current limit.

In a case where a load current flows in an energized state where a power supply is connected to a load, it is assumed that a measured voltage fluctuates due to a voltage drop caused by contact resistance of a relay contact, and thus the relay state cannot be accurately diagnosed. A relay control device that controls a relay connected between a secondary battery and a load device calculates, in a failure diagnosis during energization with the relay being closed, a contact resistance value of the relay based on a voltage applied to the relay and a current flowing through the secondary battery, and determines a first threshold set as a variable value in accordance with a temperature change amount of the relay and compares the calculated contact resistance value with the first threshold to diagnose a failure of the relay.

A method for actuating an electromechanical switching element including a plurality of contacts, a coil with an iron core, and an armature includes: in the event that a predefined condition is fulfilled, in a switch-off process pulsing on and off or in the switch-on process pulsing off and on of the switching element is carried out repeatedly at a predefined time within an overtravel range such that a coil current flowing into the coil oscillates between a predefined maximum value and a minimum value so that the armature moves within the overtravel range and the plurality of contacts thereby rub against each other without becoming detached from each other. The minimum value is defined as a current value at a time at which the armature begins to detach from the iron core.

A system includes a relay system and a controller. The relay system includes a plurality of relays, each having a first contact on an input side of the respective relay, the input side coupled to a power source, a second contact on a load side of the respective relay coupled to a load, and a spanner configured to close the first and second contacts of the respective relay when activated by a close signal. The load sides of each of the respective relays are coupled through their respective loads. The controller is configured to measure a voltage between a spanner of a first relay and an input side of a second relay. Based on the voltage between the spanner of the first relay and the input side of the second relay, the controller determines whether an electrical weld of one of the contacts of the first relay exists.