Arc welding electrical shock protection circuit

A control apparatus for controlling supply of voltage from the supply unit to the electrode of a DC electric welder for protecting a user of the electrode against electric shock when changing rods in the electrode, the apparatus comprising:

• an input terminal for connection to a the supply unit for receiving therefrom a DC current for supply to the electrode;
• an output terminal for connection to the electrode for supplying the current from the supply unit to the electrode for powering the electrode during use;
• a supply line connected between the input terminal and the output terminal;
• an SCR thyristor switch in the supply line operable to transmit or to not transmit the current from the input terminal to the output terminal;
• a detector circuit arranged to detect the electrical resistance between the output terminal and ground;
• and a control circuit arranged to actuate the SCR thyristor switch to effect transmission of current only if the resistance detected is less than a predetermined value;
• wherein the control circuit is arranged such that the gate of the thyristor is triggered only for a period of time and the gate is then not triggered during normal welding.

A control apparatus for controlling supply of voltage from the supply unit to the electrode of a DC electric welder for protecting a user of the electrode against electric shock when changing rods in the electrode, the apparatus comprising:

• an input terminal for connection to a the supply unit for receiving therefrom a DC current for supply to the electrode;
• an output terminal for connection to the electrode for supplying the current from the supply unit to the electrode for powering the electrode during use;
• a supply line connected between the input terminal and the output terminal;
• an electronic current switch in the supply line operable to transmit or to not transmit the current from the input terminal to the output terminal;
• a detector circuit arranged to detect the electrical resistance between the output terminal and ground;
• and a control circuit arranged to actuate the switch to effect transmission of current only if the resistance is less than a predetermined value;
• wherein the control circuit includes a programmable micro-controller chip which allows the chip to be programmed to specific parameters.