Abstract: If arc interruption occurs during AC arc welding, a first AC frequency predetermined for normal welding is switched to a second AC frequency higher than the first AC frequency. This allows the arc to be reignited without applying a high frequency high voltage, thereby preventing the damage of the surface of the weld bead or communication failure due to the high frequency high voltage.

Abstract: If arc interruption occurs during AC arc welding, a first AC frequency predetermined for normal welding is switched to a second AC frequency higher than the first AC frequency. This allows the arc to be reignited without applying a high frequency high voltage, thereby preventing the damage of the surface of the weld bead or communication failure due to the high frequency high voltage.

Abstract: A welder has an electromagnetic switch for turning on and off the power to be supplied to the welder, a control circuit for controlling the turn on and off of this switch according to a starter signal that starts the welder and self-holding circuit for self-holding the switch. This self-holding circuit releases the switch from the self-holding when a voltage of the control circuit lowers to not more than a turn-on voltage of the switch. Therefore, when an applied voltage decreases too low to maintain the turn-on status, the switch is released from its self-holding. A voltage can thus never be applied again to the control circuit unless the starter signal is once turned off. As a result, a coil of the switch is completely free from being burnt out. Also current can be cut off when a temperature of the coil of the switch rises to not less than a given value. Therefore, if an abnormal temperature of the coil is sensed, the coil current is cut off.

Abstract: An arc welding apparatus having output terminals of a constant current characteristic and a constant voltage characteristic is simply provided at low cost with a reactor appropriate for both the characteristics. A current control circuit 2 controls a secondary output current of a welding transformer 1 by means of a current control device, while a first reactor 3 and a second reactor 4 are constructed so that magnetic flux formed by a first winding 3a and magnetic flux formed by a second winding 4a, which are wound around an annular iron core 7, overlap each other. The other terminal of the first reactor 3 is connected to a constant current characteristic output terminal 8, while the other terminal of the second reactor 4 is connected to a welding base metal use output terminal 10.

Abstract: An arc welding apparatus is constructed of: a welding transformer 1, wherein a first tap T1 is provided at a point of half N/2 of the total number of turns N of the secondary winding of the transformer 1, the first tap T1 is connected to the electrification section 9 of a manual welding holder 8, a second tap T2 is provided at a point of N1 turns from the start Ts of the secondary winding, the second tap T2 is connected to a second thyristor 3, a first thyristor 2 and a third thyristor 4 are connected across both ends of the secondary winding, a third tap T3 is provided at a point of half N1/2 of N1 turns of the secondary winding and the third tap T3 is connected to a CO.sub.2 arc welding torch 10; a control circuit 6 for controlling these thyristors 2-4, a gate signal switchover circuit 5 for executing switchover between gate signals of the thyristors 2-4; and a reactor 7 for smoothing a welding current. The arc welding apparatus executes switchover between manual welding and CO.sub.