Arc welding current supply

An arc welding current supply providing power to welding electrodes comprising:

• a.c. to d.c. rectifier means for converting an a.c. source voltage to a d.c. source voltage;
• a controlled frequency d.c. to a.c. inverter means, connected to said rectifier means, for converting said d.c. source voltage into an a.c. voltage, said inverter operating with a half period which is less than the average duration of the current and voltage transients caused by short circuits through droplets of a welding material;
• a transformer having a primary winding connected in said inverter circuit and a secondary winding connected to said welding electrodes;
• and
• control device means for controlling said inverter in a manner such that the arc power of the welding arc remains substantially unchanged irrespective of changes in load caused by the welding operation;
• said inverter comprising first and second thyristors, at least one charge-discharge capacitor and said primary winding;
• said first thyristor, said at least one capacitor and said primary winding being connected in series and connected to said d.c. source voltage, whereby said at least one capacitor is charged during the conduction of said first thyristor;
• said second thyristor being connected in a circuit loop with said primary winding and said at least one capacitor, whereby said capacitor is discharged during the conduction of said second thyristor;
• said control device means comprising an open loop system including means for alternatingly igniting said first and second thyristors at said controlled frequency, the duration between the ignition and cutoff of each said thyritor being sufficient to completely charge and discharge said capacitor.