Current unit for arc welding

Claim 1

An arc welding current supply unit arranged to be fed with alternating current voltage and to provide direct current for welding electrodes, said unit including a controlled frequency converter 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 the weld material and adapted to be connected to the welding electrodes through a transformer in series with a rectifier, a control device for controlling said converter in a manner such that the arc power remains substantially unchanged irrespective of changes in load caused by the welding operation, wherein current pulses are formed in the secondary winding of the transformer by alternatingly charging and discharging at least one capacitor which is connected in series with said primary winding of said transformer and which is discharged therethrough, and said at least one capacitor being charged by a direct current voltage intermediate source and being connected to said source by a number of thyristors equal in number to the number of said capacitors, said thyristors being connected to said control device, and wherein said control device further comprises means for alternatingly making said thyristors conductive at a frequency which is substantially inversely proportional to the square of said voltage applied to said current supply unit.