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Alternating current (AC)

In resistance pressure welding, electric current flows through the workpieces which are to be joined. The workpieces are, through resistance heating, molten in the welding zone. Spot welding is a common procedure for joining workpieces; the welding current input is carried out via pressure electrodes. The method has, by the way, been invented by an Englishman, E. Thomson, in the year 1877.

The nowadays still widely used power source for applications in the field of resistance welding is based on single-phase alternating current machines. The adaptation of the welding current is carried out via the setting of the phase angle. For short welding times, this leads inevitably to a deteriorated controllability, as the control steps do not run faster than 10 ms.


  • low-priced - due to simple design


  • smallest controllable unit of time ½ period (10 ms at 50 Hz)
  • therefore hardly suitable for short welding times
  • high residual ripple of the welding current diminishes "welding window"
  • high inductive losses
  • mechanical wear in the secondary circuit through "electromagnetically induced movements"
  • unsymmetrical system load

Our products: Due to the numerous disadvantages we no longer offer products from the field of alternating current technique.

Alternative solutions:
Alternatives, however, are the welding power sources based on medium-frequency and high-frequency inverter power sources from the field of the direct current technique.