- High Frequency Inverter Welders use submillisecond pulse width modulation (switching) technology with closed-loop feedback to control the weld energy in submillisecond increments. Three phase input current is full wave rectified to DC and switched at (up to) 25 kHz to produce an AC current at the primary of the welding transformer. The secondary current is then rectified to produce DC welding current with an imposed, low-level, AC ripple. The high-speed feedback circuitry enables the inverter power supply to adapt to changes in the secondary loop resistance and the dynamics of the welding process. For example, a 25 kHz inverter power supply adjusts the output current every 20 microseconds after rectification, which also allows the weld time (duration of current) to be controlled accurately in increments as small as 0.1 milliseconds.
- The high frequency closed loop feedback can be used to control (maintain constant) either current, voltage, or power while also monitoring another of the same three parameters.
Additional benefits of high frequency switching technology include reduced power consumption, smaller welding transformer, and the use of a very short pre-weld “check pulse” to test electrode and parts positioning prior to executing a weld. The result of this pre-weld check can be used to inhibit the weld by setting check limits.
Constant Current can be used for 65% of all welding applications including those that exhibit low contract resistance, small variability tin contact resistance, flat parts, and multiple part “sandwiches.”
Constant Voltage can be used for applications where the workpieces do not have flat surfaces, e.g. crossed wires, and where the resistance varies significantly, and for extremely short welds (less than 1 millisecond).
Constant Power can be used for applications with significant variations in electrical resistance from weld to weld, including applications where the plating erodes and builds-up on the face of the welding electrodes.
Due to their extensive programmability, small transformer size, and robustness, high frequency inverter power supplies are generally the best choice for automation applications.