Duty cycle

In order to use the components of a resistance welding device economically and technically correctly, the duty cycle of the expected welding task must be taken into account. This is becoming increasingly important, especially due to the increased use of technologies that are advantageous for welding, such as medium frequency and direct current. The greatest possible safety against current overload (or thermal overload) is obtained by dimensioning the thyristor or inverter continuous currents equal to or even greater than the machine short-circuit current. In terms of economic efficiency, this can almost never be realised.

The thyristor or inverter is selected according to the primary current to be switched, the operating cycle time and the relative duty cycle. The manufacturer provides current load diagrams for the thyristors (power units) or inverters.

There, the output current is plotted as a function of the duty cycle. One must also consider the different integration times for determining the percentage duty cycle. For electronic components such as thyristors or power semiconductors in the inverter, 2 seconds are specified as integration time, for transformers 1 minute. However, with medium-frequency transformers, attention must be paid to the diodes in the rectifier, which are also specified with an integration time of 2 seconds. This means that when dimensioning medium frequency systems, 3 components must be considered: the inverter, the diodes in the rectifier set and the transformer itself.

Your Harms & Wende partner will help you with the dimensioning of your welding task, taking into account the duty cycle. Talk to us.