METHOD AND APPARATUS FOR DETECTING EFFECTIVE CURRENT IN SPOT WELDER

摘要

PURPOSE: An effective current detecting device of a spot welder and a detecting method thereof are provided to detect an effective current through a thyristor within the conduction angle of the thyristor. CONSTITUTION: A spot welder welds a weld metal with an electrode receiving current by controlling the firing angle of a thyristor corresponding to alternative voltage having a regular cycle. To detect the effective value of the current fed to the electrode, the thyristor is driven in a specific firing angle and a non-conduction angle is detected for informing the spot welder of the output point of maximum current. Then, effective current is detected from the non-conduction angle and a power factor angle is detected according to the firing angle and the non-conduction angle. A constant K standing for the ratio of the maximum current to effective current, is detected according to the power factor angle and the non-conduction angle. Finally, the maximum current is multiplied by the constant and the effective current is obtained.