Automatic voltage compensator for resistance welding control

AMONG the more recent developments in a-c resistance welding control is the voltage compensator. This compensator is an auxiliary control used in conjunction with a standard type of phase-controlled welding panel, the circuit of which is shown in Figure 1. The function of the voltage compensator is to maintain the weld current substantially constant irrespective of line-voltage variations. The inability to obtain new feeders and the burden of added loads in war plants have in many cases made the power systems incapable of supplying several welding machines simultaneously without experiencing an appreciable drop in line voltage. Welding heat, which varies with current squared, will be reduced by 19 per cent for a ten per cent drop in line voltage; a line drop of 20 per cent will reduce the welding heat 36 per cent which is intolerable for consistent welding. These conditions can be remedied by the addition of a small inexpensive auxiliary control, such as the voltage compensator. The regulation of many overworked high reactance welding feeders can then be tolerated because consistent welds will be produced, whereas without proper compensation, poor welds would inevitably result. A compensator unit is shown in Figure 2 installed just in front of the current transformer in the bottom of a portable welding-machine control panel.