Ac Welding Output - Lincoln Electric PRECISION TIG 185 SVM169-A Service Manual

E-6
Rotating the polarity switch to the AC position changes the welding power circuit. One lead (X1) of the main
transformer secondary is connected to the machine output work terminal. The other secondary lead (X2) is
connected to one of the AC connections on the SCR bridge. The electrode terminal is connected to the other
AC side of the bridge. The choke is now electrically across the negative and positive SCR bridge connections.
With the ability of the choke to store energy and the SCRs to turn on at the appropriate times, an AC square
PRIMARY
1Ø
FIGURE E.6 AC Square Wave Welding Current Generation.
THEORY OF OPERATION

AC WELDING OUTPUT

wave is developed and applied to the output terminals.
CHOKE
G
G
PRECISION TIG 185
G
G
E-6
ELECTRODE
AC
DC
WORK