Ac Welding Output - Lincoln Electric SQUARE WAVE SVM141-A Service Manual

E-6
INPUT
RECONNECT POWER
PANEL SWITCH
"A"
115VAC
RECEPTACLE

AC WELDING OUTPUT

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's
output work terminal. The other secondary lead (X2) is
connected to one of the AC connections of the SCR
bridge. The electrode terminal is connected to the
other AC side of the bridge. The choke is now electri-
cally across the negative and positive SCR bridge con-
nections. With the ability of the choke to store energy
and the SCRs to turn on at the appropriate times, an
AC square wave is developed and applied to the out-
put terminals.
FIGURE E.8 – AC SQUARE WAVE WELDING CURRENT GENERATION
PRIMARY
1Ø
THEORY OF OPERATION
FIGURE E.7 – AC WELDING OUTPUT
MAIN
TRANSFORMER
H1
X1
H2
X2
H3
H4
23VAC
18VAC
18VAC
115VAC
FAN
REMOTE
RECEPTACLE
DOWNSLOPE
CONTROL
SQUARE WAVE TIG 275
BY-PASS
BOARD
POLARITY
SWITCH
C
H
O
AC DC+
K
SCR
E
BRIDGE
SHUNT
DC-
AC
F
E
E
D
B
A
C
K
CONTROL
BOARD
GAS POSTFLOW OUTPUT
BALANCE
VALVE CONTROL CONTROL
CONTROL
CHOKE
WORK
ELECTRODE
HI-FREQUENCY
TRANSFORMER
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
115VAC
MODE
SWITCH
THERMAL
LIGHT
THERMOSTATS
ELECTRODE
WORK
E-6
DC