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PRECISION TIG 185
THEORY OF OPERATION
E-2 E-2
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INPUT POWER CIRCUIT
The desired single-phase input power is connected to
the TIG 185 through an input power switch located in
the front panel of the machine. The machine can be
configured for either 230VAC or 208VAC input voltage
by connecting the appropriate lead (H2 or H3) to the
input power switch. When the input power switch is
turned “ON” the input voltage is applied directly to the
primary of the main transformer.
The main transformer changes the high voltage, low
current input power to a low voltage, high current out-
put which is available at the main secondary winding
(X1 and X2). In addition three auxiliary windings are
incorporated in the main transformer. The 115VAC
winding supplies power to the fan motor and also,
through the control board, powers the gas solenoid
valve and the high voltage transformer. The 18VAC
winding provides power to the trigger circuitry. The
other 18VAC winding is rectified and regulated to a
15VDC supply which operates the circuitry on the con-
trol board.
FIGURE E.2 Main Transformer and Input Power
INPUT
POWER
SWITCH
MAIN
TRANSFORMER
POLARITY
SWITCH
SCR
BRIDGE
X1
X2
AC
AC
DC+
DC-
CONTROL
BOARD
18VAC
18VAC
115VAC
FAN
REMOTE
RECEPTACLE
H1
H2
H3
SHUNT
115VAC
HIGH VOLTAGE
TRANSFORMER
CIRCUIT
BY-PASS
BOARD
HI-FREQUENCY
TRANSFORMER
C
H
O
K
E
WORK
ELECTRODE
THERMAL
LIGHT
GAS
VALVE
THERMO-
STATS
OUTPUT
CONTROL
MODE
SWITCH
POWER
"ON"
DIGITAL
DISPLAY
F
E
E
D
B
A
C
K
AUTO
BALANCE
LED
TIG
LED
STICK
LED
PULSE
FREQ.
LED
BYPASS
ASBLY
AC
BALANCE
CONTROL
PULSE
CONTROL
POSTFLOW
CONTROL
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
GENERAL DESCRIPTION
The PRECISION TIG 185 is a member of our field
acclaimed Precision TIG family of industrial arc weld-
ing power sources. Premium features include:
1. Precise constant current output.
2. Full range square wave AC/DC TIG (GTAW) weld-
ing.
3. Enhanced version of the patented MicroStart
TM
Technology for its lower Minimum (5amps) to high-
er Maximum (185 amps) output control range.
4. Built-in high frequency stabilization for DC TIG
starting and continuous AC TIG welding.
5. AC/DC Stick (SMAW capability.)