General Description; Input Power Circuit - Lincoln Electric PRECISION TIG SVM186-A Service Manual

E-2
INPUT
POWER
SWITCH
115 VAC
Receptacle
Circuit Breaker
Protected

GENERAL DESCRIPTION

The PRECISION TIG® 225 is a member of our field
acclaimed PRECISION TIG® family of industrial arc
welding power sources. Premium features include:
1. Precise constant current output.
2. Full range square wave AC/DC TIG (GTAW)
welding.
3. Enhanced version of the patented MicroStart
Technology for its lower Minimum (5amps) to high-
er Maximum (225 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.)
THEORY OF OPERATION
FIGURE E.2 - General Description & Input Power Circuit
MAIN
TRANSFORMER
BYPASS
ASBLY
H1
X1
H2
X2
H3
18VAC
18VAC
115VAC
FAN
REMOTE
RECEPTACLE
AUTO PULSE TIG STICK
BALANCE
FREQ. LED LED
LED LED
TM
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
PRECISION TIG® 225
BY-PASS
BOARD
POLARITY
SWITCH
C
H
O
AC DC+
K
SCR
E
BRIDGE
HIGH VOLTAGE
SHUNT
TRANSFORMER
AC DC-
F
E
E
D
B
A
C
K
115VAC
CONTROL
BOARD
THERMO-
THERMAL GAS OUTPUT
STATS
LIGHT VALVE CONTROL
AC
BALANCE
CONTROL

INPUT POWER CIRCUIT

The desired single-phase input power is connected to
the TIG 225 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.
winding supplies power to the fan motor, the 115 VAC
receptacle, and also, through the control board, pow-
ers the gas solenoid valve and the high voltage trans-
former. The 18VAC winding provides power to the trig-
ger circuitry. The other 18VAC winding is rectified and
regulated to a 15VDC supply which operates the cir-
cuitry on the control board.
WORK
ELECTRODE
HI-FREQUENCY
TRANSFORMER
CIRCUIT
POWER
"ON"
DIGITAL
DISPLAY
MODE
SWITCH
POSTFLOW
PULSE
CONTROL CONTROL
The 115VAC
E-2