Theory Of Operation - Lincoln Electric SVM188-A Service Manual

E-2
CONTROL POWER
TRANSFORMER
SWITCH
115VAC
•
Pilot
Light
w
CR2
•
Secondary
Thermostat
Primary
Theromstat
1CR Coil
CONTACTOR
CR1
GENERAL DESCRIPTION
The DC-600 is a three-phase, SCR controlled DC
power source. It is capable of either constant current
or constant voltage output. It is rated at 600 amps,
100% duty cycle with outstanding arc characteristics
for multiple welding processes.
INPUT CIRCUIT AND MAIN TRANS-
FORMER
The desired three-phase input power is connected to
the DC-600 through an input contactor located in the
input box at the rear of the machine. Two phases of the
input line are also connected to the control transformer.
The secondary of the control transformer supplies 115
VAC power to the control board and to the input con-
tactor through the fault protection relay.

THEORY OF OPERATION

FIGURE E.2 - INPUT AND TRANSFORMER
FAULT PROTECTION
32VAC
32VAC
32VAC
14-pin
115VAC
Amphenol Receptacle
T • 115VAC
S
E
T
R
R
M
I
I
P
N
A
2
L
42VAC
115VAC
MAIN
TRANSFORMER
R
E
C
O
N
N
E
C
T
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
DC-600
OUTPUT
CONTROL SIGNAL
FIRING
BOARD
S
G
I
A
Fan G
T
Motor N
E
A
L
CONTROL
OUTPUT
TERMINAL
SWITCH
SHUNT
LATCHING
RESISTOR
SCR BRIDGE
CHOKE
A reconnect panel allows the user to configure the
machine for the desired input voltage. This three-
phase AC input is applied to the primary of the main
transformer. The transformer changes the high voltage,
low current input power to a lower voltage, higher cur-
rent output. The finishes or "neutrals" of the main sec-
ondary coils are connected together, and the six starts
of the secondary windings are connected to the SCR
rectifier assembly.
In addition, the main transformer also has five isolated
secondary windings. There are three 32 VAC windings,
which provide power and "timing" to the firing board.
The 115 VAC winding powers the fan motor and pro-
vides the user with up to 20 amps of 115 VAC auxiliary
power at the receptacle or 14-pin MS type connector.
The 42 VAC winding provides 10 amps of power to the
14 pin MS type connector to power a wire feeder.
TERMINAL
STRIP 1
OUTPUT
CONTROL
SWITCH
OUTPUT
CONTROL
BOARD MODE
SWITCH
F
E
E
D
B
A
C
POSITIVE
K
TERMINAL
F
E
E
D
B
A
C NEGATIVE
TERMINAL
K
E-2