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GENERAL DESCRIPTION
The DC-400 is a multiprocess welder power source
capable of both constant voltage and constant current
operation. Its power system is SCR controlled with
solid state electronic circuitry. Minimum to maximum
output is obtained with a single potentiometer control.
INPUT LINE VOLTAGE,
CONTACTOR AND MAIN
TRANSFORMER
The desired three-phase input power is connected to
the DC-400 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 trans-
former, which, through the power switch, supplies
power to activate the input contactor.
A reconnect panel allows the user to configure the
machine for the desired input voltage. This AC input
voltage is applied to the primary of the main trans-
former.
The transformer changes the high voltage, low current
input power to a lower voltage, higher current output.
The finishes or “neutrals” of the main secondary coils
are connected together, and the three starts of the
secondary windings are connected to the rectifier
bridge assembly. In addition, the main transformer has
separate and isolated 115VAC and 42VAC auxiliary
windings. The 115VAC winding supplies power to the
cooling fan and also offers 10 amps of auxiliary power,
at the terminal strip and 14 pin amphenol, to operate
wire feeding equipment. The 42VAC auxiliary power is
available at the 14 pin amphenol only and is protected
by a 10 amp circuit breaker. The three 21VAC phase
angle windings are also housed in the main trans-
former assembly. These windings provide power and
“timing” for the control board.
THEORY OF OPERATION
E-2 E-2
LINCOLN
®
ELECTRIC
IDEALARC DC-400
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FIGURE E.2 – INPUT LINE VOLTAGE, CONTACTOR AND MAIN TRANSFORMER
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
FAN
115VAC
42VAC
14 PIN
AMPHENOL
REMOTE
CONTROL
TO
CONTROL
BOARD
CONTROL BOARD
OUTPUT
CONTROL
ARC FORCE
CONTROL
CONTROL
TRANSFORMER
POWER
SWITCH
R
E
C
O
N
N
E
C
T
INPUT
CONTACTOR
T
E
R
M
I
N
A
L
S
T
R
I
P
TRANSFORMER
MAIN
SCR DIODE
HYBRIDBRIDGE
/
PART
OF
MODE
SWITCH
CAPACITORS
SHUNT
REED
SWITCH
START
BOARD
PART
OF
MODE
SWITCH
OUTPUT
CHOKE
NEGATIVE
OUTPUT
TERMINAL
POSITIVE
OUTPUT
TERMINAL
PART OF
MODE
SWITCH
OUTPUT
G
A
T
E
S
I
G
N
A
L
S
FEEDBACK
F
E
E
D
B
A
C
K