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GENERAL DESCRIPTION
The DC-655 is a three-phase, SCR controlled DC
power source. It is capable of either constant current
or constant voltage output. It is rated at 650 amps,
100% duty cycle with outstanding arc characteristics
for multiple welding processes.
INPUT LINE, CONTACTOR,
RECONNECT, FAULT PROTECTION
AND TRANSFORMERS
The desired three-phase input power is connected to
the DC-655 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. The secondary of the control transformer sup-
plies 115 VAC power to the control board transformer
and to the input contactor through the fault protection
relay. The control board transformer supplies 42 VAC
to the control board.
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 volt-
age, low current input power to a lower voltage, high-
er current output. The finishes or “neutrals” of the
main secondary coils are connected together, and the
six starts of the secondary windings are connected to
the rectifier assembly.
In addition, the main transformer also has eight isolat-
ed secondary windings. There are three 32 VAC wind-
ings, which provide power and “timing” to the firing
board. The 115 VAC winding powers the fan motor
and provides 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 up to 10
amps at the 14-pin MS type connector. Three other
isolated coils are used to power the optional digital
meter PC board. One winding is rated at 42 VAC, and
the other two are each rated at 10 VAC.
THEORY OF OPERATION
E-2 E-2
IDEALARC DC-655
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FIGURE E.2 – INPUT LINE VOLTAGE, CONTACTOR, RECONNECT,
FAULT PROTECTION, MAIN AND CONTROL TRANSFORMERS
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
CONTROL
TRANSFORMER
R
E
C
O
N
N
E
C
T
CONTACTOR
FAULT PROTECTION
115VAC
MAIN
TRANSFORMER
CONTROL
BOARD
SHUNT
OUTPUT
CONTROL
MODE
SWITCH
POSITIVE
TERMINAL
NEGATIVE
TERMINAL
LATCHING
RESISTOR
F
E
E
D
B
A
C
K
F
E
E
D
B
A
C
K
SCR BRIDGE
42VAC
115VAC
42VAC
T
E
R
M
I
N
A
L
S
T
R
I
P
TO OPTIONAL
METER BOARD
HIGH
LOW
ARC FORCE
CONTROL
FIRING
BOARD
SNUBBER
FAN
BOARD
CR2
CONTROL
BOARD
TRANSFORMER
CR1
CHOKE
14-pin
Amphenol
115VAC
Receptacle
Fan
Motor Fan
Thermal
Sensor
42VAC 10VAC
10VAC
32VAC
32VAC
32VAC
SIGNAL
G
A
T
E
S
I
G
N
A
L
GATE
SIGNAL
OUTPUT
CONTROL