GENERAL DESCRIPTION
The CV-655 is a three-phase, SCR controlled con-
stant voltage DC power source. It is rated at 650
amps, 100% duty cycle with outstanding arc charac-
teristics for multiple welding processes.
INPUT LINE, CONTACTOR,
RECONNECT, FAULT PROTECTION
AND TRANSFORMERS
The desired three-phase input power is connected to
the CV-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
supplies 115 VAC power to the control board trans-
former and to the input contactor. 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
windings, which provide power and “timing” to the fir-
ing 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
CV-655
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FIGURE E.2 – INPUT LINE VOLTAGE, CONTACTOR, RECONNECT,
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
115VAC
MAIN
TRANSFORMER
CONTROL
BOARD
SHUNT
OUTPUT
CONTROL
SWITCH
POSITIVE
TERMINAL
NEGATIVE
TERMINAL
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
LOW
FIRING
BOARD
SNUBBER
FAN
BOARD
CONTROL
BOARD
TRANSFORMER
CR1
CHOKE
14-pin
Amphenol
115VAC
Receptacle
Fan
Motor
Fan
Thermal
Sensor
42VAC 10VAC10VAC
32VAC
32VAC
32VAC
SIGNAL
G
A
T
E
S
I
G
N
A
L
GATE SIGNAL
OUTPUT
CONTROL
CAPACITORS
OUTPUT
CONTROL
R
E
A
C
T
O
R
