Theory of operation, General description, Input line voltage, contactor and main transformer – Lincoln Electric IDEALARC R3R-500 User Manual
Page 30
GENERAL DESCRIPTION
The Idealarc R3R welder is a three-phase transformer
rectifier type constant current power source designed
for DC manual welding and air carbon arc cutting. Its
power system is SCR controlled with solid state elec-
tronic 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 R3R 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 primary of the
control transformer. The secondary of the control
transformer supplies 120VAC power, via the power
switch and thermostats, to activate the input contac-
tor.
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, three 66VAC phase
angle windings are housed in the main transformer
assembly. These windings provide power and “timing”
for the control board. Two of these coils provide
120VAC for the fan motor.
THEORY OF OPERATION
E-2
E-2
IDEALARC R3R
FIGURE E.2 – INPUT LINE VOLTAGE, CONTACTOR AND MAIN TRANSFORMER
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
CONTROL BOARD
OUTPUT
CONTROL
ARC FORCE
CONTROL
CONTROL
TRANSFORMER
POWER
SWITCH
R
E
C
O
N
N
E
C
T
INPUT
CONTACTOR
TRANSFORMER
MAIN
SCR
DIODE
HYBRID BRIDGE
/
SHUNT
OUTPUT
CHOKE
NEGATIVE
OUTPUT
TERMINAL
POSITIVE
OUTPUT
TERMINAL
G
A
T
E
S
I
G
N
A
L
S
FEEDBACK
F
E
E
D
B
A
C
K
THERMOSTATS
FAN
MOTOR
TERMINAL
STRIP
REMOTE
SWITCH
DIAL
SELECTOR
SWITCH
SNUBBER
BOARD
AMPHENOL
POLARITY
SWITCH
OPTIONAL
OPTIONAL
AMPTROL
PC BOARD
OPTIONAL
AMPTROL
TRANSFORMER