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INPUT VOLTAGE AND MAIN TRANS-
FORMER
Single-phase input power is brought into the rear of the
Power MIG 300 through a three-prong plug and input
cable. A reconnect panel, also located on the rear of
the machine, allows the user to configure the Power
MIG 300 for either 230V, 460V, or 575V input supply
power. An ON/OFF line switch is located on the front
panel. When the line switch is ON, AC input voltage is
applied to the primary winding of the main transformer.
The main transformer converts the high voltage, low
current input power to a low voltage, high current out-
put. The main transformer also has two isolated auxil-
iary windings. One supplies 30 VAC to a Diode Control
Rectifier, which converts the 30 VAC to 40 VDC to sup-
ply the Power Board and the Spool Gun Board. The
Power Board in turn supplies 20
VDC to the Chopper Board and +15 VDC, -15 VDC and
+5 VDC to the Weld Control Board circuitry. The other
auxiliary winding provides 115 VAC to operate a ther-
mostatically controlled fan motor through a relay, which
also receives signals from the Weld Control Board.
The fan is designed to come on automatically when the
trigger is pulled. The fan will stay on as needed for a
minimum of six minutes after the weld arc is terminat-
ed. The fan will also stay on when the machine's weld-
ing and feeding are disabled during thermostatic over-
temperature protection. (See Thermal and Overload
Protection.)
THEORY OF OPERATION
E-3 E-3
POWER MIG 300
FIGURE E.3 – INPUT RECTIFIER, CHOPPER ASSEMBLY AND FEEDBACK
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
IGBT
+
LINE
SWITCH
RECONNECT
PANEL
MAIN
TRANSFORMER
RELAY
SPOOL
GUN
BOARD
FEEDER
BOARD
MSP
BOARD
ENCODER
BOARD
DISPLAY
BOARD
RS232
CONNECTOR
WELD CONTROL BOARD
SPOOL GUN
PUSH-PULL
SWITCH
WIRE DRIVE
MOTOR
OUTPUT
RECTIFIER
CHOPPER
ASSEMBLY
OUTPUT
CHOKE
CURRENT
TRANSDUCER
GUN
POS
OUTPUT
TERMINAL
NEG
OUTPUT
TERMINAL
POWER
BOARD
DIODE CONTROL
RECTIFIER
FAN
MOTOR
FOOT AMPTROL OR REMOTE (6-PIN AMPHENOL)
SPOOL GUN OR PUSH-PULL GUN (7-PIN AMPHENOL)
GAS
SOLENOID
SEC
THERMOSTATS
_
+
115
VAC
30
VAC
60
VAC
80
VAC
40 VDC
40
VDC
40 VDC
24 VDC
20 VDC
PWM
SIGNALS
+15/-15/+5 VDC
SHIELDED
CABLE
GUN TRIGGER AND THUMB SWITCH
SHIELDED CABLE AND SPI COMMUNICATIONS
ARCLINK
+5 VDC
CURRENT
FEEDBACK
VOLTAGE
FEEDBACK
FROM WELD
CONTROL BOARD
TO FAN RELAY
IGBT
DRIVE
T
A
C
H
CHOPPER
(Below code 10900)
Mechanical Encoders
(Above code 10900)