Single-phase input power is brought into the rear of the
Power MIG 350MP 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 350MP for either 230V, 460V, or 575V input sup-
ply power. An ON/OFF line switch is located on the
front panel. When the line switch is ON, AC input volt-
age is applied to the primary winding of the main trans-
former. The main transformer converts the high volt-
age, low current input power to a low voltage, high cur-
rent output. The main transformer also has two isolat-
ed auxiliary windings. One supplies 30 VAC to a Diode
Control Rectifier, which converts the 30 VAC to 40 VDC
to supply 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. The 115 VAC winding also
supplies power to the 115 VAC auxiliary receptacle
located on the back of the machine. This offers 15
amps of auxiliary power. (See Thermal and Overload
Protection)

THEORY OF OPERATION

E-3

POWER MIG 350MP

FIGURE E.3 – INPUT VOLTAGE AND MAIN TRANSFORMER

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)

GAS
SOLENOID

115 VAC AUX.
RECEPTACLE

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