Theory Of Operation - Lincoln Electric INVERTEC V275-S Service Manual

E-2
FIGURE E.2 – GENERAL DESCRIPTION, INPUT BOARD & AUXILIARY TRANSFORMER
Input Switch
Input
& 100A Breaker Rectifier
+
-
-
Aux.
Trans
Fan
Relay
Fan Fan
Motor
Motor
230VAC 230VAC
6
Pin
Amphenol
GENERAL DESCRIPTION
The Invertec V275-S is an inverter based welding
power source that offers multi-mode (TIG and Stick)
constant current welding and is rated at 275 amps at
31VDC at a 35% duty cycle.
operated on either single phase or three phase input
power. The welding response of this Invertec has been
optimized for the stick (SMAW) and TIG (GTAW) weld-
ing processes.
INPUT LINE VOLTAGE, AUXILIARY
TRANSFORMER, AND PRECHARGE
The Invertec V275-S can be connected to a variety of
three-phase or single-phase input voltages. The initial
power is applied to the V275-S through a line switch
located on the front of the machine. Two phases of the
input voltage are applied to the auxiliary transformer.
The auxiliary transformer develops an 18VAC sec-
ondary voltage. This 18VAC is applied to the control
board and is rectified and regulated to power the elec-
tronic circuits that are incorporated in the control
board.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.

THEORY OF OPERATION

Main Switch Board
Reconnect
Switch
IGBT Drive Signal
Precharge Relay Control
To
Shut Down Signal
Fan
Motors
18 VAC
Relay Control
The machine can be
V275-S
#1 Primary
Current
Feedback
Choke
To Control
Board
#2 Primary
Current
Feedback
Output
Diodes
#1 Primary
Current
Feedback
Control Board
Hot
Arc
Output
Mode
Start
Force Control
The input voltage is rectified by the input rectifier and
the resultant DC voltage is applied to the switch board
via the reconnect switch assembly located at the left
side of the machine. The reconnect switches connect
the two input capacitors either in a parallel (lower volt-
age) or in a series (higher voltage) configuration to
accommodate the applied input voltage.
When the machine is first turned on a precharge
sequence is initiated. During the precharge time the
DC input voltage is applied to the input capacitors
through a current limiting circuit that is located on the
switch board. The input capacitors are charged slow-
ly and current limited. An over or under voltage pro-
tection circuit located on the switch board monitors
the capacitor voltages. This protection signal is cou-
pled to the control board. When the input capacitors
have charged to an acceptable level, the control board
energizes the input relay located on the switch board,
making all of the input power, without current limiting,
available to the input capacitors. If the capacitors
become under or over voltaged the control board will
de-energize the input relay and the V275-S output will
be disabled.
E-2
Positive
+
Output
Terminal
Negative
-
Shunt
Output
Terminal
Thermostats
Thermo.
LED
Local
Remote