Lincoln Electric LN-25, Service Manual

Page: 37 / 90

THEORY OF OPERATION E-4 E-4
LN-25
OPTIONAL CIRCUITS
CONTACTOR
The contactor , contactor PC board, and cold
inch switch are commonly incorporated in the
LN-25. This feature enables the user to have an
electrically ÒCOLDÓ gun even though the power
sources output terminals are electrically ÒHOTÓ.
Upon receiving a command from the control
board, the contactor PC board sends a current
signal to activate the contactor
. The signal
closes the welding current path from the cable
to the conductor block, making the gun
electrically ÒHOTÓ. The cold inch switch allows
the user to feed wire without closing the
contactor . In this manner , the electrode wire can
be fed through the gun with the gun tip
electrically ÒCOLDÓ. See Figure E.3.
GAS SOLENOID
The gas solenoid feature permits the LN-25 to
be used for gas metal arc welding (GMA
W)
processes. When the gun trigger circuit is
activated, the control board signals the solenoid
PC board to activate the gas solenoid, which
allows shielding gas to flow through the gun to
the arc.
FIGURE E.3 Ð OPTIONAL CIRCUITS.
ELECTRODE
INPUT CABLE
TO WORK
SENSING LEAD
P
O
L
A
R
I
T
Y
S
W
I
T
C
H
VOLT
METER
CONTROL
BOARD
WIRE FEED
MODE SWITCH
SOLENOID
PC BOARD
GAS
SOLENOID
WIRE SPEED
CONTROL
RANGE
SWITCH
CONDUCTOR
BLOCK
M
O
T
O
R
HALL
EFFECT
MODULE
GUN
TRIGGER
CONNECTOR
OPTIONAL
CONTACTOR
BOARD
COLD
INCH
SWITCH
OPTIONAL
CONTACTOR
GUN CABLE
RPM FEEDBACK
ARMATURE VOLTAGE
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.