Lincoln Electric LN-15 WIRE FEEDER SVM166-A Service Manual page 35

E-3
ELECTRODE
INPUT VOLTAGE
TOROID
ASSEMBLY
FULL
WAVE
BRIDGE
ON/OFF
SWITCH
WORK
SENSING
LEAD
"WORK" VOLTAGE FEEDBACK #21
TRIGGER AND CONTROL CIRCUITS
When the gun trigger is closed (activated) the Feed
Head Board is "signaled" to apply armature voltage
to the drive motor, activate the gas solenoid and
close the LN-15 internal contactor. When the con-
tactor is closed the welding current path from the
electrode cable to the conductor block is completed.
This sequence will supply electrode wire, arc voltage
and current to the welding gun.
The Cold Inch/Gas Purge Switch allows the user to
feed wire without closing the contactor. This feature
gives the operator an electrically "cold" electrode
even though the power source's output terminals are
electrically "hot". This switch also allows the user to
activate the gas solenoid without feeding wire or
closing the contactor.
When activated the Trigger Interlock Switch keeps
the gun trigger circuit closed even when the operator
releases the trigger. This is useful when making long
welds.
NOTE: Unshaded areas of Block Logic Diagram are the subject of discussion.
THEORY OF OPERATION
FIGURE E.3 – TRIGGER & CONTROL CIRCUITS
CONTACTOR
FEED HEAD
BOARD SUPPLY
BOOST
POWER
SUPPLY
MOV
BOARD
DRIVE MOTOR
SUPPLY
LN-15
GAS
SOLENOID
"ELECTRODE"
FEEDBACK
VOLTAGE #67
ARMATURE
FEED HEAD
CONTROL BOARD
TRIGGER TRIGGER
COLD
WIRE
INPUT &
INTERLOCK
INCH
FEED
PROCEDURE SWITCH
SWITCH
SPEED
CONTROL
E-3
WELDING
FEED
PLATE
M
O
HALL
T
O EFFECT
R
MODULE
RPM FEEDBACK
SPI COMMUNICATIONS
SHIELDED CABLE
DISPLAY
BOARD