Theory Of Operation - Lincoln Electric LN-25 Service Manual

E-2
GENERAL DESCRIPTION
The LN-25™ is a portable semiautomatic wire
feeder designed to operate from a DC arc
ELECTRODE
INPUT CABLE
P
O S
L
W
A I
R T
TO WORK
I
C
SENSING LEAD T H
Y
CONTROL CIRCUIT
OPERATION
INPUT POWER CIRCUIT
The DC arc voltage from the power source is
applied to the LN-25™ through the electrode
cable and work sensing lead. This DC voltage is
connected to the polarity switch, which allows
the wire feeder to be used in either electrode
positive or electrode negative polarity. The
voltage is then coupled to the voltmeter and
control board. A wire feed mode switch is
included to give the user the capability of using
a constant voltage or, in some processes, a
constant current power source. See Figure E.2.
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
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THEORY OF OPERATION

FIGURE E.2 – INPUT POWER CIRCUIT.
COLD
OPTIONAL
INCH
CONTACTOR
SWITCH
BOARD
VOLT
METER
CONTROL
BOARD
WIRE FEED
MODE SWITCH
SOLENOID
PC BOARD
EARLY MODELS ONLY - LATER MODELS HAVE CIRCUITRY
voltage. It is designed for maximum versatility in
a variety of field applications. It can be used with
most constant voltage or constant current DC
power sources without the need of a control
cable.
OPTIONAL
CONTACTOR
CONDUCTOR
ARMATURE VOLTAGE
RPM FEEDBACK
RANGE
SWITCH
WIRE SPEED
CONTROL
GAS
SOLENOID
INCLUDED ON CONTROL BOARD
WELDING CURRENT CIRCUIT
The electrode voltage is also applied to the
conductor block through a heavy current
carrying cable. The welding gun cable is
connected to the conductor block. This
combination of welding cable, optional contactor,
conductor block and gun cable constitute the
welding current path to the electrode wire. See
Figure E.2.
LN-25™
GUN CABLE
BLOCK
GUN
M
O
TRIGGER
HALL
T
CONNECTOR
O
EFFECT
R
MODULE
E-2