Theory Of Operation; General Description; Input Power Circuits - Lincoln Electric NA-3 Service Manual

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GENERAL DESCRIPTION

The NA-3 and NA-4 are fully automatic wire
feed control units. The NA-3 can be used with
either a constant current or a constant
voltage DC power source. The NA-4 is to be
used only with a constant current AC power
source.
These control boxes are designed to be used
with a variety of wire feeder heads, contact
nozzles, and welding processes.
CIRCUIT
BREAKER
115 VAC
115 VAC
FROM
WELDING
POWER
SOURCE
115 VAC

THEORY OF OPERATION

FIGURE E.1 – INPUT POWER CIRCUIT.
TRAVEL
RECEPTACLE
TRAVEL
SWITCH
115 VAC
2CR TRAVEL
RELAY CONTACTS
INCH UP
SWITCH
R1
CONTROL
115 VAC
VARIABLE VOLTAGE
BOARD
115 VAC
ELECTRODE
VOLTAGE
SENSING
LEADS
WORK
115 VAC
NA-3 AND NA-4

INPUT POWER CIRCUITS

The NA-3 and NA-4 control units are supplied
with 115 VAC power usually from the welding
power source. The 115 VAC power is
connected to the control box circuitry through
the on/off "Control Power" switch and a
5 Amp circuit breaker. The input power is
then applied to the variable voltage board
and through resistor R1 to the control board.
The 115 VAC is rectified and regulated by the
control board, which supplies 24 VDC to the
logic board.
The 115 VAC input power is also coupled to
the travel receptacle through the travel relay
(2CR) and the travel switch. See Figure E.1.
115 VAC
WIRE
DRIVE
MOTOR
LOGIC CONTROL
BOARD
SIGNALS
24 VDC
ARC VOLTAGE
SENSING SIGNALS
START
SWITCH
STOP
SWITCH
INCH
DOWN
SWITCH
WIRE FEED
ARC SPEED CONTROL
VOLTAGE
METER
WELD CURRENT SENSING
REED SWITCH 4CR
OPTIONAL
START
BOARD
OPTIONAL
CRATER
FILL
BOARD
LOGIC
BOARD
1CR
2CR
3CR
POWER SOURCE
OUTPUT CONTROL
115 VAC
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