Variable Voltage Board - Lincoln Electric NA-3 Service Manual

E-4
VARIABLE VOLTAGE
BOARD
Arc voltage is monitored by the voltmeter
and variable voltage board. When the NA-3
and NA-4 are being operated in the constant
current mode, the variable voltage board is
essential in the control of the wire feed
speed. As the arc length changes, the arc
voltage will also change. The variable
voltage board recognizes this change and
signals the logic board to either increase or
decrease the wire feed speed depending on
CIRCUIT
BREAKER
115 VAC
115 VAC
FROM
WELDING
POWER
SOURCE
115 VAC
115 VAC
THEORY OF OPERATION
FIGURE E.3 – VARIABLE VOLTAGE BOARD.
TRAVEL
RECEPTACLE
TRAVEL
SWITCH
115 VAC
2CR TRAVEL
RELAY CONTACTS
INCH UP
SWITCH
R1
CONTROL
BOARD
115 VAC
VARIABLE VOLTAGE
BOARD
115 VAC
ELECTRODE
VOLTAGE
SENSING
LEADS
WORK
NA-3 AND NA-4
the arc length. This function is necessary to
maintain a constant electrode arc length and
a stable, high quality weld.
The variable voltage board also generates a
low DC voltage that is applied to the
electrode during the inch down mode. When
the electrode makes contact with the work
piece, this low voltage is "loaded down",
signaling the control circuitry to stop the
wire feed motor. This feature allows the
operator to utilize "work touch sensing". See
Figure E.3.
115 VAC
WELD CURRENT SENSING
REED SWITCH 4CR
WIRE
DRIVE
MOTOR
LOGIC CONTROL
SIGNALS
24 VDC
ARC VOLTAGE
LOGIC
SENSING SIGNALS
BOARD
START
SWITCH
STOP
SWITCH
INCH
DOWN
SWITCH
WIRE FEED
SPEED CONTROL
ARC
VOLTAGE
METER
E-4
OPTIONAL
START
BOARD
OPTIONAL
CRATER
FILL
BOARD
1 CR
2 CR
3 CR
POWER SOURCE
OUTPUT CONTROL
115 VAC