Wire Drive Motor And Feedback - Lincoln Electric POWER MIG SVM170-A Service Manual

E-5
FIGURE E.5 — WIRE DRIVE MOTOR AND FEEDBACK.
AUX
115 VAC
LINE
SWITCH
RECONNECT
TRANSFORMER
WIRE DRIVE MOTOR
AND FEEDBACK
The wire drive motor is controlled by the control board.
A motor speed feedback signal is generated at the
motor tach and sent to the control board. The control
board compares this feedback signal with the com-
mands set forth by the Wire Speed Control poten-
tiometer and sends the appropriate armature voltage to
THEORY OF OPERATION
GAS
MOTOR
SOLENOID
WIRE
SPEED
CONTROL
ARC
BOARD
VOLTAGE
RECTIFIER
DIODE
G
BRIDGE
A
T
30 VAC
E
SNUBBER
S
BOARD
I
G
N
A
L
POWER
ENHANCEMENT
CHOKE
MAIN
SCR
RECTIFIER
NOTE: Unshaded areas of Block Logic
Diagram are the subject of discussion
POWER MIG 255C
SPOOL
FAN
GUN
WIRE
DRIVE
MOTOR
TACH
GUN TRIGGER
FEEDBACK
C OUTPUT
POSITIVE
F
A CHOKE
TERMINAL
E
P
E
A
D
C
B
I
A
T
C
O
NEGATIVE
K
R
TERMINAL
S
SHUNT
the wire drive motor. The drive motor speed is thus
controlled which in turn regulates the electrode wire
feed speed through the gun.
The control board also provides a 3-24 VDC operating
voltage for the optional spool gun. To achieve full WFS
control at the spool gun, the WFS knob on front of the
PM-255C must be set at max.
E-5