Protective Circuits; Overload Protection; Current Limiting Circuit - Lincoln Electric SVM 106-A Service Manual

E-6
CIRCUIT
BREAKER
FROM
115 VAC
WELDING
POWER
SUPPLY

PROTECTIVE CIRCUITS

Protective circuits are designed in to the
LN-7 GMA to detect trouble and shut down
the wire feeder before any damage to the
feeder can result. The wire feeder contains
overload protection for the entire machine, a
current limiting circuit for the feed motor, and
a ground lead protection circuit.

OVERLOAD PROTECTION

The wire feeder is equipped with a circuit
breaker in the 115 Vac input power circuit to
protect the feeder in the event of an electrical
fault. Refer to Figure E.5. If the feeder draws
more than 2.5A, the circuit breaker will trip to
prevent any damage to the wire feeder.
NOTE: Unshaded areas of block logic diagrams are the subject of discussion.
LN-7 GMA WIRE FEEDER
THEORY OF OPERATION
FIGURE E.5 – PROTECTIVE CIRCUITS.
OPTIONAL
METER KIT
8.8 VAC
TRIGGER
TRANS-
FORMER
DIODE
24 VAC
RECTIFIER
24 VDC
NETWORK
WIRE
SPEED
CONTROL
OPTIONAL
GAS
TIMER OR
SOLENOID
BURNBACK KIT
115 VAC
SCR CURRENT
POWER LIMITING
CIRCUIT CIRCUIT
115 VAC
CONTROL
BOARD
CR1
CONTROL
RELAY
GROUND
LEAD
PROTECTOR

CURRENT LIMITING CIRCUIT

The current limiting circuit limits the current
that is sent to the feed motor. A precision
resistor in line with the feed motor produces
a voltage drop that is directly proportional to
the current draw of the motor. If the signal
exceeds 10VDC, which equates to a 10A
draw from the feed motor, the current limiter
sends a signal to the SCR power circuit to
limit feed motor current to 10A. Refer to
Figure E.5.
5-95 VDC
WIRE DRIVE
MOTOR
TO WELDING
CONTACTOR
GUN
TRIGGER