Protective Circuits - Lincoln Electric SQUARE WAVE SVM141-A Service Manual

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THEORY OF OPERATION

PROTECTIVE CIRCUITS

Protective circuits are designed into the Square Wave
TIG 275 to sense trouble and shut down the machine
before the trouble damages the internal machine com-
ponents. Both thermal protection and current overload
are included.
THERMAL PROTECTION
Thermostats protect the machine from excessive oper-
ating temperatures. Excessive operating temperatures
may be caused by a lack of cooling air or by operating
the machine beyond the duty cycle and output rating.
If excessive operating temperature should occur, caus-
ing a thermostat to open, the Thermal Light will illumi-
nate, the fan will continue to run and welding output will
be disabled. Once the machine cools sufficiently, the
thermostats are self-resetting. If the shutdown is
caused by excessive output or duty cycle and the fan
is operating normally, the power may be left on and the
reset should occur within a 15 minute period. If the fan
is not functioning properly or the air intake louvers are
obstructed, the input power must be removed and the
fan problem or air obstruction corrected.
OVERLOAD PROTECTION
The machine is electronically protected from producing
excessively high output currents. The output is limited
to 350 amps.
SQUARE WAVE TIG 275