Theory of operation, Protection circuits – Lincoln Electric PRECISION TIG 275 SVM162-B User Manual
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PRECISION TIG 275
PROTECTION CIRCUITS
Protection circuits are designed into the PRECISION
Tig 275 machine to sense trouble and shut down the
machine before the trouble damages internal machine
components. Both thermal protection and current over-
load are included.
FAN-AS-NEEDED (F.A.N.)
The PRECISION Tig 275 has the F.A.N. circuit feature,
which means that the cooling fan will operate only
while welding; then for about eight minutes after weld-
ing has stopped to assure proper machine cooling.
This helps reduce the amount of dirt and dust drawn
into the machine along with the cooling air. The cooling
fan will operate briefly when the machine power is ini-
tially turned on, and continuously while the yellow
Thermal shutdown light is lit.
THERMAL PROTECTION
This welder has thermostatic protection from excessive
duty cycles, overloads, loss of cooling and excessive
ambient temperatures. When the welder is subjected
to an overload, or inadequate cooling, the primary coil
thermostat and/or secondary coil thermostat will open.
This condition will be indicated by the illumination of
the yellow Thermal Shutdown light on the front panel.
The fan will continue to run to cool the power source.
Postflow occurs when Tig welding is shut down, but no
welding is possible until the machine is allowed to cool
and the yellow Thermal Shutdown light goes out. Once
the machine cools sufficiently, the thermostats are self-
resetting. If the shutdown is caused by excessive out-
put or duty cycle and the fan is operating normally, the
power may be left on and the reset should occur with-
in a 15 minute period. If the fan is not functioning prop-
erly 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.
THEORY OF OPERATION