E-8

THEORY OF OPERATION

E-8

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PROTECTIVE CIRCUITS

Protective circuits are designed into the PRECISION TIG 185 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. Fan as needed (F.A.N.) Fan runs for 5 seconds at power-up and stops at idle 8 minutes after welding.

THERMAL PROTECTION

9. OVER TEMPERATURE LIGHT-

If the welder

overheats due to blocked air flow,

high ambient air

temperature, or exceeded duty cycle, an internal ther- mostat will open disabling the welding output and this yellow light will illuminate. The cooling fans will contin- ue to run to cool the unit during this time. The light will go out when the unit cools and the thermostat resets. Once the light goes out, the machine will again become available to weld.

Once the machine cools sufficiently the thermostats are self-resetting. If the thermostat shutdown is caused

by excessive output or duty cycle and the fan is oper- ating 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, then 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 200 amps.

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PRECISION TIG 185

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Lincoln Electric SVM169-A service manual Protective Circuits, Thermal Protection, Overload Protection