Lincoln Electric SVM118-A Protective Circuits, Thermal Protection, Overload Protection

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E-8 E-8

THEORY OF OPERATION

PROTECTIVE CIRCUITS

Protective circuits are designed into the Square Wave TIG 355 to sense trouble and shut down the machine before the trouble damages the internal machine com- ponents. Both thermal protection and current over- load are included.

THERMAL PROTECTION

Thermostats protect the machine from excessive operating temperatures. Excessive operating temper- atures may be caused by a lack of cooling air or by operating the machine beyond the duty cycle and out- put rating. If excessive operating temperature should occur, causing the secondary thermostat to open, the input contactor will shut the machine off. If the prima- ry thermostat opens, the machine will stay on (pilot light, meters and fans running), but output current will be limited to no more than 5 amps.

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 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, then the input power must be removed and the fan problem or air obstruction corrected.

OVERLOAD PROTECTION

The machine is electronically protected from produc- ing excessively high output currents. Should the out- put current exceed approximately 400 amps, an elec- tronic circuit will reduce and limit the output current. The machine will continue to limit the output current until the overload is removed.

SQUARE WAVE TIG 355