Thermal Protection, Protective Circuits | Lincoln Electric SVM159-A

E-6

THEORY OF OPERATION

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THERMAL PROTECTION

Three normally closed (NC) thermostats protect the machine from excessive operating temperatures. These thermostats are wired in series and are con- nected to the control board. One of the thermostats is located on the heat sink of the switch board, one is located on the output choke and the third thermostat is located on the DC Bus Board. Excessive tempera- tures may be caused by a lack of cooling air or oper- ating the machine beyond its duty cycle or output rat- ing. If excessive operating temperatures should occur, the thermostats will prevent output from the machine. The yellow thermal light, located on the front of the machine, will be illuminated. The thermostats are self- resetting once the machine cools sufficiently. If the thermostat shutdown was caused by excessive output or duty cycle and the fan is operating normally, the power switch may be left on and the reset should occur within a 15-minute period. If the fan is not turn- ing or the air intake louvers are obstructed, then the power must be removed from the machine, and the fan problem or air obstruction corrected.

PROTECTIVE CIRCUITS

Protective circuits are designed into the POWER WAVE 355/405 to sense trouble and shut down the machine before damage occurs to the machine's internal components.

OVER CURRENT

PROTECTION

If the average current exceeds 450 amps for one sec- ond, then the output will be limited to 100 amps until the load is removed. If the peak current exceeds 600 amps for 150 ms, the output will be limited to 100 amps until the load is removed.

UNDER/OVER VOLTAGE PROTECTION

Protective circuits are included on the switch and con- trol boards to monitor the voltage across the input capacitors. In the event that a capacitor pair voltage is too high, or too low, the machine output will be dis- abled. The protection circuits will prevent output if any of the following conditions exist.

1.Voltage across a capacitor pair exceeds 467 volts. (High line surges or improper input voltage connections.)

2.Voltage across a capacitor pair is under 190 volts. (Due to improper input voltage connections.)

3.Any major internal component damage.