Thermal Protection, Protective Circuits | Lincoln Electric SVM156-A

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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 output rectifier, one on the DC bus, and one on the output choke. Excessive temperatures may be caused by a lack of cooling air or by operating the machine beyond its duty cycle or out- put rating. 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 intake air louvers are obstructed, the power must be removed from the machine and the fan condi- tion or air obstruction corrected. On later production machines (above code 10500) the cooling fan runs only when necessary. The F.A.N. (fan as needed) sys- tem is controlled by the Control Board via a solid state relay.

PROTECTIVE CIRCUITS

Protective circuits are designed into the Power Wave 455/R to sense trouble and shut down the machine before damage occurs to the machine’s internal com- ponents.

OVER CURRENT PROTECTION

If the average current exceeds 570 amps, the peak cur- rent will be limited to 100 amps until the average cur- rent decreases to under 50 amps or the system is re- triggered.

UNDER/OVER VOLTAGE

PROTECTION

A protective circuit is included on the Control Board to monitor the voltage across the input capacitors. In the event that a capacitor voltage is too high, too low, or becomes unbalanced side-to-side, the protection cir- cuit will de-energize the input contactor. Machine out- put will be disabled, and the "soft start" mode will be repeated. The protection circuit will prevent output if any of the following circumstances occur.

1.Capacitor conditioning is required. (This may be required if the machine has been off for a long peri- od of time and is connected for high input voltage operation.)

2.Voltage across a capacitor exceeds 390 volts. (This could result from high line surges or improper input voltage connections.)

3.Voltage across a capacitor is under 70 volts. (This would be due to improper input voltage connec- tions.)

4.Internal component damage.