Thermostats protect the machine from excessive
operating temperatures. Excessive temperatures
may be caused by a lack of cooling air or by operat-
ing the machine beyond it’s duty cycle or output rat-
ing. If excessive operating temperature should occur,
the thermostat will open and prevent output. The
meter will remain on during this time. Thermostats
will normally self-reset once the machine cools suffi-
ciently.

If the thermal shutdown was caused by excessive
output or duty cycle and the fan is operating normal-
ly, the Power Switch may be left on and the reset
should occur within a 15-minute period. If the fan is
not turning or the air intake louvers were obstructed,
then the power must be switched off for 15 minutes
in order to reset. The fan problem or air obstruction
must also be corrected.

PROTECTIVE CIRCUITS

Protective circuits are designed into the Invertec
machine to sense trouble and shut down the machine
before the trouble damages the internal machine
components. Both overload and thermal protection
circuits are included.

OVERLOAD PROTECTION

The machine is electronically protected from produc-
ing excessive output current. Should the output cur-
rent exceed 340 to 360 amps, an electronic protec-
tion circuit will reduce the current to approximately
150 amps. Lincoln Electric refers to this current
reduction as “Fold Back.” The machine will continue
to produce this low current until the protection circuit
is reset by removing the load.

Another protection circuit is included to monitor the
voltage across input filter capacitors. In the event
that the capacitor voltage is too high, the protection
circuit will signal the Control Board to prevent output.
The protection circuit may prevent output, if any of
these circumstances occur:

1. Capacitor conditioning is required

(Required if machine has been off for prolonged
periods of time.)

2. Line surges over 500 VAC

3. Internal Component damage

4. Improper connections