Lincoln Electric 11141 Service Manual page 44

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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 temperatures
may be caused by a lack of cooling air or operating the
machine beyond its duty cycle or output rating.
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 turning or
the air intake louvers are obstructed, then the power
must be removed from the machine, and the fan prob-
lem or air obstruction corrected.
PROTECTIVE CIRCUITS
Protective circuits are designed into the POWER
WAVE 355M/405M to sense trouble and shut down
®
the machine before damage occurs to the machine's
internal components.
THEORY OF OPERATION
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
If
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.
2. Voltage across a capacitor pair is under 190 volts.
3. Any major internal component damage.
POWER WAVE ® 355M/405M
(High line surges or improper input voltage con-
nections.)
(Due to improper input voltage connections.)
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