Protection Circuits - Lincoln Electric PRO-CUT 55 SVM140-A Service Manual

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PROTECTION CIRCUITS

Protection circuits are designed into the Pro-Cut 55
machine to sense trouble and shut down the machine
before the trouble damages internal machine compo-
nents. Both overload and thermal protection circuits
are included.
OVERLOAD PROTECTION
The Pro-Cut 55 is electrically protected from produc-
ing higher than normal output currents. If the output
current exceeds 50-60 amps, an electronic protection
circuit limits the current to within the capabilities of
the machine.
Another protection circuit monitors the voltage across
the input filter capacitors. If the filter capacitor voltage
is too high, too low or not balanced the protection cir-
cuit may prevent machine output.
THEORY OF OPERATION
THERMAL PROTECTION
Two thermostats protect the machine from excessive
operating temperatures. One thermostat is located on
the output choke and the other on the power board
IGBT heat sink.
caused by a lack of cooling air or by operating the
machine beyond the duty cycle and output rating. If
excessive operating temperatures should occur, the
thermal status indicator will light and the thermostat
will prevent output voltage or current.
Thermostats are self-resetting once the machine cools
sufficiently. If the thermostat shutdown was caused
by excessive output or duty cycle and the fans are
operating normally, the power switch may be left on
and the reset should occur within a 15 minute period.
If the fan or fans are not turning or the air intake lou-
vers are obstructed, the input power must be removed
and the fan problem or air obstruction must be cor-
rected.
PRO-CUT 55
Excessive temperatures may be
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