Protection Circuits - Lincoln Electric PRO-CUT SVM146-A Service Manual

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PROTECTION CIRCUITS

Protection circuits are designed into the PRO-CUT 80
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 80 is electrically protected from pro-
ducing higher than normal output currents. If the out-
put current exceeds 85-90 amps, an electronic pro-
tection circuit limits the current to within the capabili-
ties 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 fan is oper-
ating 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, the input power must be removed and the
fan problem or air obstruction must be corrected.
PRO-CUT 80
Excessive temperatures may be
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