Thermal Protection; Protective Circuits - Lincoln Electric POWER WAVE SVM173-A Service Manual

E-9

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.
THEORY OF OPERATION
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
2. Voltage across a capacitor exceeds 390 volts. (This
3. Voltage across a capacitor is under 70 volts. (This
4. Internal component damage.
POWER WAVE 455M/MSTT
required if the machine has been off for a long peri-
od of time and is connected for high input voltage
operation.)
could result from high line surges or improper input
voltage connections.)
would be due to improper input voltage connec-
tions.)
E-9