Protective Devices And Circuits - Lincoln Electric IDEALARC R3R-300 Service Manual

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PROTECTIVE DEVICES AND
CIRCUITS
Two thermostats protect the R3R from excessive
operating temperatures and overload conditions.
Excess operating temperatures may be caused by
insufficient cooling air or by operating the machine
beyond the duty cycle and output rating. One ther-
mostat is mounted on one of the main transformer
secondary leads. The other is mounted on the choke
assembly. These two thermostats are connected in
series with the input contactor coil. If either of the
thermostats opens, the input contactor will be de-
energized and the main transformer will be removed
from the input line. The amber High Temperature Light
will turn on and the machine will remain inoperative
until the thermostats cool and reset.
THEORY OF OPERATION
The R3R power sources are also protected against
output current overloads. This overload protection
circuit, located on the control board, will reduce the
welding current to a safe level if the machine is over-
loaded for two or three seconds.
If the control leads are accidentally grounded or short-
ed to the case of the machine, the welding output will
be low and no damage should occur to the control
board circuitry.
IDEALARC R3R
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