THEORY OF OPERATION
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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.
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.
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