Theory of operation – Lincoln Electric CLASSIC III SVM 137-A User Manual
Page 58
THEORY OF OPERATION
E-6
E-6
Classic III and IIID
CURRENT RANGE SELECTOR
The selector switch acts as a coarse current adjustment
by allowing varying amounts of series windings to be
included in the welding current path. The series coils
and selector switch are connected in series with the
negative output terminal.
FINE CURRENT ADJUSTMENT
The field rheostat control functions as a fine output cur-
rent adjustment. By controlling the current through the
shunt windings, it controls the amount of magnetism
created in the shunt field windings. Open circuit weld
voltage is also controlled by the field rheostat control.
ENGINE IDLER CIRCUIT
The idler solenoid is mechanically connected to the
engine governor linkage. When welding current is being
drawn, the reed switch CR2 is closed. This signals the
idler PC board to release (deactivate) the idler solenoid,
which then lets the machine go to a high speed condi-
tion. Also, when auxiliary power is being used, the cur-
rent is passed through the current transformer. This sig-
nals the idler PC board to release the idler solenoid.
When welding ceases or the auxiliary load is removed,
a preset time delay of about 15 seconds starts. After
approximately 15 seconds, the idler PC board activates
the idler solenoid, and the machine returns to a low
speed condition.