Interpole And Series Coils; Current Range Selector; Fine Current Adjustment; Engine Idler Circuit - Lincoln Electric SHIELD-ARC SVM128-A Service Manual

E-4

INTERPOLE AND SERIES COILS

The generator armature rotates within the magnetic
field created by the field shunt windings. A DC voltage
is induced in the armature and is transferred, through
the armature commutator and brushes, to the series
and interpole coils. The interpole coils, which are con-
nected in series with the positive output terminal, are
located so as to counteract any magnetic influences
that could cause mechanical distortion in the rotating
armature. The series coils are designed to oppose or
"buck" the DC voltage that is generated in the arma-
ture.

CURRENT RANGE SELECTOR

The selector switch acts as a coarse current adjust-
ment by allowing for varying amounts of series wind-
ings to be included in the welding current path. The
series coils and selector switch are connected in series
with the negative output terminal.
THEORY OF OPERATION

FINE CURRENT ADJUSTMENT

The field rheostat control functions as a fine output cur-
rent adjustment by controlling the current through the
shunt windings. In this way it controls the amount of
magnetism created in the field shunt windings. Open
circuit weld voltage can also be controlled by the field
rheostat control.

ENGINE IDLER CIRCUIT

The idler solenoid is mechanically connected to the
engine governor linkage.
being drawn, the reed switch CR2 is closed. This sig-
nals the idler PC board to release (deactivate) the idler
solenoid, which then lets the machine go to a high
speed condition. Also, when auxiliary power is being
used, the current is passed through the current trans-
former, which signals 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 will return to a low
idle speed condition.
SA-250
E-4
When welding current is