Lincoln Electric SAE-300 HE, Service Manual, Page: 11 / 84

LINCOLN ELECTRIC SAE-300® HE Service Manual
6
EXCITER / AUXILIARY ALTERNATOR OPERATION
FIGURE F.4 – EXCITER / AUXILIARY OPERATION
The exciter alternator is the smaller power generator that is
located at the end of the main welding generator. It
provides power to energize the rotor, the shunt fields of
the main welding generator and about 3 KVA of 120/230
volts, 60 Hz. for auxiliary power.
Flashing:
The exciter alternator requires that DC power be applied to
the slip rings to start the power generation process. This DC
power is often referred to as “Flashing” voltage.
Flashing voltage is low voltage (about 4 to 6 VDC)
generated by the main armature spinning in a weak
magnetic field. This magnetic field is caused by residual
magnetism in the iron poles of the generator.
Flashing current passes through a flashing diode and is
applied to the rotor field winding through the exciter
brushes and slip rings.
Building output:
The flashing current produces a weak magnetic field in
the rotor, which is coupled to the now running engine.
This rotating magnetic field begins to generate AC output
from all of the stator windings. Output from the exciter
winding is rectified by a diode bridge and then fed back into
the rotating field winding, through the brushes, making the
magnetic field stronger. This stronger magnetic field then
produces higher voltage from the stator windings, which
feeds back to the rotor, making its magnetic field even
stronger.
This process of strengthening the magnetic field through
feedback from the exciter winding continues to increase
the output of the alternator until the design voltage is
reached.
The field voltage is now higher than the voltage produced
by the welding generator. The flashing diode will now block
the higher voltage from intruding into the weld circuit.
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