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Unlike a generator, the alternator is not self-exciting
at start-up. A generator has field poles made of soft iron which hold a
residual magnetism. The alternator field
structure has little residual and thus has almost no
output unless field current is supplied.
To get the alternator going, a tiny field current must be
supplied. In most designs, this current is initially provided by the
dash warning light or the "exciter light" With the Ignition
switch closed, current flows thru the Lamp to the regulator and into the
field winding. If the dash warning light is burned out or
disconnected, the alternator probably won't begin charging.
As the alternator speeds up, stator voltage increases
until the Trio diode voltage is sufficient to provide field excitation.
As the voltage approaches 12 Volts, the dash Lamp goes off because it
has the same potential on both sides.
The alternator system will
not charge unless you have an exciter (idiot light)
installed. Any low amperage light
will do the trick in either case. If you are using a
small dash
light, like most of the
automotive stores sells, they will work as long as
they are not LED. LED lights will only
pass current in one direction and even if it is
wired
correctly, it does not carry enough current to activate an alternator.
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