Hi Terry
RE : Alpine V Alternator Warning Light Simulator (WLS)
Ah another fine example of darkness engineering from Lucas.
They put just about everything needed in to do it right but
proceed to hook it up bass ackwards...
I suppose they had an excuse.. it was one of their first alternator
attempts with a solid state (transistorized) regulator...
The AL terminal on the 10AC alternator produces about 12V AC
when the alternator is working. The 3AW warning light simulator
is a thermal relay that breaks the warning light bulb circuit
when the AL terminal is over a few volts.
To test a 3AW measure the resistance between the WL and E
terminals, it should be less than 1 ohm with no other connections.
Then apply about 6 Volts between the AL and E terminal the
circuit between WL and E should open.
I have found the 3AW WLS to be less than robust and the last
time mine died (about 15 years ago...) to be overly expensive. I
was particularly bent when the second replacement lasted less than
three months. My solution.. because I wanted to keep the show Alpine
stock.. was to take the dead 3AW and replace it's guts with a 3
transistor circuit. The modification and circuit was published
at the time in the TEAE newsletter. The $3 (in parts) circuit
has worked quite reliably.. If I can find it I'll try to dig
out the old tech tip and post it.. It should be on a floppy
somewhere.. Now where will I find an 8" drive?
The prince of darkness dilemma is that with just a slight
rearrangement of the parts a much more reliable system could have
been designed.
The problem with the stock system is that if the warning light
comes on the alternator is in danger of burning out. When the
voltage regulator senses no alternator output it applies full
current to the field winding. Without air circulation this can
cause the field to go open in less than an hour. Ironically this
places a heavy, several amp, load on the battery just as you have
lost the charging source. If you find you must drive some
distance without the alternator turning, unplug the field
connector at the alternator or regulator. The same failure can
occur if the ignition is accidently left on with the engine
stopped. The main design fault is that the alternator field
current is supplied directly from the battery. When the warning
light comes on .. don't just ignore it you could be killing your
alternator.
Modern alternator designs neatly solve this problem and avoid the
need for a 3AW WLS by suppling the starting current for the
field via the warning light itself. As the alternator comes up
to speed a set of diodes in the alternator feed power to the field
circuit, reducing the current drawn through the warning light
there by turning it off. If the alternator stops producing for
any reason the field current again comes via the warning light
but is limited to a fraction of an amp by the series light bulb.
Fortunately the Alpine warning light is connected such that with
a modern alternator a direct connection to the equivalent of the
AL terminal accomplishes the proper function without the need for
a 3AW. Often one finds a resistor in parallel with the warning
light. This slightly increases the starting current but more
importantly assures alternator start up even if the warning light
has burned out.
It would seem to be possible to modify the 10AC alternator by
adding 3 internal diodes to convert the AL terminal to DC, make
another internal connection to feed the field from the AL terminal,
and add a jumper connection inside a 3AW shell to accomplish the
modern design and retain the appearance of stock. I haven't tried
this so you are on your own to work out the details. Let me know
if you try.
Steve F
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Steve Finberg W1GSL w1gsl(at)mit.edu
PO Box 397082 MIT Br Cambridge MA 02139-7082 617 258 3754
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