All:
<<<snip>>>
In an alternator the warning light is connected to the field
winding
<<<snip>>>
Nope
<<<snip>>>
and fed via a different set of diodes to that which feed the
output
<<<snip>>>
Nope
<<<snip>>>
The dynamo light is triggered by amperage, the alternator by
voltage.
<<<snip>>>
Nope
<<<snip>>>
Any defect in either diodes or regulator *always* causes
problems.
<<<snip>>>
Yep.
After some research with no clear answer, and careful thought,
here's my take now.
The warning light is a potential difference (voltage) measuring
device. It measures the voltage differential between the battery
and the charging device. It doesn't tell which item has the
least voltage. You have to guess.
An ammeter is a current measuring device. It measures how much
current (amps) is flowing through it and the direction (+ or -).
And those are the keys.
Tonight, inside, I experimented with a dash light and D cells.
One cell, no light. Two cells, very dim light which may not be
visible behind a colored lens in the daylight. That means that
the voltage differential between the battery and the charging
device must be at least 2-3 volts before you'll see the light.
(Pun intended.)
If the load on the battery is greater than the charging rate from
the alternator or dynamo, the warning lamp will only glow WHEN
THE BATTERY VOLTAGE HAS FINALLY DROPPED TO ABOUT NINE VOLTS.
That's just about dead, and at that voltage it may not crank a
car especially in cold weather. I'm not ready to ruin a good
battery running it down to nine volts, and starting the car with
a crank or a push start just to see if the warning lamp glows for
a while.
POI: When my Datsun pickup was new, winter starting was
interesting. If it hadn't electronic ignition, it probably
wouldn't have started. In exteme cold, the warning lamp would
almost go out as the each piston came to the top during
compression. The engine would go ugh, ugh, ugh. At every ugh,
the warning light would dim significantly and almost go out. So,
the voltage across the lamp had to drop to around 3 volts.
So, If you have a reasonably charged up battery, and the warning
light glows, the charging system is wonky. If you have too many
current using devices, a good battery, and a good charging
system, then the warning light may come on very dimly at first
after several hours and as time goes on it will gradually get
brighter. By then, you may fried something in the charging
system as alternators or dynamos aren't usually designed to run
at maximum output for several hours. They'll overheat, throw
solder and/or windings, or fry the insulation and short out.
So if you really want to know if you've overloading the charging
system, you need an ammeter.
Blake
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