>Date: Sat, 26 Dec 1998 18:10:37 -0500
>From: "Paul Tegler " <wizardz@amdyne.net>
>Subject: Alternator Light - Pulses?
> Once again, I need the TECH'ies to come out of the wood work....
> On my 1973 BGT, my alternator light has been popping on, sometimes
>bright, sometimes dim. Revving the engine will turn it off briefly,....
>sometimes!
> I Checked the WHT ckt. connections, (which is the return side of the
>ignition idiot light ) things look fine. I then added a dash mounted
>Voltmeter across the WHT ckt. to GND and using a clamp on Amp Meter on the
>PLUS battery cable (at the battery) I could then monitor the charging
>system.
> The Volt Meter easily rises to +14 - 14.5 volts, when the car is
>first started from it's initial 12 volts. While the light is off, the Amp
>Meter will show a charge rate or roughly 3 - 5 amps. When the battery gets
>to 14 volts, ( a minute or two) the light comes on, and I'll see no
current
>flow on the amp meter. Gunning the engine will occasionally turn off the
>ignition light at first, but after a few minutes it will just stay on.
> Watching the Volt Meter, I can see a rhythmic pulsing of the voltage.
>It's only a 1/2 a volt or so drop, but is rhythmic and doesn't seem to be
>related to engine RPM. I'm assuming this pulse is the Fuel pump being
>energized.
>Conditions: Starts quick and easily. All ace. turned on, only drops the
>voltage a max. of 1 volt. (with the idiot light on or off)
>QUESTION #1: Do I suspect the battery, alternator, or something on the WHT
>ckt. that is loading down the line.
>QUESTION #2: If it's the alternator, would it be the brushes? regulator?,
>diode array?
>QUESTION #3: Could the battery being at 14.5+ volts, make the alternator
>think it's not charging, so the light comes on, since the alternator output
>voltage is the same as the battery voltage?
Paul, my suspicion is that your alternator is the source of your concern
but your alternator may not be in too bad of shape. With a poor alternator
there is no way you can have operating voltage of 14.5 V. I've seen several
Lucas 16ACR's which generate 30-35 amps at 14 - 14.5 V and yet the indicator
lamp would glow or in one case shine brightly. The indicator lamp is fed
battery voltage and grounds through the alternator circuit. Once the
alternator starts generating, voltage is supplied to the indicator lamp by
the alternator also, blocking the ground path and causing the lamp to not
light.
As one diode plate does nothing but supply current to the indicator lamp it
is possible for the remaining diode plates to operate properly while the
indicator set has failed. This would imply a problem when actually the unit
is still charging.
Check the voltage of the system with the lights and accessories turned on at
idle. If the system voltage stays near 14 V your problem is probably the
diodes in the alternator which supply the indicator light. If the system
voltage drops below 12V try revving the engine to see if voltage and current
increase.
Either diodes, regulator or brushes could cause the lamp to illuminate, but
if you are able to maintain 14.5 volts your brushes and regulator are not
too bad.
Fred Pixley
Napanee, Ontario, Canada
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