RE: [No HA content] Car "alternator warning light"

[Keith Doxey <keith.doxey@xxxxxxx>]

The alternator warning light is connected beween the output of the
alternator and the Ingition circuit 12V supply. (12V being the nominal
voltage - as you point out this will rise to about 14.4)

A permanent dim glow can indicate either excessive voltage drop on the
ignition circuit (disconnect that 3kW Sound system NOW!) or the alternator
not being 100%.

>From my experience it has always been the brushes worn in my alternator
and
replacing these for abpout 2 quid cured the problem.

The WL (warning light) terminal on the alternator is at 0V when not
charging
so the lamp lights due to the other side being connected to 12V. For you to
see the light glowing dimly means that the WL terminal is at about 1 or 2
volts difference to the ignition circuit. If its around 10-11V then the
alternator isnt charging properly. If its higher than the ignition circuit
voltage then either there is excessive drop on the ignition side or the
connection between the main alternator output and the battery is suspect
with the alternator giving out its proper 14.4v but it is getting
"lost"
between there and the battery.

Check for volt drop from alternator to battery. I once had a badly corroded
main output plug, the result of hitting too many deep puddles :-(

HTH

Keith

> -----Original Message-----
> From: Geoff [mailto:Geoff@xxxxxxx]
> Sent: 27 November 2000 08:04
> To: ukha_d@xxxxxxx
> Subject: [ukha_d] [No HA content] Car "alternator warning
light"
>
>
> We are having a discussion on one of the uk car NGs about car ignition
> warning lights and *exactly* what they mean so I thought I'd ask you
> guys as Electronics Consultants   :-)
>
> Several of us have had cars where the ignition/alternator/
> call-it-what-you-will light on the dashboard glows dimly all the time
> the engine is running.  It's not mechanical - e.g. slipping belt - and
> the alternator seems fine and the battery doesn't run flat.  Battery
> voltage is 12.6-13.0 at rest and 14.2 when engine running and
> on-charge.
>
> Change either the battery or the alternator and the problem sometimes
> goes away.
>
> Increasing the load - lights, heater blower, etc - makes little or no
> difference to battery state or intensity of the glowing light.
>
> So what does this mean?   How do these lights work?  Someone suggested
> "There are all sorts of types of alternator warning light
> arrangements, although I *think* the most common sort these days picks
> up its (+) from the ignition switch, and its (-) from the
> regulator/field diode connection. I'd measure the volts at the warning
> light output from the alternator - this should tell whether the fault
> is in the alternator or the lamp wiring."
>
> Any thoughts on what these warning lights *actually* mean?   And how
> you'd decide whether it was (a) alternator (b) battery (c) duff
> wiring?
>
> TIA
> Geoff
>
>
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