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

[Martin Howell <grizelli.associates@xxxxxxx>]

The light picks up its signal from the alternator.  It should be off or on,
not partly on, if the alternator is charging properly.  If it glows a bit,
there's probably a fault in the alternator internals.  In some alternators
the light is driven separately from the main output, and there can be a
fault without the battery losing charge.

Martin

Geoff wrote:

> 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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