Started van and noted the red battery light stayed illuminated.
Got home and whilst the engine was running, and without stopping and restarting, measured battery voltage.
It was 14.4V indicating that it was being charged.
Turned off engine so I could look under the bonnet to make sure nothing was untoward and then restarted engine.
The light now went out!
Does anyone have a possible explanation?
I did powerwash the bodywork the night before, but very little should have got to the alternator, or indeed anywhere else under the bonnet. I wouldn't have thought this would have any effect.
The most common bit by far (IME) to fail on an alternator is the control unit (regulator). Costs about 30 quid for a new one - and usually quite easy to change with the alternator on the bench. But finding a source of the correct regulator can be tricky.
Ha! Just did a Y2k TD5 Disco with 212k on the clock :-) Mind you, it's taken all that time to get through only about 10mm of brush so that makes them "lifetime fit" easily. I suppose just running on plain copper sleeve is a lot less wearing than a commutator.
I never checked the voltage but this happened to me on a number of our transits from 2004-2008 vintage. I found it happened when I rushed the starting and drove off suddenly. If a bit more time was taken to wait for the engine lights to go out it didn't seem to happen.
You clearly never had a car from the early 1980's that had done more than 80K miles.
That's the mileage my '84 Celica 2.0 XT had done when the brushes wore out. 50p each from an auto electrical place that doesn't exist any more.
Sometime in the mid 80's they started "super polishing" the slip rings and then the life increased a lot, factor of 2x. But life is now dependent on amount of dust the car has been subjected to.
First car I had with an alternator was a '69 Rover P6 3500.
Obviously if it gets subjected to lots of dust the life would be shorter. But I'd guess you'd get warning by needed new air filters etc much more frequently.
Some cars use the same old simple regulator that is either built in to the alternator, or a separate component. Much more common is to delegate regulation to the main ECU. Complex algorithms are then used to both maximise battery state, and reduce fuel consumption.
For example, BMW (and possibly others) turn off the alternator altogether when certain criteria are met. For example, constant speed cruising with minimal electrical consumption and a reasonably healthy state of charge. During braking, the alternator switches on at the maximum current the battery can withstand, effectively charging the battery for free.
Just to confuse things, some cars use a combination of both; they have a built in regulator that will do basic charge control on its own, plus a connection to the ECU that will modify charge rate under certain conditions.
Probably the most complex system is used in the VW Touareg V10 diesel. This is a dual-battery system with various possibilities of how they are both used and charged, determined by the ECU. The alternator is water-cooled and gear-driven via a two speed gearbox. This enable high charging current at idle, but prevents the alternator from disintegrating at speed. If you are interested, have a look here from page 20:
The regulator could be pushing out some juice but not enough to turn the light off. IIRC the light is wired between the alternator output and the field winding.
On a basic alternator - no idea about fancy ECU controlled ones - the warning light circuit usually supplies the 'exciting' volts to start the alternator charging.
This is a common fault and is usually the triple wire connector to the alternator, a new bit of loom is about 20 quid, or you can pull it apart and look for the break. The smart charge system will/can still charge with the light on, just won't be so smart.
Most (all?) newer Fords do this now - they even go as far as calling it 'regenerative braking' which I think is stretching the term somewhat!
They way they implement it is to have put a clutch on the alternator which disengages during acceleration, with a full battery, etc and engages when braking.
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