"Arfa Daily" wrote in message
...

"Ron Lowe" ronATlowe-famlyDOTmeDOTukSPURIOUS wrote in message
...
Hi, all.

I have a Land Rover Discovery 3 here ( still in warranty ).

The vehicle has a voracious appetite for light bulbs: I'm replacing tail
/ brake lamps every couple of weeks, and the same with headlamps. And
at around a tenner a pop for the headlamps, I'm getting a bit fed up.

Also, the kid's DVD players ( after-market ) in the back seats have
started shutting down, usually when I start the engine.

Fault-finding the DVD players, I was checking for the presence of 12v at
the power cable.

I found it to be 15.6v with the engine running.
IMHO, that's too high, and possibly the cause of the lamp problem.

Bench testing the DVD players shows that they indeed shut down at around
15.5 v ( protection, I guess. )

What is reasonable maximum voltage on a vehicle 12v system with the
engine running?
I'd guess around 14v.

Googling this, I have seen people saying the disco uses some fancy
automatic system to optimise the charge voltage which takes into account
all sorts of things including vehicle electrical load at the time, and
temperature ( the battery is apparently temperature sensitive ), and
possibly phases of the moon.. This can apparently cause the charge
voltage to vary up to 15.5v, I've read. ( It's -9 degrees here at the
moment, and the vehicle electrics are often well loaded with heated
windows and seats, wipers, fan blowers etc. )

Am I seeing a fault ( voltage regulator on the alternator ), or is this
just within normal tollerances with these vehicles?

Is it reasonable for the thing to run at 15.5v, and chew up headlamps?
I don't think it is.
I'm looking for some opinions before I need to argue with Mr. Land Rover
for a warranty claim.

Otherwise, I need to put a 7912 regulator in the DVD player power lead!

--
Ron



You might be able to get a more definitive answer over on
uk.rec.cars.maintenance

There's some good well-savvy lads on there.

Arfa


There's actually an interesting thread in progress regarding exactly this
question over there, right now. Seems that some modern charging systems -
notably Ford - make use of a stepped output voltage from the alternator,
controlled by the EMU. The highest output of over 15 volts seems to be as a
result of, amongst other things, outside air temperature, to compensate for
the slightly different charging requirements of a cold battery against a
warm one. Maybe the Disco uses the same or a similar system, and it's not
working correctly ?

Arfa