Land Rover Disco 3 voltage regulator levels

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!

Reply to
Ron Lowe
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That will kill the battery prematurely too.

I think you mean 7812, but you would probably need a low dropout higher current regulator. ;-)

Reply to
Andrew Gabriel

"Ron Lowe" coughed up some electrons that declared:

That's been my experience.

15.5V seems high. 14V-14.5V would be more like the sort of voltages I've been used to seeing with the alternator going flat out *and* the battery fully charged *at the battery terminals* (lower at the load terminals, due to drop in the wiring).

Thing is, 15.5V I reckon will damage the battery - and if the battery is not fully charged, it should be holding the vehicle general supply voltage down to something more sane**

** Meaning the alternator might produce a high-ish output voltage in order to drive lots of amps into the battery via it's connecting leads, but the voltage at the battery terminals shouldn't actually get that high, I wouldn't have thought.

Do they still use "Lucas, Prince of Darkness" electrics?

I would challenge it's operation to the dealer.

It seems too high by a good volt - my old Daewoo, I think, used one spare bulb in it's whole time I had it (8 years) and that was the interior light. Maybe it had a new headlamp bulb too - certainly nothing else.

Cheers

Tim

Reply to
Tim S

electrons

replacing tail /

terminals, due

battery is not

voltage down

headlamps?

To get more evidence, get the specifics (make / model) of the battery and get the tech spec from the manufactures web site re max voltage for charging. If it's being exceeded then thump Landrover !

AWEM

Reply to
Andrew Mawson

Agreed, stop faffing about and take it to the dealers to sort out. Report the blowing of bulbs and the voltage you have found. It's not right, stand your ground firmly and politely.

Reply to
Dave Liquorice

I wonder if something's nuked itself and you're actually getting a level out of the alternator/regulator that's fluctuating wildly; putting a meter on it might be showing it as an almost-stable 15-odd volts, whilst nasty spikes are quite happily killing various bits attached to your vehicle...

The DC level you're getting definitely sounds too high - I'd expect somewhere betwen 13V and 14V (probably toward the 14 end) for a vehicle system.

It might be worth checking that the alternator has a good ground connection - if that's bad due to dirt / corrosion / something working loose then it could really mess your charging system up.

cheers

Jules

Reply to
Jules

Yes - about 14.5 max is more usual. But if the battery is fully charged, less than that. Any time I've looked at my newest car (10 years old) it's sitting at the classic 13.8.

Reply to
Dave Plowman (News)

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

Reply to
Arfa Daily

15.5 has fried everything even the battery if its been in long, 13.3

-13.5 is all you should have, It shoud not be an argument.

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pg 13 should give you info on battery charge. 15.5, I would not want your vehicle out of warranty.

Reply to
ransley

Around 13·8V is the usual - that's why so-called 12V power units for mobile CB and amateur radio are normally rated at 13·8. I would reckon that anything much in excess of 14V needs looking at.

I suspect that LR's ethos is that Discos are likely to be fitted with lots of accessories such as internal and rear working lights where a higher rate of charge may seem appropriate.

Reply to
Frank Erskine

Why would a poor earth increase the voltage of an alternator?

Reply to
Doctor Drivel

14.4 v is the normal from an alternator. 14.5 should be fine. It should drop about a volt when the lights and demister are on. That is how you test the alternator with a volt meter.

If you have a clamp on ammeter. When battery is dead the amps should be 0 then rise until around 20 amps once he battery starts to take the charge. If it goes to around 10 amps or less, do the battery test.

The battery test is, charge until it is 12.2 volts. Disconnect the ign coil, so engine does not start. Turn over the engine for 15 seconds. If the battery dies, then it fails the test.

Reply to
Doctor Drivel

Quite, new alternator time.

NT

Reply to
meow2222

Make sure you've got several hundred quid spare for a new cat at the next MOT.

Reply to
Andrew Gabriel

The vehicle is still under warranty, take it back and get it fixed.

As the voltage is so high what stress is it putting on the expensive computers than control almost everything in a D3? Getting the problem sorted by the dealer gets it on to the vehicles records which you then might be able to thump Land Rover with at a later date when other things die early.

Reply to
Dave Liquorice

Wonder if it's the Ford designed system where the engine ECU controls the alternator? IIRC, called smart charge.

This might be some help. But just found by Googling so...

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Reply to
Dave Plowman (News)

And of course it's more than likely a diesel.

Reply to
Dave Plowman (News)

Many modern cars charge at a much higher voltage than the old standards - it's part of efficiency measures I think. My car has a 120A, 14.7V alternator (that's the nominal volatage, it will actually output higher voltages). The alternator has three wires specifically for the engine management to set the required output voltage (removing the plug defaults to high output). The high voltage *will* damage normal batteries, therefore these cars need specific battery types.

SteveW

Reply to
Steve Walker

Donno, but as the vehicle is also chewing through bulbs it indicates that the entire +v rail is elevated not just the charge circuit.

Reply to
Dave Liquorice

None, I'd hope. It should all be designed with overvoltage in mind. Even a bog standard voltage regulator found in most electronics can cope with perhaps 40 volts higher than its output continuously. And those designed for car use are even more tolerant.

Car electronics need to be designed to cope with a *very* dirty power source.

Reply to
Dave Plowman (News)

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