Thread: WARNING, the dangers of an Alternator failure.

Sounds like you've given us a timely warning - thanks.

Just out of interest Tim, can you give us a quick summary of the electrical failures that occur to add up to the catastrophic failure.

Is this beyond the scope of all but a LR dealer to fix?

Originally Posted by drivesafe

Just a few minutes ago I got a call from a D4 owner who had just had a total systems failure

Do you know if the engine is a 2.7 TDV6?

Hi 87County, if it occurs, you can go to any business/company competent at changing an alternator.

It does not have to be a dealership, unless the Land Rover is still under warranty, or if a dealership is your preferred choice.

If I was in Melbourne, I would go to MLR, I wouldn't go anywhere else.

But here on the Gold Coast, the LR dealership is the last place I would go.

With a catastrophic alternator failure, all electrical equipment and anything that depends on that electrical equipment fails.

I had never heard of this type of catastrophic failure, until the alternator in our RR Vogue failed while my wife was driving it.

Not only did all electrical power fail, but the steering lock applied while she was driving.

I got a phone call about the failure and when I got there, the ignition was still turned on but the steering lock was also on.

She had stopped in the middle of a busy country road, Right on dusk and in the middle of peak period but she could not put the hazard lights on, to warn other road uses, as there was no battery power.

I measured the battery and it was at 7v.

87County, once the alternator is repaired/replaced, everything should return to normal.

Hi Graeme, I didn't ask him what D4 it was, but so far I have been contacted by D4, RRS and RR owners.

Oh for the "good old days" when you could see the alternator light then casually drive home and then pick a repairer.
Or in my case once my wife drove into the driveway and told me there was a red light on the dash, and it had been there some time. The old RRC 3.9 would go for quite a while with low voltage.

The day I bought my D2 I was driving home and all of a sudden the dash lit up like Christmas lights , and then the engine stopped, and of course the power steering and brakes went. All it was was a corroded battery terminal.
Sounds worse now. Progress?
Regards Philip A

Hi Philip and while the end result was similar and just as dangerous, the cause was different.

When my RR alternator failed, the auto electrician measured a 155 amp short through the alternator.

With the huge battery they have in the L322, this sort of current load should have taken around 20 minutes to flatten a fully charged cranking battery, but even if the battery was not fully charged, it still would have been at least 10 minutes from short to flattened battery.

This is ample time for the Battery Light to have be displayed.

But in many of the cases I have been told about, including how my RR failed, there was no indication until seconds before the TOTAL failure of all systems.

That means there is something seriously wrong with the Land Rover battery/alternator warning setup, and a very dangerous short fall in my opinion.

AFAIK the alternator used with the 2.7 in the D4 is the same as the one used in the D3, which is known to fail by its Zener power diodes reverse conducting because they have deteriorated with use causing their reverse trigger voltage to lower to normal alternator o/p voltages. LR skimped on cabling and design by using a short cable to connect the alternator B+ to the starter motor cable. The starter cable is protected by a 500A fuse which does not blow when the Zener diodes in at least the 2.7's alternator reverse conduct, thus causing the battery to drain very quickly with somewhere around a 160A/180A load.

LR went to tender for a new alternator for the 3.0 so it may or may not use Zener power diodes, but 3.0 alternators have not been failing so perhaps no Zener power diodes in those. I've not heard of petrol V8 alternators failing.

So what you are saying is effectivelly 100A or so alternator is protected by 500A fuse in this case. Nice one LR! Id be quick to install extra 1 metre of cable (if one can afford it since LR can't by the looks of it) and wire the thing properly!

Sent from my GT-I9305T using AULRO mobile app

Originally Posted by Graeme

AFAIK the alternator used with the 2.7 in the D4 is the same as the one used in the D3, which is known to fail by its Zener power diodes reverse conducting because they have deteriorated with use causing their reverse trigger voltage to lower to normal alternator o/p voltages. LR skimped on cabling and design by using a short cable to connect the alternator B+ to the starter motor cable. The starter cable is protected by a 500A fuse which does not blow when the Zener diodes in at least the 2.7's alternator reverse conduct, thus causing the battery to drain very quickly with somewhere around a 160A/180A load.

LR went to tender for a new alternator for the 3.0 so it may or may not use Zener power diodes, but 3.0 alternators have not been failing so perhaps no Zener power diodes in those. I've not heard of petrol V8 alternators failing.

Hi graeme, i have seen a dead shorted d3 v8 alternator. Around 120k old and it flattened the battery in about 10 minutes. When i got to it there was a stench of melted plastic in the engine bay and only 5v left in the battery.

Jc