Alternator problems

[Jack]

Mavis has been running sweetly for far too long (30,000 miles including a trip to Monaco without anything other than normal service items!) and so this morning, as I was about to set off to collect some new shock absorbers (see other thread) a problem has finally occurred.

The drive belt on the alternator has been a bit squeally lately, but being a lazy git I had not got round to tightening it. This morning I got into the car (normally aspirated diesel) to find the battery light on. The key was not even in the ignition so I found this very strange. Anyway, I tried to start it and it wouldn't. I suspected a flat battery (reason unknown) and so jump started it from my other half's car. No problems.

On the journey I noticed the battery light come on again. It was (and still is) getting brighter with engine revs. At tickover the battery light is almost totally out, and it gets brighter the higher the revs the engine does. Have I got a knackered alternator?:(

[MG1600S]

Yes you have got a knackered alternator. The light being on without the ignition on means that the alternator is live all the time and discharging the battery overnight...

[wemyss]

I reckon so Jack.. A couple of winters ago I got home and switched the engine (diesel) off. The red light stayed on even with the keys out.
Thought I would leave it until the morning before doing anything as surely a little bulb couldnt fetch the battery down. But next morning the battery was completely flat.
Took many hours to charge back up again and ran straight down to Harrisons electrical at Etwall who confirmed that the alternator was short circuiting and fitted a new one for for £70 or so.
I imagine the you light is showing exactly what its supposed to do and telling you theres no charging taking place and probably a discharge at the same time.
nick

[H48HPE]

many people have suffered this problem including my dad on his diesel maestro, the problem is that the alternators rectifier has gone closed circuit so the diodes dont work as they should. you either need to get a second hand alternator from the scrap yard, get a whole ew alternator or replace the rectifier in the alternator. there are several threads covering this on the forums, might be worth searching for them.

Andy

[E_T_V]

Most likely the alternator, but it is also just worth checking that the ignition relay isn't sticking on.
My betting is an alternator diode is dead though.

[Jack]

Just to let you know, all is now well with the alternator. £51 from a local motor factors (with £25 surcharge until I take the old one back).

It's even cured the horrible dry bearing squeak that I thought was the water pump on it's way out! Result.

[wemyss]

Nice to get a good result Jack...theres always that feeling when you replace something the same fault is going to be there when its finished.
You caught me just as we are packing to go away tomorrow.
nick