Possible Battery / Alternator issues?

Retrogamer

arcon5 wrote: »

Sooner a later it will go mate. May last a few weeks, few months or whatever but will at some point. Diesels require twice the power from the starter motor than a petrol as well, they are not easy on the electrical system.
Is the battery light coming on at idle?

Nope, no sign of the battery light at idle.
Could have been doing this since i got the car for all i know. I only noticed it happening when checking with a voltmeter.

arcon5

The light is wired in a way that when power is coming from the battery it feeds the light whereas if it comes from the alternator there is no supply to the light, can't remember how, probably a diode and earth circuit or something, I don't know.
If the lights off then the alternator is at the very least feeding the electrical components and the battery, even if not enough to put plenty of charge in.

It really comes down to how important your car is. It will fail eventually, if you don't mind one day, randomly having starting issues or suddenly finding the battery light on (in which case whatever you do don't turn the engine off until you're at a place of fixing it) then just leave it.
Personally I couldn't because public transport to my OHs work is non-existent. But many would just leave it - plus you never know, you may just get a good life out of it.

I've driven a car with a failing alternator before, got a few thousand miles out of it until battery light starting coming on intermittently. To many, that could be another half year or so out of it!

Retrogamer

I've had an alternator fail before and it was as you described. Light came on when cold and intermittent / dim but over a few months was on brighter and more often until it gave it completely.

No issues on this one so far and if it does fail i've AA cover with relay service and VW / Audi were nice and put the alternator in a nice easy to swap place at the top of the engine bay.

Strider590

arcon5 wrote: »

The light is wired in a way that when power is coming from the battery it feeds the light whereas if it comes from the alternator there is no supply to the light, can't remember how

The lamp is in the exciter coil circuit. When the engine is off the coil acts as a ground and the lamp comes on, but when the engine and alternator are running, the coil raises to 12v and the lamp turns off.
The lamp is actually very important, as without it, no voltage would be applied to the exciter coil and the alternator might not work at all.

fred246

The two common problems are the alternator clutch pulley and the regulator. I first took off the alternator. I checked the regulator and brushes which are one item. It looked fine. I took it to the local alternator specialist who tested the output and it was fine. He said the regulators are the only part that ever fail. I put it back and it worked a bit until the belt squealed and I realised I needed a new tensioner. I replaced it but the tensioner was still very bouncy. It was at this stage I checked the pulley and it was seized. I put a new pulley on (it needs a lot of force to get old one off), and everything fine since. I think the pulleys fail by slipping first and then seizing solid (but I may be wrong on that). I was surprised that the alternator specialist didn't appear to check the pulley at all so the diagnosis was missed.

fred246

http://www.myturbodiesel.com/wiki/alternator-pulley-removal-and-fan-clutch-bearing-removal-b5-passat-tdi/
May be helpful.

forgotmyname

I wouldn't trust the battery light. Usually it works. But there are occasions when it will fail to detect the alternator not charging.