So what does an alternator DO??

[Alexphil20]

I have a mk3 97 golf cabrio 1.8. Had it for a few months. Recently the battery light started coming, and staying, on and my lights dimmed intermittently so I suspected the battery or alternator. On checking it, I discovered the battery use-by date was 2006 (!) and that it was marked diesel so I'm impressed it had worked this long. Stayed dead after two days' trickle charge, which seemed to confirm my suspicions, so I replaced it with a new, correct one.


Unfortunately the battery light still comes on - sometimes only dimly. I've only driven the car twice since replacing the battery as I dont want all my lights conking out while I'm driving my 3 yr old about, or at any other time come to think of it!


What I want to know is this: what exactly is an alternator? Does it have specific parts to it that can be individually replaced? If so then which parts should I be focussing on? How do I test them? And, most important of all, if I need to replace it, how much will it cost me??


Thanks all. don't know what I'd do without this forum

[manclad]

I assume the battery light is the alternator light and if glowing dimly is usually indicates that one or more of the diodes stacks (the electronics that convert the generated a/c to d/c for the car electrics) have failed.

If the car has a dashboard voltmeter it should read around 14 Volts at around 2000rpm.
If no voltmeter the place you bought the battery should have one and be able to check if it's charging or not.

[phil miller]

sounds very much like a regulator fault, altho if it was me id check the charge rate at the alt aswell as the batt, just to be sure its not a broken wire

[manclad]

Does it have specific parts to it that can be individually replaced? If so then which parts should I be focussing on? How do I test them? And, most important of all, if I need to replace it, how much will it cost me??

I reply, yes an alternator does have specific parts that can be replaced such as the regulator and diodes, but sourcing these parts and replacing them is not a simple DIY job and probably the cost would outweigh purchasing a reconditioned unit.

[Boardboy]

I replaced the one on my MKII. I can't remember the cost but it was cheaper than an new alternator. A good auto electricians should be able to get one.
Attached is a picture of brush length out of the manual.

Hope this helps

[manclad]

Another possible solution is to source a second hand one from a breakers yard