Alternator not charging.

[Mk2Kezza]

I swapped out the old tired alternator 18 months ago and popped in a replacement from the scrappy. Its been fine until this summer when I noticed that it isnt charging the battery correctly. When I measure the voltage of the battery at idle, it was 12.4 volts and this doesn't change as you rev the engine up. With the nights drawing in and the need for lights, wipers, radio, heater, i'm having trouble starting her up. I have a 40 mile motorway run to work so you would expect the battery to be nicely topped up but its not the case. The battery is also 18 months old and is a Bosch S3 so has a guarantee.

Do any of you recognise the alternator? I ask this as the black plastic cover was not present on the original alternator...





Any idea what the B+ symbol means? Is it to add additional voltage/current feed to the battery? Is this why she is not charging correctly?



Is it a case of getting a new voltage regulator? The problem is that its my daily driver and its dark by the time I get in so its putting me off removing the alternator, then the black plastic cover to check what type of regulator, then refitting. A pain during the day....

All the other wires are correctly wired up.




Cheers in advance..

[Mr Blue]

Looks like an earlier one but get on ebay and find a 90A Audi 80/90 one if you are going to replace yours. You can find them for as little as £30. Direct fit and improved my electrics and charging. 

[Mk2Kezza]

Cheers Mr Blue.

Ended up getting an alternator from GSF (£65). Seems to have sorted the issue - 14.4v at idle! Need the juice this time of year!

[sparkplug]

"Any idea what the B+ symbol means? Is it to add additional voltage/current feed to the battery? Is this why she is not charging correctly?"

yes
 you need a 12volt supply to excite a field in the alternator