Battery not charging

[DiscoTony]

The battery is not charging all the time on my Touran diesel. The battery is less than three months old. The belt is on the alternator, turning as it should with what appears to be adequate tension. (belt hasn't been off since early December and no issues from then until this weekend). There is no battery warning light when I have the engine running. The battery light on the dash does work as it illuminates when the ignition is turned to position 2. I have used the car for work over the weekend, git in on Fri night, would not start. Bumped it, drove 40 mile, worked my 12hr shift, came out, car only just started. Drove home, went to bed, got in to go to work, battery flat, bumped it. Drove to work, did shift, came out, battery flat. Drove home, went to bed, got up to go to work, car started (just), went to work, did shift, came out, battery flat, got up today, just enough in it to start the car (12.47 volts when I got home this morning, 12.3 when I got up and it started), drove for 10 miles or so, checked voltage with engine running, 11.8v, drove home, turned off, 11.7v. Have not used lights or wipers excessively over the weekend as weather has been fine, have left radio off and not used heated rear window etc. I am stumped.

[vwcabriolet1971]

Normal alternator charging voltage should be over 14V (say14.2V at least) so there is a problem with your alternator. My guess is that your voltage regulator brushes are worn and the regulator needs replacing. Most garages will replace the complete alternator as this is the quickest & easiest for them.
a new voltage regulator ( which is part of the alternator) is only about £25).

[itavaltalainen]

yeah, i'd say voltage regulator too...

easy fix. if you need instructions let me know.... might even be possible with alternator in situ...

[DiscoTony]

Thanks for the pointer guys, after looking round, it was easier to buy a used alternator, it arrived at 5pm, I only ordered it at 11am! As I'm selling the car (hopefully this week), going to any more expense than this does not make a lot of sense. I've swapped the alternators but given up after an hour of trying to get the belt back on in the cold and dark so I'll go back to it in the morning. I appreciate your help, Tony