Passat Repaired Alternator Problem

[Gunner786]

Passat B7 2011 2.0 Diesel

Got my Alternator repaired last week as battery light was comimg on more frequently.
All was fine till yesterday morning on startup battery light came on for 1 minute.
Got the voltage tested today.

Engine off 12.56-57
Engine on 12.56-57

Seems like battery isnt getting any charge but the car is running all day so it must be getting some sort of charge.
Light only comes on and off once in morning.
Alternator guy reckons its the regulator in the alternator.
Any idea's?

[Decky_Q]

Is it the original alternator after a repair or is it a new alternator?

I had similar on a mercedes I was working on, I fitted a new alternator and output wasnt high enough to charge the battery, turned out there were 6 versions of the alternator for that same engine and I'd got a spurious version that had been copied from one version and then the part number for all versions were listed on the box. Genuine part sorted it.

Also check if the charge voltage increases with revs, should be 13.5 by 2k rpm, idling charge is pretty limited.

Edited by Decky_Q on Tuesday 12th April 21:36

[stevemcs]

Put the lights on, heated window on, heating on and then see if the voltage increases.

[Gunner786]

Ok done an overnight test

[Gunner786]

Very weird now going to do it when its hot after couple hours running

[E-bmw]

Alternator is working then.

[Gunner786]

Just tested it again after 2 hours running. Not charging now

[Polly Grigora]

Gunner786 said:

Just tested it again after 2 hours running. Not charging now

What's the light showing at present?

Is there a good + & - @ the alternator when it's not charging?

[littleredrooster]

Gunner786 said:

Just tested it again after 2 hours running. Not charging now

Smart alternator? Only charges when needed, and usually when slowing down on the over-run. Energy efficiency and all that, but makes them a bugger to test!

[E-bmw]

littleredrooster said:

Gunner786 said:

Just tested it again after 2 hours running. Not charging now

Smart alternator? Only charges when needed, and usually when slowing down on the over-run. Energy efficiency and all that, but makes them a bugger to test!

^^^^ Wot 'e said.