Alternator output voltage

The car is a 2017 2.0TFSI 190 with 11,500 on the clock.

What would you expect the alternator's output voltage at idle to be after a cold start, and are there any normal circumstances under which it might vary?

Measuring at the battery - which may well not be holding charge as it should - I got 12.54V this morning

That seems pretty low.

The other day I got 13.33V, which would appear to be a bit more like it, but why might it be different this time?

Thanks

Pete

P.S. It's going in for an investigation next week, but I'm trying to get my head round what might be occurring out of curiosity.

P.P.S. While I appreciate its limitations, I'm not getting any faults on the full version of Carista.

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AlS3BE

Registered User
I’ve been looking at this as I think my battery could be faulty or possibly alternator. Had a few low battery warnings in the dash but car still starts every time.
While ticking over the car hovers around 14v which is fine. As soon as the car is off the battery drops to 12.2v and within a few minutes with the stereo running it drops below 12v sometimes as low as 11.5v. The dashcam is set to turn off at 12v so sometimes it doesn’t make it through the night.
Mine is going in for a service soon so will get them to check it out.
 

ZipZap01

Registered User
The alternator voltage is adaptive to engine load, battery condition, etc.

The alternator will be also be disabled when not needed, and the car will temporarily run on battery only.

Voltage while the car is running can be anything between 12 and about 14.6 volts.

The ECU will set a fault code if the voltage is not what it wants it to be. These cars are very sensitive to electrical load and will set fault codes for things like dashcams as unknown power drain.
 
I’ve been looking at this as I think my battery could be faulty or possibly alternator. Had a few low battery warnings in the dash but car still starts every time.
While ticking over the car hovers around 14v which is fine. As soon as the car is off the battery drops to 12.2v and within a few minutes with the stereo running it drops below 12v sometimes as low as 11.5v. The dashcam is set to turn off at 12v so sometimes it doesn’t make it through the night.
Mine is going in for a service soon so will get them to check it out.
Nothing untoward on the dash here, and like yours it's never failed - or been in any way reluctant - to start.

Summink ain't right though.

I've tested the battery as low as 12.03V in the past, and I don't recall having seen a fully-charged 12.6/12.7V for yonks. 12.3 to 12.4 ish is about the best it's been.

There ain't much in there at 12.03, that's for sure...

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AlS3BE

Registered User
Nothing untoward on the dash here, and like yours it's never failed - or been in any way reluctant - to start.

Summink ain't right though.

I've tested the battery as low as 12.03V in the past, and I don't recall having seen a fully-charged 12.6/12.7V for yonks. 12.3 to 12.4 ish is about the best it's been.

There ain't much in there at 12.03, that's for sure...

.

That’s my worry. I would expect a fully charged battery to be around 12.5v+
Even after a 2 hour drive it drops to around 12.2v as soon as ignition is off.
Will see what the dealer says.
 

AlS3BE

Registered User
In order to leave space for engine braking energy recovery boost charging, the battery is not allowed to charge to 100%.

Normal battery voltage on these cars is about 12.2—12.3
So that’s creating the problem for the dash cam.
Main reason is I travel a bit for work so car is either at airport car park or somewhere like a hotel. Would like to keep the camera running so it will catch anyone who decides to bash my car.
What’s the lowest voltage the starter will run at?
 

ZipZap01

Registered User
The car will still start down to about 11.7 V - but the car will complain about it. Dash will light up like a Christmas tree with low battery warnings, and the car will disable stuff to save power . There will be no cabin lights, MMI, headlights, etc. until the engine has started - you won't get the auto lights on unlock and various other things.

I've found you get about 4 hours of camera run time reliably off the car's battery. Above 4 hours, and ECU starts to set fault codes about excessive battery drain. With the camera set to 12 hours, while it will usually record the full 12 hours, there are days when the camera will shut off early due to low battery (12 V cutoff). Setting the cutoff below 12 V has the car going into panic battery save mode, and beeping and flashing dash lights at you, although I've never had it fail to start.
 

Boydie

S3 8V DSG
VCDS Map User
61B9C781-630C-4DDF-9764-E14C3DB4FD71.jpeg
This popped up this morning on my 2014 S3 :(

Anyone a part number for the alternator or an idea of what to check before replacement

thanks
 

desertstorm

Moderator
Staff member
Moderator
VCDS Map User

Boydie

S3 8V DSG
VCDS Map User
@desertstorm thanks for the advice - where is the regulator located? part number?

I assume its a bumper off job to get the alternator out, handy enough to put the belt back on? Never done this job before and mechanic cant see me for 2 weeks :(

Battery was replace end of 2019 and was reading 11.5v yesterday evening after driving home with the fault FYI
 

desertstorm

Moderator
Staff member
Moderator
VCDS Map User
Regulator is mounted on the end of the alternator fairly easy to replace once the alternator is off.
You need to find out if you have a Valeo or Bosch alternator as they have different regulators.
The Bosch part number for the regulator is 0272220854
https://www.autodoc.co.uk/bosch/8205604
https://www.autodoc.co.uk/era/9258401
Stick you hand down the back of the alternator with your phone and see if you can take a picture of the rear of the alternator.
Looks like they come out without removal of the front of the car. Do a google search
A genuine new Bosch Alternator
https://www.ebay.co.uk/itm/VW-GOLF-R-GENUINE-OEM-BOSCH-ALTERNATOR/192358191945?
 

Morris39

Registered User
In order to leave space for engine braking energy recovery boost charging, the battery is not allowed to charge to 100%.

Normal battery voltage on these cars is about 12.2—12.3
Not quite. Standard, normal and usual are not the same meaning, knowing the difference is useful,
Standard applies to a new battery at a specific temperature (chemistry). Usual is just an undefined statistic. Normal (for your particular service) is what you can observe as limit of satisfactory performance. Practically this is the one that is important to know but some work is needed to observe.
 
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