Originally Posted by
glintoz
Yeah, that is normal believe it or not. They are a 'smart' alternator that charges on demand to save fuel.
When you are coasting or decelerating (foot fully off the accelerator) the alternator will jump up to 14.7v or so. Sometimes it will run at 13.8v sometimes 12v, sometimes 14.4-14.8v. I had a pile of issues last year and did a whole pile of monitoring but could never predict exactly what voltage it would output except when decelerating with the foot off throttle where is was 14.7 V.
If you have the VC go to the trip computer function and look at the fuel consumption screen. When you back off the throttle you will see the indicator drop back to the LHS to the battery icon and change to green. This is when the alternator is outputting max voltage.
There are digital voltage displays that plug into the 12V socket (cig lighter) in the console that will show you what is happening.
Are you having problems with the battery going flat?
My neighbour disabled the smart charging using VCDS on his Toureg - it is something like 'energy recuperation' but I haven't had a change to get him to come and look and see what can be done on the S3.
Thanks for your inputs and confirmation on how the charging system operates on your car. Seems like your experience exactly mirrors mine.
The VC indicator does correlate with my voltmeter readings when the battery icon change to green, which is expected. What I found alarming was the "none charging" aspect of it. I certainly didn't expect it to drop all the way down to just 12.0V at idle and at load with the lights on. When this happens from past experience, it usually indicates the alternator is about to poop it's pants. Now that I think about it some more, if 12.0V can be maintained (and doesn't drop any further), it makes perfect sense that the alternator is outputting just enough "juice" as needed.
I'm not having any issues with the battery or the electrical system. I was just super concerned when I saw this for the first time monitoring it at night when I saw the "low" 12.0V operating voltage with the headlights on. Other than this S3, I've never seen an alternator output that bounces all over the places during operation. I'm relieved to hear that you're seeing the same on your end and could just be the "Standard Operating Procedure" for this car. Again, very much appreciates your inputs.
Originally Posted by
MikTip
I DIY replaced the entire alternator. It was quicker and less expensive to get the entire alternator vise a pulley and the special tool set required to R&R the pulley...
On my 2015 its a constant voltage when the engine is running. I check with a volt-meter at the battery terminal connectors. Don't have a cig lighter volt meter.
The alternator is producing voltage the entire time the engine is running...
There's a black box under the dash which controls the cars electrical system and the alternators voltage regulator to vary the voltage based on demand.
How old is the battery?
Seeing that "glintoz" is observing similar behavior on his car, it does appears that Audi changed their charging algorithm for the FL since you're seeing a constant charging output when the engine is running on your Pre-FL.
My battery just past it's 5th birthday, which did attributed to my initial panic. I usually replace the batteries on my cars every 5 years or so just as a precaution. I will be getting a new battery soon, regardless.
Your lead have been very helpful and thank you for that! Thankfully, I don't believed that I need to chase this down any further...I think
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