Charging Voltage Issue?
 

Hello again Pelicans.
I worry about things. However, when I see something change I figure there must be a reason.
Case - 2006 Chevy Tahoe 160k miles or so...
Volt meter on dash reading about 14 or just above since I owned the car. Recently it jumped up to 15 or maybe slightly above. I checked the voltage using a handheld meter at the battery and a digital meter that plugs into the cigarette lighter. They all seem to be reading close so I believe the 14->15v really is happening.
The high reading doesn't happen until I've been driving for awhile. Then it stays high. Some times it drops to 13 or a bit lower and then goes back to 15 while driving.
I got a new battery yesterday thinking it might be the battery.
The issue is still happening.
I went to my local Napa store and got the charging system "tested". Of course the volts didn't go up to 15v (only read 14.2) while the guy was testing so I didn't buy the new $230 alternator.
I'm thinking of driving it for a few days to see what happens but I don't think the higher volts coming out is right. What do you think?
Thanks,
-Henry

If I had to guess, I'd say it's an alternator issue, but that's just a guess.

The voltage regulator and alternator determine what is put out (VR internal to Alt 99% of the time). So if you're seeing too much power sometimes, then I'd expect that to be an issue with the VR/Alt combo.

If you have the time, just have your current alternator rebuilt by a local repair shop. Take it off, drop it at the shop, and ask for a non Chinese bearings, and a rebuild. It will be cheaper than a "refurbished" unit from the loacal parts store, and likely a better unit, not built in some factory where price and speed of the rebuild is the only things they care about.

At this point - I agree. I'll probably get the new alt. and see what happens. The current alt. has 4 or 5 years on it so it could be due. I can't remember if I've replaced it before or not. I got the car with 100k miles. Thanks for the comment.

Okay - good idea. There used to be a good rebuilding place near here. I'll see if I can find another one. When I got my Porsche alt. rebuilt the guy installed the good bearings and other parts, but he was only doing Porsche alts. at the time.

First off, I would want to see the actual voltage from the alternator measured with a good voltmeter. Your dash gauge is probably right, but I would want to see a proper confirmation before I did anything drastic.

If it's out of spec why not change the voltage regulator, or have a rebuilder do it?

I'm looking at 3 volt meters (dash, old volt meter, new digital meter) and they seem to be reading the same. It is difficult to put leads on the battery while I'm driving.
My plan is to go to the rebuild place and see what they can do. I don't mind the cost I just want the regulation to be correct.

Your lighter outlet is all you need to check.

You need a new voltage regulator. It's probably easy to swap.

Check the connections to your alternator? It does sound like the regulator is acting up, with too high voltage you will end up boiling the water from your battery.

Update in case people want to know....
I took it to the rebuilding guy. He knew (thought he knew) exactly what it was wrong said the brushes were worn down too far. In a few minutes replaced the regulator module with brushes. I took it back home and installed. Voltage was still not stable. Readings to 15 volts and then reads 13.1 volts.
Now he ordered a new alternator or might rebuild my old one. I'm not sure.
One thing he said... The alternator is controlled to some degree by the computer and we hope that is not the issue. I hope that is not the issue. Stay tuned.

voltage regulator. are they now internal to the alternators?

Interesting. So he changed the VR and it's still wonky? Very interesting. I was unaware, but would not be terribly surprised if the ECU had some amount of input or control over what was going on. Still, I'd be replacing the alternator if the VR didn't do the trick.
In most cars, they are internal and have been for a long time. There were some manufacturers that held out. I want to say maybe FoMoCo or Chrysler/Dodge had external VR for many years after most others had gone internal.

It sounds like he swapped the internal VR and is still having the same issue.

Yes, No and now I'm not sure. Good question.
There is a "regulator" module on the back of the alternator.
The "expert" explains that the "computer" controls the voltage or is somehow involved.
Maybe someone can chime in and let us know.
The application is huge - 2006 Tahoe 5.3 motor. This means there is a huge population out there with the same setup.

Looks like that model has a battery current sensor, you could try changing that, pretty cheap. All this added electronic crap to save a gallon of fuel every year.

The other comment he had is that one or more of the diodes are out or are intermittent.
This makes some sense as I watch the volts while driving. We should find out by the end of today.

I used to sell rebuild kits. I'd have thought that if he was going to tear into an alternator, that he'd replace the bearings, brushes, VR, and diodes.

I wouldn't be all that worried at only 15 volts instead of 14.....

Changing the regulator module is very easy. The brushes are attached to the regulator module so you get those for "free". The other items (bearing, diodes) you mentioned are much more involved to change. Per some of his comments I got the impression that the bearings are very good in the original OEM. The replacement bearings he has or can get might not be as good. I think the alt. is original and has 168k miles at this point and still spins very quiet. Still worse new bearings might be better than better 168k mile bearings.
Another thought I had....
The computer(s) in the car are very dependent on getting good clean power. It is a question - Should the computer be responsible for regulating the power?

Seems like shooting 15v into a fully charged battery wouldn’t be good for the battery.

^^ On top of that, the voltage is out of control, so it could go higher.