Usually my self installed volt meter shows the car running at 14.3 Volts all the time. However, yesterday I noticed it showing 12.5 volts. A short while later, it went back to 14.9 Volts for a short time. Then went back to 12.6/12.5. Did this a few times. I haven't been out today yet. I assume it's a faulty alternator, but no CEL or anything showing on dash. Drive belt appears to be correct tension.

If it is faulty, how big a job is it to replace? Looks as if it wouldn't be the easiest of access. Plus I'd have to find an alternator.

Any comments would be appreciated, thanks.

 

Are you measuring the voltage across the battery, or somewhere else?

 

Hi JM. Hooked into the driver's fuse box. Right hand drive. Wondering today if it might be the regulator, as opposed to the actual alternator, although I assume the regulator is built into the alternator instead of being separate. It takes a while before it starts playing up, presumably after it is well warmed up. It has been okay until a couple of days ago. I will be checking directly across the battery in a couple of days or so, but I don't expect it to be any different, although one can but hope!

 

To take the alternator off, do you drop it down through the bottom, or pull it up through the top? A quick look from the top, looks as if there is more room to drop it down.
Does anybody know if there are instructions anywhere on how to go about removing it?

It seems that driving at night, it may not be a problem, but only done so twice, so can't be sure. I don't know if it may be because it is cooler, or because there is more load on the alternator with the lights on.

 

When the charging system determines the battery is fully charged it reduces the output (voltage) to save fuel. Today's alternators are nothing like the ones from 25+ years ago especially on more advanced cars and trucks.

Its 24 minutes long but a good watch:

 

Thank you Protholl. Very interesting. I have watched a lot of his videos, mainly based on the LS430, but haven't seen that one before.
Haven't had the problem since I reported it, but that may be because I haven't done any longer trips over about 30km. I have also tapped on the alternator in situ with a hammer, reasonably hard, but not too hard, in case it may have been stuck brushes, so it remains to be seen

 

It's fine, modern cars have monitoring and managing systems to not overcharge or waste energy charging an already full battery.

 

Protholl, thanks for going to the trouble of posting this video. Once again CCN mentioned a couple things I'd never heard before.
He enumerates all the key points @22:00:

1. Don't try to run or drive a car with a dead or failing battery; the alternator will overheat and destroy itself trying to charge it.
2. Keep alternator clean and dry; to clean an alternator, don't use water nor brake cleaner, use electrical contact cleaner only.
3. When alternator makes a whining noise (that varies with engine speed), it needs to be replaced.
5. Don't buy an aftermarket alternator - use only OEM alternators .