Alternator light on - but Voltage fine?

[HastaAlaska]

Hey guys,

I'm 150 miles from my last problem, time for another one

The alternator light has just come on (and staying on) on the highway towards Rome. I've pulled over, and troubleshooted it but it looks like the Voltage is at 13.7V - 14v and stable.


The red light goes off at idle but comes on again over 1500 RPM.

I have a volt meter on the dash which is reading 13+v and stable.

I checked the alternator bushes:

I'm a little confused about this behavior and unsure if it is OK to continue to drive. I'd really appreciate your thoughts on what's going on. Thanks


EDIT: Battery 1 year old with battery maintainer so it's not that
Wiring 4 years old so probably not that either?
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[telford dorr]

Measure the voltage at the alternator B+ (stud) terminal and at the alternator D+ (1/4" spade terminal). They should be very close to the same voltage - 13.8 to 14.4 volts. Compare that to the voltages found at the fuse block red and black wires (again, 13.8 to 14.4). If the light is on, you'll find one or more of these voltages significantly different. Knowing the values can suggest a diagnosis.
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[HastaAlaska]

ok I will do that and report back. Thanks for the help, it's appreciated.
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[HastaAlaska]

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[HastaAlaska]

I've checked the tranny ground strap, it's fine.

The alternator B+ and Battery are both registering 14v whilst the D+ is registering 17v

Does this definitely mean it is the regulator? Or could there be another cause/something to check?

Back in 2012 the Alternator regulator went bad in Bolivia, but in that instance, the alternator and battery were registering 17v as well. A handy guy in the middle of the Andes adapted the alternator to have a new external regulator - not sure if the Italians would be willing to take the same approach or just install a new alternator

Mine here is also the Bosch 55A internal regulator style (i think AL82).
If it is definitely the regulator, is that something I can replace myself in the (literally) field?

If the battery and B+ are putting out 14v can I drive for parts? I'm off the road, 50 miles from Rome. Help appreciated.
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[Wildthings]

[HastaAlaska]

Anyone know, Is a Bosch AL82 alternator only used in vintage VWs or is there a wider use. Just wondering how likely someone would be able to fix the internal regulator? I’m not clued up on this area so input appreciated.
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[HastaAlaska]

Could these symptoms be caused by bad alternator brushes?
They one have 30k miles on them which is way under the expected 75k norm but the alternator is used heavily in my application. Brushes I might be able to tackle myself, assuming I can source them.
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[telford dorr]

A major voltage difference between the alternator B+ and D+ terminals is usually an alternator diode problem, not a regulator or brushes. Unfortunately, the alternator is a dog to remove, involving an engine pull and fan housing removal. You know the drill.

If you're getting 14 volts at the battery, go ahead and drive it to some place where you can work on it. Can't hurt the alternator any more than it already is...
_________________
'71 panel, now with FI
'Experience' is the ability to recognize a mistake when you're making it again - Franklin P. Jones
In theory, theory works in practice; in practice, it doesn't - William T. Harbaugh
When you're dead, you don't know you're dead. The pain is only felt by others.
Same thing happens when you're stupid. - Philippe Geluck
More VW electrical at http://telforddorr.com/ (available 9am to 9pm PST)

[kreemoweet]

The stock AL82 regulator is located in the front of the alt housing, and replacement requires removal and disassembly of the alternator. This can be done, with the correct tools and a fair measure of patience, without removing either the engine or fan housing. However, there are aftermarket regulators for the AL82 which is combined with the brush assembly (incidentally, the photos above indicate your brushes are fine). If you had one of those, you could just pull the existing brush assembly, clip off the 2 wires going to the existing regulator, and install the combo unit. But it does seem likely yours is not a regulator problem.
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[bsairhead]

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[mikedjames]

As B+ and D+ are both connected via diodes to the stator windings, if there is 17V on D+ it means the regulator is correctly commanding an increase in voltage.. as B+ is not getting to about 14.2 volts .

So its likely that one or more of the big diodes has gone open circuit.
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[HastaAlaska]

[Abscate]

An EFI will have a bigger draw, yes.

You can pull Alternator without an engine drop by raising the fan shroud and propping it up to access the bolds facing backwards. It’s probably comparable time to an engine drop but easier work.
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[HastaAlaska]

[richparker]

Just buy a new alternator and move on.
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