TheSamba.com :: View topic - Alternator light on

Tue Oct 10, 2023 5:53 am

Hey guys,

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

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?

Tue Oct 10, 2023 11:21 pm

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.

Wed Oct 11, 2023 2:20 am

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

Wed Oct 11, 2023 7:13 am

telford dorr wrote: 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.

B+ is 14.4 v
D+ is 17v

I didn't check the fuse block end as I'm thinking this is enough to show the regulator is bad - what do you think?

Wed Oct 11, 2023 8:24 am

HastaAlaska wrote: telford dorr wrote: 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.

B+ is 14.4 v
D+ is 17v

I didn't check the fuse block end as I'm thinking this is enough to show the regulator is bad - what do you think?

I agree. That 3V difference is enough to Light up the idiot light. Fix it soon so that the 17V doth not your battery cook.

Wed Oct 11, 2023 9:07 am

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.

Wed Oct 11, 2023 10:54 am

HastaAlaska wrote: 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.

I would not think it would hurt anything assuming you keep an eye on the battery voltage. Also you should be able to easily drive 50 miles with the alternator disconnected and run on the battery alone.

Wed Oct 11, 2023 11:11 am

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.

Wed Oct 11, 2023 11:29 am

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.

Wed Oct 11, 2023 6:50 pm

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...

Wed Oct 11, 2023 9:03 pm

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.

Wed Oct 11, 2023 9:59 pm

Wildthings wrote: …you should be able to easily drive 50 miles with the alternator disconnected and run on the battery alone.

:lol:

With solar and a wire you can drive indefinitely off the leisure battery.

Robbie

Wed Oct 11, 2023 10:31 pm

airschooled wrote: Wildthings wrote: …you should be able to easily drive 50 miles with the alternator disconnected and run on the battery alone.

:lol:

With solar and a wire you can drive indefinitely off the leisure battery.

Robbie Get a magneto and park on hills :wink:

Wed Oct 11, 2023 11:52 pm

airschooled wrote: Wildthings wrote: …you should be able to easily drive 50 miles with the alternator disconnected and run on the battery alone.

:lol:

With solar and a wire you can drive indefinitely off the leisure battery.

Robbie

I hadn’t run the math on that.

Ignition coil draw about 4 amps, 50 watts.

Need a 150-200 watt panel to keep that in charge neutral condition , maybe a bit less in sunny Italy with panel on top

:)

Thu Oct 12, 2023 12:55 am

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.

Thu Oct 12, 2023 1:04 am

telford dorr wrote: 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 someplace where you can work on it. Can't hurt the alternator any more than it already is...

I woke up this morning determined to get new brushes, but by the sounds of it that isn't my problem. Thank you for sharing your experience and saving me a big headache. :vw:

I have the type-1 engine, so I think I can remove the alternator with standard tools, without dropping the engine. Mexico, 9 years ago was the last time I had to do it and I think the engine was out then. I can barely remember the process, so please somebody speak up if I'm about to discover a world of pain / need special tools, as I won't be able to drop the engine where I am.

I have a spare alternator back home, perhaps the best course of action is to get it shipped down to Italy ASAP.

Abscate wrote: airschooled wrote: Wildthings wrote: …you should be able to easily drive 50 miles with the alternator disconnected and run on the battery alone.

:lol:

With solar and a wire you can drive indefinitely off the leisure battery.

Robbie

I hadn’t run the math on that.

Ignition coil draw about 4 amps, 50 watts.

Need a 150-200 watt panel to keep that in charge neutral condition , maybe a bit less in sunny Italy with panel on top

:)

I think probably a bit more than 4amp for our Gen4 EFI system. Still, we have 370W of solar and 400ah of lithium batteries so that should keep us running for a while. :lol: In reality, it would require a re-wire of our current system to make this happen - but it would be an interesting experiment to see how far we get wouldn't it :lol:

Thu Oct 12, 2023 3:00 am

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.

Thu Oct 12, 2023 5:43 am

mikedjames wrote: 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.

Just retested, does this support your theory about the diode being the issue?

Unloaded (all house battery system off and isolated):

14.2 - 14.5 on B+ terminal
17 - 19 on D+ Terminal

Loaded ( house battery system charging at about 20-25 amps)

max 13.7 on B+ Terminal
17 - 19 on D+ Terminal

Also, there is a bit of a droning noise audible at a certain RPM, have a listen to the video. Is that the alt bearings?

Note this video is with the house battery system connected and charging so it is not showing the full potential output of 14.4v. I've disconnected all house batteries from the alt now as I just want to focus on the alt related issue.

Thanks v.much

Thu Oct 12, 2023 6:07 am

Just buy a new alternator and move on.

Thu Oct 12, 2023 6:46 am

richparker wrote: Just buy a new alternator and move on.

This made me laugh. Yes you have an Alt problem. Get a new one.