Alternator Issue on BEW, diodes?

turbotorq · Jan 11, 2017

Battery voltage is 12.6v

Idling voltage is 13.5v

Idling while using all possible amp drawing settings, voltage drops to 12.4 and jumps back up to 13 then drops again.

Should alternator keep above 13.5v's at idle even when using headlights heated seats radio etc?

My original symptoms was dead battery, but after my battery charger reading "fully charged" after only 30 mins of charging, I assumed my problem was starter. Pulled starter off my ALH parts car, exact same problem. Pulled murano battery, threw it in BEW, VVVOUURRMM….. is my alternator killing my 790cca battery?

Tdijarhead · Jan 11, 2017

Idling voltage should be 14.3+. Your alternator or alternator pulley is soon for the boneyard.

turbovan+tdi · Jan 12, 2017

Get the revs up to check, you can't diagnose it at idle, need more rpm, raise it to 1500 and take a reading.

turbotorq · Jan 14, 2017

turbovan+tdi said:
Get the revs up to check, you can't diagnose it at idle, need more rpm, raise it to 1500 and take a reading.

At 2,000 rpm, battery is showing 14.1 volts. At idle, even my dome lights are flickering. Need to rev it up to find stuff at night!

turbotorq · Jan 14, 2017

Alt pulley passed test, only free wheels counter clock .

Tdijarhead · Jan 14, 2017

Pulley should turn in only one direction. Not the other. Your alternator sounds like it's toast. If you're at idle just sitting in the drive way and you don't have 14+ volts your battery is not being charged properly.

turbovan+tdi · Jan 15, 2017

turbotorq said:
At 2,000 rpm, battery is showing 14.1 volts. At idle, even my dome lights are flickering. Need to rev it up to find stuff at night!

Yep, sounds like the alt. I usually just replace the diode/rectifier portion of the alternator, I do it in the car. If the armature is too worn, then you have to replace the alt.

turbotorq · Jan 15, 2017

turbovan+tdi said:
Yep, sounds like the alt. I usually just replace the diode/rectifier portion of the alternator, I do it in the car. If the armature is too worn, then you have to replace the alt.

I did replace regulator last year, the one brush was badly worn and other had at least 1/8" more meat. I assume its diodes but could be bearing. I have 2 other parts alternators a 90 AMP and 120 AMP. I also have a parts alh that still has its alternator on. Maybe ill pull that one. The amount of issues I've had with alternators with this car I should of just bought a brand new one rather than used ones. Used parts seem to only last 50 k miles then I have another problem. Pretty frustrating, but at least its a BEW where the alternator is so easy to get at! ( Shots fired at ALH owners

)

pdq import repair · Jan 15, 2017

How many amps does it produce when loaded? Do you have A/C voltage riding on top of the charge lead?

Dimitri16V · Jan 15, 2017

turbotorq said:
I did replace regulator last year, the one brush was badly worn and other had at least 1/8" more meat. I assume its diodes but could be bearing. I have 2 other parts alternators a 90 AMP and 120 AMP. I also have a parts alh that still has its alternator on. Maybe ill pull that one. The amount of issues I've had with alternators with this car I should of just bought a brand new one rather than used ones. Used parts seem to only last 50 k miles then I have another problem. Pretty frustrating, but at least its a BEW where the alternator is so easy to get at! ( Shots fired at ALH owners )

Alternator is one of those parts that is never troubleshot correctly and unnecessarily replaced
If voltage is low , replace the regulator ( brushes are worn )
If diodes are dead , you will not get 12V DC

turbotorq · Jan 15, 2017

pdq import repair said:
How many amps does it produce when loaded? Do you have A/C voltage riding on top of the charge lead?

sorry don't understand your question please explain.

turbotorq · Jan 15, 2017

Dimitri16V said:
Alternator is one of those parts that is never troubleshot correctly and unnecessarily replaced
If voltage is low , replace the regulator ( brushes are worn )
If diodes are dead , you will not get 12V DC

So what is my problem then

? Regulator and brushes are new.

Tdijarhead · Jan 15, 2017

If you have a known good one just swap it out.

Vince Waldon · Jan 15, 2017

turbotorq said:
So what is my problem then? Regulator and brushes are new.

What was the communtator like when you replaced the brushes? Often when the brushes are worn the communtator is too... and if so it can very quickly wear out the next set of brushes.

PB_NB · Jan 15, 2017

turbotorq said:
( Shots fired at ALH owners )

My 17 year old (original) alternator is still working fine

turbotorq · Jan 15, 2017

Vince Waldon said:
What was the communtator like when you replaced the brushes? Often when the brushes are worn the communtator is too... and if so it can very quickly wear out the next set of brushes.

Good question. I should definitely check that out. Im going to pull the alt soon and tear it apart.

turbocharged798 · Jan 15, 2017

I have done a lot of fooling around with the common Bosch 120A unit used on the manual ALH and BEWs. The most common problem is that the brushes on the voltage regulator wear out and then the alternator quits. The brushes are part of the voltage regulator which can be replaced on car for about $50 or so. The problem is that the slip rings also wear out and that requires the alternator to be completely taken apart.

Also common is the rear bearing to fail. I don't know what will happen if you let it go a long time but 50% of them have failing rear bearings. The front bearing is much larger and lasts longer even though its under more load.

The diode packs do fail but its rare. My 99.5 had a diode failure and it caused the alternator to go into meltdown as it resulted in a direct short. Nearly started a fire. If concerned about the diode pack you can always use a multimeter with diode check feature to check them.

turbotorq · Jan 15, 2017

turbocharged798 said:
I have done a lot of fooling around with the common Bosch 120A unit used on the manual ALH and BEWs. The most common problem is that the brushes on the voltage regulator wear out and then the alternator quits. The brushes are part of the voltage regulator which can be replaced on car for about $50 or so. The problem is that the slip rings also wear out and that requires the alternator to be completely taken apart.

Also common is the rear bearing to fail. I don't know what will happen if you let it go a long time but 50% of them have failing rear bearings. The front bearing is much larger and lasts longer even though its under more load.

The diode packs do fail but its rare. My 99.5 had a diode failure and it caused the alternator to go into meltdown as it resulted in a direct short. Nearly started a fire. If concerned about the diode pack you can always use a multimeter with diode check feature to check them.

well said. Ill assume its not the diodes. Check my other threads I started, Im having issues with trans & thermostat in my BEW maybe you can help ?

turbovan+tdi · Jan 15, 2017

turbotorq said:
I did replace regulator last year, the one brush was badly worn and other had at least 1/8" more meat. I assume its diodes but could be bearing. I have 2 other parts alternators a 90 AMP and 120 AMP. I also have a parts alh that still has its alternator on. Maybe ill pull that one. The amount of issues I've had with alternators with this car I should of just bought a brand new one rather than used ones. Used parts seem to only last 50 k miles then I have another problem. Pretty frustrating, but at least its a BEW where the alternator is so easy to get at! ( Shots fired at ALH owners )

ALH is a little harder but easily done on the car.

turbotorq said:
well said. Ill assume its not the diodes. Check my other threads I started, Im having issues with trans & thermostat in my BEW maybe you can help ?

If you don't diagnose, inspect parts properly, how can you expect anything to work, last?

The regulator and diode assembly is one unit but won't do a thing if the slip rings are worn or the stator has an open. If you can't properly test your parts, best course of action is a new/reman alt with a warranty.

turbotorq · Jan 17, 2017

turbovan+tdi said:
ALH is a little harder but easily done on the car.
If you don't diagnose, inspect parts properly, how can you expect anything to work, last?
The regulator and diode assembly is one unit but won't do a thing if the slip rings are worn or the stator has an open. If you can't properly test your parts, best course of action is a new/reman alt with a warranty.

Uhhhh are you sure about the regulator / diode assembly being ONE unit? As far as I know the regulator comes off with 3 philips screws, The diode assembly beneath reg, is soldered onto the windings?

turbotorq · Jan 17, 2017

update; pulled alt, pulley is fine, slip rings look fine. Brushes are full length, What does that leave me with? diodes, loose connection, rear bearing?

turbovan+tdi · Jan 17, 2017

turbotorq said:
Uhhhh are you sure about the regulator / diode assembly being ONE unit? As far as I know the regulator comes off with 3 philips screws, The diode assembly beneath reg, is soldered onto the windings?

Hmmm, now you have me thinking. I'll have to look at one of my spares tomorrow.

turbotorq said:
update; pulled alt, pulley is fine, slip rings look fine. Brushes are full length, What does that leave me with? diodes, loose connection, rear bearing?

Rear bearing won't cause it unless its totally shagged. Could be faulty parts. I think at this point, you're better off just getting a good used one or a reman/new unit or find a local rebuilder, I have one in my complex and he's great.

Wankel7 · Apr 17, 2017

Sooooo....how did it pan out?
Working on this issue....
http://forums.tdiclub.com/showthread.php?t=460528&highlight=regulator+amazon

rotarykid · Apr 25, 2017

turbotorq said:
update; pulled alt, the pulley is fine, slip rings look fine. Brushes are full length, What does that leave me with? diodes, loose connection, rear bearing?

did you check to make sure the engine ground was not damaged or corroded? A faulty ground can cause charge problems....

JB05 · Apr 25, 2017

I was wondering where the OP purchased his replacement regulator.

Fahrvegnugen · Apr 28, 2017

I think diodes can be tested with car running, put low ac volt reader on battery terminals and if there is anything other than zero the alternator is garbage. I'm getting ready to replace mine

pruzink · Apr 28, 2017

Remove the nuts for the alternator fuseable link & inspect/replace the link. To the eye, the fuseable link can look perfect; however, under the nut there is galvanic corrosion due to copper wire connecting to aluminum link held in place by steel nut.

Fahrvegnugen · Apr 29, 2017

Fusible links and connection look perfect, but copper cable ends are a little brown. Today car wouldn't start at all, no glow plug light, lots of clicking and buzzing. Sprayed deoxit all over the fuse box and then battery terminals. Ground terminal started smoking. Started up like normal after this.

Alternator Issue on BEW, diodes?

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