Alternator Question

tdihopeful

Veteran Member
Joined
Oct 23, 2008
Location
California
TDI
03 2dr 5sp Golf
In an attempt to keep my car somewhat healthy as it is sitting waiting for me to install a new clutch, Helicoil in wheel bearing housing and general cleaning I decided to start and run the engine for a while. I noticed that the alternator wasn't spinning at idle. Is this normal? From what I understand the ecu makes changes to the output of the alternator based on electrical requirements from various systems on the car but it seemed to me that the alternator shouldn't be standing still. I don't really know however to be honest thus thanks for taking the time to help me understand this.
 

csstevej

Top Post Dawg
Joined
Aug 12, 2004
Location
north nj
TDI
2001 golf tdi 4 door auto now a manual, mine, 2000 golf 2 door M/T son's,daughters 98 NB non-TDI 2.0, 2003 TDI NB for next daughter, head repaired and on road,gluten for punishment got another tdi 2001NB,another yellow tdi NB
Sounds like your freewheeling clutch is toast.
it can be changed while on the car. You just need the metnerds tool kit to do it.
 

Tdijarhead

Top Post Dawg
Joined
Nov 10, 2013
Location
Lawrenceville PA
TDI
2003 TDI Jetta Daughters Car, 2001 TDI Beetle, Daughters car, 2005 Golf TDI Mine, all 5 spds
If your car is at idle do you mean that the alternator pulley is spinning but the fins inside the alternator housing are not turning? If so your alternator pulley is in need of replacement. Or are the fins turning so fast you can’t see them on either car?

The only reason you alternator shouldn’t be spinning at idle is because you have removed the serpentine belt. If you’ve not done that and the alternator is not spinning then you’re car is not charging.
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
🤯🤯🤯
Not sure what to think... Yes, it should spin at idle, both on the TDI and on your Subaru. If it isn't, then there's a problem, and that would most likely be the clutch pulley on either of those.
 

eddieleephd

Top Post Dawg
Joined
May 27, 2012
Location
Asheville, NC
TDI
2002 jetta Wagon
The freewheeling pulley will always turn the alternator like pedaling a bike it will continue spinning once the engine slows down to prevent damage.
Check voltage present when running and not running. If it's higher when running the alternator is turning
 

tdihopeful

Veteran Member
Joined
Oct 23, 2008
Location
California
TDI
03 2dr 5sp Golf
Prairieview why do I ask for assistance? There is a saying-The only stupid question is the question that isn't asked. I don't want to be stupid? Ignorant? The more information I have to work with the better my chances are of gleaning useful information essentially however in spirit. I assumed that the information I was provided was accurate and then thought just out of curiosity I would compare my Jetta alternator to my Subaru alternator. Found that they seem to function the same. Both cars seem to have no battery charging trouble thus? Was there or is there something wrong with my methodology that you would like to bring to my attention?
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
Prairieview why do I ask for assistance? There is a saying-The only stupid question is the question that isn't asked. I don't want to be stupid? Ignorant? The more information I have to work with the better my chances are of gleaning useful information essentially however in spirit. I assumed that the information I was provided was accurate and then thought just out of curiosity I would compare my Jetta alternator to my Subaru alternator. Found that they seem to function the same. Both cars seem to have no battery charging trouble thus? Was there or is there something wrong with my methodology that you would like to bring to my attention?
It comes down to that if they aren't turning at idle, there's a big problem that needs to be addressed.
 

U4ick

Veteran Member
Joined
Nov 16, 2014
Location
texas
TDI
2003 jetta tdi
There is something wrong with your observations, the cars functions, or the description of their functions.
tdihopeful........Abandon your methodology and bring the help that you have asked for to your full attention.
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
No alternator ever spins. Not one. Never.
The pulley spins as it rotates the stator and fan and clutch.
You are correct that your alternator is not to spin at idle. If you take the bolts off ot might spin for you thought.


All alternators have a rotating pulley 100% of the time. All the time when running.
Regulators and clutches help keep it from spinning too fast or putting out too much current.
 

AndyBees

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Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Mongler98, what have you been smoking/drinking? (the stator doesn't spin, the armature does)

The voltage regulator's function is to "regulate" current/voltage and it doesn't do it by regulating the speed of the armature.

The Overrunning Alternator Pulley (OAP) has a one-way clutch mechanism inside the hub that allows the belt to turn the alternator in one direction, but allows the alternator to free-wheel and spin at its on speed when the engine suddenly decelerates, such as when the engine is shut-down.

The OAP reduces stress on the belt, and engine I suppose. As you should know, the OAP only comes on the 120 Amp Alternators and that is due to their much heavier armature. Also, considering that the diesel engine abruptly stops when the ignition is turned Off the over-ride affect is needed.

I've never seen one free-wheel as a result of being worn out. I've seen them lose their ability to free-wheel and perform like the typical non-free-wheeling pulley because the clutch mechanism is locked-up.
 

Mozambiquer

Vendor , w/Business number
Joined
Mar 21, 2015
Location
Versailles Missouri
TDI
1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI, 2005 VW Passat wagon TDI X3, 2001 VW golf TDI, 1980 VW rabbit pickup,
Mongler98, what have you been smoking/drinking? (the stator doesn't spin, the armature does)
Shall I make a slight correction there? A starter and generator have an armature, an alternator has a rotor. Interestingly, a generator has the fields in the case (where the main magnetism happens) whereas the alternator fields are the rotor. The regulating happens by applying more or less power to the rotor, which changes the magnetic forces, which creates electrical pulses from the stator. They are AC voltage at this point. They then go through the rectifier, which is a set of diodes which converts the power to DC voltage which is what the car needs.
Obviously it's a bit more complicated than that, but that's the basic operation.
And I'm not picking on you for calling it an armature, as it's similar.
The VW ones don't generally fail by freewheeling either direction, but I've seen that happen a lot on Honda, Toyota and Chrysler products.
 

Ragdude

Well-known member
Joined
Aug 18, 2021
Location
Phx
TDI
2015 VW Golf SEL TDi
I think it's fine. I looked at my Subaru Forester Alternator and it isn't spinning at idle either.
Could you please post a video of these 2 alternators not spinning while engines are running.
 

TurboABA

Veteran Member
Joined
Jul 24, 2010
Location
Kitchener, ON
TDI
RIP-2010 Jetta 6spd 2014 Touareg Execline
Yes please.
Maybe his alternator is spinning becuase he hot torques the bolts on it!
Speaking of, if it was me, I'd get custom oversized bolts, dip them in liquid nitrogen, and only then torque them.... The interference fit should hold them in place.
 

PakProtector

Veteran Member
Joined
Jan 5, 2014
Location
AnnArbor, MI
TDI
Mk.4 and the Cummins-es
I believe the generator uses a beastie called a commutator in order to deliver DC. The alternator clearly delivers AC to a set of rectifiers. The generator takes full output through its brushes, and the alternator just has to feed its rotor field through 'em.

and youse do your own timing belts??? LOL
cheers,
Douglas
 

tdihopeful

Veteran Member
Joined
Oct 23, 2008
Location
California
TDI
03 2dr 5sp Golf
If there's anymore popcorn left go ahead and throw it at me maybe it'll stick to the egg on my face. Yeah I thought I needed to see the coils spinning. While adding gear oil yesterday I looked at the alternator and thought why is it charging the battery? Looking at the pulley I realized/remembered that the coil is stationary on an alternator and the magnets spin within the coil... I had wanted to see a type of motor/generator that as far as I know doesn't actually exist I guess. I hope I posted this in TDI 101...
 

Mongler98

Top Post Dawg
Joined
Mar 23, 2011
Location
COLORADO (SE of Denver)
TDI
98 Jetta TDI AHU 1.9L (944 TDI swap in progress) I moved so now i got nothing but an AHU in a garage on a pallet.
If there's anymore popcorn left go ahead and throw it at me maybe it'll stick to the egg on my face. Yeah I thought I needed to see the coils spinning. While adding gear oil yesterday I looked at the alternator and thought why is it charging the battery? Looking at the pulley I realized/remembered that the coil is stationary on an alternator and the magnets spin within the coil... I had wanted to see a type of motor/generator that as far as I know doesn't actually exist I guess. I hope I posted this in TDI 101...
It's all good.
We all have a good laugh at each other now and again
I for one probably have more egg than anyones face here!
No matter how many cold air intake threads and newbs there may be..... us veteran popcorn makers get the best of the shame.

Laugh at yourself.... or grow a thick skin. You need both here sometimes.
 
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