Alternator or Regulator?

[L8Apexr]

I have an 86 Carrera with a bad alternator and/or voltage regulator! I have read the posts and my Bentley's manual and still don't have a clear answer as to which one is the culprit. I have lived with the flickering headlights but I'm tired of them now.

Symptoms:
flickering headlights and other lights
engine/alt wa-wa-wa-wa sound in sync with flickering (like the load on the engine is pulsing)
sometimes an intermittent ALT light when idle is low (in sync with flickering)
When the engine is idling and the headlights are on the flicker isn't noticeable (batt voltage still 14) but as soon as I rev a bit it starts again.

Readings:
Battery voltage is 12.5 at rest
Battery voltage is 14.8 - 15.0 engine idling
Battery voltage is 13.9 - 14.2 engine idling with headlights on
increase engine speed=same reading, higher frequency of flicker

I know if I replace the alternator my problem will be solved but I hate to turn in a perfectly good core alternator for a new regulator!

I appreciate any help you can offer, I see there is a wealth of expertise here!

-Chuck

[scottb]

My gut tells me alternator, but I'm sure some of the electrical gurus will chime in with more informed opinions. Either way, the problem doesn't sound too serious. Could be a good opportunity to pull the fan and shroud and polish them!

[304065]

The output from the alternator stator can be thought of as three overlapping sine waves spaced 120 degrees peak-to-peak from each other. This pulsing current flow gets fed through the six output diodes and changed into a constant DC current. It's not a perfect, flat-top wave but you get the idea.

Anyway, when one of the diodes fails, there's a gap in that current flow that can manifest itself as pulsing output from the alternator.

The other alternative is that the internal VR has failed.

[pwd72s]

Since the regulator is internal, you gotta pull the alternator anyway, right? In other words, let the rebuilder worry about it?

[Eric Coffey]

Even if it is just a bad VR, I would just bite the bullet and swap the complete unit for a rebuilt one from a reputible shop. Shouldn't cost more than $200. You would really be angry if you just replaced the VR, and 3 months later your bearings, brushes, or diodes went TU.

[targa80]

This all depends on how cheap you want to be and how capabable you are with doing your own work. If I were in your situation this is what I would do. I would pull the alternator apart and check the condition of the replacable parts and all the internal connections. If nothing is found out of the ordinary I would replace the V/R and reinstall. If it did not work then I suggest replacing the whole unit. In my own case I would probably next buy the diodes/brushes and bearings and replace them. Worst case would be time spent and a bunch of spare parts and hopefully you would learn something in the process.

What can I say I'm cheap and I like doing my own work. I also enjoy the satisfaction of repairing something that is broken. There have been times where it has cost me more than it should have, but I have always learned something from the experience.

[Wil Ferch]

The voltage numbers you quote under the various operating conditions would lead me to believe a bad VR.
A compromise ( and one I did myself) would be to replace the VR..and while the alternator was out for that...have the alternator bench checked and also rebuilt with new slip rings and bearings plus whatever else the bench test says.
A few years ago..the whole rebuild along these lines cost me $75 from a local shop plus the $55 or so for a German HUCO VR...in place of the OEM French unit. The HUCO came in a box that had the proper official Porsche part number ....but the metal / ribbbed heat sink was much more substantial than the OEM piece.
---Wil Ferch

[scottb]

Originally posted by pwd72s
Since the regulator is internal, you gotta pull the alternator anyway, right? In other words, let the rebuilder worry about it.

Excellent advice. If you're going to the trouble of pulling the alternator, why stop at just replacing the regulator? The brushes, if not already bad, may be on the brink. Same with the bearings. I had a local foreign alternator and starter shop rebuild mine for $89. While it was at the rebuilder, I had Al Reed polish and powdercoat my fan and housing.

[L8Apexr]

Thanks to all that have replied, I knew I could count on Pelicans!

I have decided to go ahead and replace/rebuild the alternator. My next question would be where can a guy get the parts? I should be able to perform the work but 4 years ago when the alternator did go I was in San Diego and couldn't find the parts so I paid $170 for a rebuilt unit. I see some of you mentioned much lower rebuild costs, feel free to make a recommendation (the closer to Spokane, WA the better).

Thanks,
Chuck

[Eric Coffey]

Originally posted by L8Apexr
....I see some of you mentioned much lower rebuild costs, feel free to make a recommendation (the closer to Spokane, WA the better).

Thanks,
Chuck

These guys helped my out in the past, and had a rebuilt unit in stock for a quick exchange:

Alstar Electric
Bellevue, WA
425-454-7933

[Randy Webb]

"It's not a perfect, flat-top wave ..." = ripple

I don't know the % ripple, but it can be seen with a scope.

[L8Apexr]

I spoke with someone from Systems Consulting, he very quickly diagnosed my alt over the phone and let me know that the regulator was almost definitley the culprit. I took it to a local shop, they're bench test showed no defects but I knew better than that. I replaced the VR and bingo! I did find a broken terminal to a resistor between the two rectifier assys. It was supposed to be crimped to a lug that was allen screwed to the alt case. At any rate, voltage is right at 14.4, and there is no more flickering or wa-wa-wa sound.

Again, thanks to all for your input.

[RoninLB]

Originally posted by L8Apexr
I replaced the VR and bingo!

thanks for update