Alternator assistance - Dorkiphus.net
Navigation » Dorkiphus.net > Technical & Track Disussions > Porsche Technical Discussions » Alternator assistance

Porsche Technical Discussions Porsche related technical discussions and questions go here.

Reply
 
Thread Tools Display Modes
  #1  
Old 03-05-2021, 09:34 AM
86911TLCAB 86911TLCAB is offline
Tito
 
Join Date: Nov 2005
Location: Bristow VA
Posts: 2,166
86911TLCAB
Default Alternator assistance

Need a little help understanding an alternator/ external radiator issue.
78 3.0 911 engine. External voltage regulator.

When running battery is not getting a charge.
Wiring appears to be all there and connected.
When I turn car to on the light on the dash illuminates. When running it stays on.
Alternator and vr are properly grounded.

I donít really understand where I should be checking for 13+ v to determine if issue is alternator or voltage regulator. Does alternator actually provide voltage to the vr which then regulates that to the car/battery. Where can I check to determine issue. Any help appreciated.
__________________
Tito

82 911 SC with 3.2
73 RSR project
97 328is
99 328is
97 Lexus SC300 Manual

86 TL (gone)
993 (gone)
75 911S (gone)
Reply With Quote
  #2  
Old 03-05-2021, 11:57 AM
cmartin's Avatar
cmartin cmartin is offline
 
Join Date: Sep 2003
Location: Pasadena, MD
Posts: 7,375
cmartin
Default

Basic process

start with a charged battery, ~12.6v. at ~2k rpm check voltage at battery, should be ~13.5-14.5v. Make sure regulator is grounded, clean. usually higher than 14.5v replace regulator, if lower than 13.5v test/replace alternator.
__________________
78 SC, the 'Red Car'
Reply With Quote
  #3  
Old 03-05-2021, 12:02 PM
HoodPin's Avatar
HoodPin HoodPin is offline
Building a Worm Hole.....
 
Join Date: Dec 2004
Location: Monrovia, MD
Posts: 10,533
HoodPin
Default

Many FLAPS have an alternator test bench. A good easy way, once removed from the car, to confirm that the alternator is outputting properly while its rotating. Most will test for free.
__________________
- Tony P.

Currently
- 1984 944 SP2 racer
- 1977 911 KM Special vintage racer
- 1989 944S2
- 2012 Cayman R (also the wife's)
- 2000 Boxster S (the wife's)

- 1995 993 (garage queen)
- 1979 RX7 enduro
- 2017 F350 (tow monster)

Gone but not forgotten
- 1986 944 (under new mgmt)
- 1991 944S2 (in car heaven...)
- 2001 Chevy Suburban 2500 (FIL's beast now)

"Keep your eyes on the road and your hands upon the wheel." - The Doors
Reply With Quote
  #4  
Old 03-05-2021, 12:10 PM
cmartin's Avatar
cmartin cmartin is offline
 
Join Date: Sep 2003
Location: Pasadena, MD
Posts: 7,375
cmartin
Default

Good advice. For a 911 take the alternator in the fan housing as an assembly.
__________________
78 SC, the 'Red Car'
Reply With Quote
  #5  
Old 03-05-2021, 12:20 PM
Vicegrip's Avatar
Vicegrip Vicegrip is offline
Porkchop & SGB for prez!
 
Join Date: Jan 2003
Location: The other Woodstock.
Posts: 12,976
Vicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threads
Default

Look everything over too. You can inspect the connections and brushes . Many a bad alt was loose connections.
__________________
http://vimeo.com/29896988

"There is grandeur in this view of life...." Darwin.

The mountains are calling and I must go.

You Matter.
(Until you multiply yourself times the speed of light squared. Then you Energy)
Reply With Quote
  #6  
Old 03-05-2021, 12:25 PM
Patrick3000's Avatar
Patrick3000 Patrick3000 is offline
I need another Porsche
 
Join Date: Mar 2005
Location: Bethesda
Posts: 2,578
Patrick3000
Default

If you need a replacement, Arlington Armature may be a source for a rebuilt alternator.

http://www.starrad.com/home/3840084
__________________
Karl

18 GT3T -
11 997 C2S - Aerokit Cup
04 996 GT3 - HPDE
08 535i 6 Spd - DD
19 Beetle Conv - Hers
13 S60 T5 - Kids

Sold: 86 951, 14 911-50, 79 911SC, 74 914/6, 11 997.2 C2S, 88 944, 16 GT4, 13 Boxster, 1973 914/4 2.0, 1980 911SC ROW w/3.2, 77 911S Targa, 1970 914GT 3.2, 71 914/4 2.4, 76 912E, 89 944S2, 1980 924 Turbo, 98 Boxster, 70 911T, 72 914, 75 914, 73 914, 87 944, 74 911, 72 914 - 97 M3, 06 M3, 95 M3, 98 328is, 95 530i, 95 328is
Reply With Quote
  #7  
Old 03-05-2021, 08:00 PM
86911TLCAB 86911TLCAB is offline
Tito
 
Join Date: Nov 2005
Location: Bristow VA
Posts: 2,166
86911TLCAB
Default

When I run it the battery is leaking volts. I need to test at 2k rpm. I just did it at idle. So if not getting any increase in voltages at battery then alternator is the issue. It can’t be just the voltage regulator?
__________________
Tito

82 911 SC with 3.2
73 RSR project
97 328is
99 328is
97 Lexus SC300 Manual

86 TL (gone)
993 (gone)
75 911S (gone)
Reply With Quote
  #8  
Old 03-06-2021, 06:14 AM
Vicegrip's Avatar
Vicegrip Vicegrip is offline
Porkchop & SGB for prez!
 
Join Date: Jan 2003
Location: The other Woodstock.
Posts: 12,976
Vicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threadsVicegrip has six HoF threads
Default

Quote:
Originally Posted by 86911TLCAB View Post
When I run it the battery is leaking volts. I need to test at 2k rpm. I just did it at idle. So if not getting any increase in voltages at battery then alternator is the issue. It canít be just the voltage regulator?
This is hard to understand well enough to reply to. It can just be the regulator. It can be tested too.
__________________
http://vimeo.com/29896988

"There is grandeur in this view of life...." Darwin.

The mountains are calling and I must go.

You Matter.
(Until you multiply yourself times the speed of light squared. Then you Energy)
Reply With Quote
  #9  
Old 03-06-2021, 10:10 AM
86911TLCAB 86911TLCAB is offline
Tito
 
Join Date: Nov 2005
Location: Bristow VA
Posts: 2,166
86911TLCAB
Default

Ok. Sorry for the confusion.

With the car running I check the battery and the voltage is at 12 and dropping.

Based on an earlier answer I presumed if the regulator was at fault I would be seeing a higher than normal charging voltage at the battery(14+).

What I really don’t understand is where can I check to verify if the alternator is providing an output to the regulator and the regulator is then not working. There are three wires between the alternator and the voltage regulator. Blue wire (d+), black wire (df) and brown (d-).


Is is safe to run the car with the vr disconnected and check voltage output at one of the lines coming from the alternator to the voltage regulator? If so should I expect to see some higher than 12v at the blue or black wire positions.
__________________
Tito

82 911 SC with 3.2
73 RSR project
97 328is
99 328is
97 Lexus SC300 Manual

86 TL (gone)
993 (gone)
75 911S (gone)
Reply With Quote
  #10  
Old 03-06-2021, 12:33 PM
HoodPin's Avatar
HoodPin HoodPin is offline
Building a Worm Hole.....
 
Join Date: Dec 2004
Location: Monrovia, MD
Posts: 10,533
HoodPin
Default

I'm not expert at your car's specifics, but I would guess that 1 VR wire is the voltage in from alternator. 1 wire is the field wire that would tell the alternator to energize or not, once battery is fully charged. And 1 wire is a ground.

I believe there's multiple failure modes available. If the VR is not properly measuring voltage it could fail in 1 of 2 ways; either not provide current to battery and battery runs down, OR field wire doesn't alert alternate to stop charging and battery overcharges. Additionally, a failed alternator could also not provide current to battery which allows battery to run down, regardless of what the VR tries to do.

Not sure if car will run with VR disconnected, but my guess is that it won't. That's why I suggested taking alternator to a FLAPS to be bench tested. If alternator is bad, its the alternator. If alternator is good, its probably the VR.

If the battery is below 13.2 volts (most batteries have 6 2.2 volt cells in series) then alternator should be charging.
__________________
- Tony P.

Currently
- 1984 944 SP2 racer
- 1977 911 KM Special vintage racer
- 1989 944S2
- 2012 Cayman R (also the wife's)
- 2000 Boxster S (the wife's)

- 1995 993 (garage queen)
- 1979 RX7 enduro
- 2017 F350 (tow monster)

Gone but not forgotten
- 1986 944 (under new mgmt)
- 1991 944S2 (in car heaven...)
- 2001 Chevy Suburban 2500 (FIL's beast now)

"Keep your eyes on the road and your hands upon the wheel." - The Doors
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump