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SL...alternator with a rebuild from ac-delco..mounted..New alternator…

Customer Question
I have serious issues with...
I have serious issues with charging on my 72 450 SL.
I have replaced the alternator with a rebuild from AC-Delco. No change in behavior between "new" and original mounted alternator. New alternator has been dyno tested, test docs supplied with it. Alternator is 55A.

Replaced Voltage regulator with original Bosch part.
Replaced wiring between alternator and regulator
Rewired B+ terminal to battery. Regrounded engine to battery, no voltage read between -on battery and alternator ground, so grounding seems good.

When idling without any load, the battery read 13.3 V, when increasing engine speed to 2000 RPM, charging voltage increases to 13.7
If main headlight is on (which is mandatory during daytime in Norway), the idle voltage drops to and charging light starts to lid. As engine speeds increases the charging light dims, and finally at 2000 RPM's goes off. Charging voltage at 2000 RPM and headlight on is 13.4 V, which is to low.

Alternator gets pretty fast pretty warm, 5 minutes of idling on cold engine heats the alternator to approx 70 degrees.
Submitted: 8 years ago.Category: Mercedes
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Answered in 16 hours by:
6/24/2010
Mercedes Mechanic: Don, ASE Certified Technician replied 8 years ago
Don
Don, ASE Certified Technician
Category: Mercedes
Satisfied Customers: 1,746
Experience: 30 years journeyman experience on classic cars
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hi there my name is don i will try to help you on this
first thing do you have a wiring diagram for your car

don
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Mercedes Mechanic: Don, ASE Certified Technician replied 8 years ago
hi there is this the alternator you have

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Customer reply replied 8 years ago
HI. this is not the alternator. Mine is 55A, with a V belt pully and external voltage
regulator. Yes I have the wiring as I have the original MBNA service doc CD.
The wiring has been replaced (no major change slight increase in output voltage)
The picture of the alternator is found here: http://www.rockauto.com/catalog/moreinfo.php?pk=1000447
It is a ACdelco rema for bosch. Interesting enough replacing alternator did not make any
major improvements. Additional info:
low beam headlight 60 W each, draining 10A, no aux fan, only fan for ventilation. No
other major consumers. At 2000 RPM I believe stock generator should be able to
charge with low beam turned on.
Mercedes Mechanic: Bill Barrow, Technician replied 8 years ago
Bill Barrow
Bill Barrow, Technician
Category: Mercedes
Satisfied Customers: 140
Experience: over 25 years specializing in electrical other fields brakes, suspension and running/starting
Verified
On the plug going to alternator with key on what is voltage reading between DF terminal and alternator case ground? With plug disconnected.
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Customer reply replied 8 years ago
Hi, No reading between ground and DF terminal. Any comment on the temprature issue mentioned above?
How could defects in D+ wiring (charge lamp) be tested and verified?
Mercedes Mechanic: Bill Barrow, Technician replied 8 years ago
At the regulator do any of the wires get power when key is on that do not have power with key off? If yes what terminals?
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Customer reply replied 8 years ago
Hi,

I cheked the gauges with all terminals conected and ignition turned on, engine not
running. The charge lamp was bright, and mesureded to ground level. The
mesurement was done with a jumpwire, hooked up to the plug into the voltage regulator.
Readings were:
- DF side 1, 1.1 V
- DF side 2, 1.8 V
- Sence 0.0V

As teh alternator is new and all other readings are the same as with the other alternator, I still believes the alternator it selves is bad. How could the sence cable be checked? (bad wiring grounding in the dash?)
Mercedes Mechanic: Don, ASE Certified Technician replied 8 years ago
hi there what you are explaining with the improvement and decline of voltage with the rpm of the car leads me to believe that one of the diodes or exciter has failed

since this is indeed a new or rebuilt one i would take it back and exchange for another or have them excite that one and see if it changes
hope this helps
don
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Customer reply replied 8 years ago
Hi,

Thanks for the update. I normally don't believe in coincidents, so the mesurements is similar with the old and the new. So two different alternators having same problem is a bit to coincidently.The old was dynotested a year a go, and was basically OK, I replaced it due to sound from the bearings. >The new is factory rebuilt by ACdelco, and I improted it overseas from US, so it is not easy ship back and have replaced. The test certificate supplied from ACdelco was also good. Co\uld you please reconsidder and assume that the alternator is good? When engine is not running but ignition is on, what should the readings on the sence terminal at the voltageregulator be, and what should the current comsumption on the sence cable normally be?

Thanks and regards,

Inge
Customer reply replied 8 years ago
Hi,

Turned out to be bad grounding in the dashborad, causing the sence led to be floating and
hence not giving the correct value to the regulator.

Regards,

Inge
Mercedes Mechanic: Don, ASE Certified Technician replied 8 years ago
thank you for that information
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