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  #1  
Old 08-04-2013, 01:54 PM
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Join Date: Jul 2011
Posts: 528
Lazy w108 alternator

I went to start the car today and after a few revolutions the starter did the typical dead battery 'click-click'.
I jumped it and measured alternator output. With no accessories on it's ok, but once I turn the AC on it drops to ~12.5 Volts at idle. Ouch! I does raise up when revved.

Is this normal? I would assume there would be enough capacity in the system to supply enough current for some accessories at idle.

I wonder if there is an adjustable voltage regulator available for this alternator?
Thanks,

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1972 280SEL 4.5, silver
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  #2  
Old 08-06-2013, 12:03 AM
Pooka
 
Join Date: Sep 2005
Posts: 664
In the past, like 40 years ago, when I ran into something like this I would run a large battery of tests to determine the problem or if there was one and if so where it was.

But today it is easier to just run down to Autozone and have them test it for free. I'm not trying to shill for AZ, there are other suppliers that will do this service quickly, for free, with the alternator still on the car.

The problem may be simple or it may be complex, but to start with you must know: Is the alternator working as it should?

They can tell you, and then you can move on from there.
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  #3  
Old 08-06-2013, 08:06 AM
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Join Date: Aug 2002
Location: near Scranton, PA
Posts: 5,210
There isn't an adjustable regulator, but the alternator has an external regulator that can die over time causing this. Like Pooka suggests, have the system tested free. They can tell if the alt is weak (only 55A on this car so a modern radio and speakers may drain it quite quickly) or if it's the regulator.

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