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1998 E320 base sedan @ 160kmiles
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Do not go by the voltage you read on the climate controller. It is not designed as a voltmeter, and it is not accurate. The only reason why it is there is to turn off the REST function when the battery voltage goes down below around 11V. Have your charging system checked again by a competent shop with the right equipment that can check the rated capacity based on load, and proper diagnosis for diode issues which are more apparent on a scope, than multimeter reading.
 

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1982 300SD (340k miles), 1998 E300 Turbo Diesel (331k miles), 1982 300D Turbo (330k miles)
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52 Posts
Discussion Starter #22
Do not go by the voltage you read on the climate controller. It is not designed as a voltmeter, and it is not accurate. The only reason why it is there is to turn off the REST function when the battery voltage goes down below around 11V. Have your charging system checked again by a competent shop with the right equipment that can check the rated capacity based on load, and proper diagnosis for diode issues which are more apparent on a scope, than multimeter reading.
I also checked it with my voltmeter and get about the same results. Maybe 0.2 volts higher, so 13.3 volts when running. Still a bit low IMO. I've got a scope I could hook up to it.

When y'all say diode issues, are there other diodes besides the ones inside the voltage regulator? AFAIK that's the only diode in the charging system.

I've ordered a Bosche reman. Given how bad the slip rings or poles or whatever are I don't really want to risk it.
 

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1998 E320 base sedan @ 160kmiles
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7,215 Posts
What do you think the charging voltage should be ? 14.1V all the time ? If you apply anything over a float voltage to a battery CONTINOUSLY, you will overcharge and destroy the battery. So just because you read less than 14.1V on the battery during charging, it does not mean the alternator is bad. It means the charging circuit is trying to keep the fully charged battery at float voltage.

Have a look at the attached and you will find your answers.
 

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E250 Bluetec Sprinter250 Bluetec
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37,026 Posts
Alternator has huge diodes inside, who convert AC to DC current. Those seldom fail, but it happen. I think there is like 6 of them and when 2 fail, the alternator will not hold the voltage.
Acid batteries have maintaining voltage at 13.5V . Some charging systems go over 14V (just like my Ford truck) for faster recharge, but that is shortening the battery life (3 years on my Ford).
MB keeps charging below 14V and batteries could last up to 17 years.
 

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1982 300SD (340k miles), 1998 E300 Turbo Diesel (331k miles), 1982 300D Turbo (330k miles)
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52 Posts
Discussion Starter #25
Well 13.7 is more or less what I'd expect. It's still only 12.9 on startup and idle. It's not until I rev it a bit that it goes to 13.3. There's a lot of wear on my alternator poles so even if it's working acceptably I'm not super comfortable with the state of my alternator.

I'm mostly replacing it due to concerning wear. The slightly lower than expected voltage is not the main reason.
 

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1982 300SD (340k miles), 1998 E300 Turbo Diesel (331k miles), 1982 300D Turbo (330k miles)
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52 Posts
Discussion Starter #26
The reman from Bosch is in and it's worse than my old one was. Battery light keeps coming on, car running the voltage is 12.2 with a load it drops to 12.1. What a crap shoot.

I guess I'll pull it out and get another one ordered. :-/
 

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E250 Bluetec Sprinter250 Bluetec
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Unfortunately alternator rebuild in USA does have very bad reputation.
I had 1 on my Ford and when it was very frustrating becouse the alternator would show charging light intermediately.
It passed bench test when I took it back, only to give a ghost 2 months later.
Where did you get this Bosch?
 

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1982 300SD (340k miles), 1998 E300 Turbo Diesel (331k miles), 1982 300D Turbo (330k miles)
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52 Posts
Discussion Starter #28
Unfortunately alternator rebuild in USA does have very bad reputation.
I had 1 on my Ford and when it was very frustrating becouse the alternator would show charging light intermediately.
It passed bench test when I took it back, only to give a ghost 2 months later.
Where did you get this Bosch?
Online from Parts Geek. They had the best price. Not sure if it was damaged in shipping or what. Not impressed. Gonna order one from carquest.
 
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