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  #1  
Old 10-15-2007, 03:51 PM
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Battery dead - why?

My 1970 280 SEL has a dead battery. The battery itself is not the problem, it is brand new. On the last few trips around the neighborhood I noticed the generator light ever so slowly becoming brighter and then going dark again.
And - much to my surprise - when I was doing some work on my window motor and had the ignition switch on, the same thing happened after a while - the warning light slllooooooooowwwwly going half on, then dark again.
I've never had alternator trouble with any of my cars. Does the fact that the light goes on after a few minutes without the alternator even running mean, that it's not the alternator???

If so - what is it?

Thanks!

Dietrich

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  #2  
Old 10-15-2007, 03:54 PM
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Others can chime in here, but on my w123, those symptoms pointed to a worn-out voltage regulator.
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  #3  
Old 10-15-2007, 11:52 PM
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Try the Search feature

This was covered a while back, but I can't remember the 'fix'.
Matt_B prob'ly is right.
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  #4  
Old 10-16-2007, 06:26 AM
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Quote:
Originally Posted by dspeer View Post
My 1970 280 SEL has a dead battery. The battery itself is not the problem, it is brand new. On the last few trips around the neighborhood I noticed the generator light ever so slowly becoming brighter and then going dark again.
And - much to my surprise - when I was doing some work on my window motor and had the ignition switch on, the same thing happened after a while - the warning light slllooooooooowwwwly going half on, then dark again.
I've never had alternator trouble with any of my cars. Does the fact that the light goes on after a few minutes without the alternator even running mean, that it's not the alternator???

If so - what is it?

Thanks!

Dietrich

Sounds like one of the diodes in the regulator is failing.

Jim
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  #5  
Old 10-17-2007, 09:20 PM
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Not sure if you have an internal regulator or not but this will be interesting reading.

http://**************.com/node/243

Michael
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  #6  
Old 10-18-2007, 08:03 AM
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I suspect that you have a failing diode in the alternator.

A '70 280SEL should have the external regulator. If you have the original relay-type regulator, then I suggest you replace it. They are prone to fail suddenly and will drain the battery in seconds. I had that happen on my 280SE and 280SL. The Bosch replacement is kind of neat - they put a solid state regulator in an aluminum case so it looks not too unoriginal.

Here is a post that I did on the Pagoda forum on how to sort out what's going on.

http://www.sl113.org/forums/topic.asp?TOPIC_ID=5964
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  #7  
Old 10-21-2007, 08:59 PM
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They shouldn't sell old Mercedesses to Idiots

I started this thread. For about 2 weeks now I've been reading about Voltage Regulators and generators. Today I decided I was going to tackle this, which meant getting the car with the dead battery into the garage first. Jump started it, disconnected the cable, put it in the trunk, then closed the hood. Clunk. Motor dies. I think 'what the heck' . And when I try to connect the cable again, one of the connectors falls off the battery post. I had installed a new battery a couple of weeks before the trouble started happening and neglected to tighten one of the connectors.

What do we learn from that?

1. If your battery doesn't charge when the motor is running - check the battery cables first.

2. If you don't know how to install a new battery, don't buy an old Mercedes.
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  #8  
Old 10-21-2007, 10:22 PM
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Quote:
Originally Posted by dspeer View Post
I started this thread. For about 2 weeks now I've been reading about Voltage Regulators and generators. Today I decided I was going to tackle this, which meant getting the car with the dead battery into the garage first. Jump started it, disconnected the cable, put it in the trunk, then closed the hood. Clunk. Motor dies. I think 'what the heck' . And when I try to connect the cable again, one of the connectors falls off the battery post. I had installed a new battery a couple of weeks before the trouble started happening and neglected to tighten one of the connectors.

What do we learn from that?

1. If your battery doesn't charge when the motor is running - check the battery cables first.

2. If you don't know how to install a new battery, don't buy an old Mercedes.
Don't blame the car...if you don't bother to check your own work..pay someone competent to do it.

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