Electrical smell, alt light - PeachParts Mercedes-Benz Forum

Mistel · #1 07-01-2008, 05:12 AM

My 1985 300 TDT started making that burnt electrical smell this afternoon. The alternater idiot light also came on. I stopped for a few minutes, restarted, and drove home and the light never came on. There is still a slight smell, so something is deffinately wrong. I would like to attempt to fix this myself. Does this sound like the voltage regulater is gone?

Also, for a few months before this, the alt and brake idiot light would stay on after I stared the car at low idle until the engine revved up a bit.

Thanks

Peter

LUVMBDiesels · #2 07-01-2008, 07:39 AM

Take a voltmeter and check the voltage coming from the alternator. It does sound like the regulator could be bad. Voltage should go from the battery voltage (~12v) up to about 13.5v at idle and top out at 14v at say 2000 RPM

Mistel · #3 07-01-2008, 10:24 AM

I will check the voltage this afternoon. Does anyone know if a smell is associated with a bad voltage regulator?

I read the DIY on Diesel giant. It looks like the voltage regulator has two brushes on it. Are these the brushes that "pick-up" the electricity, or are there more brushes in the alternator? It seems like a really smart system were you can just change the small part. I can only imagine how many garages who don't know any better just change the whole alternator and charge the customer big bucks.

Jeremy5848 · #4 07-01-2008, 11:12 AM

The regulator, which is mounted at the back of the alternator and comes out with a couple of screws, is indeed the place where the generated electricity is "removed" from the alternator and sent out to the "consumers" (as Mercedes calls them). It is possible that the regulator is the source of your burned smell.

A garage will charge you about $300 to change the whole alternator. You can change just the regulator for about $50.

vstech · #5 07-01-2008, 11:17 AM

a smell from the alternator is unlikely to make it into the cabin of the car.
more likely, you have an electrical short somewhere in the cabin. My bet is blower motor associated... it's stinky when an electrical part overloads, and the blower motor is in the cabin.

barry123400 · #6 07-01-2008, 08:38 PM

Simple rule of electrical. If it smells it is getting hot. Feel various components or wires for excess heat. Occasionaly following your nose helps as well.

anghrist · #7 07-01-2008, 08:57 PM

Yeah Toast!!

I smell toast again.

bustedbenz · #8 07-01-2008, 10:22 PM

Quote:

Originally Posted by barry123400

Simple rule of electrical. If it smells it is getting hot. Feel various components or wires for excess heat. Occasionaly following your nose helps as well.

Or following the smoke/fire.

Mistel · #9 07-01-2008, 10:31 PM

So I checked the voltage this afternoon.

Battery 12.6
Alternator at idle 13.6
Alternator revved 13.8

I took out the voltage regulator and the brushes looked a little short, so I will change that.

I don't think the smell came from in the cabin. The AC was off and the back window was open and my son in the back noticed the smell first.

I drove it for 25 miles today and it seemed fine? Smell seems to be gone.

One thing I did notice when I was looking under the hood is there is a groove worn in the top of one of the belts that turns the alternator.

Any more ideas?

Thanks

Peter

LUVMBDiesels · #10 07-02-2008, 08:04 AM

Yeah, replace that belt!

vstech · #11 07-02-2008, 10:04 AM

are you sure it's a groove "worn" into the belt?
older belts have cords in them that can shred. if that's it, REPLACE that sucker... you better get power steering and A/C belts too... they all gotta come off to change that alt belt.
I can't think of anything that would wear a groove in the belt, but if it is worn, get in there with a light and find what is hitting the belt.