Dead Battery, new battery, new alternator, still don't like the voltage - PeachParts Mercedes-Benz Forum

dmorrison · #1 11-23-2004, 04:50 PM

I'm down at Texas A&M. Replace my Daughters Alternator with a lifetime rebuilt from Oreilly's. Not happy with the voltage.
Here's the story. 2 month old battery went dead. Had it tested at Oreilly's and failed first test, marginal on second test. Gave her a new battery.
She brought the car to Sears for a charging system test. The results, "excesive voltage drop".
Figured it was the alternator, or more likely the voltage regulator. She measured the voltage. Car off 12.8 volts. Car on and at idle 12.4 so time for a new alternator. Flew down this morning and replaced the alternator with a rebuilt unit, in the parking garage, lots of fun.
Now we get, Car off 12.8, Car on at idle 12.7, at 2000 RPM 13.2.
I hope the new alternator is not bad. Were going to drive it home at about 7pm tonight.
I'm thinking that these items may be a problem. Battery - cable, battery + cable or the wire harness from the altenator to the starter contact, which meets the battery + cable at the starter.
battery + cable is a little rusted but I wire brushed the contact point. I'm afraid the interior of the wire is corroded.

Read all the "search" posts on alternator and this particular problem was not discussed.

Your ideas???

Dave

Let me add the battery warning light works as advertised. On bright with the key on but not started and then immediately goes out upon start. Also no dim glow. As I said works as advertised.

jbaj007 · #2 11-23-2004, 05:07 PM

This is a quote from a previous post on how I dealt with increasing alternator voltage. Ignore the alternator "swap" as obviously it doesn't apply, but the voltage regulator part might interest you. FWIW.

"I use the AL69X on my 300SD with a Transpo IB373A 14.4 volt adjustable regulator and am very happy with the increased amperage available for the electrical accessories I've added.

http://www.transpo.de/catalog/US_cat.html

Go to regulator>bosch>IB373A and you'll see what I found to be a fairly easy solution.

On the AL69X swap, I believe there was a slight belt issue, that was easily dealt with (1035 vs. 1000 belts comes to mind)."
__________________

autozen · #3 11-23-2004, 05:50 PM

Sounds like you are dealing with marginal parts. Get some good quality parts including battery and you won't have any more problems.

Peter

dmorrison · #4 11-24-2004, 08:24 PM

Well today I worked on the car. Removed the alternator and battery and had them tested ( I'll discuss the difficulty in removing the alternator out of the 240D on another post). Both tested good. Upgraded the alternator to a 65
AMP unit at Oreilly's. And tested the new one also which passed. Tested the voltage at the battery and got. 12.8 volts car off. 12.7 volts car running. Tested the voltage at the starter. Same reading. so the wire to the plus side of the battery is good. But I will replace both battery cables while I'm at it.
Talked to the W123 guys at the dealer and we concluded the wire from the alternator to the starter is corroded or broken. So I am in the process of replacing the 2 wires from the alternator to the starter.
I'll post the results tomorrow when I get it done.

I knowautozen feels it inferior products but the battery was tested twice and passed. 2 alternators were installed with identical results so I do agree with the mechanics that it is the wire harness.

Again I will post the results.

Dave

mpolli · #5 11-24-2004, 08:38 PM

Quote:

Originally Posted by dmorrison

Now we get, Car off 12.8, Car on at idle 12.7, at 2000 RPM 13.2.

Looks normal to me. Does anyone think these readings are wrong? Often alternators don't have much output at idle. In my limited experience 13.2 seems a little low but I have seen in other posts that these Mercedes regulators don't run at 14.4 like some of the others, if I understood correctly.

Mike

petaling · #6 11-24-2004, 09:37 PM

my car ignition off:12.8 V with new battery Intersate 91HD
idling 13.9V at battery.
2000 rev 14.1

manny · #7 11-24-2004, 11:27 PM

Quote:

Originally Posted by petaling

my car ignition off:12.8 V with new battery Intersate 91HD
idling 13.9V at battery.
2000 rev 14.1

I like your numbers.

Southern · #8 11-25-2004, 10:14 AM

Dave,

When you replace your battery cables make sure there is no corrosion where they connect to.

I have had good luck cleaning corroded cables by using baking soda mixed with vinegar. I place the baking soda into a baby food jar poor the vinegar in and stick the end of the corroded cable into the mixture. The chemical reaction between the vinegar and baking soda will clean off the corrosion. This only works if the corrosion is near the cable end, if it is corroded within the insulation its time for a new cable.

afmcorp · #9 11-26-2004, 12:05 AM

dave

i think you found the area of your problem. the only thing "common" between the initial and your last scenario would be the wiring. last summer my 72 wouldn't start and the only problem was corroded primary ignition wiring.

i now keep a supply of metric stainless steel bolts, nuts and a bunch of connecting ends and i automatically change at least the end connectors and screws or nuts with new.

nglitz · #10 11-26-2004, 09:34 AM

Check all of the ground wire connections, too.

They are as important as the positive wires.

One rusty ground can keep you busy for a long time.

autozen · #11 11-26-2004, 09:44 AM

Craig,
The terminals you are changing routinely should be changed often, because they are temporary terminals. You can save all the hastle by having a shop with all the tools replace those with permanent crimp ons. All the grease and little red and green felt things that people put on batteries are entirely unessecary. The biggest cause of all the corossion problems at the terminals is continuing to use a battery that is well past its prime and is gassing severely. When a battery gets to that stage, it only has about $8.00 worth of useful life left. To me it isn't worth the mess and unreliability. I install a new battery before it leaves me stranded.

Peter

Rockman59 · #12 11-26-2004, 10:52 AM

The biggest cause of all the corossion problems at the terminals is continuing to use a battery that is well past its prime and is gassing severely
_________________________________________________________________
So you are saying that a battery that is in good condition will not cause corrosion problems at the terminals? And when the corrosion starts it is time for a new battery?

autozen · #13 11-26-2004, 10:59 AM

Rockman,
That is what I have observed as an MB mechanic over the last 30 years. Have you ever noticed how a tired old ready to die battery is always all wet on the outside compared to say a 2 year old battery?

Peter

Rockman59 · #14 11-26-2004, 11:26 AM

Never noticed....but I will start looking for signs of battery breakdown. Thanks for the tip.

tangofox007 · #15 11-26-2004, 11:30 AM

Quote:

Originally Posted by autozen

Craig,
The biggest cause of all the corossion problems at the terminals is continuing to use a battery that is well past its prime and is gassing severely. When a battery gets to that stage, it only has about $8.00 worth of useful life left. To me it isn't worth the mess and unreliability. I install a new battery before it leaves me stranded.

Peter

This is a great piece of advice. Getting that last "$8" out of a battery can be an expensive proposition.