Charging System
 

I have a problem with my Battery holding a charge, I charged it and it lasts about a week. I had it tested at Autozone and the results were Good Battery but needs to be charged, The Charging light goes out on the dash, i checked the output of the Alernator and at Idle about 11.95v at about 1500-2000 Revs
it goes to about 12.01v, I removed the voltage reg and no obvious sign of problems, So my question is Voltage Regulator or Alternator?. Also what does it take to put out the dash charging light, Just any output from the alternator?.:confused: Thanks

11.95 and 12.01 are LOW readings........ should be closer to 13 volts. Wally's world tested my 240D alternator at 12.27 just before i replaced it. Check the fanbelt for tension too. I was getting 4-5 days (no nights) per out of car battery charge. And they say it destroys your battery to keep draining it.

Yeah, with a charging system like that...
 

I would look for an auto electric shop and take the alt to them to field test it. lots of possibilities on an altinator. brushes, V.Reg etc.

Agee with vstech, take your alternator to a shop for testing. Your voltage should be near 14 volts. What's the voltage at idle with the lights, fans, radio, rear window defroster and any other load you can put on it? Let it run for a few minutes. If the voltage falls, then the alternator can't keep up with the load probably indicating a bad phase or two in the alternator. So after a week, the battery becomes discharged since the battery is supplying some of the load instead of the alternator. I doubt if its the voltage regulator but you can replace it for only $25. I don't know on your MB, but on my 2000 VW, I believe there's a voltage sensing circuit in the alternator and the light comes on when there's no voltage in the alternator indicating no output.

As others have said, the voltage should be more like 13.5 volts. When you said the voltage regulator had "no obvious sign of problems" what does that mean? Were the brushes worn, the new ones should look like this:

http://catalog.eautopartscatalog.com/mercedesshop/sophio/quote.jsp?clientid=catalog.mercedesshop&cookieid=1CQ0J3JZ41SQ1B4DS8&baseurl=http://catalog.peachparts.com/&partner=mercedesshop&year=1982&product=F4010-30110&application=000272327

I have had worn brushes, resulting in low voltage, without the dash light coming on.

Alternator
 

Ya, The brushes look like the picture.
Thanks

Well, I guess the next step is to have the alternator tested. If you end up replacing the alternator, it will come with a new regulator anyway. I would make sure the belts a tight enough first.

I just went through this ordeal myself.
http://www.peachparts.com/shopforum/diesel-discussion/152021-q-how-do-you-turn-30-minute-job-into-13-hour-nightmare-1986-300sdl.html

My decision to replace the entire alternator was more difficult than yours should be. I got lucky and found my rebuilt Bosch alternator on sale for $165.00. I figured since I didn't know when it was last replaced, or how long the vehicle had sat, it wasn't worth spending $30 on a regulaotr, only to end up having bad windings, a flat spot, etc.

I just looked up your alternator and it's $98.00.
That makes it a no-brainer as to whether you replace just the voltage regulator for $25-$30, or the whole unit for $98.

Hope your install goes smoother than mine.

Upgrade the alternator
 

I just put a Bosch AL129X (115 AMPS) in my 240D after the failure of 2 55 AMP rebuilts over the past few years. It's great having 14.1 volts, and all the power I could ever need. Even at idle lights are bright, the fan blows strong and my stereo and amp have all the power they need. Picked mine up on ebay for $45 plus shipping. An easy install see:
http://www.peachparts.com/shopforum/diesel-discussion/93569-alternator-115-amp-bosch-al129x-works-123s.html

John

For sure, the 123 alternator bracket is a screaming joke. Ultimately you will have to pull the idiot bracket along with the alternator..... Then it's wise to cut off the top portion of the bracket well below the dopey bent ears and then break off the stupid adjusting screw/bolt combo and treat it like a regular nut and bolt arrangement instead. What you will end up with after cutting off the over-engineered screw assembly is simpler manually adjustable alternator bracket with 3 easy 17mm mounting bolts that wont give you trouble ever again.

Regarding alternators 14v sounds high to me. Most dashboard mounted truck voltmeters ballance at/near 13. And if you're shopping for a build, nothing beats small electric machinist shop for doing the best work. Can recommend Fowler's at Bardstown Rd.


(edit: Hey JCW, what year/model Benz carries those 15" rims that fit the 123??

The rims were used on mid eighties 126 S Class, ET 25. In my case, off my 87 SEC. A number here have put them on 123's. Just don't use the ones off 124's with a higher ET (44 I think).

John

13.8 volts is the normal nominal voltage of modern cars in operation...for quite a few years now. true it was a little bit lower on the older ones.

[QUOTE=1badav]I just went through this ordeal myself.
http://www.peachparts.com/shopforum/showthread.php?t=152021

My decision to replace the entire alternator was more difficult than yours should be. I got lucky and found my rebuilt Bosch alternator on sale for $165.00. I figured since I didn't know when it was last replaced, or how long the vehicle had sat, it wasn't worth spending $30 on a regulaotr, only to end up having bad windings, a flat spot, etc.

I just looked up your alternator and it's $98.00.
That makes it a no-brainer as to whether you replace just the voltage regulator for $25-$30, or the whole unit for $98. [QUOTE]

Of course this depends on how easy it is to replace the voltage regulator. The function of the alternator can be tested in the car by the Autozone device that they roll out to your car. It gives a reading in amps for output. On my 420SEL (yeah, I know, it's not a diesel, but I have a diesel), the supposed 80 amp alternator was putting out 43. this confirmed the results of a $3 battery/alternator test device I got from Harbor Freight, which indicated the battery was good, but the alternator was questionable. The voltage regulator was pretty accessible and easy to replace, and I thought it was the original alternator. I bought a new Bosch regulator for $25 and removed the old one. The brushes were less than 5mm, which is the specified replaceement length. When I put the new one in, my output went to 60amps and my Harbor Freight thingy read strong output. So, my alternator core is probably worn a bit, but still functional for a while. The rebuilt alternator is $143 from Bosch, and considerably more work to install. I have never tried to replace the voltage regulator on a 617, but it seems less accessible, thus possibly necessitating removing the entire unit to replace. In that case, given the time, one might as well replace the entire alternator, though my price for that 65 amp alternator is $117, and basically with the voltage regulator, your gambling $25 (partly) on the voltage regulator being the culprit. Comes down to how much you times worth and if yu have a backup car to use while the car potentially waits for new parts to come in.

Thanks, I want to put em on my junkyard watch list for the 240D..... 126 S-class 15" rims!! But what does the "ET" number refer to?

alternator
 

Well Good news, i brought the Alt to Autozone and it checked good, i just cleaned everything up and it now charges at 13.5-7 volts, so hopefully it will be allright.
thanks for all the info.:)

OK, so I have to admit when I was wrong :o . The voltage regulator on my 300TD was easy to access and replace from the bottom of the car. My alternator in the car was only putting out 7 amps, so I reaplced the voltage regulator with a used one that I knew was good and it did not go, so my problem is something inside the alternator. So now I'll do the work to replace the alternator.

ET is the offset number stamped on the inside of the rim. Maybe a German abbreviation? Do a search on wheel offset and you will have plenty of reading.

John

Thoughts?
 

So I replaced the alternator in 300TDT 1983 with a Bosch rebuilt 65 amp. Tested is again, putting out about 7 amps again, according to autozone. My voltage meter also indicates that Im. not getting good charging. I read somewhere that you should charge the battery prior to checking the alternator. Does this make a difference?

If you didn't charge the battery, you should get a whole lot more than 7 amps out of the alternator, due to the battery charging. By the way, how are you measuring this current?

Another question, does your alternator light illuminate when you first turn the key to position 2 (run) but before you start the car, then extinguish once the engine is started?

Dumb question: Are you sure you have a good ground connection from the battery to the chassis? Try using a jumper cable between the negative terminal and ground to see if it improves things.

Also, if you have an "extended glow" glow plug relay, make sure you wait until the glow plugs time out before taking measurements. The voltage across my battery only reads about 12V until the relay times out.

The seven amps was what was read by the Autozone apparatus that they connected. However, my little idiot tester light from Harbour Freight that lights (I think based on Voltage) indicated that the battery was good, but when the car was running, it didn't hit the "good region," so it agreed with the Autozone result.

The ignition panel light does light up prior to starting the car and goes out once the car is started.

Can the ground cable from battery to chassis go bad in such a way that car can still be started, but battery does not charge well?

Good question. :o I suspect a bad connection would also affect starting, but it might be worth a try just to eliminate the possibility.

The only other thing I can think of is a bad connection someplace between the alternator and the battery, but I'm just guessing.

Well, I think the jumper cable approach is pretty easy to try. The only other possibilities are (1) the rebuilt bosch alternator is bad (I would think unlikely, although possible) (2) the wiring from the alternator to battery is bad (it is 23 years old, after all) (3) Belts not tight enough (But I pressed down on them and they seemed as firm as other belts).

Now, I must say that the auxiliary fan was on when the tests were done (this is Arizona and it's about 101 today), but I wouldn't think that would draw so much current that only 7 amps is read as the alternator's output). I still don't understand why I remember being told that the battery needs to be fully charged after installation of the new alternator. I would think that the alternator would do the charging in that circumstance. I guess another question is at what point does the idiot light on the dash come on to indicate no alternator output. When there is total alternator failure? Would seem like it would be better if it came on earlier.

False alarm
 

So, I got all worried about something that I shouldn't have. Charging system is now fine, after the new alternator charged up my drained battery. Take home message: charge your battery when installing a new alternator prior to testing the alternator.