[BlueBabyBenz91]

So I bought the car in September 2019 and, the battery voltage was always super low (9-10v). Basically I couldn't drive it without needing to jump it. First thing I do was check for parasitic draw which there was none and test if the battery was good at Canadian tire. No problems there, battery was healthy (2 years old only). Then, replaced alternator with a more powerful one. Worked for about a week but still with 3k revs voltage wasn't higher than 12.5v. Now, I'm back to square one. I can't even enjoy a short ride to the store. Just an hour ago, car died while driving on the road. Also to note, I installed an aftermarket head unit, but I'm sure it isn't drawing too much power. I still don't know what to do. This car has truly been a money pit. I don't want to sell it anymore as 1. I'm 17 and will be out 3-4 grand. And, I love the damn thing and I want it to run well. I'm contemplating on going to the dealership if they can pinpoint the issue.
thanks for any advice or help you guys might have.

Update: It kinda feels to me like the alternator charges the battery just enough (to 12v). Obviously when the car is at 12v and left for a day or 2. It gets lower and lower slowly. When I drive, sometimes, alternator isnt even able to keep up with charging. I just refilled my AC and can't use the darn thing because voltage drops to 10,5-11v. Its 30 degrees and I have working AC that I can't use. Sucks so much.

Update 2: sorry that I've been gone for so long. I talked with a MB specialist. Basically a hobbyist. He said to forget about it and put in a bigger alternator. Even more powerful. This seems to solve my issue. Something must be drawing lots of power while the car is on specifically as there is no parasitic draw when car is off. At idle, without AC, I get 12-12.5v. with AC it dips to 11.5-12v. If I'm hammering it on the freeway 3-4k revs it goes as high as 13.5v. these numbers seem ok so I won't go further into the problem. Now, I've discovered a new issue. Either my key is bad or I've got a bad tumbler. Took me 25 minutes to start the car last night. Key wouldn't turn into first position.

 

[Nate Y]

I had this problem with a 350SDL years ago. New battery and within days it was dead. Left me stranded on the side of the freeway. Turned out to be a voltage regulator in the alternator. Brushes were worn down to nubs. Fortunately it was an easy fix.

You mentioned you bought a new alternator. Did you change the VR when you put in the new alternator? If not, Pelican Parts has many to choose from.

1959 Mercedes-Benz 220S - Electrical - Charging System & Battery - Alternator Pulleys

Charging System & Battery for 1959 Mercedes-Benz 220S : Alternator Pulleys

www.pelicanparts.com

 

[BlueBabyBenz91]

Yes, when alternator was replaced, the voltage regulator was also changed. The thing that worries me is why doesn't the alternator give more than 12.5v when at 3-4k revs. The belt isn't slipping, earlier I even bought a new belt tensioner (mine was broken). So no issues there.

 

[Nate Y]

How's the condition of the battery wires and connections from the alternator? You are correct, you should be getting 14v+

Hang in there. I'm sure it's something simple. I'm not the best at electronics, hopefully someone else has ideas too.

 

[dolucasi]

I would definitely start with the batter ground connection under the engine (and other connections). Clean that up and re-connect. The system should put out nearly 14V when first started even at idle.

 

[BlueBabyBenz91]

How's the condition of the battery wires and connections from the alternator? You are correct, you should be getting 14v+

Hang in there. I'm sure it's something simple. I'm not the best at electronics, hopefully someone else has ideas too.

The connectors have been cleaned thoroughly. Max I'm getting is 12.5v if I really rev up the engine.

 

[BlueBabyBenz91]

I would definitely start with the batter ground connection under the engine (and other connections). Clean that up and re-connect. The system should put out nearly 14V when first started even at idle.

Connectors were sandblasted clean. They are super shiny. Only other thing I can do is buy new ones at this point.

 

[dolucasi]

Good to know. Since a new alternator and regulator did not solve your problem, I would still keep looking in wiring.
Are you measuring the voltage at the battery or elsewhere?
Must be a ground loop issue. I would take measurements at various points, at alternator, regulators, battery, etc etc to see if some of the voltages show a culprit.

These cars generally do not develop electrical problems, so yours appear to be not the norm.

Not having faced your issue in the past on my car, I will have a look at the wiring diagram for possible issues that can develop. But hopefully someone who faced your issue in the past can chime in.

 

[ewee]

I wonder if it will help if you could measure the current draw with engine off but with key at ON? then remove fuses in the fuse box one by one to check with of the items might be drawing current?

 

[dolucasi]

I thought about this too but the current draw would have to be many 10's of amps which most meters can not measure, you would need a current probe (inductive).
Also most of the fuses (except maybe the 25A ones) would blow with such high current draw so such current may not be flowing thru the fuses.

Never done this but are there not shops that can test the charging system with the proper equipment?
This does not sound like a W201 specific problem.

Also it would be interesting to know if the voltage drops drastically when there is current draw at 2500rpm. Perhaps turn the blower to max, and turn on hignh beams and let us know how much the voltage drops.

 

[Nate Y]

"This does not sound like a W201 specific problem"

Agreed. Maybe a straight up Google search with the symptoms.

 

[Dave Kost]

If it were mine, I would start by cleaning all the ground connections. Paying close attention to the grounds out in the weather. Don't forget the ground strap - engine to the body, as well as the connection of the battery ground cable to body. Inside the battery cable could be corroded too. I use a product called Deoxit and clean ALL electrical connections. Don't forget to replace all fuses with copper ones. It is time consuming but is worth it in the long run.

Using your multimeter reading volts, put the black lead on the negative terminal and the red lead on a body ground . Should be close to zero. If you have any resistance in the ground side of the circuit, you will read a couple volts.

Im not convinced that your battery is good. What is you battery voltage after the car hasn't been run for 2-6 hours? The voltage could be good but the capacity low. I just had to replace 6 -8 volt battery's on my golf cart, the voltage read good but would not keep a charge for long. Hooked up a voltmeter and under load ( I drove the cart while voltmeter connected) volts dropped to 6 volts should be ~8.1 volts. Replaced batterys.

Also, when you start car the car if the battery voltage goes under 10 volts, I was told by AAA, it is time to think about replacing your battery. Maybe someone can confirm this as true or false.

Hope my 2 cents helps.

Dave

Dave

 

[326218]

Is there any chance the car has an aftermarket security alarm on it? If it does, it might be the security alarm that's draining the battery. I had this issue with my W201 years ago. No trouble since it was fixed. If that's not the case, you might try contacting the MB Classic Center. Electrical issues for W201s are pretty rare because they don't have all of the electronics the newer MBs have.They're very knowledgeable with the W201. They've helped me alot with my W201 over the years. Good luck and keep us posted. Let us know if you need any more help.

 

[Betterdaze]

Not sure if you solved your problem yet, but my 190e’s battery would die sitting after few days and would stall on short drives. It could be as simple as replacing all your fuses, my car hasn’t stalled since replacing all fuses and the battery is still good after sitting. They are cheap and easy to put in

 

[mbarvo]

So I bought the car in September 2019 and, the battery voltage was always super low (9-10v). Basically I couldn't drive it without needing to jump it. First thing I do was check for parasitic draw which there was none and test if the battery was good at Canadian tire. No problems there, battery was healthy (2 years old only). Then, replaced alternator with a more powerful one. Worked for about a week but still with 3k revs voltage wasn't higher than 12.5v. Now, I'm back to square one. I can't even enjoy a short ride to the store. Just an hour ago, car died while driving on the road. Also to note, I installed an aftermarket head unit, but I'm sure it isn't drawing too much power. I still don't know what to do. This car has truly been a money pit. I don't want to sell it anymore as 1. I'm 17 and will be out 3-4 grand. And, I love the damn thing and I want it to run well. I'm contemplating on going to the dealership if they can pinpoint the issue.
thanks for any advice or help you guys might have.

Update: It kinda feels to me like the alternator charges the battery just enough (to 12v). Obviously when the car is at 12v and left for a day or 2. It gets lower and lower slowly. When I drive, sometimes, alternator isnt even able to keep up with charging. I just refilled my AC and can't use the darn thing because voltage drops to 10,5-11v. Its 30 degrees and I have working AC that I can't use. Sucks so much.

it seems to me that the battery is not good; it should not discharge at the rate you are saying unless there is a device connected in your car drawing the current.
maybe you have some adapter or ... which is making the battery work even after car is off