Today I had something really weird.

The battery in my Mercedes was flat, so I started the Benz with starting cables from my Chrysler (with motor running)
The Benz started easily and I decided to measure if there was a problem with charging.
I measured 20+V on my Mercedes battery (with running motor)

I removed starting cables

I thought, that's strange so I measured my Chrysler too (who was still running) Again 20+ V

So I thought maybe the small battery on my multimeter is nearly dead and gives me bad readings so I removed it and put that in a charger.

I went back to my mercedes (which engine was still running) and I noticed strange behavior, my Rev counter was behaving strange (up and down) and my ABS lights where on. I killed the engine and tried starting again > Nothing, dead battery.

Tomorrow I will start again and measure both cars with my newly charged Multimeter and see whats going on, but I suspect a broken regulator/rectifier on my Mercedes..

But is it possible I blew up the regulator on my Chrysler too when I had the startercables attached to both car batteries with both cars running?

 

Yes its possible, but unlikely with modern regulators, the potential for damage happens when you leave both vehicles connected for a while and one is empty while the donor [the Chrysler] is full, particularly if you have a high-draw with for example the headlights on. Try a re-set by removing the NEG for 15 minutes. Best of luck !

 

I found that the strange measurements appeared to be due to empty battery
Chrysler is still ok!
So I replaced the carbon brushes in the Benz but still voltage stays to low for recharging.. <12.x V
Im afraid the MB alternator is bad

 

I fixed up a friend's digital multimeter, the wrong voltage reading he was complaining about was due to a dodgy 9volt layer-battery in the meter. The meter was reading way too high.
It's handy to know that a new 1.5volt zinc-carbon cell should read EXACTLY 1.5volt off load. This applies to any zinc-carbon cell but not any other type like cadmium, lithium etc. The cadmium is 1.2volt nominal and most lithium 3.7volt, both off load, off charge. So using a new zinc-carbon, you can soon establish if your meter is reading correctly.
The old charging voltage for 12volt nominal lead-acids starter batteries was 14.4volt, i.e. the pre gassing voltage. The modern designers seem to have switched to the float-charge voltage of 13.8volt. This will make your headlamps dimmer and yellower out of proportion if they too are not altered. My previous car, an S-type Jag., had the choice in the control micro's program of either voltage for maintaining charge.
The voltage a good alternator produces depends directly on the current into the rotor/slip rings.. Before condemning an expensive part like the alternator, you should check there is some kind of voltage to the slip rings connector. An easy check is to connect your digital meter to the battery, engine running, then observe the reading.
Increase the current to the slip rings connector by wiring almost any bulb/lamp from battery +ve to slip rings connector*. This should INCREASE the voltage across the battery. If you are in the field and only have a test lamp, switch on the side lights, engine running and use your test lamp from battery +ve to slip ring connector . The should be an immediate definite bright-up in the side lights. This proves your alternator is charging.
One of my postings shows you how to make a little LED indicator in a cigar lighter plug to leave in the RH cigar to indicate charge. You can also buy these cheaply ready made. You'll notice from these flickering in use just how impulsive the so-called dc from the alternator really is.
*This applies to one side of the slip rings connector being ground, i.e. the +ve side being controlled. Some cars do it the other way round, i.e. full battery +ve to one terminal, then current to GROUND from the other terminal being controlled instead. In this case you would increase charge current by connecting your test lamp from -ve terminal to ground. I use an old stop/tail lamp as my test lamp, leads soldered on directly, terminating in crocodile/alligator clips. I carry it in the car at all times -- very handy. You can establish which style of control you have -- if one slip rings terminal always seems to have battery +ve voltage on it, then it's the latter. If one terminal always seems to be ground, then you have the former.

Leedsman.

 

Thx for the info.
Ill check the alternator before replacing thats for shure