Electrical issue: Battery or Alternator again? - Page 2 - PeachParts Mercedes-Benz Forum

Diesel911 · #1 01-24-2015, 01:52 AM

Quote:

Originally Posted by mach4

You are absolutely correct!

All I was suggesting was that most of the electrical issue posts start with something along the lines of "all of a sudden my car would't start", and then a string of helpful suggestions ensue. Since the first sign of trouble is only the result of a period of time where the problem existed previously, it would be nice to conveniently at a glance reference the battery voltage before starting and monitor the voltage while driving as early warning of an electrical problem headed toward a non-start situation, often in less than optimal conditions. I realize that volt meters that plug into the cigar lighter do not provide that information (unless they are plugged in at the time) and are therefore less than useful. A cheap HF multimeter is preferred for troubleshooting, but it's kind of inconvenient to try to get a voltage reading while driving as manipulating those little probes are tricky one handed and popping the hood to get a battery reading all the time is kind of a pain.

Recognizing the lack of utility I didn't get one of those cheap cigar volt meters, choosing to add voltage monitoring to my other system status monitors - fuel pressure, EGT, trans temp, oil temp, intake temp, engine bay temp, boost and vacuum.

I have 2 of the Voltmeters that plug into the Lighter Socket. One is analog and the other is digital.
What I mean by being more usefuel is that the a Harbor Freight Meter can be used for more thing like checking the Glow Plug and so on; making it more useful.

Also when I conpare the Voltage taken with Multimeter to the one with the Plug in Volt Digital Meter; the plug in one uses up almost 1 volt to power itself.
That means you could actualy be charging an acceptagle 13.5 Volts but the Digital Plug in Meter is going to make it look like someting like 12.65-12.75 Volts. But that is with the one that I have. I cannot say they all have the same issue.

I also prefer using the Multimeter (Volt/Ohm Meter) to using a Test Light because it give you better information.

Diesel911 · #2 01-24-2015, 02:02 AM

Quote:

Originally Posted by mach4

You are absolutely correct!

All I was suggesting was that most of the electrical issue posts start with something along the lines of "all of a sudden my car would't start", and then a string of helpful suggestions ensue. Since the first sign of trouble is only the result of a period of time where the problem existed previously, it would be nice to conveniently at a glance reference the battery voltage before starting and monitor the voltage while driving as early warning of an electrical problem headed toward a non-start situation, often in less than optimal conditions. I realize that volt meters that plug into the cigar lighter do not provide that information (unless they are plugged in at the time) and are therefore less than useful. A cheap HF multimeter is preferred for troubleshooting, but it's kind of inconvenient to try to get a voltage reading while driving as manipulating those little probes are tricky one handed and popping the hood to get a battery reading all the time is kind of a pain.

Recognizing the lack of utility I didn't get one of those cheap cigar volt meters, choosing to add voltage monitoring to my other system status monitors - fuel pressure, EGT, trans temp, oil temp, intake temp, engine bay temp, boost and vacuum.

I have a Plug/Connector to go into the Cigar Ligher that simply has to wires coming out of it with Alligator Clips. One of the things I can do with that is use the Alligator Clips to connect it to a regular Volt Meter. However you need to keep the leads separated.

The Alligator Clips are also handy if you need to power something to test it inside of the Car.

Cadin · #3 01-23-2015, 01:08 PM

I have a battery charger that will tell you the amount (%) that the alt. is contributing to the system, it has come in handy on more than one rig.

Otherwise shoot the resistance (Ohms) on each wire, and then check for 12v with the key on. Do you get a charge light when you turn on the key before you start the motor? What is your charged battery voltage?

I had a similar situation with another vehicle, after I rebuilt the alt. and it turned out to be a loose wire to activate the Alt., it eluded me until I actually shot the wires with the multi-meter; and then I was kicking myself since I had torn apart the properly rebuilt alternator multiple times looking for troubles. I ended up having the local part store bench check the Alt., so I knew it was good, and it must be the wiring.

JHZR2 · #4 01-26-2015, 02:43 AM

Link didn't work for me. IIRC, the intent was to modify the regulator by putting a diode in series with the chassis ground on the regulator (via its screw), which gives a 0.5-0.9v drop depending upon type. Thus the alt charging voltage will increase by that much. This could be an issue in very hot conditions but otherwise seems smart.

One can very easily see is alternator ground is an issue by installing a small jumper with alligator clips between the alternator and the engine, the chassis and the battery, and noting changes.

Thing with that is that even a high impedance neutral should still be sufficient to set charging potentials...

Diesel911 · #5 01-26-2015, 11:49 PM

I found the thread of the Member that did the mod:

Alternator Low Voltage - this worked apparently

Alternator Low Voltage - this worked (apparently)

Unfotunately it still has the defunct website as the source of the info.