PeachParts Mercedes-Benz Forum - View Single Post

JamesDean · #8 01-14-2014, 01:56 PM

Quote:

Originally Posted by 87merz

1987 300E
1-year-old battery
3rd re-man alternator + 4th new voltage regulator
Battery voltage at full charge - 12.4 V
Voltage indicated at the battery terminals with engine on but no electrical load - 13.6 V
Voltage indicated at the battery terminals with engine on with all accessories on - 11.6 V and steadily drops until the battery loses all charge
Bench test of all alternators shows normal alternator, diode and voltage regulator function;
Diagnostic tester with alternator installed and engine operating without an electrical load shows normal alternator, diode and voltage regulator functions;
Diagnostic tester with alternator installed and engine operating with all accessories engaged shows normal alternator and diode but a failed voltage regulator function (4th new voltage regulator).

Any ideas?

Can you elaborate on the electrical load you place on the system? A full combined load will draw down the stock alternator. Nearly all MB's of this are have undersized alts.

But beyond that, a few things:

Are you sure the exciter wire is connected to the alternator? This is the much smaller wire. I think its connected to the D+ terminal.

I believe this wire goes up to a dist. block then into the car and connects to the "battery" idiot light. Also make sure that light is good.

Your alternator might be able to internally excite up to a certain load/point.

I have a 143A and 150A alternator installed in my 190E and 300D respectively. Neither have charging problems at idle. The 300D will put down 14V at idle.