I noticed a while back that the headlights on my new (to me) '95E300D would suddenly get brighter shortly into my morning commute.

Last night I finally got my DVOM out and I clipped it to the lighter socket this morning to watch the voltage. Sure enough, the voltage jumped from around 11V to typical charging voltage of around 14V+/-, after I had been driving for perhaps 20 - 30 seconds.

I have not observed this phenomenon closely enough to note if the voltage increase occurred when I reached a certain RPM for the first time or not. But my '88 5 series BMW will not start charging until the throttle is blipped up past 1200 - 1500 rpm or so, which is common for that older 5 series Bimmer.

Maybe it's characteristic of Bosch alternators? I know that when the diesel starts, there is no surge in RPM at all, it just goes up to its relatively slow idle speed and stays there, and because I baby it until it's warmed up it doesn't see much RPM. I'll be observing more carefully but I just wanted to ask.

Rgds,
Chris W.
'95 E300D