Hey guys, When I was thinking about wiring my aftermarket back up camera into the reverse lamps I could only measure 9 volts at the lamp (and the car running). I have never seen anything similar in other vehicles. The voltage across the cigarette lighter was 14+. I mention it because it is weird!

Where are you measuring the voltage? Is it across the battery terminals? If so, and you have a door open, the lights are on and I think the glow plugs might be operating (I read somewhere that they come on when you open a door??). If that is the case, this will drop the voltage across the battery. Maybe that is the high pitch whine we hear when the car is off but a door or hood is opened?:dunno:

Well, checking the realoem parts list, it appears bmw has a possible solution, but it ain't cheap. It appears BMW uses a 180 amp alternator for most models, but has a 220 amp version for a particular option configuration which includes "4 zone heating" and and auxiliary heat. I suspect that a 220 amp alternator would go a long way to improving charging performance for short trips.

RealOEM.com BMW E70 X5 3.0si Generator

Typically, 13.5 - 14.5 volts:

Automotive Charging Systems -* A Short Course on How They Work


But you never know about BMW and Bosch...

It would seem to me that if there was one fried diode in the alternator, it would reduce the output and show the symptoms people are reporting. Makes me wonder if they've got some bad alternators out there...

I've been measuring the voltage at the positive lead in the engine compartment (i.e. the one with the little red plastic cap where you can hook up jumper cables) with the doors closed and the hood open. But of course, I open the driver's door to reach the hood release. So as you suggest, maybe the glow plugs are cooking while I'm measuring. The next time I do the measurement I'll check to see if it changes when the whine stops.

Frankly I've been trying to think of a way to test the voltage without triggering yet another E70 automatic response that makes the measurement suspect. Measuring the voltage on the battery of a E70 is getting way too close to the issues in particle physics, where the mere act of observation changes the result :(

Funf Dreisig

Hummm... looks like maybe a software fix could be the solution... but I wonder if their hands are tied a bit, as modifying this approach might affect the EPA numbers and be a legal problem if it is done retroactively?

I've got an earlier version of this, and it works on my 2004 Z4:

CarChip® Pro by Davis

You plug it into the OBD-II socket and it will monitor any 4 parameters of you choice and store a time curve that you can download to your computer. I've used it on the Z4 to monitor battery voltage while driving.

for what it's worth, the 3.0d doesn't have the brake energy regeneration system

I'm with penguin on: "I also would find this unacceptable. If short trips are enough to do this, then either BMW (a) under-sized the alternator for the electrical system, or (b) has gotten some alternators that are not putting-out their rated amperage."

they need to fix it for you

Thanks that sounds interesting. I'd probably buy one but the docs say it only works with variants of the windows OS.

FWIW monitoring voltage while the engine is running is relatively simple using a cigarette lighter volt meter like i think you posted in another thread. The trick is measuring voltage when the X5 is supposedly "at rest" without triggering one of it's automatic electrical responses to simply unlocking, or even opening, a door, etc. AFAIK the only way to do this is to securely clip longish test leads onto the Red Battery Terminal and a ground in the engine compartment and close the hood with them extended through the hood fender seam. That way I can measure the voltage without touching the X5. Of course, this is not very handy, since I'd have to remove/replace the test leads every time we drive the X5 :( Any better ideas are welcome :)

Funf Dreisig

Are you sure?

The "Models and Technical Data" pdf on the BMW.com site says it does.

Funf Dreisig

I must admit I haven't confirmed recently, but I'm pretty sure in australia the X5 still has the pre-efficient dynamics configuration for the 3.0d. I think the X3 here with the 3.0d has brake energy regen though.