Help! Baffled by charging issue

[RenaissanceMan]

I'm having some issue where I'm getting intermittent alternator operation, or something similar. Occasionally, battery light will flicker and by monitoring the voltage using Torque Pro, I'm able to confirm that voltage at the battery is under 12 volts and steadily dropping for a while before suddenly jumping back up to 14 volts. Yesterday I almost got stranded because on my way home system was not charging and I went from 11 volts all the way down to nine volts while traveling on the highway, and then I had all sorts of warnings and system failures occur. I got off at an early exit thinking that it would be safer to get towed from there, but as soon as I got off the highway and came to a stop, voltage jumped back up to 14 volts and charged the battery again. I was sure that the problem was either a failing alternator or ignition switch, but I replaced the ignition switch with a spare to no avail, and the alternator tested fine three times in a row at the auto parts store just now. What the heck could be going on? Will a failing alternator display these intermittent symptoms? I've never had one do this before.

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[TwinTurboGTR]

More than likely it is the voltage regulator. Battery and amp test from the store will test positive because it is not under load.

Im assuming this problem is on the E53 3.0 that is in your sig. Since you are monitoring the voltage and can see the drop, more than likely, its the regulator.

[BigBody]

Shouldn’t the battery always be around 12 volts? I’m curious as to why it hit as low as 9... I have been having this problem with my car too, the issue had caused my battery to deplete and my car was getting transafe failures and so ons. I bought a float charger and completely charged up the battery and all is well. I still get this issue on occasion with a cold start but there are no symptoms. Might be something worth trying. It’s worth noting my voltage never goes below 11.5 in general.

[RenaissanceMan]

After I posted I went ahead and picked up an alternator and swapped it out. Problem appears to have disappeared for now. Maybe I was premature in not just changing out the voltage regulator, but I figured I'd go ahead and knock the alternator out since I got a pretty good discount on it.

BigBody, the reason the voltage went down to nine is because the X5 was only running off of the battery, which was not being charged by the alternator. If you are taking a reading off of the battery from a car that is running properly, you should not have only 12 volts. It should be closer to 14, because you're getting regenerative power off the alternator. When mine stopped charging, the voltage I was reading off of the battery was the same as if I had the battery out of the car, so the longer I drove the more the battery was depleted. That's what took me so far down to 9 volts in the first place. My alternator had momentarily stopped working for about 20 miles worth of driving.

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[BigBody]

Originally Posted by RenaissanceMan

After I posted I went ahead and picked up an alternator and swapped it out. Problem appears to have disappeared for now. Maybe I was premature in not just changing out the voltage regulator, but I figured I'd go ahead and knock the alternator out since I got a pretty good discount on it.

BigBody, the reason the voltage went down to nine is because the X5 was only running off of the battery, which was not being charged by the alternator. If you are taking a reading off of the battery from a car that is running properly, you should not have only 12 volts. It should be closer to 14, because you're getting regenerative power off the alternator. When mine stopped charging, the voltage I was reading off of the battery was the same as if I had the battery out of the car, so the longer I drove the more the battery was depleted. That's what took me so far down to 9 volts in the first place. My alternator had momentarily stopped working for about 20 miles worth of driving.

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Yes it should be around 14 when all is working correctly, and it is. I meant my voltage never goes below 11.5 when car is running off the battery and the charging is malfunctioning. Regardless, glad to hear you fixed the issue.

[dkl]

This is the exact symptom I had when my alternator was going bad - The battery light would flicker intermittently and eventually it was turned on permanently.

[dkl]

Originally Posted by BigBody

Yes it should be around 14 when all is working correctly, and it is. I meant my voltage never goes below 11.5 when car is running off the battery and the charging is malfunctioning. Regardless, glad to here you fixed the issue.

This is because your alternator hadn't completely failed yet. It's outputting SOME current to run the car, but not enough to charge the battery. But if your alternator had completely failed and the car is running 100% off of the battery, the voltage will continue to drop until system shutdown. Just because the battery light is on doesn't mean the alternator had completely failed - it just means that it's unable to maintain charge.

[TwinTurboGTR]

Ha at least you guys with the M52 engines have air cooled alternators... Us guys that need to have the extra 2 pistons... you know because we like THAT many more problems have a water cooled alternator. lol

Don't call em BM Trouble U for nothin!

[BigBody]

Originally Posted by dkl

This is because your alternator hadn't completely failed yet. It's outputting SOME current to run the car, but not enough to charge the battery. But if your alternator had completely failed and the car is running 100% off of the battery, the voltage will continue to drop until system shutdown. Just because the battery light is on doesn't mean the alternator had completely failed - it just means that it's unable to maintain charge.

I believe this is the case. The car would shut off and die during idle. I would have to assume this means the car was running off the battery...