Electrical Gremlins; Alternator, VR or otherwise?

[vinceinIL]

2000 528i manual sport wagon....mileage around 200k.

Car always starts with no issues. "Battery" light comes on and sometimes flickers on and off, other times stays on, at idle or higher revs, lights or heater blower makes no difference. Today I noticed the positive cable lug on the battery was real hot after a 12 mile drive. The lug is factory and on all the way and tight. Ground is also tight. Key off, I get a reading of a little over 12v at the battery. Key on, car at idle, I get a reading of about 13.8 volts at the battery, regardless of whether the Battery light is on or off. Voltage regulator or something else?

Thanks,

Vince

[JimLev]

Clean the inside of the lug and the battery post. Do it to both of them.

[StephenVA]

Like JimLev said: Remove them, clean with a Battery brush, clean post, reinstall. While OFF remove and clean your jump point under the hood. The temp means the terminal is not tight and is arcing. Soon there will be additional issues though out your electrical systems.

Next get out your volt meter and read the running voltage at idle, 1500, and 2500 rpm hold for 15-20 sec at each level and look for a volt drop like 13.8V down to battery voltage 12.5V

More than you wanted to know posted below:

Starting & charging systems testing techniques
Without spending way too much time on starting & charging systems testing techniques, here are the steps you need to do to determine do you have a battery issue, a charging system issue, or a primary wiring issue.

You need to read battery voltage before starting any test on an electrical system as it will influence the results: Starting, Charging, electrical tests of any kind. (Note: battery must be fully charged, see chart)

Step one: Get out a digital volt meter, Read battery voltage (Key off). Read voltage (Key on) at the following points Battery, under hood jump point, and at the alternator. You only need to determine if you have 12 volts at the alternator with the key on (BIG FAT WIRE). A simple hand held digital wave form tester will get you in the ball park when it comes to batteries. (Further discussion on these testers is for another engineering forum). I have a hand held Chrysler tester that was put out in 1980 to help low skilled techs determine charging system functionality. It has three lights: Battery voltage good (12.6v), Alternator good (13.5v), Fault (anything else). That’s it. I had this in my bag of tricks when I sold auto testing equipment.
Second: You need to read the voltage at the BATTERY at idle, 1500, and 2500 RPM to determine voltage regulator function. Better still would be a Volt Amp tester (VAT-40 Image below) to induce a correct AMP load to read actual AMP/Volt output from the alternator and battery, as that is the only true testing method.
Three: Remove and clean each and every ground in the trunk, jump point, and at the frame rail for the block (bad grounds = lots of electrical issues)
Four: Failure to get correct output on running test means DEAD alternator (volt regulator, brushes, windings, etc.) Remove and bench test the unit or drag it to your local auto parts store for a second opinion (which will be worth exactly what you pay for it....)

Base line numbers
Battery Voltage should be 12.6+V (Key off) See chart below.
Battery voltage should be 13.5v - 14.5v on running tests (note large fluctuations at running RPMs is a SURE sign that the Volt Regulator is not doing its job. Smack with rubber hammer and retest. Rebuilt units have large variance of quality control from good 85% of the time to approx 50/50%.
NOTE: The exact charging voltage will vary according to the battery's state of charge, the load on the vehicle's electrical system, and temperature. The lower the temperature the higher the charging voltage, and the higher the temperature the lower the charging voltage. The "normal" charging voltage on a typical application might be 13.8 to 14.3 volts at 77 degrees F. But at 20 degrees F. below zero, the charging voltage might be 14.9 to 15.3 volts. On a hot engine on a hot day, the normal charging voltage might drop to 13.5 to 14.3 volts.

Alternator tips
To quote another poster...

How to load the alternator at engine idle for alternator output tests:


Note: Alternator output should be tested with the engine idling under the following four loads after at least 15 seconds of idling (for the alternator to ramp up):
Turn the high beams on
And, turn the rear defroster on
And, turn the fan on (full force, I guess)
And, turn the wipers on (to the regular setting, I guess)

These loads should be left on while the alternator output tests are being performed.

Once access to the alternator is gained (access for the I6 is vastly easier than the V8):

• Check the voltage from the alternator #30 post and ground
  
  • It should be the same as the battery voltage
  
  
• Now disconnect the harness connector to the alternator:
• Check voltage from terminal 15 and ground (field voltage)
  
  • It should be the same as the battery voltage

More info: Another way to check alternator output is with an oscilloscope. Observing the "ripple voltage" pattern will tell you at a glance whether or not all the alternator windings are functioning. A "good" pattern should look like the top of a picket fence. If any of the humps are missing, it means one or more of the windings is grounded or open, or there's a bad diode. Most battery/charging system testers also have a test function that can detect bad diodes.
info: http://www.pvv.org/~syljua/merc/TooSeptST07.pdf

ANOTHER QUICK CHECK FOR BOSCH ALTERNATORS

One way to check the integrity of the alternator and diodes on Bosch alternators is to check the voltage readings at the D+ (blue wire) terminal and B+ terminal. The voltage reading should be the same at both terminals. A difference of more than one volt would indicate faulty diodes and the need to replace the alternator.
Tips link: https://www.diyauto.com/manufacturer...ion-by-bluebee

Volt Drop testing (Image below) can show you issues with grounds and wiring problems. Read the text and test a few spots to determine if your car has clean connections.
https://www.engine-light-help.com/voltage-drop.html

Are you having other electrical issues? Alternative issues: Ign Key switch failure, wiring junction box rusted (see water leaks and under passenger seat wiring connectors), etc....

Tip Sites for more info:
https://www.aa1car.com/library/2002/cm10220.htm
https://www.bimmerfest.com/forums/sh...d.php?t=510579 (Everything you wanted to know about BMW starting and charging systems for DIY)

Helpful?

[CPHES]

Wow - good info - that should be a sticky post e39 and e38 at least. Not stuck in Touring land.

[vinceinIL]

Wow, Stephen, thanks for the awesome response! Good thing I have tomorrow off work to go through everything you mentioned. Oddly enough, back in January I noticed that the negative terminal at the battery wasn't as tight as it should have been and I tightened it. Yesterday I checked both terminals and they were both tight. Tomorrow should be interesting...

Vince

[StephenVA]

lots of info and i have posted all of this multiple times when the same question/posting comes up, so it is all over the forum.

[Mike WW]

Both from recently on my E39 and from a decades earlier E3. Voltage regulator. More specifically brushes. They're most likely just at the very limit. Of course used alternators are cheaper than a new regulator, and rebuilt alts aren't much more than a new regulator, but I'll leave that equation for you to figure out. A least on some brushes can be replaced once you get in there, but not many are into doing that. Don't ignore it like I did, since it went away for a couple of months.

It'll come back to bite you, I speak from experience. It's not good when the wife calls you from 350 miles away saying the battery light is on.

I should add, this is not an absolute statement, but what I'd do and why.

[vinceinIL]

My apologies for not responding sooner. I needed to have a good day to fiddle with the car, and see what I could find.

First, I checked the battery cables to see if they were tight. The ground cable was good, tight at both the body and battery terminal. The positive cable was likewise tight when I tried to snug up the terminal. And then I noticed that even though the terminal was tight as possible, it wasn't that tight on the battery lug. So I made a thin shim from an aluminum can until I can find a piece of brass or copper to make a better shim.

I also checked the other heavy gauge cable that piggy backs onto the main positive terminal. It was tight, but I found quite a bit of corrosion between the two, so I sanded both parts and reassembled with some grease on it to prevent further corrosion.

And that seems to have solved the problem! No more flickering battery light once the engine starts!

Of course, Stephen, thanks for all the extra info that is really handy to have!

Now the alternator or VR will decide it wants attention soon.....

Vince

[StephenVA]

Congrats on your discovery. Many have struggled to resolve this common issue as they all think that by tightening the little terminal clamp bolt is all that is required. The arching that was going on when the terminals were loose, "burned away" material from either the post or the clamps. You can double check your work with a volt drop test (instruction and graphic below) as it will show any loss of voltage/resistance between the post and the clamp battery terminals. Many times the solution is to "pinch" down the bottom or top of the clamp as the taper has been deformed somewhere in its life.

Volt Drop testing (Image below) can show you issues with grounds and wiring problems. Read the text and test a few spots to determine if your car has clean connections.
https://www.engine-light-help.com/voltage-drop.html