Voltage regulator is probably the issue.. Don't run it like that too long . The high voltage can damage the modules .. Try throwing a new charging relay . It's only 25 bucks or so, it's quick to replace it in the trunk fuse box . Just to rule it out before changing out the alternator

 

Can the voltage regulator be replaced? I heard of the charging relay, where can I get one at? Local auto parts store or online source?

 

When you find a charging relay, please post a picture.

Otherwise pull the Alternator ASAP and have it rebuilt.
My E38 was charging 16.67 Volts.
An Alt is controlled by the Voltage regulator (Internal to the Alternator) controlling Field Voltage.
The "Field" is a magnetic winding used instead of permanant magnets. (Electricity=Magnetism with Motion)
A short in the regulator causes a huge overvoltage.



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My E61 also charges pretty high - I see a max of 15.1V. During starting it drops below 10V (when it's below freezing outside) but always starts. I'm planning on replacing the battery, but it hasn't failed me yet, and I've got a portable battery jumpstarter in the car (which is probably why it hasn't failed me yet). My charge voltage isn't steady at 15.1 though - it starts off lower, when you can see the charging brains are "feeling out" the battery to see how it's doing. Then the alternator output slowly ramps up to hit the 15ish point. After driving for a while, stopping and idling while sitting at a traffic light the voltage will cycle down, check battery's capacity, and then boost back up.

Here's a huge writeup from the WDS on bmw-planet ... alternators in our cars are way smarter than a fixed voltage regulator module inside the alternator. The car computer controls charging, and measures battery voltage using the IBS right at the battery. The brains will store a code if there's a fault that causes overvoltage (among other reasons).

-tom


BSD interface to the alternator

The alternator with BSD interface can actively communicate with the engine control unit. The alternator is not linked to the charge indicator lamp, only to the engine control unit. The alternator can detect a variety of faults.
Function

The following functions have been implemented in the engine control unit for the alternator with BSD interface:
-Activating/deactivating the alternator on the basis of appliable parameters
-Specification of the maximum permitted degree of utilisation of the alternator
-Control of the alternator's load response
-Calculation of the alternator moment degree of utilisation
-Diagnosis of the data line between the alternator and the engine control
-Filing of alternator faults in the defect code memory
Activating the load control lamp in instrument cluster via CAN
In comparison to alternators used so far, the display strategy of the load control lamp does not change when the alternator with BSD interface.
The basic function of the alternator is also ensured if the communication between the alternator and the engine control is interrupted.
Possible faults

The following possible faults can be distinguished from fault entries:
High temperature control: The alternator is overloaded; to be safe, the alternator voltage is reduced until the alternator has cooled down again. The charge indicator lamp does not light up.
-Mechanical fault: The alternator is mechanically blocked or the belt drive has failed.
-Electrical fault: Exciter diode defect, excite interruption, overvoltage due to controller defect.
-Communication failure: Line defect between the engine control and alternator.
The following cannot be detected: Coil interruption or short-circuit
Battery charge indicator lamp

The signal for the charge indicator lamp to light up is transferred across CAN to the instrument cluster. The charge indicator lamp lights up if there is mechanical and electrical fault (see above).
Detection

The above-mentioned calculation of the alternator moment and the rate of utilisation of the alternator are heavily dependent on the type (performance) and manufacturer.
This is why the alternator provides the engine control with this data. The engine control adapts its calculation and set values to the exact type.
Aim

The precise calculation of the alternator moment and control of the load response function enables good idling of the engine.
Control of the alternator voltage based on nominal values from the engine control enables a good charge balance of the battery.

 

The voltage you are talking about is on the high side, but it depends what battery type is registered, what the temperature conditions are, and if the system voltage always stays high or is just for a short time.

Normal E60 system voltage for charging a battery in good health that is over 80% charged is generally 14.1-14.3 volts. For accelerated charging in cold weather the ECM may in rare instances charge AGMs as high as 14.7V and FLA as high as 15.5V as directed by the ECM/CAS based upon IBS feedback. If the battery is approaching a full charge and you are on a long road trip you may also begin to see the system voltage reduced to around 13.75V in an effort to avoid overcharging the battery.

FLA type batteries (and the car's electrical system) can easily take 15.5V and the ECM may drive system voltages that high if the battery state of charge is low, the ambient temperature is very low and the battery negative terminal temperature is low. Damage to electrical modules could begin at 16V.

But if you have AGM battery registered and the alternator is putting out 15.5V then you can be sure your alternators voltage regulator is going bad (the ECM would never let a registered AGM battery see more than 14.7V).

And if the system voltage is always above 15V or jumps wildly up and down to below 12.5V then it is definitely the voltage regulator (module screwed to the back of the alternator). When my voltage regulator failed it was jumping from 11V up to 18V.

A relay cannot vary system voltage. A relay is just a switch which can be signaled with a very low current to close a high current connection.

 

A relay cannot vary system voltage. A relay is just a switch which can be signaled with a very low current to close a high current connection.

Fun fact: prehistoric (middle of the 20th century) cars actually used special relays to regulate the charging voltage.

 

If a relay is defective it can intermittently turn off and on . Which will then turn off the charging system and won't let the alternator fully charge the battery . On the other hand it won't turn off and keep the charging system running,, it works in conjuction with the voltage regular. It will not shut off the alternator and over charge .

I would replace both together just to ensure the charging system is in tip top shape

 

If a relay is defective it can intermittently turn off and on . Which will then turn off and won't let the alternator fully charge the battery . On the other hand it won't turn off ,, it works in conjuction with the voltage regular. And will not shut off the alternator and over charge .

I would replace both together just to ensure the charging system is in tip top shape.

Ok cool, thanks.

 

What say we go have a few beers while HF finds that relay?
I totally forgot earlier how the E60 has the "Power Management System"
(Neither my E38 nor E39 have that)
The system is sort of complex, but uses a MPM module under the spare. (Unless wisely moved) Also included is the Engine Mgt Computer, a sensor on the battery and then input from the CAS and EWS.
15.3 volts is a bit steep, but if the System allows it, and battery is up to spec and registered....
Just for my opinion, I replace batteries at 36 months, testing ok or not. (Actually I dont let them test the old one. Never thought putting a huge load on an old battery just in front of your face is a good idea.


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What say we go have a few beers while HF finds that relay?
I totally forgot earlier how the E60 has the "Power Management System"
(Neither my E38 nor E39 have that)
The system is sort of complex, but uses a MPM module under the spare. (Unless wisely moved) Also included is the Engine Mgt Computer, a sensor on the battery and then input from the CAS and EWS.
15.3 volts is a bit steep, but if the System allows it, and battery is up to spec and registered....
Just for my opinion, I replace batteries at 36 months, testing ok or not. (Actually I dont let them test the old one. Never thought putting a huge load on an old battery just in front of your face is a good idea.

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Yes, the power management system has its advantages and disadvantages. When my voltage regulator pumped out 17V the dash would light up like a Christmas tree as the system shut down a number of modules to protect them.

And of course when a battery is failing other kinds of gremlins can jump in on the fun as the power management system attempts to react to the situation and systems like the active steering are affected.