[Opie55]

I do not own an F-chassis 5 series, but have an F25 X3 (N20) and an F12 650i (N63TU). I'm asking this here because 5-Series guys often seem to be more knowledgeable about the finer points of their cars, and reading online has my head spinning. For all practical purposes I assume an F10 has the same type of charging system as an F25 and F12.

My question relates to the proper operation of the Brake Energy Regeneration system that charges the battery. Both of my cars have brand new and properly registered 105ah AGM batteries. I have Bimmerlink to monitor the voltage live. What I can't figure out is why the cars' voltage behaviors are totally different. The voltage in the F25 is always around 14.7 - 14.8 volts regardless of whether I am driving down the street or coasting/braking. If it varies, it's not by more than a couple tenths of a volt. The state of charge stays at 92% or so. This behavior seems at odds with BMW's own words that the alternator often "decouples" when you are using the gas, and charges when you coast or brake.

My F12 charges at 14.8 volts only when coasting/braking, but is all over the place when I am using the gas. It can be as low as 12.3 volts if I have been driving a while, and never seems to go above about 14.0. It is typically in the mid-13s. On that car the state of charge drops to the 80% range, which I have read is where it should be for an AGM battery.

So at this point I'm just looking for data points to see what "normal" is. Have any of you monitored your voltage that can share what you get while coasting and using the gas, or if you have Bimmerlink or another means, could you check and post them? Thanks.

[Hoa]

F25 sounds normal. Voltage is regulated so you won’t see it jump up and down coasting or on the gas. It’s job is to keep your voltage steady. Your car is designed to not fully charge the battery so it is normal to not be at 100%. If you plug in a trickle charger to bring it to 100%, it will slowly drain back down.

Sounds like your F12 alternator may have an issue. It should not be at 12.3V when engine is running. Even without the engine running, your battery should be ideally at 13.5V. When engine is running, it will be slightly higher at 14-15V.

[kohsin]

I have p3 gauge on my F10 N63. The voltage ranges from 13.5 to 14.7 after I replace the battery. The depleted old battery was as low as 13.2 v and as high as 15.1v and it throw random codes and that's why I replaced them. It was 7 years old.

[Opie55]

Originally Posted by Hoa

F25 sounds normal. Voltage is regulated so you won’t see it jump up and down coasting or on the gas. It’s job is to keep your voltage steady. Your car is designed to not fully charge the battery so it is normal to not be at 100%. If you plug in a trickle charger to bring it to 100%, it will slowly drain back down.

Sounds like your F12 alternator may have an issue. It should not be at 12.3V when engine is running. Even without the engine running, your battery should be ideally at 13.5V. When engine is running, it will be slightly higher at 14-15V.

I have never seen a number as high as 13.5volts for a battery standing on its own. Every reference I've seen, and it's a lot, is that a fully charged battery is supposed to be about 12.6 volts. And that is what I have observed myself. Do you have a reference for that higher number?

As for the voltage jumping around, or being less when not coasting, I found a number of older "that's normal" posts from people discussing what is normal. If it does not change, then I don't understand how the Regenerative system works if the alternator is working the same no matter what. Anyway, that is why I was asking if people have actual data points to share.

[HighlandPete]

Originally Posted by Opie55

I have never seen a number as high as 13.5volts for a battery standing on its own. Every reference I've seen, and it's a lot, is that a fully charged battery is supposed to be about 12.6 volts. And that is what I have observed myself. Do you have a reference for that higher number?

As for the voltage jumping around, or being less when not coasting, I found a number of older "that's normal" posts from people discussing what is normal. If it does not change, then I don't understand how the Regenerative system works if the alternator is working the same no matter what. Anyway, that is why I was asking if people have actual data points to share.

I often monitor my F11 voltage, using a voltmeter in the central power socket as aI drive.

Typical sleeping voltage is around 12.6V with charged battery. Can drop by 0.4V unlocking and services awake. Typical running voltage is ~14.4V.

With a battery running in the typical 75 - 80% SoC range, I'll see an increase to 14.7V on the overrun, when the display is indicating a regeneration charge.

It doesn't always go to 14.7V (or stay there), on the overrun, can return to 14.4V. I sense the SoC has a lot to do with whether increased voltage is required to boost the charge.

Say I've used a maintainer and the battery is fully charged, (or a long trip, 100 miles+), I've noticed the running voltage may be lower, even in the 13V range. But once the SoC drops to typical working range, ~14.4V is the typical reading.

All this fits with energy management data, of how the Intelligent Alternator Control (IGR) works.

[Opie55]

Originally Posted by HighlandPete

I often monitor my F11 voltage, using a voltmeter in the central power socket as aI drive.

Typical sleeping voltage is around 12.6V with charged battery. Can drop by 0.4V unlocking and services awake. Typical running voltage is ~14.4V.

With a battery running in the typical 75 - 80% SoC range, I'll see an increase to 14.7V on the overrun, when the display is indicating a regeneration charge.

It doesn't always go to 14.7V (or stay there), on the overrun, can return to 14.4V. I sense the SoC has a lot to do with whether increased voltage is required to boost the charge.

Say I've used a maintainer and the battery is fully charged, (or a long trip, 100 miles+), I've noticed the running voltage may be lower, even in the 13V range. But once the SoC drops to typical working range, ~14.4V is the typical reading.

All this fits with energy management data, of how the Intelligent Alternator Control (IGR) works.

What you say makes sense. I have not been able to find any authoritative and detailed description of how the system is supposed to work. For example, in the abstract I think most people (including me) would be surprised to learn that normal SoC is only 75-80%. It makes sense that the alternator has to work harder at that SoC, but I still don't get how that saves much on gas. Seems like the system is designed to require the alternator to work pretty hard most of the time. When does it "decouple" - to use BMW's own terminology? I guess I'll stop putting my car on the tender for a while and see where it normalizes and see if the resting voltage drops. So far it's at 12.7 resting overnight even though I rarely see readings above 14 while driving except on overruns.

[HighlandPete]

Originally Posted by Opie55

What you say makes sense. I have not been able to find any authoritative and detailed description of how the system is supposed to work. For example, in the abstract I think most people (including me) would be surprised to learn that normal SoC is only 75-80%. It makes sense that the alternator has to work harder at that SoC, but I still don't get how that saves much on gas. Seems like the system is designed to require the alternator to work pretty hard most of the time. When does it "decouple" - to use BMW's own terminology? I guess I'll stop putting my car on the tender for a while and see where it normalizes and see if the resting voltage drops. So far it's at 12.7 resting overnight even though I rarely see readings above 14 while driving except on overruns.

If you want to understand it more read up on "Intelligent alternator control IGR".

From BMW's document...

In contrast to conventional charge control, the intelligent battery control avoids a 100 % charge. The charge level of the battery reaches about 70 - 80 % of the maximum possible charge.

The intelligent alternator control is suppressed cyclically in order to allow 100 % battery charge to maintain the full capacity of the battery over time (regeneration).

One of the illustrations of IGR function.

[Opie55]

Thanks for that. I will read more about it now that I know the terminology. The bottom of the three illustrations seems to explain what I'm seeing in my 650. I was starting with a battery at about a 97% SoC. At that SoC, it seems the alternator just sits back and has a beer. Still not sure why my other car - the X3 - seems to maintain an SoC of at least 92%.