Power supply. Reality

My car (E60 LCI) has a two-year-old (new) battery, which has been just recently registered in appropriate way, with correct SOC and statistics data. When colder weather came (thermometer dropped down to -10 oC), during several days SOC dropped down to limit of 40 %. One time after turning off the engine KOMBI even lighted up the yellow icon with the symbol of the battery.

Due to these reasons (and seeing, that in many internet forums the topic regarding power supply arrives), I decided to see, what is the true situation with a power supply of BMW E series vehicles.


Basic data of alternator can be found here: ../F5/F5/Shift+F2


At first, I determined the current, which car need’s uses as a “subsistence minimum”, it means, by the temperature of -5 oC:

  • the engine runs idle;
  • headlights turned on;
  • IHKA vent around 15 .. 20 %;
  • all “surplus” consumers – heating of seats and windows, etc. – are turned off.

Such “set” consumes around 40.0 A.


Next step: I identified max current, which is produced by the alternator in idle (660 RPM).

The alternator of my car in idle is able to develop current of 80.0 A! It is A LOT! I was positively surprised by this parameter.

Using simple maths, you can calculate, that for “extra” consumers there are 80.0 – 40.0 = 40.0 A left.


In step three I measured, how much do the “extra” consumers require:

  • heating of steering wheel: 8.0 A (120 W);
  • heating of one seat: 15.0 A (220 W);
  • heating of rear window: 20.0A (300 W);
  • defrosting of front windshield (IHKA vent on 100 %): 20.0 A (300 W).


At this moment the situation becomes more interesting. We can clearly see, that, for example, we can turn on defrosting of the front and rear windshield, but there will be not enough energy left to warm up the steering wheel or both (even one) seats! Or, you can turn on the heating of steering wheel and seats, but there will be no energy left for windshields!

Moreover, we talk about the petrol engine. Cars with diesel engines are equipped with electrical saloon heater, which consumes 50 A of current! With such heating, the situation with electrical supply is even worse!

Let’s see, what does BMW AG say. BMW AG says, that in case of lack of current, its consumption is limited in following (exactly in such order):

Of course, there is a mistake already in the title: we have to save electricity, not fuel!

As we see, a program of the electrical economy provides more than 20 (!) steps. I tested this algorithm in performance. Yes, the algorithm trully works – turning on all possible consumers, the heating of steering wheel works on almost 0; speed of INKA vents is reduced; rear windshield is almost not defrosted!


And at this moment we come to the first conclusion – in cold weather, BMW is not BMW anymore! Let’s imagine the situation: it’s cold outside, the car has frozen. After a hard day in an office – go out, start the car, turn on defrosting of the front and rear windows, heating of all seats and steering wheel, go back to the office for 5 minutes and hope, that the saloon will be getting warm. But – it will not be warm! Because, as we see, the heating of steering wheel and seats, also defrosting of windshields will be done just partly!

Yes, I understand, that alternator has fundamental problems supply full power in idle. Bet – maybe then the solution is to increase the idle? Well, at least to 1400 RPM! It’s not allowed, because then the car will not be able to fit in CO norms? Introduce some kind of a “winter mode”, which can be activated via KOMBI/CCC/CIC! Also, this is not possible? Introduce hidden settings, which can be turned on, using NCS or tool32!

You will say – this is an old car, developed over a decade ago! True. Only – do you think, that F series has some fundamental improvements?


Short note.

Every time, when I get in my car, I have a question to BMW AG engineers: gentlemen, is there any special reason, why I should enjoy ice-cold steering wheel or seats? If not, why these elements are not heated automatically, if the temperature outside is below 0 oC (or any other threshold)? Why the activated status (or heating) lights out even in cases when the car has been gone to sleep for even a short time? With thought – after 20 minutes I came back from a shop, and suddenly the summer has started? Why there is no automatical mode, which provides thermostabilized heating? Why the heating of steering wheel has a same on/off button? I turn it on – after several minutes the steering wheel is hot. Turn off – after several minutes the steering wheel is cold again because the frame of the steering wheel has not even warmed up – only the outside cladding. Now it dropped down to a temperature of the frame, the warming up has to be turned on again. Why this solution of saloon heating is in a level of the stone age? And yes – nothing has changed also for F series. Only the button of steering wheel heating is placed in a more comfortable position.


Returning to research.

Yes, the amount of energy, missing in short-term, can be taken from the battery. This is a solution only for a short time because otherwise the battery will be emptied very quickly!

Here, data from my car’s IBS system. Marked value: the total amount of energy (Ah), which are “taken” from the battery, while the car runs idle. Around 20 % of all energy, which has traveled “in/out”. It’s a lot! It’s clear, that these “taken” 200 Ah have to be “placed back”, charging the battery during driving.

Next part fo the experiment – check, how does IBS succeed with the charging of the battery in cold time. When the outside temperature was around -10 oC, at the end of the day, IBS of my car has calculated SOC around 39 %.

On the next day the temperature has risen to 5 Oc, SOC, re-calculated during the night, has been reached 46 %. Obviously, when the temperature increases, chemical processes of the battery are performing slightly better.

At first, I would like to tell also some good words about BMW AG engineers – by SOC 40 %, IBS system doesn’t allows to take any amount of energy from the battery. If the requirement of consumers reaches over possibilities of the alternator to ensure the required amount of energy, these “requirements” are immediately limited. The voltage of alternator for a second drops down required but is restored immediately.

For the cold engine, IBS maintains onboard voltage of around 14.8 V. Unfortunately, also here – not without surprises. In the situation, when the appetite of consumers is limited, the alternator is held close to its max power, its voltage regularly drops below the set value. Not a lot, but… From desired 14.8 V the voltage in short-term (for less than a second) dropped to 14.5 .. 14.6 V. Here, an example: short-term alternator’s voltage drop to 14.6V.

Hopefully, in other conditions this problem is not so pronounced.


After a moment I noticed, that for the warm engine the voltage of 15.0 V is maintained: max, what is intended.

So, the BMW AG engineers have done some modifications in IBS management and max charge (on-board) voltage is increased from 14.8 V to 15.0 V!

As we see, in such conditions (heating of seats, steering wheel, windshields was turned off) voltage, required from the alternator, is 15.4 V!

I think it’s worth to remind, what voltage is maintained by:

  • “regular” alternators: 14.0 V (for normal climate) or 14.4 V (for cold climate);
  • BMW alternator, if the IBS system doesn’t works: 14.3 V.

I hope, that now also the biggest skeptics don’t have any doubt, that in cold weather the IBS system works more efficient.


After several hours driving outside the city (90/10 mode highway/city), SOC has increased to 49 %:

After several more hours SOC reached 50 %:

During the last hours, IBS maintained the onboard voltage of 14.4 .. 14.6 V (battery voltage: around 14.7 .. 14.8 V).

As we see, in cold weather the charging of battery goes very, very slowly, not even looking at increased onboard voltage. Not without a cause, the manufacturers of batteries indicate, that the charge voltage on cold weather (at temperature -10 oC) can reach even 15.5 .. 16.0 V! To restore SOC of battery from 40 % to 60 .. 70 %, you have to drive for many hours (outside the cities, not “sitting” in the traffic jams).


Once again I offer to look at the image of alternator’s max load:

In the mode of max load:

  • the voltage on generator’s reaches: 15.5 V;
  • the voltage on DME connector: 14.5 V;
  • the voltage on battery drops down to: 14.4 V.

By such current (82 A), voltage drops in wires reach 1.1 V, in heat almost 100 W is released! One more cause, why IBS is a very necessary solution. If the voltage is stabilized not on the side of a consumed, but on alternator’s clips, the consumer receives decreased voltage – part of voltage is “lost” in wires – it’s only normal.

In an example of a solution, very popular in different forums – disconnect the IBS sensor: the voltage on the battery clips will be only 13.2 V! Such low voltage in no way will be able to charge the battery!


And here – a sequence of the car getting to sleep.

It’s very easy to calculate, that every time, when the car goes to sleep, it consumes several Ah (accordingly – several % of SOC). This energy lost has to be compensated while driving. Accordingly – every time, when the car goes to sleep, it requires more than an hour of driving!


Summary of the entry.

I didn’t like the “picture”, what I saw – charge of existing (OEM) battery, which is as if in perfect order, in cold time was very, very slow. Yes, I do understand, that 15.0 V is high onboard voltage, for some reason BMW decided to not increase it higher, for example, to 16.0 V. But I still have several other questions. BMW AG suggests connecting the vehicle to the charger during winter time:

  • are there any user-friendly, automatical chargers, which are offered by BMW? As far as I know – there are none;
  • is there a corresponding charging socket? No, there is none; the user has to open the bonnet, connect the charger to clips, the bonnet cannot be closed normally;
  • is there a “charge mode”? No there is none. Respectively – I connect the charger, but how do I know, that the battery is charged, not discharged if the vehicle has not gone to sleep?
  • why during charging (IBS sees the fact of charging!), correct information of battery charge state is indicated on CCC/CIC or KOMBI display?

Where is the reputed quality of BMW? And yes – F series (hybrids already are a different topic) don’t have any revolutionary improvements…