After I entered the report regarding the alternative alternator, I heard several versions, what could be done:

a) buy Magnetti Marelli alternator (list price around 800 EUR);

b) buy Bosch voltage regulator (list price around 50 EUR);

c) buy a Valeo alternator (list price around EUR 260).

Unfortunately, all these ideas are not in the correct direction. Why?

This time, I will explain in more detail, what is the voltage regulator, and how different versions of them differ. 

Note. I’ll add right away – some of the devices, which I will describe, actually can not be called the voltage regulators. But, as often say in my blog, one step at a time. 

The voltage regulators (as already follows from its name) are intended to stabilize the car’s onboard voltage. Till E38/39 generation, BMW used “regular” voltage regulators. These voltage regulators ensured fixed voltage on the clamps of the alternator. Persons with more knowledge in the car industry know: there are 2 versions of regulators available – one for a “normal” climate zone (14.0..14.1V) and one version (14.4V) for a “northern” climate zone.

There are typically several transistors (in more simple versions, but they can also include a specialized simple microchip or “simple” OPamp with a power transistor). Not considering its as if simplicity, even these “pre-historical” regulators are not the same! What is different?

a) (long-term) stability of the reference value of maintainable voltage. This parameter indicates how precisely the detected voltage (14.1/14.4V) corresponds to the true product. For cheap products, the +/-5% difference from the ideal is self-explanatory. So, instead of 14.1V, such regulators can actually maintain 13.4..14.8V. The precision of OEM and well-known brand (not to be confused with well-known repackers) voltage regulators will be much better: around +/-1..2%;

b) short-term stability of the maintainable voltage. Short-term stability includes both pulsations and transition processes in changeable work conditions. In the case of a car, the work conditions are changing all the time – the RPM of the alternator changes; the load changes; temperature changes. Again, the short-term stability and management transition processes will be much worse for the cheap products than for OEM solutions. How it manifests? Waving of the voltage, increased hum (noise of few kHz, depending on RPMs) in the sound equipment, short-term voltage drops when the current increases swiftly, and similar troubles. OEM solutions will react much faster and imperfectly, there will be no “waving” of the voltage, hum will be the minimally possible;

c) range of regulation. With this, I mean – how efficiently the regulator can use the potential of the alternator. OEM regulator will be able to ensure higher current in exact conditions (especially at critical moments, for example: idle);

d) overall quality. The most important here: the total proportion of the defect. Quality of the brushes; connections; overall material quality, etc. The brushes and collector of the high-quality product will serve much longer.

I hope that I managed to convince you that different “simple” regulators can be (and are) different. Not taking into account that visually they are like “simple tablets”, their technological level can differ dramatically.

At this moment, we have reached the “voltage regulators” of BMW E6X/8X/9X and newer generation. Why I put the quotes? Because these are not the “voltage regulators” anymore! Their functionality is much wider! Instead of several transistors – several millions of them!

When BMW introduced the IBS system, they made a conclusion – the simple counting of the battery energy gives nothing if you don’t have a powerful and especially manageable energy source – an alternator. What new “features” are required from the alternator?

  1. The power consumption of BMW is huge. Accordingly – a high-power alternator is required. Unfortunately, the situation is aggravated by the engine room’s obstacle; the hot air from the colling radiator is flowing in. Also, the part of the alternator’s energy “goes” to heat, and its parts (windings, rectifier, regulator) are warming up. Taking it all into account – the alternator has to measure the temperature of important hubs, the max current should be limited to protect the alternator itself from damages;
  2. the voltage maintained by the alternator should be manageable/changeable. There are several reasons for it. At first – we are interested in the voltage on the battery clamps(!), not the alternator clamps itself! These voltages are different – even the highest quality wires have resistance, and it’s quite far from 0. Second – the colder the battery, the higher voltage necessary to charge it. Third – in special cases (for example, in case of deep discharge of the battery, Overrun mode), the alternator has to develop an increased voltage to maximally charge the battery or to ensure the recuperation of the energy (save a bit of fuel);
  3. the alternator has to see the load which it gives to the engine. If DME sees the engine’s load, it can precisely manage the idle, correctly adapt (automatic) gearbox in idle mode. Knowledge of load parameters and recording it to DME is also required on the go because on the go DME performs a range of service procedures (for example, measures the injectors, other hubs). On the go DME also perform adaptation procedures of the gearbox – adapts the switching of the gears;
  4. the alternator should be able to switch to specific modes. For example – on a gentle mode, if the battery is very discharged. If the alternator does not know how to do it, then not only will the battery be damaged – also the electronic modules!
  5. the alternator has to know how to switch off for a moment and perform other service procedures, when/if DME will decide to test the battery or the alternator itself;
  6. the alternator should report its health state, should report all live parameters (temperature; developed current; the excitation winding current; mechanical load, etc.).

BMW AG decided to “put” all this functionality in the body of a “simple tablet”. Actually, this is a complicated microprocessor management system, which doesn’t have a lot in common with the “old” type of tablets. You can compare this situation with a pre-historical phone with a wheel and the smartphone we use today. With both types of equipment, you can (with the first one – could) call, but they don’t have many common details and functions. 

The data exchange protocol (communication “language”), in which the DME “talks” to the management module of the alternator, is a “know-how” (or, if you prefer – a secret) of the manufacturer (BMW AG). I will mention some self-evident (for development engineers) nuances:

  1. each such module contains the identification – a code, which describes the current module and allows DME to evaluate, is this an “own” or “stranger” part;
  2. each management module contains coding data. Coding data describe, for what kind of engine (petrol, diesel, 4/6 cylinders, what is the max current, temperature, what functionality is included, etc.) the module is intended;
  3. each module contains the adaptation data. Part of the adaptations are recorded in the factory (they compensate tolerances of the sensors and other elements); part is upgraded during the module’s work (to optimize the reaction time, transition processes, etc.).

Example: identification (part of) data of E6X/E9X alternator:

Sentence of this entry: the only possible solution is the OEM alternator and the OEM management module. 

Why exactly the OEM alternator (everything except the management module) is critical? Both winding of the stator and the rotor (their electrical parameters: resistance, conductivity), rectifier (diodes used in the rectifier, their parameters, cooling conditions) have to comply with the data included in the management module. If reality differs from the plan, the thermal protection will not work; also, the current management conditions will be far from ideal. Waving of the voltage, instability is possible.

Why the OEM management module is critical? As I already mentioned before – the communication “language” is known only to the manufacturer (BMW AG). Yes, the third parties can try to decrypt it using the reverse engineering principle. Unfortunately, as the practice shows, the result is miserable. 

Due to the reasons mentioned above, the items mentioned at the beginning of the entry will not fit: not the Bosch management module (which fits 1/3/5/6 series BMW), not the Valeo alternator, not even the expensive Magneti Marelli option.