Power Management: Battery Charge Condition
Power Management: Battery Charge Condition
Determining the battery charge state
Power management is software in the engine control module (DME/DDE: digital engine electronics or digital diesel electronics). See also functional description or SBT 'Power supply'.
One function of the Advanced Power Management, APM, is to determine the battery charge state by means of the intelligent battery sensor, IBS.
Brief description of components
The following components for power supply are described
- Battery
- Intelligent battery sensor
Battery
The capacity of the built-in battery depends on the engine used and the vehicle equipment. Selection criteria for the required capacity are:
- the cold-start characteristics of the engine
- the closed-circuit current consumption of the vehicle
- the energy requirement of the auxiliary consumer units (independent heating, telephone, etc.)
IBS: Intelligent battery sensor
The IBS is a mechatronic, intelligent battery sensor with its own microprocessor. The microprocessor is a component of the electronic module. The electronic module records the voltage, the current flowing and the temperature of the battery. The following components are fitted in the electronic module:
- a shunt (resistor for current measurement)
- a temperature sensor
- electronic evaluation unit on a board
The IBS continuously measures the following values on the battery:
- Terminal voltage
- Charge current
- Discharge current
- Temperature of the battery
For data transmission, the IBS is connected to the DME (Digital Engine Electronics) or DDE (Digital Diesel Electronics) via the BSD (bit-serial data interface).
System functions
The following system functions are described for power management ("Advanced Power Management"):
- Determining the battery charge state
Battery charge condition
The APM with the intelligent battery sensor determines the battery charge state while the vehicle is being driven and when the vehicle is at a standstill on the basis of measurement data:
- Vehicle being driven:
- Balancing the charge and discharge current of the battery.
- Calculation of the current characteristics on engine start to ascertain the battery condition.
While the vehicle is being driven, the IBS transfers the data across the bit-serial data interface (BSD) to the engine control module (DME/DDE). The software in the IBS controls the communication with the higher-level engine control module (DME/DDE).
- Vehicle at a standstill
When the vehicle is at a standstill, the measured values (open-circuit voltage measurement) are queried in cycles to detect energy losses. The measured values are entered in the IBS in the memory and transferred to the DME/DDE after restarting the engine.
For the history of the battery charge state, the following values are stored in the DME/DDE:
- Battery charge state of the last 5 days.
- Charge state histogram with duration in the ranges 0 - 20 %, 20 - 40 %, 40 - 60 %, 60 - 80 % and 80 - 100 %. The charge state histogram is reset in the following cases: programming the on DME/DDE or registering a battery replacement.
NOTE: Evaluation of the battery charge state.
If the off-load phase is not sufficiently long or if there is a closed-circuit current fault, the battery charge state cannot be determined correctly: the state of charge is implausible.
Notes for Service department
General information
NOTE: Battery condition.
The battery condition cannot be determined solely on the basis of the battery charge state. If there is a suspicion of a damaged battery, check the battery condition (e.g. with battery tester) and investigate the cause by means of the test module "Energy diagnosis". With a low battery charge state, recharge the battery before handing over the vehicle to the customer.
NOTE: Recharging the battery
The battery may only be charged using the BMW-approved chargers at a constants charge voltage of 14.8 V. If possible, the battery temperature during charging should be between 15 °C and 25 °C. Under these conditions, the battery is adequately charged when the charge current has fallen below 2.5 A.
If the charging process at carried out at low temperatures, the process is only completed after falling short of a charge current of 1.5 A.
If the battery is charged directly at the battery terminals on vehicles with IBS, misinterpretations of the battery condition and under certain circumstances also unwanted Check Control messages or fault memory entries can occur.
If the battery is charged when installed, the charging process take place via the starting-aid terminals (all models except R55, R56) if there are starting-aid terminals in the engine compartment. This is the only way to ensure that the charging process is correctly detected by the vehicle electronics on vehicles with an intelligent battery sensor (IBS).
For R55, R56:
R55 and R56 have no starting-aid terminals in the engine compartment. On these vehicles, the positive terminal of the battery charger must be directly connected to the battery. On vehicles with petrol engines, the negative terminal can be connected to the attachment eye on the transmission and on vehicles with diesel engines to a flange on the engine bearing block on the engine.
NOTE: Replacing the IBS.
The vehicle with the new IBS must be placed in the idle state for at least 3 hours: Only then can the new IBS determine the battery status.
The Check Control message