Intelligent Battery Sensor and Battery
Intelligent Battery Sensor And Battery
Brief component description
The following components are described:
- Battery
- Intelligent battery sensor
Battery
In the BMW 5-Series, 6-Series or X3 the battery is stored in the rear centre of the luggage compartment floor. In the BMW 1-Series or 3-Series the battery is stored in the rear right of the luggage compartment trim panel. Usually one AGM battery is installed (identifiable on the black housing for batteries installed ex works). In other cases (vehicles without intelligent alternator control and automatic engine start-stop function in some countries), a normal lead-acid battery is fitted.
The AGM battery primarily offers the advantage of greater rechargeability. The capacity of the battery is vehicle-specific depending on the equipment level (engine, optional equipment, etc.).
IBS: Intelligent battery sensor
The IBS is a mechatronic, intelligent battery sensor with its own microcontroller. The microcontroller is an element of the electronics module. The electronics module records the voltage, the current flow and the temperature of the battery. The following components are fitted in the electronics module:
- a precision resistor (resistor for current measurement)
- a temperature sensor
- evaluation electronics on a printed circuit board
The IBS continuously measures the following values on the battery:
- Terminal voltage
- Charge current
- Discharge current
- Battery temperature
For data transfer, the IBS is connected to the DME (Digital Motor Electronics) or DDE (Digital Diesel Electronics) via a local interconnect network bus (LIN bus).
System functions
The following system function of the power management with IBS ("Advanced Power Management") is described:
- Determining the battery state of charge
- Determining the startability limit
- Determining the battery condition
Battery state of charge
The APM with the intelligent battery sensor determines the state of charge during driving and when the vehicle is at a standstill on the basis of measured data:
- Driving:
- Balancing the charge and discharge current of the battery.
- Calculation of the current characteristics on engine start to ascertain the battery condition.
While driving, the IBS transfers the data across the LIN bus bit to the engine control unit (DME/DDE). The software in the IBS controls the communication with the higher-level engine control unit (DME/DDE).
- Vehicle 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 state of charge, the following values are stored in the DME/DDE:
- Battery state of charge of the last 5 days.
- Charge status histogram showing periods in the ranges 0 - 20 %, 20 - 40 %, 40 - 60 %, 60 - 80 % and 80 - 100 %. The charge status histogram is reset in the following cases: programming the DME/DDE or registering a battery replacement.
NOTICE: Evaluation of the state of charge
The battery voltage measured by the IBS approaches the actual open-circuit voltage slowly after the vehicle has "gone asleep". The accuracy of the measured value increases with the duration of the rest phase: The measured state of charge is reliable after at least 3 hours' rest phase. However, if the rest phase is not long enough or a standby current violation occurs, the state of charge cannot be correctly determined: the state of charge is implausible.
Startability limit
The APM calculates a lower and an upper startability limit for the battery:
- The lower startability limit corresponds to the minimum charge state of the battery so that the vehicle can still be started.
- To counteract discharge down to the lower startability limit, a certain charge volume is kept as a reserve. To achieve this, the upper startability limit is calculated. This value is used e.g. as the limit value for the requests for deactivation of terminal 30B when auxiliary consumer units are active.
The startability limit is calculated by evaluating the following measured variables:
- Average ambient temperature with vehicle parked.
- Ambient temperature of the last journey.
- Current state of charge.
- Voltage dip of the last engine start (trend for ageing of the battery).
The startability limit is therefore dependent on the ambient temperature: The colder the ambient temperature, the more energy required for the engine start. Therefore the startability limit is higher for cold ambient temperatures:
- Startability limit is approx. 30% state of charge at 15 °C.
- Startability limit is approx. 50% state of charge at -15 °C.
Battery condition
The battery's condition cannot be determined based on the battery's state of charge alone. All batteries are subject to natural wear due to the natural ageing process. The chemical reactions in the battery, consisting of the charging cycles with battery charging and discharging, mean that deposits form in the battery, preventing the battery from reaching full capacity.
The enhanced intelligent battery sensor installed enables better determination of the battery condition:
- Detection of defective battery cells
- Calculation of the remaining battery capacity
Each total discharge results in a loss of battery capacity: The longer the battery remains completely discharged, the greater the loss of battery capacity. The batteries installed at BMW can withstand several short total discharges or up to two long total discharges, however, when they are fully recharged with a constant charging voltage of 14.8 V after the total discharge.
NOTICE: Fault entry: Battery very aged or defective
If monitoring of the battery condition identifies an aged or defective battery, a fault entry is registered in the engine control unit. The fault entry can only be deleted once the battery is replaced and the battery replacement was registered.
Notes for Service department
General notes
The following general information is provided:
- Charging and trickle charging of the battery.
- Replacing the intelligent battery sensor (IBS).
NOTICE: Charging and trickle charging of the battery
The battery may only be recharged with a battery charger that has been approved by BMW and that has a constant charge voltage of 14.8V. If possible, the battery temperature should be between 15 °C and 25 °C during charging. Under these preconditions, the battery is adequately charged when the charge current drops below 2.5 amps. If the battery is recharged at low temperatures, the charging procedure should not be ended until the charge current drops below 1.5 A. If the battery is to be charged while it is still installed, it must be charges using the jump start terminal points. Only then can you be sure that charging is correctly recognized by the vehicle electronics on vehicles with an intelligent battery sensor (IBS). If the battery is charged directly at the battery terminals, this could lead to a misinterpretation of the battery condition and even unwanted Check Control messages or fault entries. The cigarette lighter gets his voltage supply by the front power distribution box via the switched terminal 30B. After terminal 30B off, the relay de-energizes. This means that a trickle charger connected at the cigarette lighter would be disconnected from the battery. Only charge the battery via the jump start terminal point.
NOTICE: Trickle charging of the battery for stored or stationary vehicles
In the case of stored or stationary vehicles the battery must be recharged at regular intervals in order to avoid a total discharge and thus damage. See the following document: Battery charging calendar and battery tag.
NOTICE: Determining the state of charge after replacement of the IBS or the battery
After replacement of the battery and registration of the battery replacement or after replacement of the intelligent battery sensor (IBS) the vehicle must be in rest state for at least 3 hours: Only then can the new state of charge be determined by open-circuit voltage measurement.
Diagnosis instructions
NOTICE: Register battery replacement
After installing a new battery, the service function 'Register battery replacement' should be run. The battery replacement has to be registered in order to tell the power management system that a new battery has been installed in the vehicle. If the battery replacement is not registered, the power management will not function properly, with the result that Check Control messages may be displayed and functions limited by individual electrical consumers being switched off or having their power consumption reduced, for example.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.