Special Battery Systems
Special Battery Systems
Special battery systems are broken into two groups:
- Vibration Compensating Battery Systems
- Dual Battery Systems
Vibration Compensating Battery Systems
Vibration Compensating Battery Systems act as vibration absorbers, smoothing out road vibrations in the E36 and E46 convertibles.
E36:
The E36 convertible is not only an energy source. The battery is designed as a vibration dampener. Due to this additional function the battery also has a special tray with an integrated vibration absorber.
NOTE: E36 convertible batteries are labeled "Vibration Proof". Replacement batteries must be of the same type.
E46:
The E46 convertible uses the same battery as the E46 sedan, coupe and touring. The battery box is specially designed to float on the vertical axis through three articulated rods.
This allows the battery to act as an inertia mass and dampen various vibrations while the vehicle is driven.
Dual Battery Systems
E31 (850i):
The dual battery system on the 850i was introduced to handle the higher level of electron C technology with increased tunctions and safety features that were added to the vehicle, as well as the added diagnostic information.
Design considerations were made to minimize electrical loads during Key Off and periods of driving with low engine speeds while certain timed operations (e.g. Glove compartment light, courtesy lights and seat heating) were active.
Special testing and charging procedures exist for the dual battery system on the 850i, refer to SIB 61 10 90 and SIB 61 06 91 for specific information.
E38 750iL:
The dual battery system on the 750iL is necessary due to the addition of the E-CATs. If a single battery system was used, the E-CATs would be provided power from the single battery just after cold engine start-up when the battery is at its lowest capacity This would increase engine loads due to charging of the single battery and cause an increase in injector "On" time during the cold engine warm-up period, which result in unnecessary tail pipe emissions.
Providing separate battery systems for the starting circuit and the vehicle circuits also minimizes the possibility of a discharged starter battery ensuring reliable engine starting.
Components of E38 Dual Battery System
- Starter Battery: Located in the right rear trunk wheel, the starter battery is connected to the starter motor and to the heating coils of the E-CATs (via the E-CAT module).
- Vehicle Circuit Battery: Located above the starter battery on a swing out mount, the vehicle circuit battery provides operating power for the balance of the vehicles electrical requirements and is directly connected to the vehicle generator.
- Battery Isolation Switch: Located on the swing out mount of the vehicle circuit battery the battery isolation switch opens and closes the circuit between both batteries based on monitored conditions
NOTE: The battery isolation switch is NOT used to boost a discharged starter battery with the voltage of the vehicle circuit battery to start the engine.
The battery isolation switch can only withstand a maximum current flow of 60 amps.
Battery Isolation Switch
The Battery Isolation Switch provides the vehicle with separate battery systems for the vehicle circuits and the starting circuit.
When the isolation switch is open, the vehicle circuit battery is the only power source connected to the power distribution center.
When the isolation switch is closed the starter battery is charged and the vehicle circuit battery is boosted by the starter battery.
Modes of the isolation switch:
- Starting Mode
- Normal Starting
- Safety Starting
- Driving Mode
- Charging Mode
- Sleep Mode
Starting Mode
When the isolation switch recognizes KL15 via the K Bus, it determines the voltage of the vehicle circuit battery.
- If the vehicle circuit battery IS sufficiently charged, it proceeds with Normal Starting.
- If the vehicle circuit battery IS NOT sufficiently charged, it proceeds with Safety Starting.
Normal Starting
- The isolation switch is open.
- Within 0.5 seconds of engine start-up the E-OAT module energizes the E-OAT heating coils (program dependent) and simultaneously signals the isolation switch that the E-CATs are "On" via signal "KATON" (low signal).
- Upon completion of the heating period, the E-CAT module signals the isolation switch that the E-CATs are off (High Signal).
- Under normal conditions, the isolation switch is not closed before the heating procedure is finished.
Safety Starting
- In response to a discharged condition of the vehicle circuit battery, the isolation switch closes to momentarily boost the vehicle circuit battery and supply all systems with starter battery voltage via the power distribution center.
This operation lasts for a maximum of 30 seconds or until confirmation of engine start up is received. (TD signal on the K Bus)
- Receiving the ID signals causes the isolation switch to immediately open for the duration of the E-CAT heating cycle
- If the engine is not started within the 30 seconds, the isolation switch opens and remains open until KL 15 is recognized on the next start-up cycle.
Driving Mode
The vehicle circuit battery is permanently connected in parallel to the generator and is charged when the engine is running. When the isolation switch is closed, the generator simultaneously charges the starter battery.
As the vehicle is driven the isolation switch cycles between open and closed based on:
- Voltage values of both batteries.
- Current transfer between both batteries as monitored by the isolation switch.
- Internal temperature of isolation switch.
Conditions Causing Switch To Open While Driving
- Sufficiently charged starter battery.
- Current flow through switch exceeding 0.5 amps.
The starter battery will supplement vehicle electrical needs during periods of high demand (e.g continuous wiper operation combined with lights and blower).
- The internal temperature of the isolation switch exceeds programmed maximum value.
Conditions Causing Switch To Close While Driving
- Monitored voltage of vehicle circuit battery exceeds that of starter battery by 0.7 volts.
- The voltage of the vehicle circuit battery drops below 9 volts three times within one minute.
Charging Mode (in the workshop)
The isolation switch monitors starter battery voltage during key off conditions and continues monitoring after the vehicle and the isolation switch have entered sleep mode.
- It starter battery voltage exceeds 13.8 volts during charging in the workshop, the isolation switch comes out Of sleep mode and closes.
This causes the starter battery voltage to bleed off to the vehicle circuit battery, charging the circuit battery and protecting the starter battery from overcharging.
The isolation switch remains closed until the next key on cycle.
Sleep Mode
The solation switch goes into sleep mode as soon as the engine is switched off. The current draw of the isolation switch drops below 1 mA. The isolation switch comes out of sleep more if:
- KL15 is recognized
- Starter battery voltage exceeds 13.8 volts (charging mode)
Failure of KATON signal
If the KATON signal is not received due to:
- Open or short to B - isolation switch closes for 4 seconds after start-up, TD received.
- Short to B - isolation switch opens 60 seconds after receiving TD.