Optimum Charging

Optimum Charging

The battery voltage can fluctuate between 14.0 V and 15.5 V. The optimum charge voltage is set according to the charge level of the battery, the battery temperature and the status of the external lights (higher charging voltage with lights off). The maximum setting is 16V.

Battery Charge Level Detection

The Power Module knows what the charge level of the battery is at any time by calculating the battery current when the vehicle is being driven and measuring the discharge current. When the vehicle is not in use, the charge level is re-calculated and updated by measuring the closed circuit battery voltage. If the vehicle battery is replaced it must be registered with the Power Module so that the stored values can be deleted and a new calculation started. This operation is described in "Service Functions".

Temperature-Dependent Battery Charging Voltage

By using a charging characteristic map stored in the PM, the charge voltage of the generator is adjusted according to the battery temperature. The diagram below shows the communication path necessary for the Power Module to inform the generator to increase or decrease charge voltage output.







The Power Module detects the temperature of the battery and places the instruction "Increase charge voltage" on the K-CAN Periphery. The Car Access System (CAS) passes the message on to the K-CAN System bus.

The Central Gateway Module (ZGM) receives the message. Performing its function as a "gateway control unit", it passes the message on to the PT-CAN.

The DME (ECM) module receives the request to increase the charge voltage over the PT-CAN.

The generator then receives the request to increase the charge voltage via the BSD lead (bit serial data interface). The electronic evaluation unit in the generator then adjusts the charge voltage accordingly.

If the temperature sensor is detected as defective then the charging voltage will be fixed at 14.3V.




Increasing Idle Speed to Improve Battery Charging

In order to drain as little energy as possible from the battery during freezing weather (below 34°F) the idling speed may be increased.

This ensures that the battery charge level is kept high. If the charge level falls below the calculated minimum level for starting, the idling speed is increased to 750 rpm.

The calculation of the minimum level for starting takes account of the temperature and the condition/age of the battery.