Functional Description - Dual Battery Switch Module (DBSM)

Courtesy of CHRYSLER GROUP, LLC

The Dual Battery Switch Module (DBSM) is a solid-state smart device with an internal relay, sensing circuits and control logic. The normally closed internal relay can be activated (open) using an external hard-wired control signal from the Powertrain Control Module (PCM) during Stop/Start application, by LIN bus command from the Body Control Module (BCM), or by the DBSM internal logic.

Vehicles equipped with L2+ systems  use a DBSM  in place of the power control relay, and two batteries to eliminate voltage drop in the system voltage during an Auto-start event. This allows the consumer electronics and vehicle modules subsystems to continue to function in a normal manner. The DBSM is connected in-line between the Main (Cranking) Battery and the Auxiliary (Vehicle) Battery.

The engine starting system  and engine charging system  are connected to the main battery side of the system. When the DBSM internal relay is closed, the Auxiliary Battery will charge through the DBSM. If for any reason the DBSM internal relay is stuck on (open), the auxiliary battery will not charge.

When ESS is active,  and an Auto-start crank event is initiated  , the DBSM  receives a ground signal from the PCM.  When the DBSM receives this signal it breaks the connection between the batteries and allows them to work independently. When this occurs, the main battery is used to crank the engine. The auxiliary battery is now solely connected to the PDC and is not affected by cranking, and can maintain full battery voltage to the rest of the vehicle modules and subsystems.