Functional description

The auxiliary battery is only charged via the starter motor generator. It should only be charged as little as possible. The gear shifts for the cut-off relay (avoidance of overloading of auxiliary battery) are thus reduced.

Fig 1: Identifying Starter Motor Generator, Positive Battery Cable And Plug Connection

Courtesy of BMW OF NORTH AMERICA, INC.

The crankshaft starter generator is connected to the digital motor electronics (DME) via a local interconnect network bus (LIN). If there is a fault in the DC/DC converter or the high-voltage system, the starter generator can take over the supply of the 12 V electrical system.