Starting and Charging: Description and Operation

DC/DC converter (Start Stop)

In the Cayenne the DC/DC converter is installed on the right in the direction of travel, behind the instrument panel.

Situation: (Graphic Restart)

When the engine is started, the vehicle voltage collapses and various components are no longer supplied with the usual 12 V voltage. This can result in a system failure/ fault entry.







Solution:

The DC/DC converter is activated when the engine starts (only in the case of a restart) and delivers this missing voltage to the vehicle electrical system.







During Start Stop operation, the Start Stop coordinator (DME) decides to switch off the engine. When the engine is off, the electrical loads will be supplied with energy by the vehicle battery's reserves. The battery voltage falls many times below the cell open-circuit voltage (2.1 V/cell = 12.6 V). When the engine is started, voltage drops occur (when the starter engages and a second voltage drop when the main contacts of the starter are closed and the engine breaks away). Afterwards, the voltage recovers up to the charging voltage as a function of the starter speed, when the starter is switched off and disengaged and after the start of generator charging. The size of the voltage drop depends on the temperature of all the relevant components in the current path, internal resistance and the age of the battery as well as the engine resisting moment when it is turned. During the engine start (boost), the power supply remains uninterrupted and is converted in the range from 12 +/- 0.5 V.

This means that all active loads such as lighting, infotainment system or other comfort/safety features remain unimpaired thanks to stabilization of the vehicle electrical system, as the capacitors compensate for energy bottlenecks. No voltage drop is therefore measured on the generator even under load. The DC/DC control unit(C) is connected to the gateway (A) via the LIN bus; diagnosis is also performed via the LIN bus.