Automotive Electrical Power Distribution System

By Mike Donnelly - Principal Engineer at Siemens Digital Industries Software.

This automotive electrical power distribution system example includes multiple vehicle sub-systems and components. It supports sizing analysis for wires and fuses, under both static and transient loading conditions. This includes multi-discipline (i.e. electro-thermal-mechanical) dynamic operations such as incandescent lamp in-rush current and motor start-up conditions. The example also demonstrates the special characteristics and design considerations needed for constant power loads, such as switching converters used in LED Driver circuits.

This system also uses a special “direction sensitive” current monitor model that can help identify sneak circuits (i.e. unintended current paths), such as the one found in the “door-ajar”, ignition switch, chime and dome lamp interconnect circuit. Challenge: See if you can find it before running the simulation!

After you run the simulation, a "Component Messages" window will pop up and show several problems with the system. These include a "reverse current detected" (i.e. current flow in the opposite direction from the expected) in the wire that carries current to the dome lamp to indicate a door is ajar. Current reversals are often due to a "sneak circuit" in design, which can lead to undesired function or behaviour of the system. In this case, the reverse current is showing that if the driver puts the key in the ignition and turns on the dome lamp to read a map, the warning chime will sounds even though there are no doors ajar!

The other message indicates that the fuse supplying the flasher circuit has blown, shortly after the hazard flasher is turned on. Clearly this fuse is undersized to supply all 4 flasher lamps together, but operates fine with when just 2 are operated for normal turn signalling. You can try other operational conditions for this system to test for proper fuse sizing. For example, try changing the LED constant power pulse_value to 50W instead of 20W. You can also change the fan inertia to 200u Kg*meter^2, up from 100u. To fix the problem caused by the increase motor inertia (and correspondingly longer time transitioning for stall to normal operating load current), try increasing the fan fuse I^2*T value from 5 to 36, to represent the performance of a slower-blowing fuse.

Please first login to DesignSpark Circuit Simulator (opens in new tab), before trying to edit the design below.

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Do you have questions on the above? Ask in the comments section below and Mike is here to help!