Designing 48V/12V dual battery automotive systems

June 04, 2020 // By Tony Armstrong, Kevin Scott, ADI
Designing 48V/12V dual battery automotive systems
Most of the major automobile manufacturers across the globe have been working on proving out the design of 48V power systems as a necessary and crucial step in the long and arduous journey to the fully autonomous passenger vehicle. But this doesn’t mean the 12V battery is going away; there are far too many legacy systems in the installed vehicle base for this to occur, so autonomous cars will have 48V/12V dual battery systems.

The development of 48V/12V dual battery systems is a key element for the powertrains of autonmous vehicles.

The fact that autonomous cars will be equipped with a two-level DC power system means that the vehicles’ internal systems will either run off the 48V lithium-ion (Li-Ion) battery or the 12V sealed lead-acid (SLA) battery—but not both. Nevertheless, in addition to having two separate charging circuits for these individual batteries due to their respective chemistries, there must also be a mechanism that allows charge to move between them without causing any damage to the batteries or any of the systems within the vehicle. Moreover, having two batteries also allows for redundancy should one of them fail during operation.

While this certainly complicates the design of the various electrical subsystems within the vehicles, there are some advantages to be gained. According to some auto manufacturers, a 48V-based electric system results in a 10 percent to 15 percent gain in fuel economy for internal combustion engine vehicles, thereby reducing CO2 emissions. Moreover, future vehicles that use a dual 48V/12V system will enable engineers to integrate electrical booster technology that operates independently of the engine load, thereby improving acceleration performance. Such compressors are already in the advanced stages of development and will be placed between the induction system and the intercooler, using the 48 V rail to spin-up the turbos.

Globally, fuel economy regulations have been tightening, while autonomous driving capability with connectivity continues to proliferate in new automobiles. Accordingly, the 12V automobile electric system has reached its usable power limit. Simultaneously, as if these changes are not already enough, there has been a significant increase in automotive electronic systems. These changes, coupled with related demands for power, have created a new spectrum of engineering opportunities. Clearly, the 12 V lead-acid battery automotive system with its 3 kW power limit must be supplemented.

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