Easy design of 48 V/12 V dual battery automotive systems

June 08, 2020 // By Tony Armstrong, Kevin Scott, ADI
Easy design of 48 V/12 V dual battery automotive systems
The future of 48 V/12 V battery systems in automobiles is just around the corner. Most of the major automobile manufacturers across the globe have been working on proving out their systems for the past few years and it is evident that their implementation will be relatively near term. This is a necessary and crucial step in the long and arduous journey to the fully autonomous passenger vehicle that does not require a human at the controls and has true autonomous driving. Nevertheless, this doesn’t mean the 12 V battery is going away; there are far too many legacy systems in the installed vehicle base for this to occur. Autonomous cars will have both a 12 V battery and a 48 V battery.

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 48 V lithium-ion (Li-Ion) battery or the 12 V 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 48 V-based electric system results in a 10% to 15% gain in fuel economy for internal combustion engine vehicles, thereby reducing CO2 emissions. Moreover, future vehicles that use a dual 48 V/12 V 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 12 V 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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