What's this all about?

For decades car electrical systems have worked at 12 volts; however, Audi says that current (no pun intended) alternators and batteries can struggle to keep up with the demands placed on them. The solution is a subsidiary electrical system running at 48 volts. This allows wires with a smaller cross-section to be used, reducing the weight of the cable harness and cutting power dissipation. This is necessary to support the use of items that draw lots of current, such as the electric compressor used on the recent RS 5 TDI concept.

Does that mean a bigger battery?

No, the 48-volt system uses a 'compact lithium-ion battery', which supplies electrical power when the engine is not running; a DC/DC converter integrates the 12-volt electrics. To charge the battery there is a new alternator capable of supplying 10 kilowatts, more than three times the output of a conventional alternator. The entire drivetrain qualifies as a mild hybrid.

How much fuel does it save?

Audi quotes the reduction in fuel usage as 0.4 litres per 100km, which works out as an improvement of about 4mpg. There is also a drop in CO₂ emissions of up to 10g/km. The RS 5 TDI concept is fitted with a variety of systems to start and deactivate the combustion engine as required to cut fuel usage.

What's next?

Along with the electric compressor Audi has plans for other systems to take advantage of the 48-volt system. A scalable platform concept has been developed to roll out the technology, which includes dynamic chassis control and new convenience systems. Expect to hear more about further applications in the near future.