Audi is to upgrade part of its vehicle electrical system from 12 to 48 volts, as current 12 volt battery power is no longer capable of meeting the demands of new components and equipment.
Audi recently showcased the scope of the 48 volt electrical system in the Audi A6 TDI concept and RS 5 TDI concept technology demonstrators. Both models are fitted with an electrically powered compressor. This operates independently of the engine load and therefore fundamentally improves acceleration. 48 volt technology is also ideal for systems such as dynamic chassis control.
The current state of the art technology has taken 12 volt electrical systems to their limits. Especially at low temperatures, all the various static‑load consumers can account for the entire power generated by the alternator, which can deliver up to three kilowatts. The battery power is no longer capable of meeting the demands of new, dynamic‑load consumers such as high‑performance electric compressors.
The solution is a second subsidiary electrical system running at 48 volts, to complement the 12 volt power supply. The higher voltage means smaller cable cross-sections are needed; this translates into lighter cable harnesses with lower power dissipation. The 48 volt electrical system features new storage technologies and delivers much more power than the 12 volt system with lead batteries. That makes it an important element of the Audi strategy of electrifying various stages of the drivetrain. The Group’s developers have already come up with a scalable platform concept, including a version that incorporates the electrically powered compressor.
In the current highest development version, a compact lithium‑ion battery supplies 48 volts as the energy source during engine‑off phases; a DC/DC converter integrates the 12‑volt electrical system. The lithium‑ion battery operates in conjunction with a new, efficiency-optimised alternator that qualifies the drivetrain as a mild hybrid. Within this concept there are diverse ways of starting, controlling and deactivating the combustion engine as needed. The powerful alternator achieves an energy recovery output of ten kilowatts, far more than is possible at present. That adds up to a saving of up to ten grams of CO2 per kilometre, equivalent to around 0.4 litres of fuel per 100 km.