You might or might not remember that 48-volt electrical systems were going to be the next big thing for cars around 15 years ago. There were real concerns that it would not be possible to power all the on-board electrical systems needed in future without the change. Then the story quietly died, but I think we can be fairly confident that it’s back, and this time to stay.

Why and what’s this got to do with fuel consumption and efficiency, you may well ask? The answer is everything. Electric cars have just not taken off as expected, because they are too expensive. They will be an important part of the long term story, but in the meantime, 48-volt systems will provide a useful compromise. From 2021, across the European Union, car manufacturers will have to meet a CO₂ fleet average of 95g/km across their car ranges. That means lower fuel consumption and diesel, downsized engines and hybrid systems will all play a part.

Delphi, which supplies a range of systems for cars, from fuel injection to electrical equipment, believes that 48-volt micro-hybrid systems are going to provide a useful step forward in reducing fuel consumption. 48-volt systems will be able to handle higher current than a 12-volt setup and this will enable all cars with engines up to 2.0-litres to be fitted with a 48-volt starter/alternator capable of starting the engine. It will also recover braking energy, as hybrids do now. Cars would be driven for the first 100 metres electrically with such a system.

It would also mean that all other belt driven components fitted currently could be removed, and replaced with electrically driven systems. This will include power steering and water pumps, as well as the air conditioning compressor pumps. Instead of being driven all the time, they would only be used when needed, adding further to reduced fuel consumption. Power steering pumps are a good example, as a belt driven system is working hardest at the engine’s highest speeds, when it is needed least. At speed, virtually no assistance is needed, so an electrically driven system would use a lot less power.

Delphi has been testing these 48-volt micro-hybrids, which are currently reducing CO₂ emissions by between seven and 10 per cent. The company thinks that by raising the power of the alternator from 10 to 12kW in the current prototypes to 20kW (27bhp), this saving can be raised to 15 per cent, which will equate to a fuel consumption reduction of a similar amount. Delphi thinks that between 20 and 70 per cent of all hybrids are likely to become 48-volt micro-hybrids. The advantage compared with a battery electric car is that it would represent around 30 per cent of the cost, while reaching 60 to 70 per cent of the targets for electric vehicles.

Another side effect is that because the 12-volt system would be retained, so that current electrical components would not have to be re-designed, it would also offer an advantage for autonomously driven cars. These would need to have a failsafe system in case of electrical failure, and a car with both 48 and 12-volt systems would provide that. A case of watch this space…

John Kendall