Double-layer capacitor powers start-stop system

November 02, 2012 // By Christoph Hammerschmidt
Start-stop systems for hybrid and micro hybrid cars are among the most efficient approaches to reduce a vehicle's fuel consumption. This holds true in particular for commercial vehicles used in intra-urban goods transport. The downside of such systems is that they expose the vehicle's power supply to significant stress - after all, the cranking motor draws up to 600A when starting up the engine. Continental has developed a start-stop system that complements the battery by a dual-layer capacitor.

In situations with frequent stops and starts, the limitations of start-stop systems powered by a conventional battery become obvious: When multiple electrical consumers are active, the motor cannot switches off because it would overstress the electrical system to re-start the engine with so many loads. Based on expertise gathered in the development for Peugeot's eHDI micro-hybrid power trains, Continental has created a technology that complements the battery through a large dual-layer capacitor with a capacity of up to 3000 Farad per cell which stores enough energy for multiple start-ups. "This energy storage device has properties that complement classical batteries very well", said Carsten Goette who oversees the development of the system. "Within a few seconds it can be charged or discharged completely. This ability to mobilize its entire energy content within very short times makes it ideal for peak load coverage or to return the energy gained through recuperation".

In contrast to batteries, dual layer capacitor maintain their power even under very low temperatures. In addition, they sustain up to one million of charging cycles, Goette said. The Power Net concept combines the high power density of a dual layer capacitor with the high energy density of a battery. An electronic controller directs the energy flow to and from each of these power storage devices. The technology is scalable. The energy storage devices can be switched in parallel or in series. The best configuration depends on the respective environment - in some cases, the capacitor might even replace existing batteries. In its current implementation, it aims at the market of light trucks and delivery vans, but it can be adopted to any environment, the company said.