Powering up

The march of the ultracapacitor is accelerating. The energy storage system that can release rapid bursts of power looks set to find a place in more new vehicles.

The march of the ultracapacitor is accelerating. The energy storage system that can release rapid bursts of power looks set to find a place in more new vehicles.

Leading ultracapacitor (UC) manufacturer Maxwell Technologies of Rossens, Switzerland, has teamed up with wire harness and component maker Kromberg & Schubert of Abensberg, Germany to develop a high-efficiency, low-cost starter system for cars.

Ultracapacitors are already used in the Toyota Prius to store electricity from regenerative braking before releasing it to boost acceleration. Other manufacturers are investigating their potential to help meet ever-stricter emissions laws, improve fuel economy and deliver enough electricity to power everything from in-car entertainment systems to satnav and aircon.

Demonstrable benefits

The benefits of ultracapacitors have already been shown on demonstrators from major marques. Honda’s FCX has them to supplement the hydrogen fuel cell stack. BMW’s X3 Concept Hybrid SUV uses them with the six cylinder direct injection engine to improve acceleration. Their small size allowed BMW to tuck the UCs neatly away under the door sills.

The new alliance between the makers of UCs and harnesses looks likely to cash in on a developing market for minimal hybrids, according to power systems expert Chris Mellors of automotive consultant MIRA in Nuneaton. ‘In a minimal hybrid the engine shuts down when the vehicle stops and the electric motor provides the power to start it moving again,’ he said. ‘Supercapacitors can meet this kind of demand.’

Dr Richard Balanson, Maxwell’s president and chief executive, said that extensive testing and analysis show that a UC-based starter power node close to the starter will not only improve starting performance but also enable reductions in system cost, complexity and weight. ‘Incorporating UCs to relieve the battery of the demanding short-duration, high-current, starting load provides several benefits, including extending battery life, downsizing the battery and reducing cabling,’ said Balanson.

Arthur Kurz, manager of electronic integration at Maxwell, said that ultracapacitors’ burst power capabilities, cold temperature performance and long cycle life make them particularly well suited for vehicle starting.

‘Car batteries store a great deal of energy, but must be oversized to deliver current rapidly enough for acceptable starting performance, and their ability to deliver such current drops off sharply when the temperature approaches freezing,’ said Kurz. ‘Ultracapacitors store less energy but can deliver ample current for starting at temperatures as low as -40ºC, so a system combining batteries and ultracapacitors provides a superior solution.’

US legislation is also creating a potential new market for the starter system. Trucks parked overnight will be banned from running engines to power the cabin’s heating and entertainment systems. Instead, the they will have to use only batteries overnight because they don’t generate emissions or noise. But they may not have sufficient energy left to start the engine in the morning — particularly in cold weather. A UC starter could do the job instead.

Cost effectiveness

The flexibility of UCs goes some way to compensating for their high cost relative to lead acid batteries. Kurz pointed out that many newer car designs place the battery in the boot area, which requires running a heavy, rigid, expensive, 70-90mm copper cable the length of the car to provide sufficient starting current. But he noted that a small UC power module near the starter can be charged by a lighter, flexible, less expensive, 16-25mm cable.

‘In addition to providing faster, more reliable starting, this ultracapacitor-based design reduces heavy, expensive copper cabling and allows for a less complex wiring scheme,’ said Kurz. ‘Our calculations show that the system will pay for itself by lowering wire harness cost, reducing the size and extending the lifetime of the battery, as well as contributing to improved fuel efficiency by lowering vehicle weight.’

But the new alliance will not have it all its own way. Hampshire-based Nanotecture is collaborating with Johnson Matthey and HILTech Developments to develop nanostructured material in supercapacitors for hybrid vehicles (The Engineer, 28 February). MIT’s Laboratory for Electromagnetic and Electronic Systems claims to have utilised nanotubes to increase the storage capacity of UCs.

Most car manufacturers are keeping quiet about their interest in UCs, but Mellors reckons their day is dawning. ‘They will probably be mainstream on new models within 10 years, though it could be as soon as five,’ he said. One indicator will be whether UCs are to play a role in the full electric hybrid demonstration vehicle promised by Siemens VDO before the end of this year. The electrical and electronics giant has said there is a need for ‘high-performance energy accumulators’ without mentioning the word ‘battery’. So, unless it is returning to cast iron flywheels, the odds seem good for ultracapacitors.