Capacitor-Powered Cars: Capacitors in Automotive Applications

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Like virtually all electronic products, automotive systems make extensive use of capacitors. However, with the rising adoption of cars using alternative propulsion technologies where management of electrical current and circuits is becoming more important, the role of capacitors is expanding. Meanwhile, innovations in supercapacitors are making these devices suitable for use in electric vehicles (EV) and plug-in hybrids, supplementing and even replacing batteries in some cases.

Electric Vehicle Production

EV production is expected to rise rapidly, driven by new emissions regulations and incentives. Worldwide manufacturing of EVs, a category consisting of both pure electric models and plug-in hybrid electric vehicles, is expected to expand by a factor of six during the coming years. Annual production will expand to 2.4 million units in 2021, up from 409,000 in 2014, according to a forecast from market research firm HIS, Inc.

This contrasts sharply with the marginal growth of 3.6 percent expected for the overall motor vehicle market during the same time period.

Governments Help Drive Electric Vehicle Demand

Local and national governments are a major force propelling the acceleration in EV sales. For example, California’s Zero Emissions Vehicle (ZEV) regulation is expected to put more than 1.4 million ZEVs on the road in the state by 2025. California’s ZEV definition includes plug-in hybrids and fully electric battery-powered cars. The ZEV regulation is designed to put California on track to reduce greenhouse gas emissions by 80 percent by 2050.

Capacitors targeted at the car market mainly comply with the Automotive Electronics Council Q200 specification, which has emerged as the de facto standard for automotive-grade passive devices. Q200 defines operating temperatures for different types of passives, including capacitors used for varying purposes in cars. The specification sets different parameters for whether devices are installed under the hood or in the passenger compartment.

Aluminum Electrolytic Capacitors

Various types of capacitors can be found throughout automotive subsystems of all types of cars, including internal combustion engine (ICE) types that now dominate the market. Capacitor suppliers such as EPCOS AG offer a range of automotive-grade devices used in convenience, safety and engine control unit applications.

For example, the company’s aluminum electrolytic capacitors are employed in convenience systems like air conditioning, window wipers and motors used for automatic windows, seats and other purposes. These devices also are employed in key safety and control systems like power steering, airbag controls and braking systems. Furthermore, aluminum electrolytic capacitors are used in engine control units (ECU) for battery controls, gas- and diesel-engine controls and electric motor drives for uses like fuel pumps and fans. Additionally, film capacitors can be found in keyless entry systems and tire-pressure monitoring systems.

Electric Vehicles Power Up Capacitor Demand

EVs, plug-in hybrids and some other types of motor vehicles employ electric drive trains. These drive trains are putting increased demands on electronic components and subsystems.

In these vehicles, aluminum electrolytic capacitors and film capacitors are used in drive-train applications including boost inverters, DC/DC converters, motor inverters, on-board chargers and wall chargers.

Brake Energy Regeneration

Capacitors also can play a key role in regenerative braking systems, a technology employed in the popular Toyota Prius hybrid. A regenerative braking system recaptures the kinetic energy lost as heat when when a car decelerates and turns it into electricity. That electricity can be stored for a short period of time in a capacitor before it’s recycled to make the car accelerate again.

Mazda's i-ELOOP system uses a supercapacitor to perform brake energy regeneration. The charge stored in the double-layer supercapacitor is used to power car electrical systems, including the headlights, the climate control and the audio. While Mazda is using the technology in cars that are propelled by conventional ICEs, supercapacitor-based regenerative braking systems also can be applied to EVs.

Supercapacitor Car Battery

Supercapacitors promise to play a much larger role in the EV market in the future. A major factor inhibiting the acceptance of some EVs has been their limited range.

The Tesla Model S, a high-end car, can exceed 300 miles per charge when travelling at 55 miles per hour. However, other EVs have a much lower range—like the more affordable Nissan Leaf, for example, which can move only about 84 miles on a single charge.

The limitations on EV range are due to the lithium-ion batteries used in most electric cars. These batteries are expensive and often are unable to store enough charge to meet the demands of motorists. Furthermore, these batteries can be slow to charge.

Recent breakthroughs in supercapacitors could make them a viable and superior replacement for lithium-ion batteries, however. Conventional supercapacitors can charge up much more quickly than batteries, but cannot hold enough charge to power EVs.

This problem could be solved by a new graphene-based supercapacitor technology developed by the Gwangju Institute of Science and Technology in South Korea.

Often called a “wonder material,” graphene is a single-atom-thick layer of carbon atoms that possesses remarkable properties. One interesting aspect of graphene is its massive surface area per volume, with just one gram of the material capable of covering 2,675 square meters. This massive amount of available surface allows graphene to store vast quantities of static electricity.

The Gwangju Institute says its supercapacitor now can store as much energy as a lithium-ion battery of equivalent weight and could recharge in less than four minutes. Future developments in the technology are expected to allow it to exceed the capacity of lithium-ion batteries. While the technology still needs work before it is ready for commercialization, this development illustrates the potential for supercapacitor technology as a battery replacement in EVs.

Capacitors Hit the Road

With their widespread use in conventional ICE cars, along with the strong potential for growing usage in EV vehicles, capacitors and supercapacitors will continue to be a key component in the automotive market.

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