Supercaps Improve Engine Start Reliability for Wide Range of Transportation Uses

Jason Lee, the author, is Global Product Manager for Supercapacitors and Circuit Protection at Eaton Bussmann Corp. He has worked developing supercapacitor products and markets since 2008. Prior to joining Eaton, he worked at Maxwell Technologies and in the semiconductor industry. Jason has a BS in chemical engineering from the University of California and an MBA from Northwestern University.

Battery life is one of the most critical areas of system performance and reliability in many systems today. The use of supercapacitor technology is gaining momentum for improving the reliability of engine starting, extending battery life, expanding temperature range, and reducing replacement costs.

Supercapacitor technology can serve either as a supplement to or as a replacement for lead-acid batteries in a range of automotive, heavy transportation, marine, traction, and motor generator applications. With the capability to provide hundreds of thousands or even millions of high-power discharge/recharge cycles and high energy density, supercaps can dramatically improve engine start reliability over a broad temperature range for cars, trucks, boats, and motor generator sets.

Depending on the system requirements for the application, supercaps can be designed in a variety of configurations, from a simple parallel connection with a battery to a smart system with a controller between all on-board power sources.

In the case of engine starting, starting reliability is typically atop the design priority list. Lead-acid batteries draw closer to end-of-life with each start, wear out quickly in heat, and lose cranking power in the cold. Adding a bank of supercaps wired directly in parallel to the battery can supplement the battery during high current discharges associated with engine starting. Battery lifespan can be doubled when supercaps are added.

Batteries typically have a lifespan of two to four years, but by supplementing engine-start discharges with supercapacitors, battery life can by extended dramatically and avoid unplanned no-starts. The direct parallel approach offers no protection from house load drain, so a vehicle with the lights or radio turned on after the engine is turned off may still fail to restart, even with supercapacitors. A supercap starter approach offers more reliable starting.

Supercap starting involves a reconfiguration of the system. The battery is disconnected from the starter, but still powers other “house” loads, such as lights, radio, heaters, air conditioning, TVs, etc. A supercap module is connected directly to the starter. This requires a larger capacitor module, but provides higher reliability for engine starting. The lead-acid battery or batteries typically recharge the supercaps but at a much lower current than starting, in order to have a limited effect on battery life.

The trucking industry is now starting to see how supercapacitor technology can greatly reduce operating costs. Tractor trailer rigs and buses typically carry three to four batteries, but when even one of those batteries dies, it can cost an operator upwards of $600 per service call for a jumpstart. Replacement costs for one lead-acid battery for commercial vehicles averages $200. Furthermore, reliability of battery starting suffers at temperatures below -10°F, but supercaps can be used improve engine starting reliability in temperatures down to -40°F.

In supercapacitor design for heavy vehicles, there are three terminals on the device, and one of the positive terminals connects only to the starter. The other positive terminal connects to the battery for recharging. This scenario offers the longest battery life because it does not subject lead-acid cells to the typical 1,000+ amp discharges required for engine starts.

A so-called Smart Start system provides the flexibility to start an engine off either the battery or the supercap, or a combination of both. Because the starter receives a charge from the supercapacitor, it can operate at lower temperatures, down to -40°F. It also is optimized for starting and system capability. A controller determines how much energy is pulled from the supercaps, and it offers the longest battery life of the three installation schemes. Additionally, starting is also protected from house loads.

Supercaps optimize vehicle electrical systems for reliability, cost, and flexibility to meet the most pressing needs of the application, whether it’s for 18-wheelers, boats, passenger vehicles, or motor generators.

Designers of these systems should choose supercapacitors that deliver a long life-span and high reliability. One key parameter to consider in supercapacitor design is ESR performance. For transportation needs, lower ESR and performance over time translates to greater reliability and lower cost in the long term.

Eaton offers a range of supercapacitor solutions for engines, starting from the X series cells to the XVM Module. They are designed to cover a range of applications in transportation applications and can be selected based on the electrical system requirements, environmental considerations, and cost.

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