Utilizing more efficient power sources

By Chad Hall, chief operating officer, Ioxus

The automotive industry’s demand for more efficient power sources continues to drive research in battery technology, ultracapacitor technology and electronic power supply design. To utilize energy as efficiently as possible, automotive engineers have historically reduced the gross weight of an automobile. While these early efforts proved valuable, they were just the beginning of better energy efficiency in automotive design. As computer control mechanisms and sensors became more sophisticated, fuel injected systems were developed that increased engine performance and fuel efficiency. These early efforts focused on how to squeeze more useful energy out of the internal combustion engine. Alternate power sources were largely ignored due to their expense. One of the more obvious alternative power sources is the battery, but the size and weight of batteries required for an all-electric car were not available, which remains basically true today.

Internal combustion engines offer high energy density (gasoline) and high power density controlled by the rate of fuel ignition. This combination of energy and power density does not exist for batteries or fuel cells. Gasoline has an energy density on the order of 45 MJ/kg[1] while batteries are, in most instances, more than an order of magnitude less, having energy densities on the order of a fraction to a few MJ/kg[2]. Thus, the overall performance of batteries and fuel cells must be increased to make them more attractive.

Ultracapacitors offer a partial solution to this problem. Pairing a ultracapacitor with a battery improves the power density of the hybrid supply, which has the added advantage of allowing the battery to operate without seeing large current spikes that would be present in the absence of the ultracapacitor. The ability to prevent the battery from experiencing these large current spikes under load allows the battery to have a longer effective life. A typical starter battery, for example, will degrade very quickly if it is required to supply high current for any length of time. So-called deep cycle batteries are designed specifically to supply higher currents, but even such batteries with their thicker lead plates are not immune from damage due to repeated deep cycling. A parallel configuration of a battery with an ultracapacitor can dramatically reduce the deep cycling of the battery under heavy load conditions and thus extend the life of the hybrid power supply, providing a more efficient supply.

In most instances it is necessary to construct a “smart” supply; it is necessary to do more than just connect a battery in parallel with an ultracapacitor and hope for the best.[3] The typical ultracapacitor has a voltage rating of only 2.5 to 2.7 volts, and for higher voltage applications, the ultracapacitors must be configured in series strings for higher voltage stand offs. For example, an automotive application consistent with a nominal 12-volt system would require six ultracapacitors in series for a 15-volt stand off, which is necessary since voltages at that level are used for charging the battery.

The techniques available today include the construction of a ultracapacitor matrix to achieve voltage stand off requirements (series string), overall required capacitance (parallel strings), the inclusion of switch mode circuitry for DC-DC, DC-AC, or other combinations, and the control circuitry, most of which is microcomputer based. Through evaluating ultracapacitor solutions, sales and engineering teams can benefit from cost analysis and come up with the best solution for a particular application.

Chad Hall is the chief operating officer of Ioxus, Inc.  Previously, he spent 14 years with Ioxus’ parent company, Custom Electronics, Inc. (CEI).  His extensive mechanical engineering and business experience helped establish Ioxus from funding to factory to launch.

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[1] http://hypertextbook.com/facts/2003/ArthurGolnik.shtml – Physics fact book on line

[2] http://www.energyadvocate.com/fw64.htm – Table – Energy Advocate

[3] The are instances when this can be done, however they are low voltage and low power cases, which do not relate, in most instances, to automotive applications.