A Blended Battery Pack for Cars

Smart switch: Indy Power Systems has developed the Multi-Flex Energy Management System, a laptop-size power converter. The system allows makers of plug-in electric vehicles to use a combination of power sources--including lead-acid and lithium-ion batteries and ultracapacitors--and optimizes the blend to increase battery life, improve performance, and reduce cost. Credit: Steve Tolen

The race is on to find the ideal battery chemistry for plug-in hybrids and all-electric vehicles, but a startup in Indiana believes that a combination of different storage technologies might be the best way to improve vehicle performance and reduce cost. The company's technology allows vehicles to run on a combination of fuel cells, ultracapacitors, and old-fashioned lead-acid batteries.

Noblesville-based Indy Power Systems has developed an energy management system for vehicles that can quickly switch between two or more energy sources, even when their voltages are different. "It's basically a switch that directs energy in any amount and any direction," says Steve Tolen, chief executive officer and founder of Indy Power, which operates out of Purdue Research Park. "The hardware handles the switching, and the software handles the timing and amounts."

Tolen says that the power electronics package--called the Multi-Flex Energy Management System--is only slightly larger than a laptop computer. He describes it as a custom, software-controlled, DC-to-DC converter that's bidirectional and variable.

"Imagine adding hot and cold water to a tub. We can add a variable amount of hot and a variable amount of cold in different volumes to match the outflow of the drain, which can also be variable," Tolen explains. "In other words, the motor can ask for different amounts of current, and we can provide that, and in different ratios from the two (or more) power sources, regardless of the voltage of the power sources."

For example, an electric vehicle could have both lead-acid and lithium-ion battery packs. Advanced lead-acid batteries may be cheaper, but they are also heavier and deteriorate more quickly if subjected to regular depletion and recharging. Lithium-ion batteries are generally more robust and lighter but are far more expensive. Combining the two means that you can use less of each. And just as important, says Tolen, the two chemistries can be balanced against each other to optimize performance. For example, the lithium-ion battery can be used to relieve stress on the lead-acid battery and extend its life, and vice versa.

Reza Iravani, a professor of electrical and computer engineering at the University of Toronto, says that Indy Power's system is part of a trend toward greater emphasis on hybrid storage. For example, he says, Researchers in Australia have designed a car-battery system that combines lead-acid technology with supercapacitors, resulting in a fourfold increase in the life of the lead-acid batteries.