Battery maker charged up about software design tool

Danbury, CT--Electro Energy's engineers used to spend weeks, sometimes even months, analyzing candidate designs for the high-performance nickel-metal hydride (Ni-MH) batteries they develop for aerospace applications.

Now, they spend only a matter of days, using a new, rules-based software application that captures all of the complex relationships among battery design parameters. Moreover, they say, it interfaces seamlessly with FEM software for conducting thermal and structural analyses.

The custom solution, developed by Design Automation Associates (Enfield, CT), is based on Heide Corp's. (Medfield, MA) Intent!, a Windows-based software platform that runs on a standard PC.

To conduct trade-off analyses in the past, engineers at Electro Energy used an Excel spreadsheet they created in-house. While perfectly adequate for simple studies, its limitations became increasingly apparent in the face of more aggressive design requirements. As a case in point, in NASA's low-earth-orbit satellite program, the energy density goal for the battery is 100 W-hr/kg. State-of-the-art battery technology is currently only at about two-thirds that number.

"Meeting these kind of design goals is extremely challenging, because it requires the absolute minimum volume and weight for packaging and cooling." stresses Electro Energy's John Cole, program manager. "However, we can't just optimize for those two parameters. We have to consider many other interrelated attributes, such as charge-discharge cycle phenomena, power output, thermal performance, and cost."

When Electro Energy landed a contract with the NASA Lewis Research Center to conduct studies of Ni-MH battery designs for satellites, engineers weren't certain whether their Excel spreadsheet could handle the detailed analyses that would be required. "In particular, the FE modeling was a concern, because we were manually transferring all of the data from the spreadsheet," recalls Cole.

Working together, NASA and Electro Energy decided to fund the development of a rules-based design software program. The goal? Create a tool that would allow engineers to almost effortlessly perform a sensitivity analysis of their designs over a wide range of conditions.

"The 'what if' cases are completely summarized in minutes. I can change the design configuration from cylindrical to rectangular with a click of the mouse," says Cole.

A unique feature of the software, that Electro Energy runs on an IBM PC, is its ability to automatically prepare data for FEM analysis. It takes all relevant information, such as loads, boundary conditions, and material properties, and automatically creates battery geometry and meshes it for the FE analysis. Once the user selects a final design, he or she can output a 3D drawing, assembly drawings and views, a summary of input and output parameters--even a cost analysis if desired--and other information.

To use the software, an engineer does not need to be a battery expert. But Cole is quick to point out that the development effort incorporated decades of experience in battery design. "The power of the software is that it captures the knowledge of some of the world's best battery designers and allows others to access that knowledge easily," says Cole.

Recently, Electro Energy used the software to successfully land a contract to develop a new Ni-MH battery for the F-16 jet fighter. "Instead of giving us the usual basic requirements, like voltages, the Air Force said, 'Here's the old box. Design a battery that fits into it,'" explains Cole.

Engineers at Electro Energy used the analysis software to essentially work the problem backwards. "It helped us come up with a design of the same size and weight--but it has three times the existing battery's capacity. And we did it in far less time than it normally takes to develop a proposal, which is always a non-funded effort," says Cole.

What really sold the Air Force, however, was the live software demonstration given by Electro Energy. "We brought in a PC to show how quickly we could analyze different designs," says Cole. "In fact, it takes more time to print the summary reports than it does to calculate the results."

Figure this one out!

Q:When is a cylindrical enclosure heavier than a rectangular enclosure of equal volume and wall thickness and made of the same material?

A:Normally, never. So when analyzing various configurations for a Ni-MH battery enclosure, engineers at Electro Energy were surprised when their rules-based design automation software predicted that the cylindrical enclosure would weigh more. Why? The software, in following all the pre-established design rules, factored in the weight of the larger end plates that would be required for the cooling components on the cylindrical enclosure. This unfavorable weight trade-off would have been totally non-intuitive without the software design tool, which captures all of the complex relationships among battery design parameters.