Electrical Team Charged with Finding Best Batteries, Motor for Aurora-II

Fueled by the Sun, Powered by the Mind

How does a solar car work? It takes more than a sunny day to make it go.

The Electrical Team (ET) has subdivided their tasks into three areas: batteries, data acquisition, and motor system.

Batteries provide a way to store energy collected by the sun during non-driving parts of the day. The stored energy can be used during cloudy whether, and in hilly areas, and also works as an energy supplement to the solar array.

Race rules state that we're only allowed to use 309 pounds, 140 kilograms, of commercially available lead-acid batteries. Due to the total battery pack limit, we would like to store as much energy as possible. We are now testing batteries at GNB in St. Paul to see which battery has the highest energy density, and provides the most available power for our systems.

In order to win Sunrayce 95 a team must know how to strategically use the available battery energy. To determine the amount of available energy, or State of Charge (SOC) is one of several critical factors in determining how fast Aurora-II can go during the race.

Determining the SOC requires a robust telemetry system. Currently, the team is looking at data acquisition systems that will monitor the motor's draw of power from the batteries and send this information real-time via a wireless system to a computer in the chase vehicle. The system will also the solar array, and will track speed, distance, acceleration, and g-force.

The most challenging factor in the selection process is making the leap of faith jump to go with a system based solely on a manufacturer's specifications. To justify our needs, and find a motor/controller system which matches our needs, the team plans on testing Aurora-II, which will be outfitted with a solar array, shell, a telemetry system, and Aurora-I's.

This test will allow the team to answer questions regarding the car's power consumption and the size of motor needed to power the car. The test will also determine the type of forces acting on the car when it is moving. By finding answers to these questions with the Aurora-I's motor, it is then possible to review the repeatable data to determine the motor which best fits our application.

The high efficiency, permanent magnet DC brushless motors that are being investigated are just too expensive to buy several of the top contenders to test and see which one fits the team's needs in Aurora-II. Overall, these motors are the most efficient on the market today.

Alex Detrick