To ensure the car's safety, Volvo had to choose carefully what kind of batteries to use, and to engineer a sophisticated battery management system. It had to plan for how the batteries would handle heat when charging, and in the event of an accident, how they would dissipate heat and prevent electrical risks to emergency workers. Finally the automaker had to decide on the placement of the batteries in order to protect them in case of an emergency.
There are several versions of lithium ion batteries available, with differing chemical compounds. Choosing the appropriate variety depends, in part, on how the batteries will be recharged.
There are lots of ways an electric car is recharged, including regenerative braking. "It can be unscheduled, random, with a lot of variability," said Sean Hendrix, director of program management and battery management system development at battery supplier EnerDel Inc. The battery management system has to monitor the batteries' state of charge and each act of recharging "to make sure we're staying within our safe parameters," he said.
"If you've been driving aggressively, hitting the brakes a lot and causing a lot of regenerative braking, which is hot, and then you zip into your garage and want to fast charge, we may have to decide that's too much heat and override, or otherwise control" the amount of current that enters the batteries, he said.
Volvo decided to avoid that issue completely. The C30 is not set up for rapid charging at high voltages. Instead, the car is designed only for slower charging using standard household current, a nearly eight-hour process -- meaning that the car most likely would be charged overnight.
But even without quick charging, controlling the heat build-up in batteries is critical. Consumers are aware of tales of laptops' lithium ion batteries overheating and causing fires -- and that was with just a fraction of the number of batteries that an electric car needs.
Each of the EnerDel batteries that go into one of its battery packs has a thin metal plate that extends as a fin beyond the battery itself. These line up and act like the sections of a radiator, allowing air to circulate between each fin and draw off heat. If Volvo decides to sell the C30 in hot climates, the system is designed to allow liquid coolant rather than just air to circulate between the fins, but that has not been necessary under Volvo's testing so far.
Volvo also encapsulated the battery packs with heat shielding. If heat builds up in the batteries, as happened to the laptop batteries due to a microscopic manufacturing defect, "you'll have more time to get out of the vehicle," Hendrix said.
Battery management systems play a crucial role in electric and hybrid cars. They monitor the power drain on each battery, so that one set of batteries doesn't do all the work and heat up disproportionately to the rest of the battery pack. They also track the overall state of charge and the car's power demands.
And if one set of battery packs were to fail, the C30 has a second, redundant set available. It won't offer the same range alone, but provides what Stegland called a "limp-home mode" so drivers won't get stuck.