Teardown reveals Chevy Volt's electronic secrets
The 288-cell Volt lithium-ion battery pack comprises four modules in a T shape that fits below the rear seat and in the “tunnel” between the front seats. Bus bars connect the four modules, and a service-disconnect bar connects to the pack contacts (Figure 1). The pack physically divides into plastic-encased slices, or blades, each of which includes two cells. A cooling fin carrying five channels of coolant separates the two cells. Electrically, groups of three cells connect in parallel, and 96 of these groups are in series so that the 288 cells produce 360V with a capacity of 16 kWhr. To prolong battery life, the battery never fully charges or discharges, so it uses only the “middle” 9.4 kWhr of battery energy.
When the battery is operating at lower than the optimum operating temperature, the fluid heats the battery to operating conditions and then cools it to avoid overtemperature. Even if the car is not operating, the control electronics activate the coolant loop to avoid overheating the battery during hot weather or overcooling in cold weather. Thus, keeping the Volt on its external charger when the car is not in use avoids draining the battery under such conditions.
The battery-pack coolant loop connects using hose clamps, indicating that the car is a limited-production vehicle. Higher production volumes would allow use of brazed joints. The bolts clamping together the pack each have three inspectors’ paint marks, showing that the assembly is carefully inspected to ensure quality and function for this $8000 component that is at the heart of the Volt.