Making a Plug for Hybrids  

Wired has an article up on hacking the Toyota Prius to make it a plug in hybrid.

Felix Kramer thinks the next generation of hybrid vehicles is only an extension cord away. As founder of CalCars, a nonprofit group that promotes fuel-efficient autos, Kramer has high hopes for a project aimed at convincing automakers to manufacture plug-in versions of their hybrid cars. As part of the project, the group recently unveiled a modified Toyota Prius that can be charged from a household power outlet.

CalCars calls its prototype the "Prius+" and boasts that the modified car can deliver upward of 100 miles per gallon under the right driving conditions. A standard Prius gets about 55 miles per gallon, according to Toyota.

During normal operation, the Prius' main computer determines the most efficient way to operate the vehicle, usually running the gasoline and electric engines simultaneously. When a Prius driver brakes, the car's electric motor becomes a generator, creating electricity that is stored in a battery pack, which is later used by the electric motor.

However, engineers like Ron Gremban, who volunteered to be the technical lead for the Prius+ Project, thought it might be more efficient to charge the Prius' batteries using power from the grid. Such a modification would allow Prius drivers to take local trips at low speeds using only battery power, without burning any gas at all.

Once Gremban started investigating the possibility of a plug-in Prius, he discovered that the nickel metal hydride batteries that came with the 2004 model couldn't hold enough energy to get more than a few miles on electric-only mode. His solution was to replace the stock batteries with 18 lead acid scooter cells. The new battery pack was able to deliver enough power to allow the car to accelerate comfortably to 34 miles an hour, the speed at which the Prius automatically engages its gas engine.