PLUG OK license plate Making a Plug for Hybrids
Jul 11, 2005 (From the CalCars-News archive)
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Making a Plug for Hybrids
By Matthew Shechmeister 02:00 AM
Jul. 11, 2005 PT

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.

In addition to changing the batteries, Gremban faced the more daunting task of reprogramming the Prius' computer system. To find a suitable replacement for Prius' battery-management computer, CalCars turned to Southern California-based Energy CS, a company with expertise in battery controllers.

Energy CS engineers and co-owners Greg Hanssen and Pete Nortman created a battery-management system that allows the car to operate in electric-only mode and deceives the car's main computer system, telling it that the batteries are very nearly full even when they are more than half empty. To maximize the life of the battery pack, Toyota engineers designed the Prius to keep the batteries about 60 percent charged. The Energy CS controller tells the main computer that the batteries are well above 60 percent full, so the system will draw more power from the batteries. When the batteries are nearly drained, the controller switches back to standard hybrid operation.

Hanssen and Nortman thought the plug-in Prius had commercial potential, so they joined with Clean Tech, a Los Angeles company that converts gasoline cars to natural gas, and formed EDrive Systems to sell the modification to Prius owners. EDrive's goal is to have a plug-in retrofit available to people in Southern California for about $10,000 by early 2006.

"We are going to rely on the early adopters, the people who feel strongly about this, to be the trailblazers," Hanssen said.

Toyota spokeswoman Cindy Knight warned that EDrive's modifications will void the Prius' power train warranty, and said the company is "dubious" about a pluggable Prius.

"Right now we don't see this as commercially viable," she said. "We think there need to be breakthroughs in battery technology to make it commercially viable."

Despite such doubts, CalCars' Kramer remains optimistic that manufacturers will come around, declaring "people are just dying for these vehicles."

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