Wired.com: Making a Plug for Hybrids
click to see photos
[includes 3 photos: EDrive team, CalCars Team, EDrive battery pack]
Making a Plug for Hybrids
By Matthew Shechmeister
Wired.com 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
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
Despite such doubts, CalCars' Kramer remains optimistic that manufacturers
will come around, declaring "people are just dying for these vehicles."
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Felix Kramer fkramer@...
Founder California Cars Initiative
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