After a five-month wait, we finally got our Toyota Prius converted into a Plug-in Hybrid Electric Vehicle. PHEVs are considered to be the next step beyond standard hybrids and perhaps an interim step on the way to pure electric vehicles. Our Prius plug-in will be among the many green machines at Friday’s invitation-only Future of the Car event at our Auto Test Center in Connecticut. (Follow the event on Twitter and here on the Cars blog, with coverage continuing next week.)

Getting plugged in
Several conversion kits are available for the Prius. We chose the HiMotion/A123 module. Having impressed us at an industry conference, this seemed like the most mature technology available. The module is installed at seven locations nationwide. It was pricey, though, and cost us $10,875 (on top of the price of the 2008 Prius Touring — $24,803).

This conversion entails installing a lithium-ion battery pack to augment the Prius’s existing nickel-metal hydride (NiMH) battery. That adds 187 pounds to the rear cargo area. An outlet for charging was cut into the rear bumper. The new battery sits in the spare tire well, which now moves the spare onto a secured tray on top of it. All in all, this reduces luggage space.

We’re told that the Li-Ion battery can supply enough juice to propel the Prius on electric power longer distances and up to higher speeds. Battery supplier A123 claims a 35-40 mile electric-only range from full charge to depletion. Recharging is done by plugging the car into a regular 110-volt household outlet and takes about 5.5 hours to fully charge. A spokesperson from A123, as well as other PHEV advocates, claims that the converted Prius can yield more than 100 mpg. However, drawing such conclusion is neither simple nor straightforward. These claims stem from testing on a dynamometer. Plus, this figure doesn’t take into account the amount of electrical energy that goes in to moving the vehicle. We intend to run it through our regimented on-road fuel economy tests and report the findings online and in Consumer Reports magazine.   

For the purpose of testing this kit, we’ve installed a dedicated outlet with an energy monitor. This way we can see the amount of electricity in kilowatt hours (kWh) that’s going into propelling the car on electricity only. We haven’t yet hooked the car up to our fuel-measuring devices.

In a pure urban setting, our Prius runs on electric power more of the time and reaches higher speeds. We’ve teased the car up to 43 mph on electric drive on a level road. Even with the conversion, the engine kicks in every time the car climbs even a slight grade or when the driver tips into the throttle beyond a gentle prod. The energy monitor in the dash shows the state of charge (SOC) of the Li-Ion in blue. It changes to purple as the battery is close to depletion. The Li-Ion doesn’t get any regeneration from coasting or braking as does the stock NiMH battery.

At this point, our plug-in conversion is meant to give a glimpse of an emerging technology, rather than present a viable alternative to a current car. Stay tuned for in-depth testing.

—Gabe Shenhar 

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