How plug-in hybrid cars work

It all started back in fall 2004, when a group of freethinkers that later became the California Cars Initiative (CalCars) learned that the Toyota Prius built for the Japanese market had a button that allowed it to go into electric-only mode for about 1 mile at speeds of up to 34mph. They learned this technology was in the U.S. Prius, but there was no way to activate it. As the possibility of a pluggable hybrid that got even better gas mileage rolled around in their heads, they decided to see if they could make it work. It did, and since then, CalCars fine-tuned its concept, developed three prototype cars, and began talks with aftermarket companies and automakers in an effort to bring PHEVs to market.

Currently, a conversion kit to transform the Toyota Prius into a PHEV is nearing production by Edrive Systems and is expected to be on sale in early 2006. The kit replaces the original Prius nickel-metal-hydride battery and the computer that controls the battery with a larger lithium-ion battery and a battery-monitoring and control system developed by EnergyCS.

Once the Toyota Prius has been converted to a PHEV, it can operate in electric-only mode at lower speeds or at times when less power is needed. This means in some cases, such as when running at low speeds around town, the Prius can move completely under electric power. In other circumstances, such as driving at highway speeds, the Prius will receive extra power from the electric motor in essentially the way the production version of the Prius operates. It's just that the more powerful, longer-lasting batteries in the conversion-kit Prius can go faster and farther on electric power alone.

Prius owners who have the conversion kit installed will get about 50 miles of electric-only and electric-boosted power before the batteries need to be recharged. Once the batteries are worn down, the Prius automatically switches back to its normal gas-electric mode until it is recharged. To recharge, the owner simply plugs the Prius into a standard household outlet. A fully depleted battery takes about nine hours to recharge.

The kit will be sold through only approved installers and, as of this writing, just one company, Los Angeles-based Clean-tech, had been approved to install the devices. Since Edrive's conversion kit is not yet in production, final costs have yet to be determined but are expected to be around $12,000. Felix Kramer, founder of CalCars, said it is conceivable that the price for PHEV conversions could come down to about $5,000 above the vehicle's gasoline-only counterpart once the kits are produced in larger quantities.

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