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How to get more than 100 MPG from a Toyota Prius

The Toyota Prius has been the most successful and popular hybrid car produced so far but it has one weakness - it cannot go very far on battery power alone. This article tells how a large Lithium-ion battery was added to a Prius, giving it the ability to drive much further on battery power, thereby greatly increasing fuel economy.

By Jim Fell

I first converted a car to purely electric operation in 1999 and after several improvements, particularly to the battery pack, the car was moderately successful.

I was generally able to travel about 80km on a charge and considerably more if care was taken. The car completed the London to Brighton Electric Vehicle (EV) Run in 2005 and 2006.

Click for larger image
Fig.1: a much simplified diagram of the Toyota Prius drivetrain - essentially a normal car with an electric motor/generator added.

Unfortunately the Achilles heel of any EV is still the battery pack. With low-cost lead-acid batteries the range is severely limited and a long cross-country run must be planned like a military campaign.

There must be charging points every 80km or so and you need to stop for a couple of hours at each to restore some charge.

In 2005 I started looking at the hybrid cars that were available and the Toyota Prius in particular. The interesting thing about the Prius was that it could run for a limited period as an EV, however with the NiMh battery pack the electric motor can take the car only about 1.6km at less than 50km.

I wanted to reduce the fuel consumption of the Prius from 60 to 100 MPG, a massive cost saving, by the addition of a large Li-ion batterypack. This article describes how I achieved this using E-blocks and Flowcode as a control system.

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