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Souping up my Toyota Prius

Caption 1: Panels removed with existing battery visible and charger sitting in spare wheel well

Caption 2: Battery cells imported from China

Caption 3: Battery box built and wired up – ready for installation

Caption 4: Stefan figuring out where to connect to the LAN

In this series of articles, we take a look at how a self-made businessman and a self-confessed hybrid/electric nut, gave his Toyota Prius a significantly extended range.

Fifty years ago, Theo Callitz would have been installing a V8 in his Ford Anglia, but today that is rather passé, so Theo takes us through his hybrid conversion. After I bought my Toyota Prius in 2011, the first thing that went through my mind was, “Can this be improved?” Of course my answer was “yes, I think so”. Enter the plug in Hybrid with increased battery capacity. The benefits? Well, to buy power from Eskom is still way cheaper than generating from petrol (only 90%). Naturally, when the battery gets depleted and the engine has to kick in to act as a generator, this is certainly less efficient.

To convert cars to electric, especially if they are old and need a major overhaul, would have been great but it is still expensive. I believe this is going to change as electric becomes more mainstream and batteries become available second hand (less efficient maybe but still useful). The hybrid however has a definite advantage here. It already has the electric motor, control units etc. and we only need to add a battery, control unit and charger – at least in theory. So what did I do? Firstly I approached Antony English of Freedom Won who has converted his own Jeep Grand Cherokee to a pure electric (it successfully went up the Sani Pass recently – with ease). He suggested that we add 10 kWh Lithium Ion batteries (to the existing ½ kWh Nickel Metal Hydride battery) built into the Prius.

Plug in Priuses that can be bought overseas have a 4 kWh battery. The Prius battery runs at 200V and we are now adding a 250V battery. The concept is to keep on ‘topping up’ the standard battery and see if can convince the car computer to make less use of the ICE (internal combustion engine) and allow higher speeds electric propulsion. The Prius has a 60 kW motor that should allow speeds of up to 115 km/h on a level road. Time will tell…

Phase 1 – The electromechanical stuff
The first thing Antony did is to order the cells from China and to build a battery box that would fit into the recess under the boot floor. We decided that the spare wheel well is the best place for the 2,5 kW charger (meaning that the spare wheel and jack, etc. will lie in the boot, taking up space).

The cells have to be properly secured and wired up individually to the control unit (a bespoke unit developed by an American company and directly imported). The reason for this is to monitor the voltages at each cell as well as temperatures. Unfortunately Li-Ion can catch alight spontaneously if not managed well (just look what happened to the Boeing 787 Dreamliners which had to be grounded until they could sort out the battery problems).

Phase two – The control electronics
There have been a few challenges getting the control unit (as well as the charger) to talk to the vehicle’s computer as well as the charging unit. The car CAN bus is communicating at baud rate of 500 mips versus our units working at 250 mips.

Phase three – testing and fine tuning the car
To be continued…