The T-zero is constructed using a reinforced steel space frame clad in a fiberglass body based on the Piontek Sportech kit car. Double wishbone independent suspension, rack and pinion steering, and a single overall gear ratio of 9:1 are employed, the latter of which limits top speed to just over 100mph, though earlier test runs with more than one gear showed top speeds in excess of 155mph. Maximum power output is 200bhp and the car can be recharged from 0 to 95% in just one hour from any mains electricity outlet using the onboard charger.

Regenerative braking is a particular strong point of the the T-zero, providing a 30% increase in range and an ability to drive fairly hard without having to use the brake pedal (releasing the accelerator results in deceleration). A sophisticated traction and stability program monitors how power is delivered to or absorbed from the wheels in order to minimise wheelspin and the possibility of lift-off oversteer on deceleration.

The original T-zero was based on lead acid technology and had a rather limited range of around 90 miles. By incorporating lithium-ion batteries, however, AC propulsion have managed to shed more than 320 kilos from the T-zero, while at the same time increasing range to a highly impressive 300 miles per single charge.

Several years ago, this would have been unthinkable, as vehicle sized lithium-ion battery packs were either unavailable, or prohibitively expensive. In order to get around this problem, AC propulsion have made their battery packs by simply assembling many hundreds of small, off-the-shelf, laptop sized 18650 (~AA) batteries into one unit.

The benefits of taking this approach are considerable. First, the energy density of the individual cells is around 170Wh/kg, which after allowing for packing and control materials, means the outright energy density of the assembled pack is around 140Wh/kg (up from 35Wh/kg for the original lead acid pack). This means far more energy can be stored onboard, resulting in more range, less weight and greater efficiency.

Second, as the cells are already mass-produced for consumer markets, a great deal of safety and reliability has already been incorporated into their designs. For example, each of the cells in the T-zero pack contains a built-in PTC current limiter and a membrane that stops current at very high temperature.

Third, as the individual cells are of a standard size made by many different manufacturers, there is intense competition between these manufacturers to (i) reduce price, (ii) increase cycle life and (iii) increase energy density. This means that while a large battery pack may be expensive today, as the market expands for this usage, the price of Li-Ion battery packs will quickly plummet. In fact, lithium-ion 18650 storage today currently stands at around £300/kWhr, which is already cheaper than lead acid technology.

Lastly, because the cells in the pack are of a standard size, it means that the pack can be easily upgraded as time goes by with cells of the same size but improved characteristics. This therefore leads to the tantalising prospect of what may be possible when the next generation Lithium-sulphur technology filters down to the 18650 market…

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