Electric Vehicles: The Battery Pack

 Where does the motor get its energy from? It is from the traction battery pack. It replaces the petrol tank in a conventional vehicle. The electrical energy from the battery pack consisting of several cells is delivered to the motor through a controller which controls the motors speed and torque.
  The present generation of electric cars run on lithium-ion battries, similar to ones used in mobile phones and laptops, but much bigger in size. When fully charged, it will have a driving range of 80 to 200 km depending upon the power of the battery and the size of the car. When depleted, it can be recharged.
  To accelerate the car, as in a conventional vehicle the accelerator pedal is pressed. The accelerator is connected to a potentiometer which signals the motor controller on how much power to be supplied to the motor. When there is no pressure on the accelerator, the power delivered to the motor is zero. So when the vehicle is idle, say at a traffic signal, no electrical power is being processed. That is, no fuel is used unlike in a petrol engine.
  An electric car offers another advantage. In a petrol vehicle, when the brake is applied, it opposes the rotation of the wheel and it's kinetic energy is wasted as heat. However, in an electric motor, when the brake is pressed, the electronic circuits cut the power to the motors. Now the kinetic energy and momentum of the vehicle make the wheels turn the motor and the torque is reversed through a complex switching system. The reverse torque slows down the vehicle and at the same time, the motor works as a generator producing electric energy instead of consuming it. Thus, part of the kinetic energy lost in the process of slowing down is thus regenerated and fed back to the  battery pack, extending its driving range. This is known as 'regenerated braking'.
  About 8 to 25 percent, depending upon the driving conditions  (particularly in urban areas with more frequent stop-and-go) is restored in this process. However, mechanical braking system is still required to bring the vehicle to a quick standstill in a panic situation and hold there.