Further to the recent episode where the Delhi government suspended subsidy on the Tata Nexon EV supported user complaints about its real-world efficiency, we delve deeper into one among the most-discussed topics – golf range of EVs. More specifically, the certification process, to seek out out how manufacturers reach their published range figure and why it differs such a lot from what you get within the world .
The responsibility of testing and certifying vehicles in India rests with the Automotive Research Association of India (ARAI) – a Government-recognised autonomous testing and certification agency that homologates every vehicle under its purview. Amongst all the tests it undertakes, there’s the range/efficiency certification process, which is completed during a lab on a ‘rolling road’, with standardised conditions strictly maintained.
Before commencing the range test, certain fixed preconditions are set. The ambient temperature is maintained between 20 and 30 degrees Celsius inside the power , tyre pressures are set as per the manufacturer’s recommendation, all mechanical bits conform to the manufacturer’s specifications and standards, and therefore the battery is fully charged. The EV is then mounted on a chassis dynamometer (a sophisticated rolling road or ‘dyno’) whose rolling resistance is about in accordance with the car’s ramp weight (maximum permissible weight). So, if a car’s ramp weight ranges between 1,980 and 2,100kg, the rolling resistance is going to be set at the same of two 2,040kg. During the tests, all ancillary systems except those required to drive the car are kept off, including lights, air-con and infotainment.
Curiously, for passenger EVs just like the Tata Nexon EV, Hyundai Kona Electric and MG ZS EV, which belong to ‘Category M-1’ (vehicles weighing but 3,500kg and which may accommodate eight passengers plus driver and luggage), ARAI limits its testing to Part One (urban cycle) of the Modified Indian Driving Cycle only, where their average speed is maintained at 19kph, with a max speed of 50kph.
Each vehicle goes through 22 testing cycles of 195 seconds each, and through each cycle the vehicle idles, accelerates and decelerates during a predetermined pattern. On completion of the 22 cycles, the entire distance in kilometres covered by the vehicle is recorded, and therefore the battery is placed on charge with an energy measurement device placed between the most socket and the vehicle charger to live the particular charge delivered in watt-hours.
CONSUMPTION = CHARGE USED TO TOP UP BATTERY (WATT-HOURS )÷ TOTAL DISTANCE (KM )
To calculate range, the battery size is divided by the consumption to arrive at a theoretical figure, which is what’s printed and advertised by the manufacturer as the certified range.
RANGE = BATTERY SIZE ÷ CONSUMPTION
So taking the Nexon EV, which uses a 30.2kWh battery, as an example, its consumption in ARAI’s tests is 96.8Wh per km, resulting in a 312km range, which is what is advertised by Tata.
ARAI’s standardised and stringent testing protocols enable it to get consistent and comparable leads to controlled environments, for the foremost ideal scenario. However, as it’s a lab-only test, there are variations to the important world.