One of the roadblocks affecting electric vehicle adoption apart from range anxiety is high charging times. Audi puts e-tron in the lead using HPC fast charging (high power charging), bringing charge times down to 45 minutes
As automobile manufacturers race towards electrification of vehicles, most have carried out huge developments in increasing range on their respective models. The estimated range from the current crop of Teslas, Audi’s e-tron and the Jaguar i-Pace, for example, have gone past the 300-km mark, which is more than adequate for regular use. However, charging times are still a cause for concern for most customers interested in buying an all-electric vehicle.
For people used to filling in their vehicle tanks with fuel in 5-10 min, it is incomprehensible for them to wait at least an hour for their all-electric vehicles to charge before they resume their journey. Audi is of the opinion that more importance must be given to high charging speed (kWh/minute recharge) over the entire charging process for shorter recharge duration.
THE CHARGING CURVE
Larger the battery, more is the range. Audi e-tron opposes the theory by equipping high performance charging even if competitive products have a higher output. Consider this: the current 2019 e-tron is able to return 87 km for a 10 min charge time at a high speed public charger. This makes it more practical than the rest of the EV crowd. And let’s be honest this kind of charging time is adequate for majority of urban commuting.
Audi mentions that the capability of the HPC fast charging (high power charging) to provide the highest possible output at the charging terminal is a necessary prerequisite, but not crucial. However, the high current consumption on the battery for a large portion of the charging is just as important. When a vehicle charges with maximum output over a short period of time and has to back off its power early, the charging speed is reduced as well. Audi engineers have worked on an ideal charging curve with maximum output available through a longer period of time; thus reducing charge times at the terminal.
Considering the case with Audi e-tron 55, the curve of an HPC terminal with 150 kW output stands out at a high level owing to its continuity. The car charges between 5-70 % state of charge at the threshold of the maximum output before the intelligent battery management reduces the current. Most competitor vehicle systems only reach their full output for a shorter time and reduce power before reaching the 70 % threshold. As a result, a customer only has to spend 10 min charging at a terminal for a range of around 110 km. Keep charging for 30 min and the Audi e-tron 55 achieves 80 % charge, which is a much better trade-off in regular use. The remaining 20 % takes longer to charge, which equates to a total of 45 min, but that is again an advantage over Audi’s rivals. This provides customers a more usable electric range and also enables to plan longer trips considering charging station presence along the way and shorter durations, while charging.
Most manufacturers are focussing on improving thermal efficiency to squeeze the last ounce of usable range from all-electrics. Audi e-tron 55 has a liquid-cooled thermal management system that keeps the battery temperature between 25 °C to 35 °C, which is optimum. The balance needs to be adjusted between the battery performance and its longevity of use. The liquid cooling system holds 22 l of coolant and circulates it through 40 m of cooling lines in its four coolant circuits. This coolant takes away the heat dissipated due to internal electrical resistance on the battery during the direct-current charging procedure with 150 kW.
Paired with a sophisticated Battery Management Controller (BMC), the system supports quicker charging times at the station. Further, cooling optimisation is achieved by introducing extruded profiles to the core of the cooling system affixed to the battery from below. Audi uses pouch cells for e-tron batteries, which are designed to utilise space efficiently. A thermally conductive adhesive joins the cooling unit to the battery housing. The gap filler forms the contact between the housing and the cell modules placed in it. This filler is a thermally conductive gel that fills the space to the housing beneath every cell module. The gel evenly transfers the waste heat produced by the cells to the coolant via the battery housing. Additionally, this gel-separation space between the elements and the battery cells improves the overall safety of the system in the event of an accident.
Audi’s focus on quicker charging times is well founded as the race to electrification catches up with internal combustion engines. It is observed that limited range is no more a concern in modern electric vehicles, but charging times are. The concentration of maximum charging capacity over a larger period of the charging procedure puts Audi at a technical advantage against its rivals. Customers should not just look for maximum range per charge, but also look for high charging speed over the charging procedure. The current 150 kW speeds will also be further increased to 270 kW in future Audis to further optimise charging times and increase vehicle performance.
Another significant player in this ecosystem is the connected application design with most EVs that is able to plan routes and train drivers to maximise range and be informed of all possible charging locations available. This will positively improve adoption percentages of drivers switching to electric vehicles by ironing out concerns like range anxiety and charging times.
TEXT: Abhijeet Singh