Audi Shows That Its Fast Charging Curve Makes A Difference
Audi highlights its advantages in fast charging.
By the way of launching its new model, the e-tron Sportback, Audi highlights the charging performance of its electric cars and explains the difference between the charging capacity and the charging speed.
We already know that Audi’s DC fast-charging performances are among the best on the market (see previous reports about the Audi e-tron SUV here and here).
High power over a wide window of state-of-charge (SOC)
One of the most important thing that makes e-tron/e-tron Sportback charging very competitive is a relatively high charging power of up to 150 kW and the ability to charge at a near-peak level over a large portion of the charging procedure.
According to Audi, in ideal conditions, 150 kW output is possible between 5% and 70% state-of-charge (SOC).
Audi notes that the ability to stick at the peak output is unique in the competitive environment and shows a charging chart with another curve of fast charging “competitors” electric cars (with higher peak power, but only for a narrow SOC window). We could obviously find a similarity between this curve and Tesla’s charging curve.
“Therefore, many customers orient themselves toward the maximum charging capacity of their electric car to assess the charging characteristics – but this value is of only limited use if it concerns quick refueling of range at a fast charging terminal. High charging speed (kWh / minute recharged) over the entire charging process is essential for a short charging duration. In other words, a high charging capacity must be available for as long a period as possible. The e-tron models with their continuous output impress with precisely this property.”
Audi e-tron Sportback 55 quattro – Charging performance
“In the current competitive environment, the Audi e-tron takes the lead with a high-performance charging capacity even if there are already models on the market with a nominally higher output. The difference is in the details: The ability of the HPC fast charging (High Power Charging) to provide the highest possible output at the charging terminal may be a necessary prerequisite but it is not the one crucial factor.
A high current consumption on the part of the battery for a large portion of the charging procedure is, at the very least, just as important. However, if the car charges with maximum output over a relatively short period and needs to lower its power early, the charging speed is also simultaneously lowered – i.e. battery capacity recharged per unit of time. Thus, thanks to an ideal charging curve with maximum output available for a long period of time, the charging speed is the more substantial criterion when it comes to charging performance and, ultimately, it guarantees a short charging duration at the charging terminal.”
In other words, the charging speed is proportional to the field below the curve (which represents energy) over a typical charging session.
Is the charging speed really more important than the charging capacity (a peak level of 250 kW in the case of Tesla or 270 kW in the case of Porsche)? Sure, but it is still not the most important from the customer’s perspective who would like to know the range replenishing speed. It would require including also the average energy consumption to tell how many miles can be driven per minute of charging.
Charging curve above 80% state-of-charge (SOC)
Audi notes that the e-tron/e-tron Sportback can charge at a high power also beyond 80% SOC, which is “unique”. As we can see from the chart, even at the end the charging is around 50 kW!
However, here we must take into account the specific of Audi’s battery packs, which are 95 kWh total, limited to 86.5% usable. The main reason behind the high charging power at high SOC is the high upper capacity buffer. The 100% of SOC on the display is actually 91% of the real total capacity.
We believe that lowering the buffer would force Audi to lower the charging power at the end, just like in the case of many other EVs.
Overall, e-tron fast charging to 80% should take about 30 minutes, while 5-100% recharge requires about 45 minutes. At a low state of charge, just 10 minutes is enough for 110 km (68 miles) of range.
“A major difference from other concepts, which normally only reach their full output for a short time – at the “peak” – and lower their power considerably before reaching the 70% threshold. On a day-to-day basis, this means an elementary advantage: For a range of around 110 kilometers, the customer ideally spends just under 10 minutes at the charging terminal. The Audi e-tron 55 reaches the 80% mark after approximately 30 minutes. Even though it takes much longer, for technical reasons, to fill the remaining 20 percent of a lithium-ion battery, fully charging (5% to 100% state of charge) at an HPC terminal takes around 45 minutes – an outstanding characteristic in the competitive environment.”
Sophisticated thermal management
And finally, fast charging causes a considerable amount of heat in the battery cells. To not exceed the optimum range, the batteries are liquid-cooled during charging:
“The lithium-ion battery of the Audi e-tron 55 has a gross capacity of 95 kWh (net 86.5 kWh) and has been designed for a long life cycle. Its elaborate thermal management system forms the basis for well-balanced performance and durability. Liquid cooling ensures that the battery’s temperature remains in the optimum range of 25 to 35 degrees Celsius, even at high stress levels or low temperatures. 22 liters of coolant circulates in the total of 40 meters of cooling lines in the four coolant circuits. During direct-current charging with 150 kW, cold coolant takes away the heat that occurs as a result of electrical internal resistance in the battery. The core of the cooling system is made up of extruded profiles – visually comparable with a slatted frame – which have been affixed to the battery system from below. A newly developed, 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. The spatial separation of elements and battery cells carrying cooling water also increases the overall system’s safety. An additional positive side effect of this elaborate design is the high resilience in the event of a crash.”
Gallery: Audi e-tron Sportback 55 quattro – Charging performance
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