A system pioneered by Porsche has reached the mainstream. Recharging an electric vehicle (EV) from 10 to 80 per cent can now be achieved in under 20 minutes. This milestone, achieved by the Hyundai Ioniq 5 and sibling Kia EV6, was made possible by a key change in the vehicle’s electrical architecture. This departure from the norm is also reflected in the way public DC fast chargers are being manufactured, and it’s important for drivers to understand the real-world implications of this change.
A word about voltage architecture
The latest trend in electric vehicle (EV) technology involves the use of high voltage architecture. Typical EVs use a 400-volt system architecture, but the tide is turning. The shift began when Porsche debuted the 800-volt system in its Taycan sedan. To borrow an example from computer science, the change is a bit like upgrading from 32-bit CPU architecture to 64 bits.
Porsche needed to work with parts manufacturers to develop components that were compatible with this never-before-seen EV system. Every device that forms part of the drivetrain is affected by the jump in voltage. The car’s power pack is not out of the ordinary in terms of number of battery cells or power density. It’s simply wired in a way that doubles its voltage level compared to other EVs.
So why did Porsche, and now Hyundai and Kia, execute these changes? The reason is obvious once we understand the relationship between voltage and electricity’s capacity to do work.
Voltage is one variable in the equation that leads us to the all-important kilowatt, a common measurement of power. The other variable is amperage.
1 W = 1 V × 1 A
Here’s a simple analogy that can help you visualize the role of each variable: If wattage is like a flowing river, then voltage is the steepness of the riverbed while amperage is the volume of water.
In other words, voltage defines the electric potential, but amperage measures the actual strength of the current.
To illustrate how this works, imagine you’re at a public fast charging station that is built to the 400-volt architecture standard. If one advertises 50 kW of charging power, we can conclude that it is delivering 125 amps to meet the customer’s power expectations.
400 V x 125 A = 50 kW
If we then want to build a station that delivers 350 kW of power, and the voltage remains at around the 400-volt mark, nearly 900 amps would be needed for the charger to deliver on its promise.
This theoretical example unveils a slippery slope. Battery chemistry is improving and modern EVs can deal with higher power levels. But in practice, raising the amperage makes thicker cables necessary. If charging cables at public stations were of a larger diameter, they would be cumbersome and weighty.
High amperage also generates a lot of heat. As we have previously discussed, heat can be detrimental to the health of an EV battery.
This means that increasing the voltage, not the amperage, is the only way to achieve faster, safer and simpler charging in the near-term.
Otmar Bitsche, Director E-Mobility at Porsche explained that a charger providing 800 volts and a minimum of 300 amps (240 kW) can charge the Taycan from 5% to 80% in 22.5 minutes.
The pros of leveraging an 800-volt architecture go beyond faster charging. Cars like the Taycan have lower levels of current zipping through the powertrain and can use thinner wiring with less copper. This reduces the car’s overall weight, which translates into increased range.
Smaller motors can also be used without sacrificing power. In fact, more power can be transferred with less loss, and space gains can be used to add more battery cells.
Still not immune to the charging curve
EV and charger architecture upgrades clearly help reduce range anxiety, especially on long-distance road trips that require Level 3 Fast Charging.
Charging times may have reached new lows, but many drivers are still interested in knowing the specific length of time it will take to charge their EV.
The answer to that question is becoming more complicated.
When an EV is plugged into a low-power charger, drivers can get a good idea of charging time by dividing the vehicle’s battery capacity (listed in kWh) by the energy delivery rate of the charging device (in kW).
This is because the charge rate is being largely delivered as advertised up until the very end of the charging session, at which point it drops to protect the battery from over-charging.
But when you visit a 350-kW charging station in a Porsche Taycan, for instance, the vehicle will only receive the maximum amount of power it can handle (270 kW) until the battery reaches a 50 per cent state of charge. After that, the car will demand 100 kW. At around the 80 per cent mark, power delivery is reduced significantly – a phenomenon that drivers can expect at all manner of Level 3 charging stations.
All EV charging curves are programmed differently, but they are all noticeable, as we can observe in this small Level 3 comparison chart. The budget-minded Hyundai Kona can accept a maximum of 75 kW until the battery is 40 per cent full, while the small Chevrolet Bolt takes in 55 kW up to a 55 per cent state of charge.
Tesla’s Supercharger network is currently being upgraded to feature 250 kW charging stations that more than double the power output of the company’s 120-kW infrastructure. But as Motor Trend discovered, total charging times were not cut in half as a result, as Tesla had claimed. The best case scenario was observed in the 10 to 70 per cent charge window, which took 18 minutes using a 250-kW charger, compared with 30 minutes for 120-kW charging.
Fast charging tips
Level 3 chargers are most useful when an EV is very low on battery power. Drivers should not expect to receive anything near maximum power delivery at a fast charging station if they arrive with a battery that is already close to 50 per cent charged.
In short, an 800-volt EV plugged into a 350-kW charger will see the largest gains early on, with quickly diminishing returns as the battery gets closer to being fully charged.
Battery temperature also plays a large role in fast charging, so performance will suffer when ambient temperatures are extremely low. To alleviate this, some cars like the Taycan and Tesla Model 3 come with battery warming technology that gets the power pack up to ideal temperature while en route to a Level 3 charging station. Without battery preconditioning, Level 3 charging times can potentially double.
A welcome improvement
Charging times at Level 3 stations are becoming more difficult to accurately predict through a one-size-fits-all formula. As EV range continues to climb, manufacturers are expressing fast charging times in terms of miles instead of 80 per cent fill-up times. For example, Mercedes says its EQS sedan can add 186 miles of range in 15 minutes while BMW’s iX SUV can add 108 miles of range in 10 minutes.
These inconsistent metrics, along with variable charging curves, battery sizes, vehicle architectures and maximum power acceptance levels make it more difficult to directly compare and rank EVs based on their Level 3 charging times.
But the silver lining is that, thanks to higher voltage architectures, recharging times are becoming shorter than ever, and EVs are becoming increasingly compelling alternatives to gas-powered cars.
Photo by Aditya Chinchure on Unsplash
