What is DC Fast Charging?

Jessica Shea Choksey | May 10, 2021

As car shoppers weigh the pros and cons of electric vehicles (EVs), charging speed plays an important factor in their buying decisions. How long it takes to charge an EV can significantly impact a vehicle owner's daily routine. To that end, there are three levels of charging speed currently available for EVs: Level 1, Level 2, and Level 3, which is also known as DC fast charging (DCFC).

Being the fastest of the three levels, DCFC is ideal for traveling extended distances that require short recharge stops along the way. As EV ranges get longer and EV infrastructure becomes more prevalent, DCFC could be the key for EV owners to take longer road trips and travel further along America's highways in a more practical and time-efficient manner.

What Makes Level 3 DC Fast Charging so Fast?

What is DC Fast Charging EVgo Chevrolet Bolt EUV

The three levels of EV charging correspond to how quickly a charger will replenish power to an EV's battery. Charging is measured in kilowatts (kW), and each kW received by an EV equates to about three miles of driving range per hour of charging. The higher the output from the charger, the faster the EV battery will recharge.

Level 1 charging refers to plugging directly into a standard 120-volt household outlet supplying power at 1.3 kW to 2.4 kW. This output is equivalent to four to six miles of EV range per hour. An overnight charge may add 50-60 miles of range. For an EV with 250 miles of range and an empty battery, a full charge can take two full days.

Level 2 charging uses a 240-volt outlet and produces output ranging from 4 kW to 18 kW of power. This output translates to 12 to 54 miles of range per hour. At the highest rate, an EV with 250 miles of range will recharge entirely in less than five hours. At the lowest rate, it may take about 21 hours. Level 2 charging stations are in homes, workplaces, and public locations such as malls and parking garages.

Level 2 Home Charging Station

Both Level 1 and Level 2 charging utilizes alternating current (AC), which must pass through the EV's onboard rectifier for conversion into DC or direct current before flowing into the battery; EV batteries only take DC current. This conversion process from AC to DC is what makes charging at Level 1 and Level 2 time-consuming.

For a much faster and shorter charging experience, there is Level 3 charging, or DC fast charging (DCFC). Generally available at public locations, dealerships, and commercial fleet companies, DCFC chargers can range in output from 50 kW to 350 kW. They can recharge an EV battery to 80% in anywhere from 15 minutes to 45 minutes, depending on the vehicle's voltage capacity.

The higher voltage and direct flow of DC current into the battery without conversion make DCFC an option that can save EV owners hours of charging every day.

How DC Fast Charging Works

DC Fast Charger CCS and CHAdeMO Connectors

There are currently three types of DC fast charging: Combined Charging System (CCS), CHAdeMO ("CHArge de MOve"), and Tesla Supercharger. 

Each has its own unique charge port connector. The most common type is CCS, though CHAdeMO is still the standard with some automakers. However, most DC charging stations can charge via a CCS or CHAdeMO connector from the same unit. Tesla Superchargers only work with Tesla vehicles, but Tesla vehicles can also use CCS or CHAdeMO fast-chargers with an adaptor.

When charging, there is a limit on the amount of power an EV battery can accept. This acceptance rate, or maximum power rating, is measured in kilowatts (kW) and varies widely from vehicle to vehicle. Many EVs currently on the market have an acceptance rate of 50 kW, while some newer EV models can handle charging up to 270 kW. And because battery size has increased significantly since the first EVs hit the market, DC chargers have been getting progressively higher outputs to match – with some now capable of up to 350 kW.

Since the power rating for both EVs and EV chargers is broad, there could be some confusion regarding compatibility between the two. Fortunately, the kW limits of the vehicle and the kW power of the charging station do not have to match. In other words, a 200 kW charger will work perfectly fine with an EV that charges at 150 kW. The vehicle and the charger will "communicate," and the charger will only deliver what the car can accept. In this case, it would charge at 150 kW. The vehicle's battery management system is responsible for monitoring the charging process and allowing up to the maximum energy the vehicle can accommodate.

The same is true for the opposite scenario. For example, a vehicle with a maximum charge rate of 200 kW is serviceable by a 150 kW charger, but the car will charge at a slower speed than its full capability. In this case, again, it will charge at 150 kW.

When a vehicle battery's charge is greater than 80%, the DCFC rate slows significantly to reduce the risk of overcharging the battery. Due to this threshold, many EV manufacturers will often make a claim about the length of time it takes to fast-charge the battery to 80% (rather than 100%).

The Downsides of DC Fast Charging

Yellow Ford Mustang Mach-E Charging at Electrify America DC Fast Charger

Despite DCFC's apparent benefits, some challenges and limitations exist.

First, DCFC charging infrastructure is limited. There are far fewer Level 3 chargers than Level 2. So even though the time spent at a DCFC unit is significantly less than that of a Level 2 charger, they are not always easy to find or within striking distance.

Second, DCFC is expensive in terms of installation and usage due to the cost of 480-volt electrical service, which it needs for operation. This higher voltage requirement makes DCFC equipment cost much more than Level 2 infrastructure. Also, since DCFC is the fastest charging method, EV owners will pay a higher rate per minute to charge their battery. The premium in cost between Level 2 and Level 3 can be anywhere from 25% to 40%.

Third, regular DCFC usage may be harmful to the EV battery due to thermal issues. Repeatedly heating the battery from DCFC charging is thought to accelerate battery degradation over time. To mitigate this, some automakers have suggested that EV owners refrain from using DCFC every day. However, the adverse effect of DCFC on battery life is largely inconclusive, and there is debate on the topic.

Summary

Electrify America Charging Station in Desert at Dusk

As EVs become more popular in the U.S., the need for DCFC is increasing. DCFC can effectively lessen range anxiety, enable long-distance travel, and empower those without home-charging access, such as apartment and condominium dwellers, to consider buying an EV.

Unfortunately, DCFC is scarce, even though major networks like EVgo, ChargePoint, and Electrify America are expanding availability. Currently, there are only approximately 17,000 DCFC units in the U.S., and more than half are Tesla Superchargers. To put that into perspective, California alone may need as many as 25,000 units in the next five years to support its goal of having 5 million EVs on the road by 2030. 

As DCFC continues to roll out nationwide, adequately meeting demand may be a challenge into the foreseeable future.

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