September 25, 2022
When you hear EV (electric vehicle) charging, and DC (direct current) fast charging, maybe they sound like two completely different things.
DC fast charging is just the fastest “level” of EV charging. It's also called Level 3 EV charging, and it’s the only level that uses direct current (DC) power, instead of alternating current (AC) power. In this article, first we’ll quickly go over the differences between the 3 levels, then we’ll dive into the technical reasons why DC fast charging is so much faster, and why it’s also more efficient.
Level 1: 120 Volts AC Power
Level 2: 240 Volts AC Power
Level 3 EV Charging (DC Fast Charging): 480+ Volts DC Power
If you’re charging your EV with a Level 1 charger, you can simply plug in the portable cord that came with the EV into a standard electrical wall outlet. All EVs come with a portable cord for Level 1 charging. These outlets are also used for things like phone chargers, toasters, lamps, etc. As you can imagine, this method of EV charging requires the least amount of capital investment, and is the easiest to implement in a home or building. You just need a wall outlet close enough to where you park your car for it to work. The disadvantage of this method is that it’s (by far) the slowest Level of EV charging, charging at about 6 - 8 km per hour.
Even though Level 1 chargers are the slowest, speed isn't everything. The affordability of Level 1 chargers, make charging an EV or hybrid vehicle overnight possible if you don't want to spring for a Level 2 charger. In this way, Level 1 chargers suit the consumer market for EV chargers just fine.
Level 2 chargers uses a 240 V AC wall outlet. This outlet might be used for things like ovens or clothes dryers, and they charge at about 30 km per hour. However, they also require much more capital investment for installation than Level 1 chargers. Level 2 chargers have their place in the consumer market for people who prioritize EV charging speed and efficiency. Level 2 chargers are more efficient than Level 1 chargers because they distribute a higher voltage. If you review the formula for power/wattage, you'll see that when voltage increases, current decreases. When current decreases, less heat is emitted, and less heat lost means less energy lost.
As for the costs associated with purchasing and installing Level 2 EV chargers, here's a breakdown:
Finally, there’s Level 3 EV charging, which is also called DC fast charging. These chargers supply 480 Volts DC or more, and supply DC electricity rather than AC. These are often used in urban centers so that the drivers of EVs can charge up quickly if they’re travelling long distances. This, along with their steep cost, means that they are not typically purchased by everyday consumers; more often they are purchased by businesses, building owners, towns and cities (for example). They can typically charge at about 178 miles of electric drive per hour, or about 286 km of electric drive per hour (for all my fellow Canadians out there). This is obviously much faster than Level 1 or 2 chargers. The disadvantage of Level 3 EV chargers is their cost; it costs between $28,000 - $140,000 USD to install a DC fast charging station, remember that’s including the cost of electricians, labour, permits, and anything else associated with the cost of installing a DC fast charging station. Check out this article for a detailed breakdown of EV charging costs. This is a big reason why level 3 chargers are primarily found in public locations; they are typically just too expensive for an individual homeowner and, frankly, it’s usually overkill for a homeowner to install a level 3 charger if they can charge their EV overnight with a level 2 charger.
Table Source: Tesla Model 3 Charging Time
You might hear that one of the main reasons EVs haven’t surpassed internal combustion cars in the market is because they’re too slow to charge. This is true, but it’s actually a simplification of the problem. The problem is really when Level 1 or 2 EV chargers are used as the range extenders of choice in public spaces. They’re the slowest option for charging EVs, so if they’re installed in lieu of Level 3 EV chargers in buildings or along travel routes, they make it difficult for EVs to proliferate the roadways. Basically, EV drivers need to be able to charge their cars quickly in the middle of long drives but, as you can see from the table above, it takes far too long for even a Level 2 charger to charge an EV if you want to get back on the road quickly. Level 1 and 2 chargers have their place in the consumer market for people who want to charge their EVs at home, overnight. You can compare Level 3 chargers to gas stations in the way that, you wouldn't put one on your property, but you sure do need to use one sometimes in order to use your car.
According to the formula we use to calculate power (see image below), when voltage is increased, current can be decreased. More current also means more heat, and heat is actually wasted electricity. So, sending higher voltages not only means more total power is sent to a load, but also that less energy is wasted along the way.
You can’t charge EV batteries (or any battery for that matter) with AC power, so the AC electricity flowing into an EV must be converted into DC power to charge the battery. This AC to DC conversion is done by a device called an “onboard charger” that’s built into EVs.
Remember, when AC power with a lower voltage (and therefore higher current) is sent to a battery, more heat is generated, as we covered above. This heats up the AC to DC converter (onboard charger), so it can only convert at a rate where it’s not overheating. This means that, the lower the voltage, the higher the current, and the slower the onboard charger is able to convert from AC to DC power. Therefore, needing to convert AC to DC power intrinsically slows down the charging process for EVs.
DC fast charging is faster because it supplies DC power directly to an EV’s battery, and so bypasses the EVs onboard charger. When the onboard charger is not necessary, it doesn’t slow down the charging process, and this makes DC fast charging much faster than any charger that supplies EVs with AC power.
And there you have it, the two reasons why Level 3 EV charging is so much faster! But did you know that DC power distribution not only makes EV charging more fast and efficient, but also can be implemented in buildings to save energy and operational expenses?
According to the USGBC, DC consumption currently makes up about 74% of total energy loads in buildings that have EV charging stations, and HVAC equipment with DC motors. When AC power is distributed to buildings (which it usually is, unless a building has a DC microgrid), then all of these DC loads need to convert AC to DC power. Making these conversions at an individual level, every time a DC powered device is turned on, can waste a lot of energy. If you’re a building owner or manager that’s interested in saving energy and operational costs, contact the team of engineers here at Cence Power to get the answers to all your questions related to DC power.