Alternating Current and Direct Current were once the technologies of a war between Nikola Tesla and Thomas Edison. Alternating Current won the war but Direct Current still has a ton of applications today. When it comes to electric vehicles, is AC or DC the current that runs the motors?
It depends on the electric vehicle. That’s right, EVs can use either AC or DC motors. It all boils down to the preferred performance characteristics. The only difference between the two is that AC is by far the dominant of the two in EVs today.
At a certain point, electric vehicle manufacturers decided to go all-in on AC motors. It’s easy to see why. Both DC and AC have their own features to offer but AC provides a far more sophisticated system without driving the price through the roof.
Difference Between AC and DC
AC stands for Alternating Current and DC stands for Direct Current. They are as different from one another as night and day, even though they are both flows of electric current. Alternating Current can flow in two directions while Direct Current can only flow in one direction, hence the names.
Direct motors are frequently found in electric vehicles. However, they mostly extend to the operation of small features on the vehicle, such as a DC motor for the windshield wipers and a DC motor to power the up and down movement of your windows.
Alternating Current is what propels the vehicle. AC allows the vehicle to accelerate, maintain a top speed, and travel long distances without a loss of energy. A good amount of torque and acceleration power is needed to propel the weight of an EV forward and AC is the logical choice.
However, AC motors require a high degree of premium components because the system is notoriously complex and expensive. This is especially true in Permanent Magnet AC Motors. It’s not the complexity of the motor so much as the cost and difficulty in obtaining rare materials.
Direct Current is found mostly in things like E-bikes and small EVs. It has the advantage of providing a stable energy supply and, although the speed is low in relation to the high torque they provide, they are highly efficient.
Unfortunately, DC Motors tend to be quite large and would take up to much space if manufacturers wanted to go with a larger EV. They’re also limited in speed and are known for having problems overheating.
Two Most Common EV Motors
Both of the most common motors used in electric vehicles are Alternating Current Motors. The first is the asynchronous motor and the second is the synchronous motor. Asynchronous motors are also known as Induction Motors.
Induction motors operate via a rapidly spinning magnet. This magnet creates a magnetic field that fires up the rotor, itself spinning and attempting to synchronize with the rotating magnetic field. This spinning process is what creates the energy for propulsion.
Induction motors are “high output” motors and are probably a little more common in electric vehicles than synchronous motors are. Speaking of synchronous motors, the rotor is actually able to synchronize with the spinning magnetic field, whereas the asynchronous induction motors are always trying to synchronize.
In synchronous motors, since the rotor is able to synchronize, the power output isn’t as high. While an asynchronous induction motor provides a car with a little more pep and speed, synchronous motors provide slower speeds but higher torque.
That’s why you will always see synchronous motors in EVs that try to emulate diesel and offroad vehicles. In other words, vehicles that are designed to haul, off-road, and generally take a beating.
DC and AC Work Together in Some Ways
Remember, although most EVs use AC motors, the battery itself is a DC current component. It can’t accept AC unless it’s converted into DC first. This is where the charging stations come in.
It works just like plugging an iPhone into the wall to charge. The plug or the USB port converts the AC current to DC current before its delivered to the battery. The same thing happens when you charge your EV.
So, in a sense, you have Alternating Current and Direct Current working in synchronization. They’re a perfect symphony of functioning technology working together to accomplish a singular task, which is getting your EV back on the road with a full battery.
Characteristics of AC and DC Motors
There are several characteristics that help you to identify whether you are looking at Direct Current or Alternating Current.
Alternating Current allows for abrupt speed changes since the current doesn’t have to travel in a singular direction. Alternating current also has better torque at lower speeds and low torque at high speeds, the exact opposite of Direct Current.
Alternating Current motors require inverters to convert the DC current from the battery to the Alternating Current in the Powertrain. When the current changes rapidly in an Alternating Current motor, AC doesn’t respond as well.
Direct Current responds better to changes in current and the torque increases with higher speeds through the use of brushless motors. Since Direct Current is sent directly from the battery to the Powertrain, DC has no need for an inverter.
While a DC motor (brushless) doesn’t generate high heat, these motors feature overdrive. Frequent use of overdrive can cause a heating problem, as indicated above. You will also notice that there are more moving parts on a DC motor and the surrounding components.
Their top speed is lower and controlled by sending current (changing currents) to the powertrain. Unfortunately, DC motors also feature permanent magnets, which are far more expensive than their Alternating Current counterparts.
All Things Considered
While Alternating Current motors dominate the industry, there is still a place for Direct Current motors as well, at least in smaller vehicles. Even in AC motor EVs, there are several DC motors in operation, taking care of most of your moving parts and necessary functions in the cab.
As it stands today, however, AC is the reigning king in the EV department, mostly due to its high-speed production, cost-effectiveness, and longevity.