“Everybody recognizes that if you can make very efficient electric motors, you can make a quantum leap forward”. - James Dyson
"The electric motor has become a little more well-known and appreciated over the past few years with its improving integration into our cars. With most people understanding and appreciating the impact that their pollution has on the climate, there has been a greater demand for auto manufacturers to create cars that can help to improve our environment, or at the very least, do less harm."
"It is through this demand for growth and development that some of the world’s greatest inventors have refined the electric motor to now work better and be more efficient than it ever was before."
How Does an Electric Motor Work?
If you’re an electrical engineer, you know how an electric motor works. If you aren’t, it can be extremely confusing, therefore, here’s the simplified explanation (or the “how an electric motor works for dummies” version) of how a four pole, three phase AC induction motor works in a car.
It starts with the battery in the car that is connected to the motor. Electrical energy is supplied to the stator via the car’s battery. The coils within the stator (made from the conducting wire) are arranged on opposite sides of the stator core and act as magnets in a way. Therefore, when the electrical energy from the car battery is supplied to the motor, the coils create rotating magnetic fields that pull the conducting rods on the outside of the rotor along behind it. The spinning rotor is what creates the mechanical energy need to turn the gears of the car, which, in turn, rotate the tires.
Now, in a typical car that isn’t electric, there is both an engine and an alternator. The battery powers the engine, which powers the gears and wheels. The rotation of the wheels is what then powers the alternator in the car and the alternator recharges the battery. This is why you are told to drive your car around for a period of time after being jumped - the battery needs to be recharged in order to function appropriately.
In an electric car, there is no alternator. So, how does the battery recharge then? While there is no separate alternator, the motor in an electric car acts as both the motor and an alternator. That’s one of the reasons why electric cars are so unique. As referenced above, the battery starts the motor, which supplies energy to the gears, which rotates the tires. This process happens when your foot is on the accelerator - the rotor gets pulled along by the rotating magnetic field, requiring more torque. But what happens when you let off of the accelerator?
When your foot comes off the accelerator, the rotating magnetic field stops and the rotor starts spinning faster (as opposed to being pulled along by the magnetic field). When the rotor spins faster than the rotating magnetic field in the stator, this action recharges the battery, acting as an alternator.
To further simplify this process - imagine pedaling a bike up a hill. To get to the top of the hill, you need to pedal harder and may even have to stand up and expend more energy to rotate the tires and reach the peak of the hill. This is similar to pressing down on the gas. The rotating magnetic field pulling the rotor behind it creates the resistance (or torque) needed to move the tires and car. Once at the peak of the hill, you can take it easy and recharge while the wheels move even faster to take you down the hill. In the car, this happens when you let your foot off the gas and the rotor moves faster and feeds electrical energy back into the power line to recharge the battery.
What is Alternating Current (AC) vs Direct Current (DC)?
The conceptual differences behind these two types of currents is seemingly fairly obvious. While one current is consistent, the other is more intermittent. However, things are a bit more complicated than just that simple explanation, so let’s break these two terms out in a bit more detail.
Direct Current (DC)
The term direct current refers to electricity that moves in a singular and consistent direction at all times. Furthermore, a direct current’s voltage maintains a regular polarity, that is, one that does not change.
Think of how batteries have clearly defined positive and negative sides to them. They use direct currents to send the same voltage out on a consistent basis. In addition to batteries, fuel cells and solar cells also produce direct currents, while simple acts like rubbing certain materials together can produce DC as well.
In keeping with our battery concept, when considering the positive and negative sides of the battery, it is important to note that the direct current always flows the same direction between the positive and negative side. This ensures that both sides of the battery are always positive and negative.
Alternating Current (AC)
The term alternating current defines a type of electricity characterized by voltage (think water pressure in a hose) and current (think rate of water flow through the hose) which vary with respect to time. As the voltage and current of an AC signal change, they most often follow the pattern of a sine wave (in the image above, the sine wave is shown in the right voltage graph). Due to the waveform being a sine wave, the voltage and current alternate between a positive and negative polarity when viewed over time. The sine wave shape of AC signals is due to the way in which the electricity is generated.
Another term you may hear when discussing AC electricity is frequency. The frequency of the signal is the number of complete wave cycles completed during one second of time. Frequency is measured in Hertz (Hz) and in the United States, the standard power-line frequency is 60 Hz. This means that the AC signal oscillates at a rate of 60 complete back-forth cycles every second.
So why is this important?
AC electricity is the best way to transfer useable energy from a generation source (i.e., a dam or windmill) over great distances. This is due to the alternating nature of the AC signal which allows the voltage to be easily stepped up or stepped down to different values. This is why your home's outlets will say 120 volts AC (safer for human consumption) but the voltage of a distribution transformer which supply power to a neighborhood (those cylindrical grey boxes you see on the power line poles), might have voltage as high as 66 kVA (66,000 volts AC).
AC power allows us to construct generators, motors, and distribution systems from electricity that are far more efficient than direct current, which is why AC is the most popular energy current for powering applications.
Top Performing Electric Cars
As this technology continues to advance, the performance of electric cars are starting to quickly catch up to, and even outperform, their gas counterparts. While there remains some distance for electric cars to go, the leaps that companies like Tesla and Toyota have made to this point have inspired hope that the future of transportation will no longer be reliant on fossil fuels.
At this point, we all know the success that Tesla is experiencing in the field, putting out the Tesla Model S Sedan that is capable of driving up to 288 miles, hitting 155 MPH, and has 687 lb-ft torque. However, there are dozens of other companies that are seeing massive progress in the field, such as Ford’s Fusion Hybrid, Toyota’s Prius and Camry-Hybrid, Mitsubishi’s iMiEV, Ford’s Focus, BMW’s i3, Chevy’s Spark, and Mercedes’ B-Class Electric.
Electric Cars & The Environment
The reality is gas prices should be much more expensive than they are because we're not incorporating the true damage to the environment and the hidden costs of mining oil and transporting it to the U.S. — Elon Musk
Electric engines impact the environment both directly and indirectly at a micro and macro level. It depends on how you want to perceive the situation and how much energy you want. From the individual standpoint, electric cars don’t require gasoline to run, which leads to cars with no emissions populating our highways and cities. While this presents a new problem with additional burden of electricity production, it alleviates the strain from millions of cars densely populating cities and suburbs putting toxins into the air.
Note: The MPG (miles per gallon values listed for each region is the combined city/highway fuel economy rating of a gasoline vehicle that would have global warmings equivalent to driving an EV. Regional global warming emissions ratings are based on 2012 power plant data in the EPA's eGrid 2015 database. Comparisons include gasoline and electricity fuel production emissions. The 58 MPG U.S. average is a sales-weighted average based on where EV's were sold in 2014.
From a large scale perspective, there are several benefits to the rise of electric cars. For starters, there is a reduction in noise pollution as the noise emitted from an electric engine is far more subdued than that of a gas powered engine. In addition, due to the fact that electric engines do not require the same type of lubricants and maintenance that a gas engine does, the chemicals and oils used at auto-shops will be reduced due to fewer cars needing checkups.
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Jill Scott is an Electric Vehicle Efficiency Specialist at SaveOnEnergy. Professionally, she enjoys writing about electric vehicles and energy efficiency.