Welcome to EV201: How an Electric Vehicle Works!
In our first installment, we explored the basics of electric vehicle charging. If you need a refresher on the definition of a Battery Electric Vehicle (BEV), click here. In this section, we dive a little deeper and explore exactly how an electric vehicle works. Strap in! And let your curiosity shift to overdrive!
The Journey of Electrons
Electric vehicles are powered by tiny, charged particles called electrons. These electrons arrive inside an EV through either Direct Current (DC) Fast Chargers or Alternating Current (AC) Chargers.
Types of Electricity
To understand how an electric vehicle works, we first need to understand the difference between two types of electricity: direct current and alternating current.
Direct Current (DC)
In a direct current, the electrons flow in one direction.
Alternating Current (AC)
In an alternating current, the electron flow changes.
The Components Inside an EV
Next, let's learn how the components inside an EV use electricity to power the wheels.
First, your battery pack needs power, which you can get by either plugging into an outlet or an electric vehicle charging station.
Your battery pack is actually a collection of hundreds (and often thousands) of smaller lithium ion cells.The battery pack produces direct current (DC) electricity.
The inverter’s job is to convert the direct current electricity from the battery to an alternating current for the induction motor.
The electric motor uses the alternating current to produce a rotating magnetic field.
The drivetrain uses the power created by the rotating magnetic field to spin the wheels!
And lastly, during regenerative braking, the motor can also turn the rotation back into AC current, which goes back to the inverter, which then charges the battery. (Cool, huh?)
How Does a Battery Pack Work?
When an electronic device is turned on—like a phone or an electric vehicle—electrons move from the negative side of the battery through the load to the positive side, creating an electric current. To charge a battery, the electrons are moved from the positive side back to the negative side using a charger.
This process is a chemical reaction. And chemical reactions occur best in certain temperature ranges. When it’s too hot or too cold, the transfer of electrons won’t happen as quickly—or not at all. That’s why it’s important to surround all those lithium-ion batteries with coolant, to keep them at a steady temperature.
What Is the Battery Management System (BMS)?
In order to keep the battery pack happy (and not too hot or too cold—or too hungry or too full), electric vehicles have a Battery Management System (or BMS). The BMS is sort of like the battery’s brain. It monitors and reports the battery’s status to the rest of the electric vehicle systems to make sure everything runs efficiently and optimally. The BMS is often why you get varying charging speeds (it's trying to keep your battery healthy!).
What Does the Battery Management System (BMS) Keep an Eye On?
The voltage of the battery pack as a whole and the individual battery cells inside. If need be, the BMS can discharge some cells to keep the battery pack balanced.
The current in and out of the battery pack, which helps determine how much energy is inside the battery and how healthy it is.
State of Charge (SoC)
The State of Charge (SoC)—or how full the battery is, in percentages. (It’s like a gas tank indicator.)
State of Health (SoH)
The State of Health (SoH)—or how healthy the battery is over a long term.
What Is EV Range?
An electric vehicle’s range is the distance you can travel on a single charge. It varies between electric vehicle models and years, but most new EVs launching can get anywhere from 200 to 400 miles on a single charge. The EPA offers a range estimate for each vehicle based on highway and city tests, which you can learn more about here.
Range is determined by how much energy is stored inside the battery and how efficiently the vehicle uses that energy. Factors affecting range include: the weight of the battery, the body’s aerodynamic design, the use of the air conditioner or heater, the tire pressure, and the style of driving.
What Is mi/kWh? And How Do I Make Sense of all These Numbers?
As we transition from gas-powered vehicles to electric vehicles, many people feel comfortable gauging their car’s efficiency using Miles Per Gallon (or MPGs). Because EVs don’t use gasoline, they use different terms to gauge efficiency, like mi/kWh and MPGe (explained below).
In this example, we compare the yearly fuel costs of two typical vehicles: an EV (Nissan LEAF) and an internal combustion engine (ICE) vehicle (Mazda 3).
mi/kWh, or Miles Per Kilowatt Hour — represents how many miles a vehicle can drive using 1 kWh of energy. (You can learn more about terms like kW and kWh here, but just know that a kilowatt-hour is a measurement of energy. It equals 1 kilowatt of power transferred over one hour.)
MPGe, or Miles Per Gallon of Gasoline-Equivalent — represents the number of miles a vehicle can go using an amount of electricity that’s equivalent to one gallon of gas.
NOTE: For technical-minded folks, one gallon of gasoline is equivalent to 33.705 kilowatt-hours. To find out your MPGe or kWh, you can use either this web calculator, or this simple formula:
mi/kWh = MPGe ÷ 33.705
Wh/mi, or Watt Hours Per Mile — represents the inverse of miles per kWh, mostly used by Tesla vehicles. A lower Wh/mi means better efficiency.