How Do Electric Vehicles Work?

Electric vehicles are the craze nowadays. Tesla considers electric vehicles to be the future. Toyota has gone heavily into electrification as part of its plan. Many manufacturers produce electric vehicles left, right, and center. But what’s about them anyway? How do they even work? Why are they so interesting and considered to be the future? Well, let’s explain what an electric vehicle is.


Nissan Leafs
Generation Two (L) and Generation One (R) Nissan Leaf electric vehicles.

The Origin of Electric Vehicles


Electric vehicles aren’t anything new by any stretch of the imagination. The first electric vehicle appeared in 1881 and before Karl Benz patented the first-ever car in 1886. Their working principle is simple. You have a source of electricity (a battery, generally) which gives an electric motor all the power needed for it to spin.

Technically, you could even use a regular fuel generator to power electric motors, and it would still be classified as an electric vehicle. As such, hybrid cars, PHEVs, hydrogen fuel cell vehicles, cars powered by solar power, or wind can be classified as electric vehicles. However, we’re focusing on BEVs, or Battery Electric Vehicles because they are the ones you think about when you talk about Electric Vehicles.


The Workings of Electric Vehicles


A big question worth asking is how electric vehicles work, because you can’t just run two wires from a battery to an electric motor and call it a day. Let’s start with the basics:

They contain a battery pack. This pack is comprised of many batteries linked in parallel which are used to store the electricity the motors will use. These batteries use direct current. Simply put, the current flows through them at a constant rate in one direction. Think of a river flowing downstream, to get an idea of sorts.

They use a converter that changes that direct current in alternating current, or a DC-AC converter. This is because high-power electric motors use high voltages and require a bit of oomph. Not only that, but cars use AC electric motors, and not smaller DC ones. Creating these high voltages in direct current is quite difficult. Indeed, it is so hard that it is easier to convert direct current into alternating current, while changing and increasing the voltage.

PECU and an Electric Motor

They also use a PECU, a Powertrain Electronic Control Unit. Its job is like a regular car’s ECU. Based on what the driver wants and does, it changes the voltage and the frequency output by the DC-AC converter. By changing the voltage and frequency, the electric motor spins faster or slower. As such, this is also the reason why an electric car doesn’t need a transmission. The transmission’s job was also replaced by this PECU.

Importantly, they need an electric motor. This motor transforms the electricity stored in the batteries and is transformed by the DC-AC converter into mechanical energy. In contrast, an internal combustion engine does the same thing, by transforming chemical energy found in fuel into mechanical energy. These electric motors can also be used as a generator, as such they can use the car’s inertia that also spins the wheels to stop itself and recharge the batteries in the process.

Onboard Charger and DC-DC Converter

Electric vehicles also need an onboard charger. This is the fuel port, so to speak. In the fuel port, there’s an outlet into which you can plug a charger, similarly to a mobile phone but on a much larger scale. This onboard charger transforms the household AC into DC so it can charge the batteries. AC is like a sea’s waves. It comes a bit and goes away, but by doing so you ever so slightly keep getting your feet wet.

There’s also a DC-DC converter. That’s because the batteries themselves store large voltages, much higher than what the wipers use or what the infotainment system uses. Your devices also use the same voltage as those, so there’s an additional converter that changes the batteries’ voltage to a smaller more manageable one for tinier applications.

Thermal and Battery Management

The batteries get quite hot or quite cold. As such, the EV also needs a thermal management system.

While the PECU controls the motors and the drivetrain, the body control module (BCU) controls the features inside the car, such as power windows, locking and unlocking, and other similar bits and bobs.

There’s also an important battery management system (BMS) that controls and monitors the batteries. It manages how the batteries charge and communicates with the PECU and other sensors so those know how to best use the batteries. (1)


Volkswagen ID.4 electric vehicle
Volkswagen’s first dedicated fully electric vehicle is this ID.4.

Electric Vehicle Power Source


That’s the gist of it, at least for the most part. Now there’s the second important question: well, they use electricity but where does that electricity even come from?

Electricity nowadays comes from many fields, but they are split across like this: burning fossil fuels, solar panels, windmills, hydropower, nuclear power, natural gas burning, oils, and biofuels. Worldwide, around 25-percent or so of the generated electricity comes from “green” sources. Nuclear electricity is uncertain, due to us not being very sure what comes along with the radioactive waste. Still, electricity is electricity. Where is it stored? Well, in the batteries. (2)


Types of Batteries


Batteries use a bunch of reversible chemical reactions. That is, a compound can be broken down to produce electricity, and the broken-down compound can be restored with electricity to its former state. This reversibility isn’t endless, and those compounds won’t be able to “repair” themselves due to a variety of reasons. There are many types of batteries out there, which explained briefly are:

Lead-Acid Batteries

These use lead plates as a negative terminal and lead oxide as a positive terminal. They are sunken in a sulfuric acid mixture. The reaction between the two generates a voltage of 2.05 volts per cell, and each car battery has 6 cells, generating those 12 volts. They were used for cars back in the old days or small carts as a battery for an electric motor. Nowadays, they are used on regular cars to power accessories and to start the car.

Nickel-Metal Hydride Batteries

These utilize nickel and an alloy that absorbs hydrogen and transforms it into heat. They react with nickel oxide hydroxide to produce 1.2 volts per cell. They are quite light when looking at how much power they generate for the weight. Compared to lead-acid, they are at least twice as electricity dense as a lead-acid battery. They were first used in the initial Toyota RAV4 EV.

Nickel-Cadmium Batteries

They are very similar to nickel-metal hydride batteries, because they use the same principle of use. However, they are overall more toxic than the newer alternative, so they were phased out for the most part.

Lithium-ion and Lithium-Polymer Batteries

These are the batteries used nowadays. They have lower specific power than nickel-metal hydride batteries but have three times the energy density. They are also less finicky to use and have a longer lifespan. However, they are quite prone to catch on fire if burst and they heavily dislike cold weather. Cold weather makes them discharge quite a bit faster, hence that thermal management system we talked about before.

Solid-State Batteries

They are believed to be able to have even higher energy densities, up to 2.5 times as much compared to Lithium-ion. Some brands want to start manufacturing them. Prototypes exist, but they aren’t particularly durable. At least not yet anyway. (3)


A Matter of Currents


As far as how these are all linked, it all goes as follows: you charge the car using that onboard charger. Said electricity goes to the battery pack. From there, when you drive the car, the electricity flows from the battery to the DC-AC converter and to the DC-DC converter, to be used by the motors or small bits and bobs, respectively. This flow is controlled by the BMS and PECU.

This is, briefly, how a basic battery electric vehicle works and operates. Now you may wonder about more explicit facts, such as how is it built differently than a regular ICE vehicle? It’s still a car, correct? Yes, but technically no.

A regular ICE car has some constraints which need to be considered. There must be room for the engine, at least somewhere. There must also be room for a transmission…again, somewhere. Sure, there’s a transmission, but is my car front-wheel drive, rear-wheel drive, or all-wheel drive? If it’s all-wheel drive, I will also need a center differential or a transfer case. An electric car also has similar questions but with different components.

The biggest component, and the heaviest, is the battery pack. It must be placed strategically, to not alter the car’s center of mass too much or it will affect the car’s dynamics, and neither weirdly placed to not risk it burst in case of a crash. So, the best course of action would be to create the whole chassis and underside with battery storage in mind.


Ford Mustang Mach-E Electric Vehicle
The all-electric Ford Mustang Mach-E.

EV Drivetrain

There’s the problem if I make it rear-wheel drive or all-wheel drive. Front-wheel-drive electric cars aren’t all that great, because under heavy acceleration due to high power and hefty weight they will understeer quite a lot. If their electric motors are on the smaller side and quite mellow, then a front-wheel-drive format is fine.

Still, it begs the question of where to place the motor or motors. If you use a single motor in a rear-wheel-drive layout, you will need a rear differential. If you use two motors in the back for a rear-wheel-drive format, like a Tesla, then there’s no need for a differential so there’s more room for batteries or a larger trunk.

Speaking of the trunk, should you make the front trunk small to improve visibility, or make it bigger for transportation or for a very important crumple zone? The front trunk, or lack thereof, can also be altered to factor in aerodynamics to a greater extent.  There are many other caveats that manufacturers must consider now, which they haven’t done before.

Transmitting Power

For instance, why does the EV have a gear stick with Drive, Park, and Reverse? Does the EV have a transmission? If you only use a single motor, then that differential is the single-speed transmission, because that’s the final drive in a regular car. No extra transmission is required, because as stated above, the DC-AC converter acts like an automatic transmission. If the EV uses two electric motors for the rear wheels, then there isn’t even a transmission, so the car is gearless. This is done because the DC-AC converter can make it so the electric motor spins quite slowly with a bunch of torque by changing the voltage and the frequency of the AC. They use that gear stick to keep it familiar to the user. You would still need a way to make your car travel in reverse, so keeping the gear stick practice is preferred.

Do electric cars turn any different compared to regular ICE cars? Well, no. There’s still the same old steering rack that regular cars use. Even if the car is front-wheel drive and uses a differential, the same principle applies. If ICE cars can be front-wheel drive with an engine in the front, transmission, and a differential, then electric cars have plenty of room to have a steering rack too.


The Electrics v. ICE


Do electric motors feel any different compared to regular internal combustion engines? Indeed, by quite a bit. Electric motors have a lot more torque from a standstill, so they feel quite a bit peppier. They also start to fizzle out at higher speeds due to the engine’s RPM limit, like a regular old engine. Thus, this limit is more apparent due to the lack of an actual transmission. If the car would have a three-gear transmission, its top speed would be much higher. They also don’t produce any significant sound, so you won’t hear the engine roar while you step on the gas. (4)


References


Hyundai. EV A to Z Encyclopedia – 1: Understanding EV Components. [Online].

U.S Energy Information Administration. Electricity Explained. Electricity in the U.S. [Online].

Renault. The different types of electric car batteries. [Online].

McKinsley. How to Drive Winning Battery-Vehicle Design. [Online].


See AlsoFast Facts About Electric Vehicles, Battery Life

Photos copyright Stumpwater Media Group, LLC. All rights reserved.

Author: Cristian Puscasu
Cristian lives in Romania and is studying to become an automotive engineer. Currently in his third year, he enjoys writing about cars as well as tinkering with them. We are pleased to welcome him as a contributing writer, knowing that he will pursue far greater things in the years to come.

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