As climate change became more of a pressing issue in recent years, electrification of cars was not a surprising trend in the automotive world. They are largely credited for having a smaller carbon footprint and releasing less greenhouse gases to the air. The technology behind electric cars is not new at all. It has, in fact, existed as long as that of gasoline powered cars. But, they became more popular in the late 90s through the introduction of cars like the Toyota Prius. Though it’s not a full-electric car, people now see the benefits of electrification.
Electric Cars in a Nutshell
The term ‘electric cars’ is an umbrella term with a broad definition and covers many variants of electrified vehicles. These include both full electric vehicles and semi-electric vehicles. These different variants have slightly different technologies, so they work a little differently from each other.
However, there are common technical features that all electric cars have. The most salient, is that they all use an electric motor to drive the car. This is in fact, the broad definition of an electric car. A car that uses an electric motor.
Different Types of Electric Cars
The differences between electric vehicles (EVs) depend on how much of the car is run by an electric motor. An electric motor drives everything in full electric vehicles. Hence, they do not have internal combustion engines (ICEs) or use gasoline for any key function. Electricity drives them completely. Of course, these are the eco-friendliest of all the EVs.
One can differentiate Full-electric cars themselves, by the source of the electric current that drives the motor. In some EVs, these come entirely from stored electrical energy in battery packs on board the car. While iIn others, they can come from the electric current produced from a fuel cell.
In semi-electric cars, or hybrid cars, the electric motor works in conjunction with an internal combustion engine like the regular cars. Hence, they use both electricity and gasoline to drive certain functions of the vehicle, and they have both a battery pack as well as a gas tank. Hybrids alternate between gasoline and electricity, depending on which is more efficient at the present driving condition. An electronic system determines this alternating between the two types. It also decides which one is more effective, based on current conditions.
So, before delving into the technical details of electric cars and hybrid vehicles, it is best to know the different types of EVs available.
Battery Electric Vehicles (BEVs)
These are fully electric EVs with zero emissions while driving. A rechargeable battery pack in the car drives the car completely. The stored electric energy in the batteries drives the motor. They are also the most common type of EV that associate with the term ‘Electric Car’. Some popular models include Tesla Model S and the Nissan Leaf.
Fuel Cell Electric Vehicles (FCEVs)
These EVs are also fully electric. But, they use a fuel cell that generates an electric current to drive the motor. The cell uses the electrochemical reaction between hydrogen and oxygen to produce the current. FCEVs aren’t 100% clean because hydrogen fuel is a derivative of fossil fuels. They also produce water vapor or steam as a by-product of the chemical reaction.
Hybrid Electric Vehicles (HEVs)
These EVs incorporate EV technology to regular ICE powered vehicles. Both an electric motor and an internal combustion engine work together to drive the vehicle. They have both a gas tank and batteries, so they can alternate between using electricity and gasoline. Batteries in pure hybrids are not rechargable.
Plug-In Hybrid Electric Vehicles (PHEVs)
These are a variant of HEVs where the batteries are rechargeable with an external power source. They can be charged either at home or at an EV service station. These tend to be cleaner than regular HEVs because they can prioritize using electricity than gasoline. Like regular hybrids, however, they use both an electric motor and an internal combustion engine.
How Electric Cars Work
Here, we will go into all the technical details of how different variants of electric vehicles work.
Battery Electric Vehicles (BEVs)
These are probably the first types of EVs people think of when they heard the term ‘Electric Car’. As the name suggests, Battery Electric Vehicles are powered by batteries. BEVs contain a series of battery cells which are collectively known as a battery pack.
The battery pack is responsible for providing the electric current needed for the electric motor. The electric motor used is known as an induction motor. When an alternating current (current that periodically changes direction) is applied, it causes alternating magnetic fields to be produced.
As BEVs are entirely powered by batteries, the battery pack is quite heavy and usually located near the bottom of the vehicle.
The Electric Motor
This causes the motor’s poles to rotate and hence, turning the motor. However, the batteries provide DC current while the motor runs on AC current. So, there has to be a component that changes the DC current coming from the batteries into AC current. This is what the inverter does on BEVs. Technically, BEVs could use DC motors as well, so that the current doesn’t need to be converted. However, DC motors tend to be bulkier, which is not great for a vehicle that has to accommodate heavy batteries as well. So, AC motors are preferable.
BEVs are only powered by electricity, so there is no internal combustion engine or gas tank. The batteries and electric motor are the only components driving the vehicle.
The Batteries
There are many types of batteries available for EVs:
- Lead Acid Batteries: These are the cheapest batteries available and used to be the most commonly found EV batteries. These are similar to car batteries found in regular cars. However, their performance tends to be quite poor. They are not good at operating during cold temperatures and have low specific energy, so they would be too heavy to power a full-electric car.
- Nickel Metal Hydride Batteries: These batteries have a decent specific energy and power capacities. They have longer life spans than lead acid batteries and are commonly used in hybrid vehicles. However, they are very expensive and discharges too quickly. They also generate a lot of heat.
- Lithium-Ion Batteries: These are the most common types of battery found in electronics such as laptops and smartphones. They are more suitable to full electric cars because they have a higher power-to-weight ratio than other types. They also have a high efficiency, good performance at higher temperatures and high specific energy. These are the most commonly used batteries in PHEVs and BEVs.
Regenerative Braking
Another important feature of electric vehicles is the regenerative braking system. When a car brakes, all the momentum and kinetic energy will get wasted as heat due to friction with the road surface. Regenerative braking tries to recover this energy and convert it into useful electrical energy. EVs do this by having the motor turn in the reverse direction while braking. In the reverse direction, the motor now becomes a generator and the kinetic energy is converted to electrical energy. This is sent to the battery pack to be stored for future use.
Fuel Cell Electric Vehicles (FCEVs)
FCEVs use the electric current from a fuel cell to drive the electric motor. FCEVs were once hailed as the future of cars due to their high performance but has since been overshadowed by BEVs.
In the fuel cell, an electric current is generated during the electrochemical reaction between hydrogen and oxygen. Water vapour is a waste by-product of this reaction.
What Happens in the Fuel Cell
In the fuel cell, there are three primary components. There is a terminal with negative charge (anode), a terminal with positive charge (cathode) and an electrolyte. The cathode is usually made from a precious metal like platinum to speed up the reaction.
- A pipe of several pipes deliver Hydrogen fuel to the cathode from the tank.
- The cathode strips the electrons from hydrogen atoms. These become positively charged ions (protons)
- As the ions get positive charge, they attract to the negatively charged anode and will flow towards it through the electrolyte.
- The electrolyte allows only the positive ions to pass through, so the electrons travel in an external circuit.
- This flow of electrons creates a current and drives the motor.
- The electrons and protons unite at the anode.
- Oxygen from air reaches the anode, where it reacts with the protons to produce water which exits from a tailpipe.
The limiting factor in FCEVs is the amount of hydrogen, since oxygen is freely available. You can refuel FCEVs with hydrogen fuel at stations similar to regular vehicles. However, the cost and inconvenience of hydrogen refuelling has been a barrier for FCEVs. Hydrogen production happens via extraction from fossil fuels, so the technology isn’t completely clean.
Hybrid Electric Vehicles (HEVs)
These cars use both electric motors and internal combustion engines. The battery pack isn’t as heavy as in a BEV because they only partially rely on electricity. HEVs make the best of both worlds by using electricity and gasoline at different engine speeds.
At low speeds, ICEs produce a lower torque and are not efficient. Hence, HEVs use the electric motor at these speeds because the induction motor is more efficient in this range (e.g. slow speed drives). At high speeds, ICEs are more efficient, so HEVs use gasoline at high speeds.
In normal HEVs, the battery don’t recharge manually. The batteries only recharge using the energy from regenerative braking. Hence, HEVs can’t rely that much on electric power. They can only use it for small functions.
Plug-In Hybrid Electric Vehicles (PHEVs)
These are a variant of HEVs. They also have an ICE as well as an electric motor. The only difference here is that the batteries are chargeable using an external power source. You can also charge them at home using a standard electrical outlet. But, this will take ages to reach full charge.
They are also chargeable using EVSEs, which are special chargers that can charge PHEVs quicker. They operate on a 220/240 V. People can buy these units for their home or get an EV service station to charge their cars. EVSEs still take ages to be charge fully, in contrast to filling up a gas tank though. An hour of charging can only add 10-25 miles of range.
