In this section we will explore the two key components of a BEV, the battery and the motor but before that there are some important terms to become familiar with.
The Kilowatt (Power)
When talking about electric vehicles the measurement of electrical power is the kilowatt or kW (1,000 Watts). The power of an EV’s motors is measured in kW, the bigger the kW rating of the motor the more powerful it is. The internal combustion engine (ICE) analogy is engine size or power, a 150 hp, 2 litre engine will be more powerful than a 90hp 1 litre engine. Note that some manufactures advertising will use the term PS, PferdStarke (literal translation from German is ‘Horse Strength’) as a metric measure of horsepower. To convert PS to kW divid by 1.36. To convert kW to PS multiply by 1.36. Eg a car with a 100 kW motor is 136 ps (134bhp).
The Kilowatt Hour (Energy)
The Kilowatt hour is a measure of energy and while it may be a familiar term to homeowners who pay an electricity bill, it may be a new concept to many drivers. One unit of household electricity is a kilowatt hour, abbreviated to kWh. Your electric bill will state the price per unit and how many units you have consumed over the billing period.
Let’s consider a common example of a domestic electric fan heater rated at 2kW, meaning it will consume 2kW of power. Leave this fan running for an hour and you will have consumed 2kWh of electricity or 2 units, costing approximately 35p.
The capacity of a battery is measured in kWh’s. The higher the kWh rating of the battery the more energy it is capable of storing and the longer range the vehicle is capable of covering between charges. The piston engine analogy in this case is the size of the fuel tank.
Electric vehicles fuel efficiency is measured in Watt hours per mile, Wh/M. The lower watts used to cover a mile the more efficient your vehicle or driving style and longer range is achievable. Back to the ICE analogy, vehicle efficiency was traditionally measured in miles per gallon, MPG so a vehicle capable of 50MPG will cost less to operate vs a vehicle capable of 30MPG over the same distance.
The table below illustrates 3 example BEV’s powertrain characteristics. Note that other vehicles in these product lines will have different motor and battery options.
|Vehicle||Motor Power (kW)||Battery capacity (kWh)||Efficiency (Wh/M)||Range (Real World Miles)|
|Tesla Model 3||202||55||235||210|
We are all accustomed to battery powered rechargeable devices, from phones, laptops, power tools and many appliances. The same principles apply, they deliver power and need recharged, the difference being their size, weight and how they are configured.
Battery capacity is measured in kWh as described in our earlier article. If you want a long range vehicle with >200 mile range you will usually require a vehicle with a battery capacity of >50KWh.
A common voltage in an electric drill is 18 volts DC, direct current. The mains electricity in the home is 240 volts AC, alternating current. We won’t get into the technical details here of AC vs DC. The voltage in a car battery is usually 400v or 800v DC. Many people are surprised when they see a standard car battery in an EV, this 12 volt accessories battery will power lights, radio, on board computers etc. This battery is powered from the main battery rather than an alternator.
The battery in an EV is not something that is visible and it is not serviceable by the end user. The voltages and currents it is capable of producing could cause death or serious injury and only specially trained personnel at service locations should attempt any work on the battery.
The batteries in most EV’s are built into the floor, under seats, in the boot or a mixture of these approaches. Some manufacturers like Tesla have incorporated the battery packs into the structure of the vehicle making them an integral part of the vehicle’s body, leading to reduced weight, lower center of gravity and improved rigidity.
Modern EV batteries are very reliable. Manufactures will guarantee them for long durations, some for up to 10 years. If battery capacity drops over time the option does exist to renew them and at the end of the vehicle’s life they can be reused or recycled. Some first generation Nissan Leaf batteries have been converted into home storage battery packs and some companies offer capacity upgrade batteries, allowing you to extend the capacity of a Leaf by adding an additional battery pack.
The battery will need to be recharged and we cover that in the charger article.
So an EV does not have an engine but a motor. The general rule is a higher rated motor will deliver more power, acceleration and torque. One of the advantages of driving an EV is the ability to deliver energy to the wheels very quickly. Of course this will vary depending on the vehicle and how its management system is programmed to deliver power to the wheels when you push on the accelerator. Some all wheel drive EV’s will be fitted with a secondary motor to drive the other set of wheels, doing away with the need for a drive shaft tunnel in the car. The table below illustrates the performance levels in sample EV’s.
|Vehicle||Total power (kW)||Top Speed (MPH)||Torque (lb/ft)||Acceleration (0-60 MPH)||Drive|
|Porsche Taycan Turbo S||560||162||774||2.8 seconds||All wheel drive (AWD)|
|Nissan Ariya e-4ORCE||225||124||443||5.7 seconds||All wheel drive (AWD)|
|SEAT Mii Electric||61||81||156||12.3 seconds||Front wheel drive|
The Hardware and Software
One thing that is becoming more important in modern EV’s is the computing hardware and software. Since an EV is a collection of electrical components the ability to control and monitor their performance has become possible. We are talking capabilities beyond a flash infotainment system and looking towards the future capabilities of self driving vehicles. Tesla leads the industry here with many advanced driving aids available in their cars today including ‘autopilot’.
Sticking with the Tesla example the cars are fitted with multiple cameras and sensors that constantly monitor the vehicles environment and collect telemetry data from the car and feed it back to Tesla. This data is used in the development of additional features and software upgrades. Drivers look forward to software developments that could unlock additional range or tweaks to the vehicles interface. Anyone who has seen the interior of a Model 3 will recall the lack of physical buttons, many features are accessed via the screen then what those virtual buttons do can be changed.