How An Electric Car Works

Although modern-design electric cars have been available at more or less “mainstream” prices since 2011, they are still just being discovered by many consumers, so for those wanting the basics, this is for you.

First off, electric vehicle technology being discussed here will be only the pure battery electric variety, although an argument could be made that certain plug-in hybrids, and all fuel cell vehicles are by definition “electric vehicles” (EVs) too.

A second thing to note is EVs are – aside from their powertrains and some ancillary components – just normal cars. In fact, cars like the Nissan Leaf, Tesla Model S, Ford Focus EV, Honda Fit EV, and others operate in a way that would feel familiar with anyone accustomed to driving an automatic transmission car.

SEE ALSO: How Fuel Cell Vehicles Work

Their uniqueness is they, of course, function without any internal combustion engine whatsoever and instead use electricity to propel them.

At the heart of an EV’s powertrain is a battery, controller, and motor. Conspicuously absent from this list is a multi-speed transmission.

EVs are either engineered from the ground up, or converted from a conventional car by the manufacturer. True they are touted by proponents as “the future” which could suggest much greater complexity and sophistication, but that’s only partly true. In fact, their fundamentals are rather simple and that’s what we’ll focus on here.

Battery

EVs already had a heyday a hundred years ago and into the early decades of the 20th century, but those old EVs used heavier, less powerful batteries, and lacked myriad computer controls and safety technologies of today’s EVs.

Distinguishing the new crop of electric vehicles is their “Energy Storage Systems” (ESS) – their lithium-ion battery packs.

Tesla's skateboard chassis houses the battery low for better center of gravity and increased passenger compartment design possibilities.

Tesla’s skateboard chassis houses the battery low for better center of gravity and increased passenger compartment design possibilities.


Tesla Motors introduced li-ion batteries with its over $100,000 proof-of-concept 2008 Roadster. It used almost 7,000 lithium-ion laptop cells assembled into modules.

Other automakers, configure their li-ion batteries as seems best to them, but in common for now is they all are using some related form of rechargeable lithium-ion chemistry.

Recharging speed for these packs is determined by how many kilowatt-hours of stored power the pack has, how powerful the on-board charger is that replenishes the pack, and how much electrical current is fed from wherever the vehicle is plugged in.

Also, EVs all have regenerative braking which captures the energy on deceleration and routes it back to the battery. Unfortunately the returned energy is not as great as the energy needed to propel the vehicle, so – despite some suggestions we’ve heard(!) – there’s no such thing as an EV being made into a “perpetual motion machine.”

SEE ALSO: Which Electric Cars Charge The Fastest?

To recharge therefore, all EVs can plug into 120-volt U.S. house current – or other voltages around the world – but this is the slowest way. Even a mid-sized 16-kwh battery in a Mitsubishi i-MiEV can takes 20 hours. An empty 85-kwh Model S battery would take several days to recharge if only plugged into the wall.

Thus while some people have been able to get by with 120-volt current, usually part of getting an EV is setting up a 240-volt unit with the fancy and uninspired name of “Electric Vehicle Supply Equipment” (EVSE). These vary in price from a few hundred dollars to a couple thousand or more, and varying also is their amperage, thus actual power and speed to charge.

Faster home charging from AC power is not as simple as getting the biggest EVSE you can find however.
Manufacturers effectively set a threshold max at which the EV can receive power, and this bottleneck is the on-board charger which is like the sipping straw whereby the EV drinks in more juice.

Beyond this, where applicable, is DC-quick charging and these are only public, usually 480-volts – although Tesla’s Tesla-only Superchargers are more powerful – and these have ability to replenish as fast as 80-percent full in 20 minutes. Some EVs can accept this high-level DC (Direct Current) and bypass the AC-to-DC conversion in normal 120 and 240 volt charging which are also known as level 1 and level 2.

Cutaway Chevy Spark EV with DC quick-charger.

Cutaway Chevy Spark EV with DC quick-charger.

Batteries also require a built-in Battery Management System (BMS) which is software to regulate discharge and recharging. Lithium-ion batteries need these, and the BMS prevents full capacity usage of any given battery.

On the low end, it prevents deep discharge of the cells, and on the other hand, it prevents overcharging. The goal is to create a usable life – far better than a laptop computer’s battery, and more on par with the lifespan of a gasoline engine – albeit some charge holding capacity will be unavoidably lost in time.

Conservative engineers may set up the pack to be permitted to deliver a certain amount of energy until the battery is “empty.” Actually, if an EV runs to “empty” it still has current that could be used to drive the car, but that would mean compromising its durability.

Batteries are sort of like people in that they like moderate temperatures the best – and operate best in these conditions. Batteries of course can operate in hot summer conditions, and cold winter conditions, but this can limit their mileage. Also, manufacturers may actively heat and cool these packs to help regulate their temperatures. It’s normally considered better, and at least more cost-intensive, to use liquid cooling, but some vehicles get by without it.

Controller

In simplest terms, the controller is the connection between the battery’s power and the motor which drives the wheel(s).

Just as li-ion is relatively “high tech” so here too can be a degree of advancement over old rudimentary electric cars in that these are microprocessor controlled.

Actually, to control the controller, you have an accelerator pedal which does the same job as a gas pedal in an internal combustion engine car. This effectively acts like a rheostat on dimmable lights in your home.

S-HP

The pedal is attached to a type of resistor called a potentiometer and the net result is it sends a small amount of electric current variably and progressively to the controller.

The controller is thus instructed how much current in turn to provide from the batteries to the motor. It actually sends pulses of power from transistors, and not one steady flow. These pulses are in the realm of 15,000 per second or more or less.

In the case of most modern EVs which use efficient and powerful AC motors, the controller also in the process reverses the polarity of the DC power from the battery to AC.

The net result is the controller’s frequency of energy drawn from the battery determines the rpm of the motor(s). And, as you no doubt know, the spinning motor moves the car.

Motor

An EV’s propulsion motor is also called the “traction motor.” Modern EV makers have settled on either AC induction or AC permanent magnet designs which provide high torque, reliable operation, and relatively light weight.

The cylindrical motor consists of a stator which is fixed stationary, and receives alternating (AC) current to create a magnetic field. Inside the stator is a rotor, which spins on an output shaft.

model_S_motor

It takes the twisting power and turns a gear that is then routed mechanically to the wheel axle.

Also, an EV’s motor does more than just propel – it also recharges, and is actually known as a “motor generator.” This is where the aforementioned “regenerative braking” comes in – upon deceleration, the motor serves as a generator to send current back to the battery. This is an advantage no internal combustion engine car has.

EVs may have one or multiple motors. Some companies have looked at placing them in the wheels themselves, but these wheel-hub motors have pros and cons that have kept them out of consideration by mainstream EV producers.

As is often said, an electrical motor makes efficient use of the energy supplied compared to a gasoline or even more-efficient turbo diesel engine. It also does not need to get moving to a certain rpm speed before maximum torque, or twisting power, is available.

Rather, electric motors have 100-percent of their torque ready from the get go, while horsepower does increase then tapers off as speeds increase.

Simple powertrain

There are variations to this simplified overview, but in common is EVs tend to not utilize a multi-gear transmission.

Why? In short, they have so much torque off the line, that an EV can utilize a simple reduction gear with a single ratio that’s easy enough to get rolling suitably quick, and tall enough to let the car hit highway speeds.

This of course saves costs, weight, and complexity.

Some proponents have gone so far as to say an EV does not need multiple gears like a gasoline or diesel car does, but that is only correct in a qualified sense. More accurately, an EV could theoretically benefit from a transmission, but it is capable of operating satisfactorily without.

smart

So far, all nine EVs being monitored on our monthly sales Dashboard are single-speed machines.

Even Tesla’s mighty 130 mph Model S operates through a single speed fixed gear with 9.73:1 reduction ratio.

Counterexamples can bee seen such as the Porsche Panamera S E-Hybrid, a plug-in hybrid that can work all-electrically. It operates all-electrically through its eight-speed manually over-ridable automatic transmission just as it does when its gas power is on. Also, Brammo has incorporated a six-speed electric transmission in its Empulse electric motorcycle, touting advantages of keeping the bike on the boil while also more-closely creating the ride experience of a regular bike.

But again, electric cars work fine now, and true enough, have fewer parts to fix or maintain. Also, they are quiet and inexpensive to operate creating a unique set of advantages ideal for short and mid-range daily driving that emits nothing, and gets the job done.