Do Electric Cars Have Alternators?
Electric cars use energy stored in the onboard battery for powering their electric motors used for driving and for powering all other devices found in cars.
Alternators are a very important piece of electric systems of modern cars with internal combustion systems and are used for generating electric power required for charging the battery, starting the main engine, powering lights, fans, and all other electric loads. So, one may easily ask oneself, do electric cars have alternators?
Published: March 28, 2022.
What Does a Car Alternator Do?
A car alternator is an electromechanical device that transforms mechanical energy into electric energy, more precisely, into an AC current.
Car-style alternators are driven by the main engine via a drive belt, which often powers a few more devices like cooling water pump and similar.
Since cars use DC electric power, AC electric power is rectified into DC electric power via a diode bridge (also known as the Graetz bridge) combined with a few capacitors for preventing radio interferences and for smoothing out the voltage spikes as much as possible.
Final voltage stabilization is done via - the car's battery.
Many modern cars use microprocessor-controlled charge controllers, ensuring much more stable power output in terms of watts, voltage, and current, but the principle is practically the same.
For short, a car alternator is a device that transforms mechanical energy into electric energy used by many car subsystems.
Car Style Alternators in Electric Cars
Since electric cars don't feature internal combustion engines, they don't require car style alternator onboard - their electric energy is stored in the onboard battery recharged via electric cables.
Therefore, electric cars do NOT have car-style alternators. However ...
In order to increase the car's range and increase the car's energy efficiency, electric cars feature some sort of Kinetic Energy Recovery System (KERS) which allows the car to recover at least some energy when braking and to store it in the onboard battery for later use.
Note: this energy recovery system has many names, including very descriptive Kinetic Energy Recovery System (KERS) or simply - "electric brakes". Other names for such systems exist as well...
When car brakes or drive downhill at a constant speed, electric motors (or motor, depending on the design) act as electric generators that convert some of the kinetic or potential car's energy into electric energy via a rather complex charging controller.
In essence, these motors may be called alternators since they are electric generators, but they are far from being similar in size and construction to classic car-style alternators.
How do Electric Brakes Work?
When the driver hits the brakes in the electric car, the car converts kinetic energy (decreases the speed) or potential energy (constant downhill speed) into electric energy which is used to charge the battery.
Note: if the electric brakes are unable to do their job (more force must be applied), mechanical brakes (also found in classic cars) are automatically engaged.
If a car that weighs 2000kg drives at 100 miles per hour must be slowed down to 50 miles per hour, how much energy can electric brakes recover?
In order to calculate energy, first, we must convert speed from miles/hours to meters per second (m/s):
100 miles/h = 100 * 1.60934 / 3.6 = 44.7 m/s
50 miles/h = 50 * 1.60934 / 3.6 = 22.35 m/s
E = m * (v12 - v22) /2 = 2000 kg (44.72 - 22.352) / 2 = 1498567 J = ~1.5MJ = ~417 Wh
So, if electric brakes successfully slow down a 2000kg car from 100 miles/h to 50 miles/h, it also means that the electric brakes recovered ~1.5 MJ (~417 Wh) of energy, and that is a lot for a few seconds of work.
Note: for the sake of simplicity, air resistance, rolling resistance, electric energy losses, etc. in this example were ignored.
If a car that weighs 2000kg drives at a constant speed down the hill with a height difference of 500m between the starting point and the end point, and the electric car uses its electric brakes to keep the speed constant, how much energy can electric brakes recover?
Recovered energy equals the potential energy difference between these two points:
E = m * g * (H1 - H2) = 2000kg * 9.81 m/s2 * 500 m = 9810000 J = ~ 9.81 MJ = ~ 2725 Wh
So, if electric brakes are used to recover energy when a 2000kg car drives downhill with a height difference of 500m, it also means that the electric brakes recovered ~9.81 MJ (~2725 Wh) of energy - and that is a lot.
Note: for the sake of simplicity, air resistance, rolling resistance, electric energy losses, etc. in this example were also ignored.
Long Story Short: electric cars don't have car-style alternators, but their electric motors are used to recover energy when braking and in those situations, they essentially behave as alternators - they generate an alternate current which is then transformed into the electric energy suitable for charging onboard batteries.