The electric vehicle, how does it work?
10 Aug 2018
Because of the major environmental problems, congestion in cities, their high levels of pollution, and the new energy framework of Spain, the electric vehicle is taking a special role in our daily conversations.
How does an electric car work?
From Letter Engineers, we will try to explain in a clear and simple way how an electric car works. For this, we will focus on its two fundamental parts: the electric motor and the battery.
The first thing we have to understand is the concept of current as well as the two types of current that we have, continuous (DC) and alternate (AC). The current is basically the flow of electrons through a conductive medium such as a cable. Depending on the amount of flow we have more or less amperes (A), which is how the intensity or electric current is measured. For the electrons to move, a potential differential (Volts) is necessary, just as a river needs a height difference for the water to run.
If the flow of electrons is more or less constant and in one direction, from one pole to another, we are talking about direct current. On the other hand, if the flow changes every certain time (cycle), we will have alternating current. In Spain these cycles are 50 Hz, meaning the direction changes 50 times per second.
Normally we will use direct current for small electronic devices to about 24V. We use the alternating current for more voltage, for example at home we get 230V in single phase (one phase) and 400V if we had a supply in three phase (three phases). We use alternating current because unlike the continuous one it can be increased or decreased its voltage easily in transformers. If we want to move electrical energy at a great distance we will increase its voltage at the cost of decreasing its intensity so that we will have less losses (Ohm’s Law). The great advantage of direct current is that we can store it, chemically, for example in a battery, then we will see how. This is how our mobile works.
The device that converts alternating current into continuous is called a power supply, while the device that converts the continuous current into alternating current is called an inverter.
The product of the current (A) by the voltage (V) gives us the power that is measured in Watts (W); Well, this is not entirely true, but we can do for now. Do not confuse the power in W with the energy that is measured in Wh. Energy is the product of power by time.
We have summarized the most to make it clear and simple, however, if you have questions on these concepts you can contact us so that we expand these fundamentals.
It is one of the most important parts of an electric car. Not to be confused with the service battery that is 12 or 24V we currently have and that feeds the lights, radio, etc.
The traction battery is a set of cells that store continuous electrical energy in a chemical way. Electric power is obtained from an external plug (at home or on public roads where we already know that it is alternating energy), but the battery has to arrive in continuous mode so we use a power source (known as a charger).
The BMS monitors the loading and unloading status of each cell, let’s say it is the one that controls the battery. It is very useful to manage, for example, fast loading. Here what we do is take each cell up to 80-90% of its capacity leaving the rest free. In a battery which is the longest completely filled cell and fast charging it makes use of this topic.
Electric motor vs combustion
Due to Nikola Tesla in 1893, today we have AC motors, a simple way to convert electrical energy into mechanical. Due to mechanical energy we can move the wheels of a car passing previously by the transmission shaft.
An electric motor is nothing more than an enclosure where you have a stator (fixed part) and a rotor (moving part). Depending on the engine type we have some magnets which have a power to create a electromagnetic fields that move the rotor. The good thing about this is that investing in the engine cycle can act as a generator and spend mechanical energy into electricity. This is used to store energy in the battery taking advantage of braking and lowering.
Most electric cars are powered by a three-phase AC motor. From the battery, where we know that we have continuous power, we need an inverter to pass it to AC. Depending on the energy that passes through the engine we have more or less revolutions (RPM) and therefore power. Out of curiosity comment that we can reach 15,000 or 20,000 RPM. The maximum power in an electric is obtained from the initial moment since we have the maximum torque.
A combustion engine (those of a lifetime) instead of electricity works by combustion of a fuel (gasoline, diesel, gas …) in an explosion-compression engine in pistons. The main problem is that as a byproduct of the reaction, gases are generated that, depending on the fuel, are more or less polluting.
An electric motor is much smaller than a combustion engine and with many fewer parts. We also have much less friction parts and therefore less maintenance. The power curve in an electric motor is linear and we have all the power available at the start, however, in combustion we have little power at low revolutions. This causes that in an electric we do not need a gearbox.