Electric car motors are used as the driving force. It’s fairly obvious that the faster the motor turns, the faster the car goes but of course there is a limit. An electric motor needs to be told how fast to turn, which relates directly to the speed of the car. The speed of the motor is controlled by the controller: a sort of computer which gets information from the foot pedal accelerator to control the power to the motor.
Different types and sizes of electric car motors
Motors come in different types and sizes. The smallest motors fitted to a car are the ones fitted to golf carts and derivatives of the golf cart and may be as small as 1kW or occasionally, even lowerThis 40-50 kph is in power. There is no maximum size of motor, but cars like the Tesla have a total of around 470 kW. A typical motor for a cheap electric car is around 4 kW for a city car with a limited speed of about 40-50 kph. At the low-power end, some little cars like the Toyota COMS EV which was first introduced in 2000 has two motors. One for each rear wheel, but the COMS EV 2nd gen. used only one motor.
The motors in common use for affordable EVs fall into two classes. Mostly three-phase electric motors are used for their efficiency, the DC voltage from the battery pack being converter by the controller into the three-phase AC necessary to run the motor. The second type of motor is the DC motor with brushes. These motors are cheaper to make as are their controllers as the DC battery voltage is not converted to AC thereby saving on controller production costs.
The difference in use is that AC motors offer better control and responsiveness than DC motors.
Power Output by Comparison to ICEs
One thing which is not always understood is the power of an electric motor. Let’s take a look at this in more depth. An electric motor has a much higher efficiency than an internal combustion engine. A quick example is that a 4kW electric motor can move a 750kg vehicle at a reasonable speed from standstill to say 40kph in a certain time. The equivalent of this is 5hp. Can you imagine a 5hp petrol engine moving a 750 kg car away from a standstill?
Cheaper to run
If we say that the petrol engine of 5hp is producing 4kw of power output we have to remember that it is only 25% efficient. In that case to get 4kw out we have to put 16 kW in, in another form. That’s 16 kW worth of petrol. The electric motor is 80% efficient however, so it needs a supply of only around 5 kW input of electricity to produce a 4kW output. It doesn’t matter that one is petrol and the other is electricity. Energy is energy. One needs 16kW whilst the other needs only 5 kW. This is the reason that electric vehicles are more efficient and cheaper to run.
Early electric cars used DC motors and usually only 12 or 24 volts from an arrangement of 12-volt batteries. Ten 12-volt 100 Ah batteries connected in parallel gave a total of 12 volts at 1000 Ah which meant that a large vehicle could operate for a reasonable length of time, depending on its weight and load, or a smaller vehicle could operate for much longer as it would take less power from the bank of batteries.
If the batteries were connected in series, this would give 120 volts at 100 Ah but 120 volts were much more controllable than trying to control the 1000 Ah supply offered by the parallel connected bank. In recent times, high voltage has been the way to go, and some electric vehicles use a power supply of from 400V to 800V. This lowers the current required for charging. Overheating is reduced and the batteries hold their power better. The benefits of this are a longer driving range, combined with higher performance.
In the old days, electric cars used DC motors, but nowadays three-phase motors are used due to a higher power-to-weight ratio, so they can produce more power while being lighter in weight. For some vehicles, DC motors are still the best choice and are available to manufacturers. For Battery Electric Vehicles (BEVs), this is a critical factor which is necessary for power and efficiency in modern electric cars.
DC voltage from the batteries is supplied to the controller which electronically produces three-phase electricity for the motor, and its output level is controlled in turn by the foot accelerator pedal.
Motors are available in many sizes and can also be bought as a complete package of axle, ready to accept wheels fitted with a motor, a controller to control motor speed, and the foot pedal itself. This is an ideal solution for someone who would like to build their own small electric car. Little cars such as the Fiat 500 have been fitted with these axle sets and the batteries placed in the vacated engine compartment.