March 14, 2019 3 Comments

Electric vehicles are steadily becoming popular all across the world as a good alternative to traditional gasoline-powered vehicles. Electric vehicles use a different automotive technology compared to the ones used by conventional vehicles. The performance of an electric car heavily depends on its motors and battery pack.

Mainly, 2 types of motors are used in electric cars: DC motor and AC motor. We’ll discuss about each of them, but before that, here’re two major things to keep in mind about electric car motors, in general. Perhaps the biggest advantage of using these motors is the reduced level of pollutants spewed in to the environment. Electric motors enable the vehicle to be 100% emission-free, thus greatly helping in keeping the environment greener. On the flip side, as these motors are provided electricity by the battery pack, they need long time to become operational and the car can’t be used when the battery is being recharged.

AC motors in electric vehicles

An AC motor is powered by alternating current and is likely to be a three-phase motor that can function at 240 volts AC. The regenerative feature of AC motors can also work as a generator which brings power back to the battery of an electric vehicle. When it comes to performance on road, electric cars with AC motors can run more smoothly at rougher terrains, apart from offering more acceleration. Even though AC motors are more expensive than DC motors, they’re widely popular among electric auto manufacturers, especially when it comes to high-performance vehicles.

The fundamental operation of these motors depends on the principles of magnetism. An AC motor comes with a coil of wire together with two fixed magnets that surround a shaft. When the coil of wire is supplied with an electric (AC) charge, it becomes an electromagnet, thus creating a magnetic field. Put simply, upon interaction of the magnets, the shaft, together with the coil of wires, starts to rotate, thus operating the motor. AC motors can be divided into two main categories namely asynchronous motor or induction motor and synchronous motor or PM motor.

Induction motor

Induction motors are considered the most cost-effective and reliable ones among the industry. The control of these motors is quite simple to implement. Because of its simple design, induction motors don’t require high maintenance.

Synchronous motor

In synchronous motors, the rotor turns at the same speed as that of the rotating magnetic field unlike an induction motor where it turns at a lower speed than that of the field. PM motors offer an array of advantages of induction motors including higher efficiency, high torque and power density, high torque at low speed, and compact and low weight.

DC motors in electric vehicles

In a majority of the cases, a DC motor runs on anything that lies between 96 and 192 volts. In addition, more torque is generated from DC motors that lead to a cost-cutting aspect. 

DC motors are classified into three categories namely brushed DC motor, BLDC or brushless DC motor, and stepper. Brushed DC motors are widely used in electric vehicles for retracting, positioning and extending electrically-powered side windows. These motors are suitable for many uses because of their low cost. However, the commutators and brushes tend to wear relatively quickly because of their continued contact, leading to periodic maintenance and frequent replacement.

As the name implies, a BLDC motor doesn’t use brushes and employs an electronic commutator instead, which increases its efficiency and reliability by eliminating the source of power and wear loss. In addition, these motors boast of some significant advantages over induction motors and brush DC motors like higher speed ranges, noiseless operation, faster dynamic response, better speed versus torque characteristics etc. Also, the ratio of torque delivered relative to the size of the motor is higher, which makes it a good choice for electric vehicles, where high power is required but lightness and compactness are critical factors as well. While BLDC motors are mechanically simple relatively, they do require regulated power supplies and sophisticated control electronics.

Key advantages of AC electric car motors over DC electric car motors

Both AC and DC motors cater to the same purpose of powering up electric cars and contributing to a healthier planet. But there’re some key advantages of using the former over the latter, which is perhaps the key reason why major electric car manufacturers prefer AC electric car motors. Let’s have quick look at them.

  • A DC controller can be programmable, but generally it isn’t. AC inverters are just the perfect match for the motor they’re sold with and all the software parameters can be adjusted by the driver to best fit his/her driving style and the batteries.
  • Because of the nice set up of the AC system, it’s capable of taking energy back from braking and giving it out under acceleration. So, a huge amount of battery power can be recovered during the normal driving process. Though a few DC systems can also do that, it makes them more expensive and complex.
  • AC electric car motors generate favorable torque, thus helping the transmission to last longer. With them, you can be rest assured of avoiding expensive issues like twisted shafts, broken gear teeth, and damaged CV joints, among others.
  • Unlike DC electric car motors where reversing is a bit more complicated, all it takes for the inverter (in AC motor) is to swap the sequence of 2 phases, and the rotor starts running in opposite direction.
  • Absence of motor brushes eliminates issues like commutator arcing, brush advancing, and self-destroying at high RPM, among others.
  • AC motors come with only one moving part, which makes them quiet, long-lasting, low-cost, and relatively trouble-free.

Many car buyers often overlook the importance of permanent magnet motors and induction motors, but these electric motors are capable of enhancing the performance of an electric car as a whole.

Some leading electric car manufacturers using AC and DC motors in their models include Tesla, Nissan, and Chevrolet, among others.

Why you need to know about Tesla?

Before Tesla brought them into the limelight, AC motors were used in several circumstances other than electric vehicles. Perhaps the main reason was the absence of a good design that could utilize the relatively complex, dynamic rules, which govern the fields and currents in AC circuits. Prior to Tesla, direct current was the name of the game, though the DC motors had an obvious drawback of complex reversing of current direction. It was Tesla that found AC motors to be both adaptable and durable.

If you’re planning for car conversion

If you’re interested in conversion of your car, here’re some invaluable tips for selecting the best electric motor for that purpose. The motor is one of the most critical components in building an electric vehicle. It’s quite understandable if you get confused with the wide range of electric motor models available today. But careful selection of it is immensely important to accomplish your purpose.

First of all, you can find many EV enthusiasts opting for series DC motors or three phase AC motors for their car conversion. DC motors are known for their higher torque and smooth handling of heavy loads. But now, availability of AC motors is increasing steadily and they’re gaining a huge popularity because of their increased number of features compared to the DC motors. However, two good things about DC motors are – they’re easily available and they come at a relatively cheaper price compared to an AC motor. It’s advisable to avoid DC motors if you want to make the car capable of handling lots of load and varying speeds such as in a tough terrain and off road conditions. Though DC motors were popular for catering to these purposes but the trend is shifting toward AC motors these days. 3 phase AC motors offer a higher starting torque and they’re considered to have lower friction, which means using them would improve your vehicle’s efficiency. These powerful motors are available in a diverse range of horsepower and come with a long lasting life.

If you’re planning for an EV conversion, chances are you’ve already a spent significant amount of time under the hood of a car and have a good grasp of the key components and associated technologies. If you don’t, just search the internet and you’ll find a plethora of information you need to know about EV conversion – from several articles to a lot of EV conversion forums, where you can seek help. Before you start searching the web, here’re a few lines of basic tips. First of all, weight plays a crucial role in an EV conversion. A heavy, big car will require more powerful motor for propulsion together with more sophisticated control systems and bigger batteries. And in this case, bigger is synonymous to more expensive. Also, you need to chalk out your requirement of regenerative braking. With regenerative braking, you can add 10% or more to your electric car’s range assuming you’ll be doing city driving mostly. If you want your electric vehicle to have this feature, you’ll need a brushless DC or AC motor. You should also remember that regenerative braking requires sophisticated motor control systems and battery packs, which in turn would entail additional cost for your project.

 


3 Responses

Taylor Wright
Taylor Wright

January 03, 2020

It’s interesting that electric car motors can help avoid twisted shafts and damaged CV joints. My uncle is working for a moving company and they are considering changing to electric vehicles and motors. I’ll show him this so he can find a good supplier for the motors. http://www.hackworthelectricmotors.com/services

Vivek jade
Vivek jade

September 30, 2019

thanks for this blog keep doing good work

John
John

September 30, 2019

I think the compressed air car is the best one. Fast charge . Use renew power to run compressor.

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