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    All You Should Know About Electric Motors

    2022-06-17 10:42:23 1276

    Motors literally power our lives. They can be found almost everywhere - from our home appliances to elevators and even cars. Motors are the heart of any device: be it a small fan or an electric scooter. 

    For how widespread they are, motors are also often misunderstood. It’s easy to feel overwhelmed with the options available and pretty hard to pick the right one. 

    For this reason, we have gathered all the basic information you need to know to better understand electric motors. We’ll share all the knowledge you should be familiar with, from motor components to the different types of motors available. 

    Feel free to jump to the section you’re most interested to and check out our related guides coming up soon.

    The Basics

    What is a Motor?

    A motor or engine is a machine designed to convert one form of energy into mechanical energy to produce motion. Its mechanisms rely on various thermodynamic processes to convert heat to mechanical energy through the so-called “heat engines”. 

    In other words, you can imagine a motor as a flow with an input and an output. In the generic sense, a motor can use different sources to transform an input into the desired type of energy. Electric motors convert electrical energy into mechanical motion, pneumatic motors use compressed air, engines use the combustion of a fuel, and clockwork motors in wind-up toys use elastic energy. 

    What is an Electric Motor?

    An electric motor is a motor that uses electricity to convert electrical energy into mechanical energy. 

    In the case of electrical motors, the input consists of electrical energy, while the output is mechanical energy. The energy conversion process, however, is not perfect. A portion of the input is transformed into heat and does not become motive energy. This waste of energy is called “loss”.

    The challenge for manufacturers is to design motors with less loss to increase efficiency and lower the impact on the environment. 

    Loss in motor efficiency is expressed with the following formula, where all the amounts are calculated in Watts:

                                                                             Input Power = Mechanical Output + Loss

    In particular, here’s how you would come up with the input power and mechanical power of an electric motor:

                                                                             Input power (W) = Voltage (V) x Current (A)

                                                                             Mechanical power (W) = Rotating Speed (rad/s) x Rotative Force (N.m)

    Motor efficiency is calculated as a fraction of the mechanical output to input power as a percentage:

                                                                             Motor Efficiency = Output/Input x 100%

    Besides the technical calculations, motor efficiency is not only a matter of convenience. Increasing motor efficiency can have a significant impact on the global energy crisis. It is estimated that nearly half of the world’s energy consumption is consumed by motors. We at PowerMotor take this challenge very seriously. Click here to learn more on how we design our motors for increased efficiency. 

    What are the Components of an Electric Motor?

    Part of electric motor.pngAn electric motor consists of a series of components, whose placement can vary according to the type of motor you’re considering. These are some of the most common parts you’ll find in most electric motors:

    • Rotor

    • Stator

    • Bearings

    • Windings

    • Commutator

    As we dig deeper into the classification of electric motors, you’ll see many times mentioned both rotors and stators. So we’ll start from these two main components, which together make for the motor core:

    • Stator = a stationary part of the machine;

    • Rotor = the rotating part of the motor;

    What is a Rotor?

    The rotor is the rotating part of the motor, which is composed by the rotor core and the rotor winding. It is made of three parts: a rotor core, conducting rods, and two end rings. The winding of the rotor is excited by a DC supply and rotates the shaft to deliver the mechanical power. 

    There must be an air gap between the stator and the rotor so it can turn. The width of this gap has a significant impact on the motor’s electrical characteristics. Small air gaps are preferred, as large gaps have a strong negative effect on the motor’s performance. However, very narrow gaps may pose mechanical problems in addition to noise and losses. 

    What is a Stator?

    The stator is the static part of the motor and has the main function of generating the rotating magnetic field. It is made up of three parts: the stator core, conducting wire, and a frame. 

    The stator core supports and protects the three-phase winding of the stator. It usually consists of field magnets, which are either permanent magnets or electromagnets consisting of wire windings around a ferromagnetic iron core. 

    It creates a magnetic field, which passes through the rotor armature and exerts force on the windings. The rotor core is usually made up of “laminations”, which are many thin metal sheets that are insulated from each other and used to reduce energy losses. 

    What are the Bearings of an Electric Motor?

    The rotor is supported by bearings, which allow the rotor to turn on its axis. They’re sustained by the motor housing. The motor shaft extends through the bearings to the outside of the motor, where the load is applied. 

    What are the Windings of an Electric Motor?

    Windings are wires laid in coils that are usually wrapped around a laminated soft iron magnetic core to form magnetic poles when energized with current. 

    Electric motors come in two basic magnet field pole configurations: salient- and non-salient-pole. In the salient-pole motor, the pole's magnetic field is produced by a winding wound around the pole below the pole face. In the non-salient-pole motor, the winding is distributed in pole face slots.  A shaded-pole motor has a winding around part of the pole that delays the phase of the magnetic field for that pole. 

    What is a Commutator?

    A commutator is a rotary electrical switch that supplies current to the motor. It consists of a cylinder made of multiple metal slip-ring segments that are insulated from each other and from the shaft. This mechanism is used by the motor to switch the input of most DC motors and certain AC motors. 

    Electric Motor Types

    What are the Types of Electric Motors?

    Electric motors can be divided between AC motors and DC motors, where each type can then be defined with other sub-categories.

    Types of Electric Motors.png

    Both AC and DC motors find application in processes and facilities in almost every industry. Some of the most common industrial applications for AC motors include:

    • Appliances

    • Compressor drives and systems

    • Conveyor systems

    • Fans and air conditioners

    • Hydraulic and irrigation pumps

    • Transportation equipment

    Common industrial applications for DC motors include:

    • Fabrication and production units

    • Machinery that demands constant power such as vacuums, elevators, and sewing machines

    • Warehouse sorting equipment

    What is Alternating Current (AC) vs Direct Current (DC)?

    • DC: consistent current

    • AC: intermittent current

    Direct current = a type of electricity that moves in a singular and consistent direction at all times. A direct current’s voltage does not change and maintains its regular polarity. Batteries, fuel cells, and solar cells usually generate DC current. They have a defined positive and negative sides and they use direct currents to generate the same voltage consistently. 

    Alternating current = a type of electricity where voltage and current vary with respect to time. The AC’s current flow changes between positive and negative because of natural flow of electrons. AC is the standard electricity format that comes out of wall outlets. For example, when you charge your phone through a socket, your phone battery is recharged through AC current. 

    What is the difference between AC and DC power?

    The wave-like motion of AC power gives this electricity form an advantage over DC power. Because it moves in waves, this electricity format can travel farther than DC power. Most outlets in buildings provide AC power. While many electrical devices such as lamps and appliances use AC power, others require converting the electricity into DC format.

    the difference between AC and DC power.png

    What are AC Motors?

    AC motors employ alternating current to generate motive power. They rotate by using power from a commercial AC power supply. They are easy to handle and have features that can be configured. 

    Speed in AC motors is controlled by varying the frequency. This step is usually done with an adjustable frequency drive control, also known as FDC. Their work mechanism requires synchronization between the rotor rotation and the current frequency. For this reason, the speed of AC motors remains constant. 

    AC motors are the most popular motors in the industry. They have many advantages, including the following:

    • They are simple to build;

    • They are more economical (die to lower start-up consumption);

    • They usually cost less;

    • They require little maintenance;

    AC motors are most suitable for applications requiring continuous movement and few gear changes. They are perfect to be be used in household appliances, including blenders, vacuum cleaners, hair dryers, pumps, fans, and more. 


    What are DC Motors?

    DC Motors are motors that are powered by sources of direct current, like batteries, DC power supplies, and AC-to-DC power converters. They take electrical power through direct current, and convert this energy into mechanical rotation. 

    DC motors use magnetic fields that occur from the electrical currents generated, which powers the movement of a rotor fixed within the output shaft. The output torque and speed depends upon both the electrical input and the design of the motor.

    DC motors are commonly seen in home appliances as well as industrial applications, including in the healthcare and automotive industries. They’re suited for dynamic applications requiring high accuracy, especially in terms of speed - like hair dryers - or in terms of position - like robots or machine tools. They’re not that suitable for applications requiring high power.

    They’re made with brushes and a commutator, which results in higher maintenance, lower speed and a shorter motor lifespan. Speed is controlled in DC motors by varying the armature winding’s current. 

    Besides all, DC motors still have several advantages:

    • They’re accurate and fast;

    • They have a high starting torque;

    • They have a quick start, stop, acceleration, and reversing system;

    • Their speed can be controlled by varying the supply voltage;

    • They’re easy to install, even in mobile (battery-based) systems;

    What are the Main Differences Between AC and DC Motors?

    The two main differences between AC and DC motors are related to their power sources and speed.

    • Power source: AC motors use alternating current (either single-phase or three-phase), while DC motors use direct current (for example from batteries);

    • Speed: AC motors tend to run faster than DC motors. One of the reasons is that the speed of an AC motor is controlled by varying the current in the motor. For DC motors, on the contrary, speed is controlled by varying the frequency, usually with the help of a frequency converter;

    What are the Differences Between Brushless and Brushed DC Motors?

    Brushed DC motors used to be very common, but they’ve been largely supplanted by their brushless counterparts. Brushless DC motors are known for their high efficiency, controllability, and longer lifespan. They’re often found in devices that either run continuously or are in regular use. 

    Brushed DC motors are used less frequently in industrial applications. However, they are more often employed in home appliances as well as applications in the healthcare and automotive industries. For lower power, AC motors are preferred as they require little maintenance for equivalent use. 

    The issue with DC motor parts is that they’re too expensive to replace. For this reason, some manufacturers combine AC motors with an integrated electric motor controller. The combination of an AC motor and a frequency inverter has become a cost-effective solution for most applications requiring speed variations. Power Motor has done it professionally since 2001.

    How Electric Motors Work

    How does an Electric Motor Work?

    If you’re an electrical engineer or have years of experience in this industry, you know how and electric motor works. If you aren’t (or need a refresher), we have put together a simplified explanation of how an electric motor works. 

    It starts with a power supply that is connected to the motor. Electrical energy is supplied to the stator via the battery or wire. The coils within the stator (made from the conducting wire) are arranged on opposite sides of the stator core and act as magnets. 

    When the electrical energy from the power supply is shifted to the motor, the coils create rotating magnetic fields that pull the conducting rods on the outside of the rotor along behind it. The spinning rotor is what creates the mechanical energy needed to turn the gears of the device you’re trying to power. 

    Using more technical terms, we can say that the principle of an electric motor is based on the current-carrying conductor which produces magnetic field around it. A current-carrying conductor is placed perpendicular to the magnetic field so that it experiences a force. 

    The current-carrying conductor is placed between the two magnets and is connected to the battery or power source. When the battery is turned on, there is a flow of current in the conductor and magnetic field from the north to the south. In other words, there is a downward and upward force acting on the conductor. This acting force transforms electrical energy into mechanical energy.

    The Working Principle of an Electric Motor

    Take two bar magnets and keep the poles facing each other with a small space in between. Then take a small length of a conducting wire and make a loop. Keep the loop inside the space between the magnets so that it remains within the sphere of influence of the magnets. 

    Last but not least, connect the ends of the loop to the battery terminals or power source. Once electricity flows through this simple circuit, you’ll notice that your loop moves. This happens because the magnetic field of the magnets interferes with the one produced due to electric current flowing in the conductor. 

    Since the loop has become a magnet, one side of it will be attracted to the north pole of the magnet and the other to the south pole. This mechanism causes the loop to continuously rotate. An electric motor uses this working principle to transform electrical power into mechanical power.

    How does a DC motor work?

    A DC electric motor is powered by flows of direct current (DC), which usually come from wires connected to a battery or a similar power source. 

    In a DC motor, the magnet (and its magnetic field) is fixed in place and forms the outside, static part of the motor (the stator), while a coil of wire carrying the electric current forms the rotating part of the motor (the rotor). The magnetic field comes from the stator, which is a permanent magnet, while you feed the electric power to the coil that makes up the rotor. The interaction between the permanent magnetic field of the stator and the temporary magnetic field produced by the rotor is what makes the motor spin.

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