In this post, you will find everything regarding electric coils on the internet.
You will learn:
- What is an Electric Coil?
- How Electric Coils are Used
- Types of Electric Coils
- Conducting Materials for Electric Coils
- And much more …
Chapter One – What is an Electric Coil?
An electric coil, or electromagnetic coil, is an electrical conductor that contains a series of conductive wires wrapped around a ferromagnetic core that is cylindrical, toroidal, or disk-like. Electric coils are one of the simplest forms of electronic components and provide inductance in an electrical circuit, an electrical characteristic that opposes the flow of current.
There are a wide range of electrical coils that vary according to the gauge of their wires, coil diameter, wire lengths, the number of loops, and type of core material, which can be air, iron, steel, ceramic material, or iron based formless tape. The materials used for the core of an electric coil is determined by the permeability of the material, which is the core's ability to form a magnetic field.
Electric coils are found in electric motors, generators, inductors, and electromagnets. They serve as a conductor of electricity to efficiently send electrical current to electric motors. They are a consistent and reliable method for induction.
Chapter Two – How Electric Coils are Used
Electric coils are commonly found in industrial manufacturing, medical equipment, and equipment that supplies electricity to residential and commercial buildings. Since they are a common part of so many applications, there are coils designed to meet the individual specific needs of a variety of processes.
How Electric Coils are Used
Medical Electric Coils
Equipment for medical use has to meet a variety of standards regarding equipment that will be used for medical treatments. In most cases, manufacturers produce coils that follow the standards that have been established for cleanrooms. Filaments for medical equipment come in a wide variety of materials to meet the needs of the application. Medical equipment demands extremely tight inner and outer diameter tolerances to ensure proper performance in critical situations.
Military Electric Coils
Coils used by the military have to be reliable, accurate, instantly responsive, flexible, and able to perform under harsh and hazardous conditions. There are many uses for electric coils in the military that include guidance systems, navigation controls, and sensors.
Transportation Electric Coils
As with several other industries, the transportation industry makes wide use of electric coils. They can be found in railroad track transformers, lighting transformers, armatures, and signaling devices. Also, electric coils are used in the production of electric locomotives, which have coils that are specially designed to withstand the vibrations of constant use.
Energy Electric Coils
Producing components for the energy industry is a challenge since many of the locations for extracting energy are located in remote places. Oil platforms require reliable energy sources for the generation of electricity. Electric coils for this purpose are specially engineered and designed to meet the harsh environment and conditions.
Electronic Electric Coils
With the rapid rise of electronic devices, the production of electric coils has been required to devote a great number of resources to perfecting and designing electric coils to meet the demand. Coils for circuit boards are produced from finely wound wire for the production of laminated transformers and toroids.
Wind Powered Generator Electric Coils
Electric coils designed for wind turbines are capable of meeting the demands of a generator that produces between 100 W to over 1 MW. They are designed to withstand conditions that can reach up to 200o C and still maintain high performance. The coils are made of lightweight materials and insulated for protection against leakage or damage.
Flowmeter Electric Coils
The purpose of a flowmeter is to measure the volume of a liquid or gas flowing through a pipe. They are used to supply accurate monitoring and control information regarding the flow for precise calculations. Bobbin mounted flowmeter coils are molded, shaped, and designed to match the radius of the tube where the flow is being measured. Since flowmeter coils are not mechanical, they are not susceptible to wear or abrasion.
Automotive Electric Coils
A basic part of an automobile is an ignition coil that changes the energy from the battery to the thousands of volts required to create a spark in the spark plugs to ignite the fuel for the engine. As with most coils, ignition coils consist of two sets of copper wires that are wrapped around an iron core. The electric energy from the core is transferred to the distributor and on to the spark plugs. The primary winding of the coil is heavy wire, which is surrounded by secondary windings of lighter smaller wire. The concept of the ignition coil goes back hundreds of years and was adapted for use in the first automobiles.
Traffic Light Sensor Electric Coils
A traffic light sensor is a coil with an inductance meter attached. When a car enters the field of the inductance meter, it acts like the core of the inductor and changes the inductance of the coil. This lets the traffic light know that a car is present.
Transformer Electric Coils
Transformers have changed the way that electricity is delivered. Initially, all electricity was direct current (DC) and required a large network of transfer stations to be moved long distances. With the development of alternating current (AC), electricity could be passed over long distances with fewer connecting stations. A key to this development was the transformer.
With a transformer, AC could be sent over long distances at high voltage with lower current to avoid loss in the line or wire. The transformer converts the high voltage to low voltage and increases the energy of the current. Transformers use multiple coils to conduct electricity by the use of electromagnetic flux, which have primary windings on one side and secondary ones on the other side.
Electric Guitar Electric Coils
An electric guitar coil is a form of transducer that converts the vibrations of the strings to electric signals. The most common form of electric guitar coil is the single coil design as well as dual coils, double coils, or humbucker. With the dual coil design, the pickup has two coils that “buck to hum” and cancel out interference. The pickups, coils, create a magnetic field around the strings of the guitar.
Chapter Three – How Electric Coils are Made
Though electric coils are the simplest form of electrical components, they are carefully engineered to fit the applications where they are used. An electrical coil consists of a core and wiring that is wrapped around the core. Some types of electrical coils do not have a core but just wound wires. The wire and its winding are important aspects of an electrical coil and its performance.
Electrical Coil Wires
The shape and dimensions of the wire used in a coil are chosen to perform a particular function. Inductance, energy loss, strength of insulation, and power of the magnetic field are central determining factors when choosing wiring.
The most efficient coils limit the amount of materials and the volume. There is a ratio between the area of the electrical conductors and the winding space, which is referred to as the fill factor. Round wires will always have some gap, which is increased by the space between layers created by insulation and the number of turns. The fill factor is always less than one and varies between 0.01 and 0.05. The use of rectangular, square, and flat wires are a method for increasing the fill factor.
There are three types of fill factors, which depend on the ratio between the cross sectional area of the piece and the cross section area of the coil. The calculation for the fill factor ranges between 0.1 and 0.5 with high, intermediate, and low fill factor designations.
Dense packing of wires lowers the amount of air space and increases the fill factor. This, in turn, increases the efficiency of an electrical device and improves its conductivity. The best packing of round wires includes having the upper layer of wire fill in the grooves of the lower layer by 300o of the coil circumference.
Winding wire is an insulated conductor used for interchanging electrical energy with magnetic energy. In most cases, the wire is coated copper or aluminum that has some form of thin layered insulation. When examining such factors as chemical, physical, and mechanical properties, for most electric coils, copper is usually the first choice. High purity grades of copper are used for applications with high or raised temperatures or for motors that use hydrogen gas for cooling.
The diameter, or gauge, of the wire of a coil has two effects. There is a direct relationship between the diameter of the wire and its potential to slot fill or its fill factor. The second effect is the amount of current that can flow through the coil. The conductor area can easily be increased by using a larger gauge wire that requires less insulation.
The problem with increasing the diameter of wire is that it becomes stiffer, less flexible, and more difficult to handle. The stiffness of the wire makes it harder for it to conform to the slot shape, fill factor. Though it may seem to be more convenient and efficient to use a smaller gauge wire, its use increases the ratio of insulation required. Also, smaller wires increase the number of necessary turns, which can lead to wire damage during insertion.
Wires with a 22 to 24 AWG provide a good wire to insulation ratio, can be easily formed, and are readily workable. When designing a motor, engineers examine the slot opening, slot shape, and the winding as well as the insertion method.
Electroplated wires are used in environments where the conditions can deteriorate or damage the wiring. The materials to plate the wires are gold, silver, and nickel, which come in various thicknesses and are coated with an insulation material. Electroplating offers greater protection in harsh conditions. The plating of the wires significantly improves their properties such as conductivity.
Types of Insulation
Electric coils use a variety of insulation materials that vary according to the temperature range of their application. The types of materials include polyvinyl chloride (PVC), polyurethane, polyester, and the different forms of polyimide. When choosing an insulation material, polyimide is used with applications that reach temperatures of up to 250o C. During the winding process, the wires are heated such that the insulation materials bind together.
The insulation material enhances the thermal endurance and protects the wire. The main function of wire insulation is to prevent the wires from touching since it would cause them to short out. Each type of insulation material has different specifications that include thermal capacity, gauge, and application.
In some cases, electrical coil wires will have a double coat. The wire will have an undercoat as an initial cover and a topcoat. This is done to strengthen the wire and increase its durability as well as allowing it to take advantage of the properties of both forms of insulation.
Polyvinyl Chloride (PVC)
Wires insulated with PVC are able to resist oils, alkali acids, sunlight, weathering, and abrasion. The temperature range for PVC is between -20o C to 60o C. Each of the different types of PVC have different pliability and electrical properties.
Polyurethane is an insulation material that is used in harsh and hazardous environments because of its exceptional mechanical properties and high chemical resistance. Since it is a very flexible material and easily adapted, it is usually used for outdoor applications. Though it is a strong and sturdy material, it is not normally used for electrical applications.
Polyester has a high temperature rating and a very low embrittlement factor. It is highly resistant to abrasions. It has excellent windability, flexibility, and resistance to heat and solvents. An overcoat of polyamide over polyester improves its windability and thermoplastic flow.
Polyimide is one of the most widely used forms of insulation for electromagnetic coils. It has excellent mechanical properties and is able to perform in high temperature applications. Polyimide is a polymer constructed from an imide monomer, which has two acyl groups bonded to nitrogen. The mechanical and thermal properties of polyimide have increased its use with electromagnetic coils since it can withstand a temperature that exceeds 240o C and is able to survive at high temperatures for 20,000 hours without experiencing any electrical breakdown.
Types of Coil Winding
The shape, design, and dimensions of a coil winding determines its purpose and function. The factors that influence a coil winding include inductance, quality factor, strength of the insulation, and the required type of magnetic field to be produced. The structure of the winding depends on the type and geometry of the coil to be wound.
Though coil winding can be done in a variety of ways, the basic forms include wild, helical, and orthocyclic. Each of these types are completed by specially designed winding machines.
Wild Coil Winding
Wild coil winding, or jumble, is characterized by cross winding where the coils are wound unevenly. The process for wild coil winding is normally used in instances where there is high volume production. Winding is completed at very high speeds and is used for relay coils, small transformers, and smaller electrical motors with a 0.05 mm gauge wire.
Helical Coil Winding
Helical windings are described as screw or spiral windings, terms that denote the characteristics of the coil’s construction. The winding is shaped into a helix and used in low voltage windings. The process of helical winding can include a few strands of wire up to over one hundred that are wound continuously parallel to each other. The interaction between the wires is very similar to the construction of a corkscrew with one layer going in one direction and the next going in the opposite direction. With helical winding, there is a variation in the pitch angle as can be seen in the diagram below.
Orthocyclic Coil Winding
In orthocyclic winding, each layer fits into the grooves of the layer below it, which is considered to be the most optimal method for coil winding. The orthocyclic method of coil winding has a high fill factor of 70% such that a strong magnetic field is created in the smallest amount of space. The pattern of the winding is continuous over every layer with each turn being parallel to the next with a fractional shift between layers.
Sandwich Coil Winding
Sandwich windings have a unique configuration where high voltage and low voltage windings set in the same magnetic access with the high voltage unit between two low voltage units, which reduces the leakage flux. This form of winding is usually used in the production of transformers and resembles an assemblage of discs.
Bobbin Coil Winding
With a bobbin coil, wire is wound around a bobbin, which varies widely depending on the voltage and current levels, rating, and operating frequency. They are used in switch mode power supplies and power conversion units.
Coil Winding Machines and Processes
The quality, quantity, and winding pattern for a coil depends on the coil winding machine. These well engineered and technical devices use CNC programming to produce perfectly wound coils and complete the process to the specifications of the selected coil.
In the linear winding process, wire is wound onto a rotating coil body, component, or forming device. The wire is fed by a tube into the winding mechanism that is controlled by a CNC program. This method of coil winding can be completed at high speeds using three CNC axes.
In this method, the wire is fed from a roll that is attached to the flyer that rotates at a predetermined distance from the coil. The flyer winding method is used for winding products that cannot be produced by rotational winding movement. The coil is held in the winding position and does not move during the winding process, which allows flyer winding to be used for the production of large coil products.
Needle winding is used in the production of stators and has a fixed or oscillating needle with a vertical spindle to create runoffs of square track or elliptical, which allows for higher fills and improved winding. The process of needle winding can be configured for multi-needle, open core or single head, inner and outer windings. They can be designed and engineered to meet the needs of any form of winding.
Toroidal winding involves winding a conducting wire around a circular ring evenly distributing the wire over the circumference. Some of the benefits of toroidal winding are low core loss and power density. Toroid coils are used for low frequency electricity applications. As the toroid coil turns, it creates high frequency, which makes toroid coils more economical and efficient.
The core of an electric coil is designed to produce an electric field. Some cores do not have a core, while others use some form of ferrite metal. Low frequency cores normally have an iron core. The type of material used to create the core determines the strength of the magnetic field and the inductance of the coil.
Amorphous cores are made from layers of magnetic tape that reduces the flow of eddy currents and can operate at higher temperatures. They are normally used in high efficiency transformers.
Iron cores create magnetic flux and are able to retain high magnetic fields. One drawback to iron cores is the eddy currents they produce that produce heat at high frequencies.
Vitreous metals are glassy and non-crystalline. They are used for high frequency transformers. This type of metal has low conductivity that reduces eddy currents.
Ferrite ceramics are composed of an iron oxide ceramic compound and metallic elements. This form of core is produced specifically to meet the needs of a variety of electrical applications. The ceramic material acts as an insulator and helps decrease eddy currents.
Laminated cores are thin iron sheets covered with a layer of insulation to prevent eddy currents that confine them to a loop inside the laminated layers. It is the thinness of the laminate that dispels the eddy current effect.
These unique cores are made from powdered carbonyl iron and have applications across a wide range of magnetic flux and temperature levels. They are made of small iron spheres coated with a layer of insulation and reduce the effects of eddy currents at high temperatures.
Silicon steel has a high electrical resistivity and provides excellent performance over an extended period of time. They have high flux density and are chosen for high performance applications.
Molypermalloy is a powder core material that is produced by combining molybdenum, nickel, and iron. It has low core loss and signal distortion with temperature stability. It is used for audio frequency applications, resonant circuits, and loading coils.
Sendust is a metal powder that is a combination of iron, silicon, and aluminum, which is sintered into core material. These coils have excellent magnetic permeability, low coercivity, and temperature stability. They are used for abrasive applications like magnetic recording heads.
Nanocrystalline material is a polycrystalline that has a crystallite size in a few nanometers, which fills the gaps between amorphous materials. It is produced by casting molten metal into a thin ribbon that is rapidly cooled. The crystalline structure is created by careful annealing. The resistivity of NC is very high and effective at wide band frequencies. Components can be produced smaller and are ideal for complex EMI scenarios.
As with every aspect of electric coils, there are a wide variety of core structures.
Straight Cylindrical Rod
It is a rod metal rod with the coil wrapped around it.
It is like a rod but has a square shape.
C or U
C or U shapes are used with an “I” core with windings on one or both legs.
This shape of core is used to create a closed magnetic field with the circuit wrapped around the center leg that is twice the size of the other legs.
A planar core comes in a variety of shapes but consists mainly of a flat piece of magnetic material that is above and below the coil.
A toroidal core is a circle or donut shape with the circuit wrapped around the circumference of the circle.
A pot core has a wall into which the coil is inserted and protected by the walls of the pot.
Air coils do not have a core for its inductance, which is unaffected by the current it carries. They are free of iron losses that affect ferromagnetic coils, which is an advantage as frequencies increase. Air coils are capable of performing at one Ghz, unlike coils with a core.
Chapter Four – Types of Electrical Coils
The choice of the type of electrical coil is determined by how it will be used, which includes whether the project requires a DC or AC electric motor. Electric coils, regardless of what type, have electric current that interacts with a magnetic field. Different types of coils are used for motors, generators, transformers, magnetics, and sensors Electronics, electricity, and magnetism use different forms of coils for each application. The list below is a brief description of various types of coils.
Bobbin Wound Coils
Electromagnetic wire which has been wound around a plastic core, or “bobbin”. Plastic cores come in many sizes, and bobbin wound coils may be impregnated, molded, or taped to meet various medical device, sensing, relay, and automotive applications.
This form of coil is used when there is limited space and no room for a bobbin or core. Since they can be placed closer to the metal in the circuit, they have greater magnetic capabilities. They are used for clutches, magnetic locks, and audio circuits.
A choke coil has low resistance and high inductance. They are used with AC and DC currents. Choke coils block AC and allow DC to pass through. The resistance of a choke coil increases with the frequency of the current.
Encapsulated coils, or molded coils, are protected from moisture, corrosive chemicals, vibration, explosions, and harsh working environments by being encapsulated in a tough temperature resistant thermoplastic. The design of encapsulated coils provides them with additional insulation and dielectric properties.
High Voltage Coils
High voltage coils are used in applications where the voltage is higher than what is considered to be safe. The reference to high voltage indicates that the current is potentially dangerous due to sparks or electric shock. The classification for high voltage is one thousand volts for AC circuits and fifteen hundred for DC circuits. The two types of high voltage coils are ignition and Tesla.
A Tesla coil is a radio frequency oscillator that powers a resonant transformer to change high voltages to low voltages. It is two open electric circuits connected to a spark gap. For the best results, Tesla coils are made from copper wire.
Ignition coils are used to change lower voltage power to higher voltage to fire a spark plug. They are like an electric transformer and have primary and secondary coil windings. The most common and familiar use of ignition coils is in the auto industry.
With an impregnated coil, the void space in the winding has been impregnated with resin or other material to reduce the motion of the conductors. The material chosen for the process is designed to seal the openings in the structure of the coil. They have low viscosity, long usage life, good dielectric strength, and can operate at extremely high temperatures.
A solenoid coil has a conductive core with a hollow center and wire wrapped around the hollow center. As current passes through the solenoid coil, it activates a magnetic field that creates magnetic potential that converts to magnetic force for mechanical movement. In some instances, a metal core can trigger the movement of a hydraulic valve.
Tape Wrapped Coils
Taped wrapped coils are designed for mild or less severe environments that do not contain chemicals or solvents. The coil is covered with a sealing tape to protect it from weather, dirt, and vibration. Tape wrapped coils are an economical choice since their cost is much lower than other types.
Toroidal coils are used for inductors and transformers. The coil is formed by wrapping a wire around a circular core that is open in the center. The shape of a toroidal coil allows for magnetic containment of the field limiting the amount of leakage of the field outside the coil. They are used in a variety of industries, which include transportation, audio, and power supply applications.
The purpose of a transformer coil is to transform voltage from one electrical circuit to another. Transformers can reduce or increase voltage. It is a passive device that uses electromagnetic induction to step voltage levels up or down between differing circuits.
A voice coil is made up of a bobbin, wire, collar, adhesives, and lead out wire. The size of the bobbin is determined by voice coil gap diameter. A voice coil converts electrical signals into linear magnetic energy. The initial use of a voice coil was to move the cone of a speaker. Its use has expanded into moving large masses at slow speeds. The force between the voice coils magnetic field and electric current is referred to as the Lorentz force.
Chapter Five – How an Electric Coil Works
The purpose of an electric coil is to create a magnetic field, which becomes stronger with an increase in the number of turns. The strength of the magnetic field is proportional to the amount of current flowing through the field. By adding more current, the force of the magnetic field increases. Once the current is removed, the magnetic field stops, as was proven in its original discovery in the 19th Century.
All wires produce a magnetic field when current passes through them. By winding and looping the wires, the power of the produced field is increased and works to store energy.
The definition of a coil can be determined by the frequency of the current that flows through it, which are direct current (DC), audio frequency (AF), and radio frequency (RF). Electric coils are further classified by their function such as an electromagnet, transformer, electric device, or some form of inductor.
The first electric coil was discovered by Nikola Tesla and has his name forever attached to it. The purpose of the coil is to achieve resonance, which occurs when the primary coil passes current into the secondary coil.
When electricity passes through a circuit, it flows through a resistor and into an electric coil. An electric coil works to maintain stability and resists the flow of current, initially. As the current builds, the coil allows the current to pass through. As with its previous state, when the current is removed, the electric coil works to maintain the flow and resists the change, allowing the electricity to continue to flow even though the current has been removed.
The process of passing electricity through a circuit happens rather rapidly and can be barely noticed. The most interesting factor is that an electric coil has a very simple function but has a major influence on the flow of electrical current.
The inductance of a coil is determined by:
- Number of coils – The more there are, the more inductance there is.
- The core – The material the coil is wrapped around.
- Cross sectional area – The greater the area, the greater the inductance.
- Length of the coil – A short coil is overlapping, which means greater inductance.
The standard unit of inductance is measured in Henries, which is calculated by a complex formula.
Chapter Six – Conducting Materials for Electrical Coils
The basic structure of an electric coil is its conducting material, which can be classified by its resistivity and conductivity. Low resistivity material allows for movement of an electrical charge, which is quantified by how strongly it opposes the flow of electric current and is represented by the Greek letter rho (ρ). Materials that have high resistivity are poor conductors. Conductivity is the degree to which a material is capable of conducting electrical current, which is calculated as the ratio of the current density to the materials electrical field.
Silver is one of the most common conductive metals. It has equal conductivity of copper. The reasons that silver is not used more than copper is that it isn’t as prevalent in nature and is prone to oxidation, which causes it to rapidly degrade.
Copper is the most common of the electrical conducting wires and is the most used for electrical coils. It has low electrical resistance and allows current to easily flow through it. A major factor in its use is that it can be configured and shaped to produce any form of coil.
Gold is ductile and malleable, which makes it easier to form into wire. It is a soft metal and can be configured for small electronic circuits and coils. Since it does not react easily with other elements and is resistant to corrosion and tarnish, it is ideal for use in electronic circuits. The drawback to the use of gold is its cost and limited accessibility.
Aluminum has low density and can reduce the weight of an electrical coil. Its low weight allows for efficient acceleration of moving parts, which improves performance. The use of aluminum wires improves the sound quality of speakers and voice coils.
Tungsten has a very high melting point. When current passes through it, it becomes hot and gives off light without being burnt. It has a low vapor pressure at high temperatures and does not erode.
Carbon wire is less expensive to manufacture and provides suppression of radio frequency interference (RFI) and electromagnetic interference (EMI). It is found in vehicle manufacturing and as replacement wire.
Manganin is an alloy made from copper, manganese, and nickel. Also known as constantine, manganin has very little change of resistance when there is a change in temperature, is highly resistant to heat corrosion, and has long term stability.
Titanium has good mechanical and physical properties. It is resistant to acids and can be easily configured, fabricated, and welded. The corrosion resistance of titanium wire has made it a main component for the aerospace, chemical processing, and medical industries.
Nichrome wire is composed of nickel, chromium, and iron. It has resistivity and is oxidation resistant with good ductility and weldability. The various types of nichrome have a number designation, which indicates the amount of nickel it contains. The types of nichrome are Nichrome 20, 30, 40, 60, 70, and 80. The operating temperature of nichrome varies between 1050o C to 1180o C.
Kanthal is an alloy made from iron-chromium-aluminum (FeCrAl) and is used in resistance and high-temperature applications. It forms a protective layer of alumina, which is a thermal conductor as well as an insulator. Kanthal has an extremely high melting temperature of 1425o C.
Nickel wire heats up quickly and has very little resistance. Unfortunately, nickel wire melts easily at high temperatures and is used in temperature controlled applications.
- An electric coil, or electromagnetic coil, is an electrical conductor that contains a series of conductive wires wrapped around a ferromagnetic core that is cylindrical, toroidal, or disk-like.
- There are a wide range of electrical coils that vary according to the gauge of their wires, coil diameter, wire lengths, the number of loops, and type of core material, which can be air, iron, steel, ceramic material, or iron based formless tape.
- Electric coils are commonly found in industrial manufacturing, medical equipment, and equipment that supplies electricity to residential and commercial buildings.
- The wire and its winding are important aspects of an electrical coil and its performance.
- The choice of the type of electrical coil is determined by how it will be used, which includes whether the project requires a DC or AC electric motor.