What is an Electric Coil?
An electric coil, commonly referred to as an electromagnetic coil, consists of a ferromagnetic core that is toroidal, cylindrical, or disk-shaped and a set of conductive wires wrapped around it.
Coils of this nature are fundamentally known to possess inductance, which is a vital property for damaging current flow in electrical circuits.
By having different core materials, which could be air, iron, steel, ceramic, or even iron based amorphous tape, electric coils can be classified as having different attributes which are wire gauge, coil diameter, wire length, number of turns, and core material.
These electric components are crucial for augmenting the formable magnetic field that causes the fluctuation of electric current circulating the coil while also providing a solid means of containment.
Electric coils are essential components of electric motors, generators, electromagnets, and inductors. They also deliver current to motors in a smooth and controlled manner, causing efficient induction.
How an Electric Coil Works?
An electric coil generates a magnetic coil that builds up when more wires are used. The strength of Magnetism is proportional to the current flowing through the coil.
With the increase in the power, the thrust produced by the magnetic field gets stronger, too. The disappearance of a magnetic field when the power is zero has also been known as “the magnetic field paradox” since the nineteenth century.
Every single wire possessing current has to superimpose a magnetic field onto wires conducting motion. To superimpose magnetic fields and efficiently conduct motion energy transforms, wires are wound into coils.
Electric devices such as transformers and inductors are also classified into coils depending on the magnitude of the current they transmit, such as direct current(open), stereo audio frequency, or radio.
This technology is always associated with Nikola Tesla, who invented the first electric coil and forever bound himself to the field. The main task of the coil is to reachthe first decibel level once primary current from a resonant secondary coil system is supplied.
A flow of electricity traverses a circuit via a resistor and proceeds to an electric coil. At first, the coil opposes the passage of current to preserve equilibrium. As the current grows stronger, the coil allows a greater amount of current to flow through.
When the current is switched off, the coil counters the change and continues to sustain the flow of electricity for a limited time, even when the current has been disconnected.
The process of electricity flowing through a circuit happens very quickly and can be barely noticeable. Regardless of having a basic structure, electric coils considerably influence electrical current control within a circuit.
The factors affecting the inductance of a coil are as follows:
- Amount of windings: An increased amount of windings increases the amount of inductance.
- The core: The material the coil is wrapped around.
- Area of the cross-section: A greater area translates to higher inductance.
- Coil length: Overlapping short coils lead to an increase in inductance.
Inductance is determined in Henries (H) and calculated from the coil’s basic parameters using inductance formulas.
How Electric Coils are Made
Electric coils are one of the simplest electrical components, yet they are meticulously designed for their intended uses.
Coils have a core with a wire wound around it or a coreless configuration, where the wire is simply wound. Regardless of the configuration, the wire and its winding are significant factors for the coil’s performance and functionality.
Electrical Coil Wires
The wire on a coil is selected in a specific shape and dimensions based on the task that needs to be accomplished. Inductance, energy loss, insulation strength, and magnetic field strength are vital parameters affecting wire selection.
Alongside accomplishing the task, minimization of material and volume is crucial in the design of coils. One of many important measures is defined as the fill factor, which is the area occupied by the conductor in the space designated for winding it.
When using round wires, compounded with insulation and multiple layers, the fill factor is determined to be within the range of 0.01 to 0.05. These gaps can be reduced by using rectangular, square, or flat wires, thereby increasing the fill factor.
Fill factors are classified based on their relationship with both the area of the wire and the cross-sectional area of the coil. This ratio is set between 0.1 and 0.5 and is classified into high, intermediate, and low fill factors.
For optimal packing of round wires, the top layer should fill the periphery aiding in reducing air gaps. This increases the fill factor, which improves the efficiency and conductivity of electrical devices. Estimations suggest that the top layer should cover up to 300° of the coil’s circumference.
A winding wire is used to convert electrical energy into magnetic energy. It is usually made from copper or aluminum wire covered with a thin layer of insulation. The wires are classified as insulated conductors.
Due to copper’s excellent physical, chemical, and mechanical properties, it is the preferred choice for electric coils. In high temperature applications and motors that use hydrogen gas for cooling, higher purposed copper grades are used.
The diameter of the winding wire or the gauge impacts two main considerations. Firstly, the fill factor, as defined by how the wire’s diameter enables it to be fit into the coil slots has an important relationship with the wire diameter.
Additionally, a wire’s diameter has an effect on the coil’s current capacity. A larger gauge wire means having a greater area of conductor, which results in less insulation being required.
Having a greater wire diameter can stiffen the wire while making it harder to flex or handle, therefore, these would require more effort to fit into slots. This stiffness will affect the wire’s ability to shape itself according to the slot and, thus affect the fill factor.
Although smaller gauge wires would seem much efficient and convenient, these lead to greater chances of insulation being inserted as well as a greater number of turns which increases the chances of wire damage during insertion.
Wires with a gauge value of AWG 22 and AWG 24 balance well between the ratio of wire to insulation, how easily they can be formed, and their workability.
In motor design, wind engineers take into account the opening of the slot, the shape of the slot, the wiring arrangement, and how the parts are fitted to ensure that the system performs optimally.
Electroplated Wires
In cases where an environment poses a threat towards the wires, electroplated wires are used.
Gold, silver, and nickel plating are employed in various thicknesses and with insulation coating. The wires are further protected in harsh conditions because electroplating improves the wires durability and conductivity.
Types of Insulation are used to make electric coil
Tailored to each electric coil’s temperature requirements, a range of insulation materials are used such as polyvinyl chloride (PVC), polyurethane, polyester, and polyimide in different grades.
Polyimide is the most commonly used for up to 250 °C applications. During the winding process, the wires are heated to guarantee that the resinous insulating materials become rigidly bonded.
The insulation materials contribute significantly to the protection of the wires while also improving thermal resistance. As with most materials, these are made to prevent short circuits by isolating wires so that there is no contact between them.
Each thermal insulation material is unique in its thermal capacity, gauge fit for the application, and compatibility with the purpose intended.
Coating electric coil wires increases the protection they are afforded in some applications. This includes an undercoat followed by a topcoat. Strength and durability but enhanced performance is achieved by combining both types of insulation with double coating.
Polyvinyl Chloride (PVC)
The use of PVC for cable insulation helps wires resist corrosive substances, acids, oil, abrasions, sunlight, and weathering. PVC insulation is functional within the -20°C to 60°C temperature range.
Due to the different types of PVC available, each with varying softness and electrical characteristics, some may be suited for specialized applications.
Polyurethane
Due to its high mechanical strength and exceptional chemical resistivity, polyurethane is effective in hazardous and harsh environments. Polyurethane’s weakness is that its insulation is not optimal for electrical applications.
While polyurethane has its weaknesses, its flexibility allows it to withstand outdoor conditions.
Polyester
In comparison to other organic materials, polyester maintains superb flexibility and is resistant to heat and solvents, making it a preferred insulation.
Furthermore, polyester has low factors of embrittlement and self-fracture, enduring high temperatures. Strengthening polyester with polyamide enhances its ability to twist and control thermoplastic flow, making it more favorable.
Polyimide
Polyimide is one of the foremost used insulations for electromagnetic coils, due to its riveting mechanical properties and polyimide applications at high temperatures. Polyimide is a polymer made from an imide monomer with two acyl groups attached to a nitrogen atom.
With the thermal and mechanical properties polyimide possesses, it has become useful with electromagnetic coils since it can endure temperatures higher than 240°C and can sustain high temperatures for over 20,000 hours without suffering electrical breakdown.
Types of Coil Winding methods to make an electric coil
The shape, design, and dimensions of coil windings are vital consideration that contributes towards the function and purpose of a coil winding.
The factors affecting coil winding involves inductance, the tank circuit quality factor, dielectric strength, and the kind of magnetic field required. The winding structure is dedicated according to the type of coil and its geometry.
Coil winding can be achieved through several techniques. The basic forms are wild, helical, and orthocyclic. Every method of these is carried out using special winding machines.
Wild Coil Winding
Also called jumble winding, wild coil winding consists of uneven layering cross winding and cross winding. It is used in mass production.
Very high precision speeds are common in the machining of relay coils, small transformers, and compact electrical motors that require wires as fine as 0.05 mm.
Helical Coil Winding
Spiral or screw windings, too, call for helical form with strands of wire wrapped around the core like a screw. These are low-voltage windings, and these may range from a few strands of wires to more than a hundred wires arranged parallel to each other.
The screws of spending layers in one direction are scompared to happen at different angles of pitch with each layer being different from the others as the rest turn in the other direction.
Orthocyclic Coil Winding
Orthocyclic coil winding is the most advanced one in her coils. With this method, each layer of winding sits within the grooves of the wind underneath, which can achieve a high fill factor of 70 percent.
With this construction, the strongest possible magnetic field in the smallest area is developed. There is no gap in between the turns; they go on one after another parallel to the one before, with just a few degrees shift between layers.
Sandwich Coil Winding
In sandwich windings, the high-voltage and low-voltage windings are configured along the same magnetic axis, with the high-voltage winding sandwiched between two low-voltage windings.
This arrangement is common in transformer construction because it reduces leakage flux. Its appearance is similar to a stack of disks.
Bobbin Coil Winding
Wire is wound around a bobbin in a bobbin coil, however, there are different types for each voltage, current, rating, and operating frequency. Bobbin coils are widely used in switch mode power supplies and power conversion units.
What Material Is Used To Make the Core of an Electric Coil?
The various types of core materials affect the induction and magnetic field strength of the coil, due to its influence on electric field generation. Some coils use no core at all, while others employ a variety of materials.
Amorphous Steel: High-efficiency transformers make use of transformers that employ Amorphous cores, which are made from layers of magnetic tape. These cores minimize the eddy currents, allowing for operation at higher temperatures.
Iron: Iron cores are known to produce strong magnestic fux while also supporting high magnetic fields. Their main downside is the fact that they generate heat due to the eddy currents created at high frequencies.
Vitreous Metals: Compared with iron, vitreous metals hold a glassy and non crystalline constitution, which makes them useful in high frequency transformers. Their non conductive property helps in lowering eddy currents.
Ferrite Ceramics: Made from iron oxide and metallic compounds, these ferrite ceramics would fulfill certain specified electric properties. These types of ceramics are insulative, which helps reduce eddy currents.
Laminated: Laminated cores are composed of thin iron sheets coated with insulation. Due to the design, these cores are able to prevent the spread of eddy currents outside the laminated layers, leading to a reduced impact.
Carbonyl Iron: The cores of carbonyl iron transformers are made of insulated powdered iron spheres. Their efficiency is maintained through a range of temperatures and magnetic flux, and they reduce eddy currents even at high temperatures.
Silicon: Silicon steel possesses remarkable permanency and high electrical resistivity. It is appropriate for high performance applications because it provides high flux density and exhibits extremely high-value superconductive features.
Molypermalloy (MPP): Molypermalloy is a blend of molybdenum, nickel, and iron, which is used for powder core materials. Its low core loss, low distortion signal, and reasonable stability at high temperatures make it appropriate for audio frequency applications, resonant circuits, and loading coils.
Sendust: Sendust is an iron, silicon, and aluminum alloy that is known for having high magnetic permeability. With low coercivity and stability under high temperatures, Sendust is a prime candidate for abrasive applications such as those found in magnetic recording heads.
Nanocrystalline (NC): Nanocrystalline material contains regions of several nanometers in size and is classified as polycrystalline. Formed through the rapid cooling of molten metal followed by controlled annealing, it fills gaps between amorphous materials. NC is best suited to small complex components and harsh electromagnetic interference environments due to its high resistivity and effectiveness at wide band frequencies.
What are the conducting materials used for electrical coils?
An electric coil has a basic elementary bearing structure formed by its conducting material, which can be classified by its resistivity and conductivity. Resistivity, which is the Greek letter rho (ρ), is defined as a measurement of how strongly a given material opposes the flow of electric current.
When divided in terms of resistivity, lower figures tend to be better conductors of electricity, and materials with higher figures tend to be poorer conductors. Conductivity on its own tells how well a material is able to conduct electric current and is defined as the current density divided by the electric field in the considered material.
Silver: An important silver wire’s physical properties is that it is a highly conductive metal. This piece of highly conductive metal on the other hand, is not widely used due to being more expensive, solid, and would for it get it tarnished.
Copper: Copper enjoys wide acceptance in the market as the preferred metal for electrical wires and coils due to its low electrical resistance and good conductive properties. Due to the versatility of copper, it can be easily shaped into various coil forms, which makes it the preferred choice for most electrical applications.
Gold: The malleability and ductility of gold allow it to be crafted into wires and circuits for small electronics. Its tarnish and corrosion resistance are useful for electronics as well. However, its limited availability and high cost make it impractical for common use.
Aluminum: The low density of aluminum is helpful in reducing the weight of electrical coils, improving the efficiency of moving parts and performance. It is especially useful in the case of speaker wires and voice coils, where reducing weight is advantageous.
Tungsten: With an extremely high melting point, tungsten can be heated and emit light without burning up. It also has low vapor pressure at high temperatures and is erosion resistant, which are useful for high temperature applications.
Carbon: Carbon wire is inexpensive to produce and helps mitigate radio frequency interference (RFI) and electromagnetic interference (EMI). It is frequently utilized in automotive applications and as substitutes for other types of wire.
Manganin: Knowing manganin for its change of resistance with temperature fluctuations, an alloy of copper, manganese, and nickel, offers enhanced resistance to heat corrosion and constant stability or resistive thermal change, also referred to as constantan.
Titanium: Titanium is useful in various industries because of its exceptional mechanical attributes, resistance to acids, and physical properties. It is especially useful in the aerospace and medical industries because of its ability to resist corrosion.
Nichrome: An alloy comprised of nickel, chromium, and iron known as nichrome, which is highly resistive and possesses oxidation resistance. Different grades exist, with nichrome 20, 30, 40, 60, 70, and 80 having operating temperatures between 1050°C and 1180°C.
Kanthal: A FeCrAl alloy called kanthal is used in applications requiring heating and resistance to extreme temperatures. It forms an alumina layer with extraordinary thermal insulation properties and a melting point of 1425°C.
Nickel: Due to its thermal properties, nickel wire is typically used in applications where temperature control is necessary since the wire heats quickly and has low resistance but melts at high temperatures.
Types Of Electrical Coils
The application of the project determines the selection of the electrical coil type. This includes whether the project involves a DC or AC electric motor. All types of electric coils have an electric current, which may or may not pass through 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
An electromotive wire is wound around a plastic blotter commonly called a bobbin. Bobbins are plastic cores of different sizes that can be impregnated, molded, or taped.
So that bobbin-wound coils can be used in medical devices, sensors, relays, automotive systems, and many more.
Self-Supported Coils
Self-supporting coils are used under conditions where there is no space for a bobbin or a core. These coils are positioned in close vicinity to the metal in the circuit, which gives these coils stronger magnetic properties. Usually, they are used in clutches, magnetic locks, or other audio circuit applications.
Choke Coils
The inductor’s low ohmic resistance and high inductance make it compatible with both alternating current (AC) and direct current (DC) systems.
A choke coil is designed to obstruct alternate current while allowing direct current to flow. A choke coil’s resistance also increases as the frequency of the choke coil’s current increases.
Encapsulated Coils
Also known as molded coils, encapsulated coils are protected from moisture, harsh chemicals, vibrations, explosions, and other extreme weather conditions by a rugged thermoplastic that can withstand high temperatures. Such encapsulation improves the insulation and dielectric strength of the coils.
High Voltage Coils
These coils are intended for use at voltages that may produce sparks or electric shocks and are classified as being above the safe limit. High voltage is considered to be one thousand volts in AC circuits and one thousand and five hundred volts in DC circuits. High voltage coils are generally of two types: ignition coils and tesla coils.
Tesla Coil
A Tesla coil is an oscillator that generates radio frequencies. It can boost low voltages to high ones using a resonant transformer and inductor. It contains two open electric circuits that are joined together by a spark gap. To achieve the best outcomes, Tesla coils are made out of copper wire.
Ignition Coils: The primary purpose of an ignition coil is to transform low voltage power supply to high voltage in order to ignite a spark plug. Just like an electric transformer, they have primary and secondary coil windings. They stand out in the automotive field (industry) due to their ease of identification and use in motor cars.
Impregnated Coils: Impregnated coils are defined (characterized) by the filling of winding voids with resin (special firn) or other materials to make conductors rigid. This type of coupling gives sealed structure to the coil which has a very low viscosity (viscosity, the measure of a fluid’s resistance to flow, extends it’s operational life, dielectric strength, ability to work at very high temperature and of great thermal stability) and possesses long service life (prolonged durability), exceptional dielectric strength, capability to endure very high temperatures.
Solenoid Coils
Solenoid coil is made of a conductive core with a hollow center region enclosed by a wire, which creates a coil. When an electric current is sent through the coil, a magnetic field is produced, creating magnetic potential which is converted into magnetic force for motion (mechanical movement). Sometimes a metal core in the solenoid can move a hydraulic valve into its actuated position.
Tape Wrapped Coils
Wrap-around tape coil, or tape-wrapped coils, are intended to operate in less severe environments free of chemicals and solvents. These coils can be covered with sealing tape to ward off weather, dirt and vibration. These coils are cheaper than other kinds of coils.
Toroidal Coils: Inductors and transformers use toroidal coils. A coil of wire is wound around a core where the center is open. The toroidal shape possesses strong containment of the magnetic field, which reduces the leakage outside the coil. These coils find applications in many sectors such as transport, audio, and power supply industry.
Transformer Coils
The transformer coil varies the levels of voltageused in different parts of an electrical system. Transformers increase or decrease the supplied voltage. They are passive devices which transform the circuits’ voltage using electromagnetic induction.
Voice Coils
The voice coil is constructed from a bobbin, a wire, a collar, some glue, and a lead-out wire. Bobbins are made in specific sizes according to the voice coil gap. This coil transforms electric impulses into magnetic energy in straight lines.
Formerly, it was the responsibility of voice coils to shift the cone of a speaker. However, voice coils can now be used to shift large masses at slow speeds.
The charge of a voice coil is electric, while the force is a magnetic one. This charge interactions is known as the Lorentz force.
How are Electric Coils Used?
Dos coils are used for a broad range of applications, including industrial manufacturing, medical grade equipment, as well as power plants for commercial and residential buildings. The wide range of coils’ application means that their design must address specific coils processes and requirements.
Medical Electric Coils
Electric components in the medical field must undergo rigorous quality control processes, particularly in parts used for operating or medical treatment. For increased reliability, manufacturers tend to make non-cleanroom compliant knitted coils that assured cleanroom standards.
Medical devices are made out of a range of different materials suitable for the required applications, but they must also achieve very tight tolerances on both internal and external diameters for high reliability in demanding situations.
Military Electric Coils
Electric components like coils are used in military guidance systems. Military grade components must meet extreme requirements for trustworthiness, precision, immediacy, and operational capability in extreme and hostile conditions. They have a broad range of military applications including navigation controls and sensors.
Transportation Electric Coils
The use of electric coils in the transport sector is wide. They form part of most moving components in electric railways, other being signaling devices, armatures, and lighting transformers for educational facilities like police academies.
Also, they act as the electric coils in railroad track transformers for locomotives. Furthermore, electric coils are custom made withstanding the shocks from vibration for stationed locomotives.
Energy Electric Coils
The manufacture of parts for the energy sector is particularly challenging because many energy extraction sites are situated in remote areas. Oil platforms, for example, require advanced electric power generation systems for their electricity needs. In these applications, the electric coils must be able to survive hostile environments and severe conditions.
Electronic Electric Coils
The design of modern electric coils for other types of machinery has arguably been the hardest hit by the increasing use of electronic devices.
The production of circuit board revolves around a coil made of thinly wound wire, which is also integral in making laminated transformers and toroidal ones.
Wind Powered Generator Electric Coils
Electric coils for wind turbines are built for generators that range from 100 W to over 1 MW. These coils can sustain a temperature of 200°C while keeping functionality. The electric coils are constructed from froth to reduce weight. Also, they are insulated against leakage and damage.
Flowmeter Electric Coils
A flowmeter electric coil with a fitting measuring device estimates a given amount of liquid or gas flowing through a pipe and registers controlled monitoring for motored mechanical processes to give precise measurement of flow, calibrating measurement system of selection control of the registered values.
At the specific section of tubing where flow is measured, custom made and custom cast bobbin led flowmeter coils’ shapes and contours have a definitive fitting radius. Given that the coils are of non-mechanical nature, they do not suffer wear and tear.
Automotive Electric Coils
Every vehicle has an ignition coil which is an automotive electric coil of basic constituents, used to transform the energy stored in the car battery to several thousands of voltage needed for the spark plugs to create a flame needed to combust the fuel in the engine, using an violent excersize of electric voltage fire while ejecting ionized hot gas.
With most coils, ignition coils consisit of two sets of copper wiring constituting the first and second coil wrapped around an iron core. The coil transfers the electric energy from the core to the distributor and subsequently to the spark plugs.
The ignition coil is built on the idea that there is a heavy wire forming the primary winding, which it then surrounds with lighter smaller wires constituting secondary windings. This design, developed in British colonies more than a century ago, and was incorporated in early automobiles.” This is based on the early design of coils.
Traffic Light Sensor Electric Coils
Traffic light sensors utilize a coil with a built-in inductive meter. The inductive meter senses changes in the coil’s inductance, which occurs when a car enters the sensor’s range since it acts as the core of an inductor. The traffic light systems uses this inductance variation as an indicator for vehicle presence.
Transformer Electric Coils
The introduction of electrical transformers changed the entire electrical distribution system. In the past, electricity was supplied in the form of direct current (DC), which needed an extensive network of transfer stations for long distance transmission.
The introduction of alternating current (AC) made the electricity easier to send over long distances and required fewer intermediate stations. The transformer was key in this development.
They make it possible to transmit AC at high voltage and low current which significantly reduces energy loss in the lines. After which they change high voltage power to low voltage energy and alter the current’s power to deliver.
They contain several coils of multiple voltage magnetic flux, thus allowing current to flow through the primary and secondary coils.
Electric Guitar Electric Coils
An electric guitar coil is a class of transducer responsible for transforming the string’s vibrations into audible electrical signals. The most prevalent designs are single coils and dual coils, the latter including the popular humbucker.
In dual coil designs, the two coils work in unison to electrically cancel interference, or “bucking the hum.” These pickups generate a magnetic field around the strings of the guitar which enables detection of their vibrations.