There is a wide range of metals that are conductive, but the most popular types of conductive metal used in coils include copper and aluminum. Used in a wide variety of applications, electrical coils are common components in industries such as the automotive industry, in which induction coils, also known as spark or ignition coils, are essential for operation of ignition systems. Industrial manufacturing also utilizes many types of electric coils such as molded coils or encapsulated coils, for protection against corrosive environments and solenoid coils for remote activation of machinery. The electronic industry uses coils such as choke coils and transformer coils, which are often essential parts of electrical circuits. Power plants are another major employer, often using toroidal coils and high voltage coils in many machines associated with power generation. Also, electric coils can be referred to as electromagnetic or magnetic coils, and in addition to the common types of electric coils, custom coils can be made to fit atypical applications.
In order to fit the wide array of applications, there are many types of electric coils differentiating in terms of wire gauges, wire lengths, coil diameter and the materials around which the wire is wound. Electric coil varieties are all able to be customized to meet specific demands. Also, in addition to transmitting heat, sound or electricity, electric coils are required to perform several different functions. For instance, electronics, automotive, medical, computer, appliance and telecommunication industries rely heavily on electric coils in order to produce movement, regulate flow and/or transform electric currents. While these may seem like very different functions, the basic electromechanical principles used in all electric coils are generally the same: a conductive metal wire is wound around an insulator, which could be a material as simple as cardboard or plastic, or even air. The two ends of the wire are usually made into electrical connection terminals called "taps", which are then connected to an electric current. When the current moves through the coiled wires, the coil itself becomes magnetized (although in some cases it can become demagnetized), creating the movement that is used to power essential equipment such a solenoid valves, electric motors, MRI machines and many others.
The basic construction of the electric coil can quickly become complicated with the addition of more windings. A winding is defined as a complete coil assembly with taps and all. While a single winding can be utilized in some applications, others require the addition of secondary and even tertiary windings. An electric transformer, for example, is an electromagnetic component that consists of a primary and secondary winding that enables it to transfer electrical energy from one electric circuit to another electric circuit by means of a magnetic coupling with no moving parts. When a tertiary electric coil is added to an electromagnetic component, it is usually referred to as a tickler coil. In addition to the number of windings altering the function of the electric coil, differences in terms of the coil taps are significant as well. Defined as points in the wire coil that consists of an exposed conductive patch, coil taps can differ mostly in terms of size much like the diameter of the coil itself. When a coil has a large diameter, the amount of self induction is much larger and the current tries to flow on the inside of the wire instead of on the outside, which can be a problem. In addition, multi-layered electric coils can have issues with interlayer capacitance, which refers to an electrical phenomenon whereby an electric charge is stored, so the shape of the coil must be altered. As a result, for multi-layered electric coils, a spiral shape is the most practical shape to be used.
While there is a basic underlying similarity in the construction of electric coils, there are many ways in which each coil can be designed specifically to its application. For instance, some electric coils require protection from harsh environmental conditions such as moisture, salt, oil and vibration. In order to protect the fragile coils from the harsh elements, since with prolonged exposure conductivity can be easily lost, electric coils may be molded or encapsulated. While molded coils are encapsulated in plastic coverings that seal the entire coil unit, encapsulated coils are made from wire that has itself been encapsulated in a polymer epoxy. Other types of electric coils, such as toroid transformer coils, are wound around ferrite rings and wrapped in sealing tape for environmental protection. One of the more common types of electric coils, solenoid coils, is at times simply referred to as solenoids. Often used as a remote switch, solenoids are current-carrying coils of wire that become magnetic when a current passes through the coil, which is typically wound around an iron core. Other, lesser-known types of electric coils include Garrett coils, used in metal detectors, Rogowski coils, used to measure alternating current (AC), Oudin coils, which are disruptive charge coils, and Braunbeck coils, used in geomagnetic research.
Electric Coil Types
- Air Core Coils (Self-Supported Coils) - Electromagnetic coils which are wound "around air" without any core, hence the terms "air coils" and "self-supported 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
- Choke Coils - also known as choking coils, are low-resistance electric coils with high inductance that are used to block high-frequency alternating
currents (AC) of electricity while allowing low-frequency direct
currents (DC) to pass through.
- Custom Coils - provide either movement or electric current transformation.
- Electrical Coils - an alternative name for electric coils, consist of a series of loops
manufactured from conductive metallic wire and wound around a
ferromagnetic core.
- Encapsulated Coils - are electric coils which have been enclosed in a silicone rubber, polyester, liquid or thermoformed epoxy casing.
- High Voltage Coils - are electric coils that use a voltage higher than what is generally accepted as safe.
- Ignition Coils - are electrical induction coils that are used to transform lower
voltages of power to the higher voltages of power required in order to
fire a system's spark plugs.
- Impregnated Coils - Coils which have first been dipped or co-extruded into an epoxy before being wound; the laminating epoxy seals the conductive electromagnetic wire from the elements, creating a unit which is effectively protected from weather and dirt without the tooling costs of molded coils
- Induction Coils - A common synonym for electric coils, electromagnetic coils are used to create electromotive force by being activated to magnetism through electrical currents
- Magnetic Coils - Which can also be referred to as electromagnetic coils or simply just coils, include all types of electric coils that operate based on the principle of induction.
- Molded Coils - Electromagnetic coils which have been encased and sealed in thermoformed or injection molded plastic enclosures, protecting the coil from weather, dirt and vibration
- Solenoid Coils - also referred to as solenoids, are three-dimensional loops, or coils,
of wire that have been wrapped around a metallic core, and function to
provide a magnetic field when an electric current is passed through the
coil.
- Tape Wrapped Coils - Coils, usually bobbin wound, which are encased in sealing tape to protect the electromagnetic coil from weather, dirt and vibration; tape wrapped coils are not as effective at blocking these harmful elements as impregnated or molded coils, but the costs of manufacturing tape wrapped coils are much lower
- Tesla Coil - An electrical device that generates extremely high voltages, usually for the purpose of creating dramatic electric arcs and lightning effects or for producing x-rays
- Toroids/toroidal coils - Copper wire which has been wound around a ferrite, or iron, donut-shaped ring. The ferrite core amplifies the coil's inductance and may be used in transportation, audio & power supply applications
- Transformer coils - Electromagnetic coils, usually impregnated or laminated, which are used to change the voltage of an incoming electric current, feeding the current back out at the same frequency, but with a different voltage.
Electric Coil Terms
Bobbin - Plastic core around which electric coils are often wound
Coil Winding - The process of coiling electromagnetic wire around a core or in a self-supporting "air" coil; coils may be single-layer or consisting of many multiple layers. Precise technical coils often require "precision winding"
Conductor - A material, often metal (such as copper), which passes along electric currents through the movement of free electrons
Electric Current - The flow of electrically charged electrons or ions towards a positive pole, caused by the introduction of an electric energy field
Electromagnetism - Magnetism which is created by and conditional upon an electric current
Henries - The SI unit used to measure the inductance of an electromagnetic coil; inductance of single-layer coils can be found using the formula: µH = (R² x N²) / (9R + 10L), where µH = microhenries, R = the coil radius, N = the number of times the coil is wound and L = the length of the coil
Inductance - The electromotive force, or strength, of an electromagnetic coil (or circuit) created by the coil's exposure to an electric current
Transducer - An electrical device which converts energy from one form to another
Turns - The number of times an electromagnetic coil is wound, either around its core or, in the case of air coils, the number of times the coil is fully looped
