Linear alternator
Encyclopedia
A linear alternator is essentially a linear motor
used as an electrical generator
.
An alternator
is a type of alternating current
(AC) electrical generator. The devices are often physically equivalent. The principal difference is in how they are used and which direction the energy flows. An alternator converts mechanical energy
to electrical energy, whereas a motor converts electrical energy to mechanical energy. Like most electric motors and electric generators, the linear alternator works by the principle of electromagnetic induction
. However, most alternators work with rotary motion, whereas "linear" alternators work with "linear" motion (i.e. motion in a straight line).
moves in relation to a coil of wire, this changes the magnetic flux
passing through the coil, and thus induces the flow of an electric current
, which can be used to do work. A linear alternator is most commonly used to convert reciprocating (i.e. back-and-forth) motion directly into electrical energy. This short-cut eliminates the need for a crank
or linkage
that would otherwise be required to convert a reciprocating motion to a rotary motion in order to be compatible with a rotary generator.
. This is a torch (UK) or flashlight
(USA) which contains a coil and a permanent magnet. When the appliance is shaken back and forth, the magnet oscillates through the coil and induces
an electric current
. This current is used to charge a capacitor
, thus storing energy for later use. The appliance can then produce light, usually from a light-emitting diode
, until the capacitor is discharged. It can then be re-charged by further shaking.
Other devices are under development which use linear alternators to generate electricity; these devices include the opposed-piston free-piston engine, and the free-piston Stirling engine.
Linear motor
A linear motor is an electric motor that has had its stator and rotor "unrolled" so that instead of producing a torque it produces a linear force along its length...
used as an electrical generator
Electrical generator
In electricity generation, an electric generator is a device that converts mechanical energy to electrical energy. A generator forces electric charge to flow through an external electrical circuit. It is analogous to a water pump, which causes water to flow...
.
An alternator
Alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
is a type of alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
(AC) electrical generator. The devices are often physically equivalent. The principal difference is in how they are used and which direction the energy flows. An alternator converts mechanical energy
Mechanical energy
In physics, mechanical energy is the sum of potential energy and kinetic energy present in the components of a mechanical system. It is the energy associated with the motion and position of an object. The law of conservation of energy states that in an isolated system that is only subject to...
to electrical energy, whereas a motor converts electrical energy to mechanical energy. Like most electric motors and electric generators, the linear alternator works by the principle of electromagnetic induction
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
. However, most alternators work with rotary motion, whereas "linear" alternators work with "linear" motion (i.e. motion in a straight line).
Theory
When a magnetMagnet
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, and attracts or repels other magnets.A permanent magnet is an object...
moves in relation to a coil of wire, this changes the magnetic flux
Magnetic flux
Magnetic flux , is a measure of the amount of magnetic B field passing through a given surface . The SI unit of magnetic flux is the weber...
passing through the coil, and thus induces the flow of an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
, which can be used to do work. A linear alternator is most commonly used to convert reciprocating (i.e. back-and-forth) motion directly into electrical energy. This short-cut eliminates the need for a crank
Crank (mechanism)
A crank is an arm attached at right angles to a rotating shaft by which reciprocating motion is imparted to or received from the shaft. It is used to change circular into reciprocating motion, or reciprocating into circular motion. The arm may be a bent portion of the shaft, or a separate arm...
or linkage
Linkage (mechanical)
A mechanical linkage is an assembly of bodies connected together to manage forces and movement. The movement of a body, or link, is studied using geometry so the link is considered to be rigid. The connections between links are modeled as providing ideal movement, pure rotation or sliding for...
that would otherwise be required to convert a reciprocating motion to a rotary motion in order to be compatible with a rotary generator.
Applications
The simplest type of linear alternator is the Faraday FlashlightFaraday Flashlight
A mechanically powered flashlight is one of several varieties of flashlight that are powered by electricity generated by the muscle power of the user, so they do not need replacement of batteries, or recharging from an electrical source...
. This is a torch (UK) or flashlight
Flashlight
A flashlight is a hand-held electric-powered light source. Usually the light source is a small incandescent lightbulb or light-emitting diode...
(USA) which contains a coil and a permanent magnet. When the appliance is shaken back and forth, the magnet oscillates through the coil and induces
Electromagnetic induction
Electromagnetic induction is the production of an electric current across a conductor moving through a magnetic field. It underlies the operation of generators, transformers, induction motors, electric motors, synchronous motors, and solenoids....
an electric current
Electric current
Electric current is a flow of electric charge through a medium.This charge is typically carried by moving electrons in a conductor such as wire...
. This current is used to charge a capacitor
Capacitor
A capacitor is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric ; for example, one common construction consists of metal foils separated...
, thus storing energy for later use. The appliance can then produce light, usually from a light-emitting diode
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...
, until the capacitor is discharged. It can then be re-charged by further shaking.
Other devices are under development which use linear alternators to generate electricity; these devices include the opposed-piston free-piston engine, and the free-piston Stirling engine.