A linear alternator is an electromechanical type of

alternator An alternator (or synchronous generator) is an electrical generator that converts mechanical energy to electrical energy in the form of alternating current. For reasons of cost and simplicity, most alternators use a rotating magnetic field wit ...

that is essentially a

linear motor A linear motor is an electric motor that has had its stator and rotor (electric), rotor "unrolled", thus, instead of producing a torque (rotation), it produces a linear force along its length. However, linear motors are not necessarily straight. ...

used as an

electrical generator In electricity generation, a generator, also called an ''electric generator'', ''electrical generator'', and ''electromagnetic generator'' is an electromechanical device that converts mechanical energy to electrical energy for use in an extern ...

. An alternator is a type of

alternating current Alternating current (AC) is an electric current that periodically reverses direction and changes its magnitude continuously with time, in contrast to direct current (DC), which flows only in one direction. Alternating current is the form in w ...

(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 In physical sciences, mechanical energy is the sum of macroscopic potential and kinetic energies. The principle of conservation of mechanical energy states that if an isolated system is subject only to conservative forces, then the mechanical ...

electrical energy Electrical energy is the energy transferred as electric charges move between points with different electric potential, that is, as they move across a voltage, potential difference. As electric potential is lost or gained, work is done changing the ...

, whereas a motor converts electrical energy to mechanical energy. Like many electric motors and electric generators, the linear alternator works by the principle of

electromagnetic induction Electromagnetic or magnetic induction is the production of an electromotive force, electromotive force (emf) across an electrical conductor in a changing magnetic field. Michael Faraday is generally credited with the discovery of induction in 1 ...

. However, most alternators work with rotary motion, whereas ''linear'' alternators work with ''linear'' motion (i.e. motion in a straight line). Moving-magnet linear alternators are integral parts of thermoacoustic power converters.

Theory

A linear alternator is most commonly used to convert back-and-forth motion directly into electrical energy. This eliminates the need for a crank or linkage to convert a reciprocating motion to a rotary motion in order to drive a rotary generator.

Applications

The simplest type of linear alternator is the mechanically powered flashlight (shake type). This is a torch (UK) or

flashlight A flashlight (US English) or electric torch (Commonwealth English), usually shortened to torch, is a portable hand-held electric lamp. Formerly, the light source typically was a miniature incandescent light bulb, but these have been displaced ...

(USA) which contains a coil and a

permanent magnet 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, steel, nickel, c ...

. When the appliance is shaken back and forth, the magnet oscillates through the coil and induces an

electric current An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...

. This current is used to charge a

capacitor In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

, thus storing energy for later use. The appliance can then produce light, typically from a

light-emitting diode A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corre ...

, until the capacitor is discharged. It can then be re-charged by further shaking. Other devices that use linear alternators to generate electricity include the free-piston linear generator, an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal comb ...

, and the free-piston Stirling engine, an

external combustion engine An external combustion engine (EC engine) is a Reciprocating engine, reciprocating heat engine where a working fluid, contained internally, is heated by combustion in an external source, through the engine wall or a heat exchanger. The fluid t ...

. A a lightweight, double-fed induction linear alternator was created at NASA's

Glenn Research Center NASA John H. Glenn Research Center at Lewis Field is a NASA center within the cities of Brook Park, Ohio, Brook Park and Cleveland between Cleveland Hopkins International Airport and the Rocky River Reservation of Cleveland Metroparks, with a s ...

References

External links

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Linear Alternators in Free Piston Engines
{{Electric motors Alternators Electrical generators