Dynamo

A dynamo is an electrical generator that produces direct current using a commutator. Dynamos were the first electrical generators capable of delivering power for industry, and the foundation upon which many other later electric-power conversion devices were based, including the electric motor, the alternating-current alternator, and the rotary converter. Today, the simpler alternator dominates large scale power generation, for efficiency, reliability and cost reasons. A dynamo has the disadvantages of a mechanical commutator. Also, converting alternating to direct current using power rectification devices (vacuum tube or more recently solid state) is effective and usually economical. "Dynamo Electric Machine" (end view, partly section, U.S. Patent 284,110) Etymology The word dynamo (from the Greek word dynamis (δύναμις), meaning force or power) was originally another name for an electrical generator, and still has some regional usage as a replacement for the word generator. The word "dynamo" was coined in 1831 by Michael Faraday, who utilized his invention toward making many discoveries in electricity (Faraday discovered electrical induction) and magnetism  Electricity Werner von Siemens in 1882. The original "dynamo principle" of W. Siemens meant only the direct current generators which use exclusively the self-excitation (self-induction) principle to generate DC power. The earlier DC generators which used permanent magnets were not considered "dynamo electric machines". The invention of the dynamo principle (self-induction) was a huge technological leap over the old traditional permanent magnet based DC generators. The discovery of the dynamo principle made industrial scale electric power generation technically and economically feasible. After the invention of the alternator and that alternating current can be used as a power supply, the word dynamo became associated exclusively with the commutated direct current electric generator, while an AC electrical generator using either slip rings or rotor magnets would become known as an alternator. A small electrical generator built into the hub of a bicycle wheel to power lights is called a hub dynamo, although these are invariably AC devices,  and are actually magnetos. Description The electric dynamo uses rotating coils of wire and magnetic fields to convert mechanical rotation into a pulsing direct electric current through Faraday's law of induction. A dynamo machine consists of a stationary structure, called the stator, which provides a constant magnetic field, and a set of rotating windings called the armature which turn within that field. Due to Faraday's law of induction the motion of the wire within the magnetic field creates an electromotive force which pushes on the electrons in the metal, creating an electric current in the wire. On small machines the constant magnetic field may be provided by one or more permanent magnets; larger machines have the constant magnetic field provided by one or more electromagnets, which are usually called field coils. Commutation The commutator is needed to produce direct current. When a...

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Lead–acid battery

The lead–acid battery was invented in 1859 by French physicist Gaston Planté and is the oldest type of rechargeable battery. Despite having a very low energy-to-weight ratio and a low energy-to-volume ratio, its ability to supply high surge currents means that the cells have a relatively large power-to-weight ratio. These features, along with their low cost, make them attractive for use in motor vehicles to provide the high current required by automobile starter motors. As they are inexpensive compared to newer technologies, lead–acid batteries are widely used even when surge current is not important and other designs could provide higher energy densities. Large-format lead–acid designs are widely used for storage in backup power supplies in cell phone towers, high-availability settings like hospitals, and stand-alone power systems. For these roles, modified versions of the standard cell may be used to improve storage times and reduce maintenance requirements. Gel-cells and absorbed glass-mat batteries are common in these roles, collectively known as VRLA (valve-regulated lead–acid) batteries. In 1999 lead–acid battery sales accounted for 40–45% of the value from batteries sold worldwide excluding China and Russia, and a manufacturing market value of about $15 billion. Lead–acid car battery Specific energy 33–42 Wh/kg Energy density 60–110 Wh/L Specific power 180 W/kg Charge/discharge efficiency 50–95% Energy/consumer-price 7 (sld) to 18 (fld) Wh/US$ Self-discharge rate 3–20%/month Cycle durability <350 cycles Nominal cell voltage 2.1 V Charge temperature interval Min. −35 °C, max. 45 °C History The French scientist Nicolas Gautherot observed in 1801 that wires that had been used for electrolysis experiments would themselves provide a small amount of "secondary" current after the main battery had been disconnected. In 1859, Gaston Planté's lead–acid battery was the first battery that could be recharged by passing a reverse current through it. Planté's first model consisted of two lead sheets separated by rubber strips and rolled into a spiral. His batteries were first used to power the lights in train carriages while stopped at a station. In 1881, Camille Alphonse Faure invented an improved version that consisted of a lead grid lattice, into which a lead oxide paste was pressed, forming a plate. This design was easier to mass-produce. An early manufacturer (from 1886) of lead–acid batteries was Henri Tudor. Using a gel electrolyte instead of a liquid allows the battery to be used in different positions without leakage. Gel electrolyte batteries for any position date from the 1930s, and even in the late 1920s portable suitcase radio sets allowed the cell vertical or horizontal (but not inverted) due to valve design (see third Edition of Wireless Constructor's Encyclopaedia by Frederick James Camm). In the 1970s, the valve-regulated lead–acid battery (often called "sealed") was developed, including modern absorbed glass mat types, allowing operation in any position. Electrochemistry Discharge Fully discharged: two...

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Alternator (automotive)

Alternators are used in modern automobiles to charge the battery and to power the electrical system when its engine is running. Until the 1960s, automobiles used DC dynamo generators with commutators. With the availability of affordable silicon diode rectifiers, alternators were used instead. This was encouraged by the increasing electrical power required for cars in this period, with increasing loads from larger headlamps, electric wipers, heated rear windows and other accessories. Alternator (silver) mounted on a V8 engine History The modern type of vehicle alternators were first used by the military from WWII, to power radio equipment on specialist vehicles. Post-war, other vehicles with high electrical demands, such as ambulances and radio taxis, could also be fitted with optional alternators. Alternators were first introduced as standard equipment on a production car by the Chrysler Corporation on the Valiant in 1960, several years ahead of Ford and General Motors. Magnetos in early automobiles Some early automobiles, like the Ford Model T, used a different sort of alternator system: an engine-driven magneto which generated low-voltage alternating current that was supplied to trembler coils, which provided the high voltage needed to generate ignition sparks. (This was different from a true ignition magneto, which generates high voltage directly.) Since such a magneto system only depended on the engine's motion to generate current, it could even be used when starting a manually cranked engine, provided the crank was pulled sharply, so that the magneto would produce enough current for the coils to make good sparks. The Model T incorporated its magneto into the engine flywheel. The first Model Ts used the magneto solely for the trembler coil ignition. Beginning with the 1915 model year, Ford added electric headlights, also powered by the magneto. The magneto circuit was strictly AC, with no battery included. (There was a switch on the ignition coils to use a battery instead, which could be helpful when starting in cold weather, but Ford neither provided a battery nor did it encourage the use of one before it introduced an electric starter in 1919. The owner would have to install the battery himself and charge it externally.) Starting in the 1919 model year, Ford upgraded the Model T to include an electric starter, which was standard for some models and optional for others. This starter installation also included a battery, charged by a conventional dynamo, and the lights were now powered by the battery. However, the flywheel magneto still powered the ignition, and since models without the starter had no battery, they continued to use magneto-powered lights. Advantages over dynamos Alternators have several advantages over direct-current generators. They are lighter, cheaper and more rugged....

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Automotive battery

An automotive battery is a rechargeable battery that supplies electrical current to a motor vehicle. Its main purpose is to feed the starter, which starts the engine. Once the engine is running, power for the car's electrical systems is supplied by the alternator. Typically, starting discharges less than three per cent of the battery capacity. SLI (Starting, Lighting and Ignition) batteries are designed to release a high burst of current and then be quickly recharged. They are not designed for deep discharge, and a full discharge can reduce the battery's lifespan. As well as starting the engine an SLI battery supplies the extra power necessary when the vehicle's electrical requirements exceed the supply from the charging system. It is also a stabilizer, evening out potentially damaging voltage spikes. While the engine is running, most of the power is provided by the alternator, which includes a voltage regulator to keep the output between 13.5 and 14.5 V. Modern SLI batteries are lead-acid type, using six series-connected cells to provide a nominal 12 volt system (in most passenger vehicles and light trucks), or twelve cells for a 24 volt system in heavy trucks or earth-moving equipment, for example. Battery electric vehicles are powered by a high-voltage electric vehicle battery, but they usually have an automotive battery as well, so that they can use standard automotive accessories which are designed to run on 12 V. A typical 12 V, 40 Ah lead-acid car battery History Early cars did not have batteries, as their electrical systems were limited. A bell was used instead of an electric horn, headlights were gas-powered, and the engine was started with a crank. Car batteries became widely used around 1920 as cars became equipped with electric starters. The sealed battery, which did not require refilling, was invented in 1971. The first starting and charging systems were designed to be 6-volt and positive-ground systems, with the vehicle's chassis directly connected to the positive battery terminal. Today, all road vehicles have a negative ground system. The negative battery terminal is connected to the car's chassis. The Hudson Motor Car Company was the first to use a standardized battery in 1918 when they started using Battery Council International batteries. BCI is the organization that sets the dimensional standards for batteries. Cars used a 6 V electrical system, and so had 6 V batteries until the mid-1950s. The changeover from 6 to 12 V happened when bigger engines with higher compression ratios required more electrical power to start. Smaller cars, which required less power to start stayed with 6 V longer, for example the Volkswagen Beetle in the mid-1960s and the Citroën 2CV in 1970. In the 1990s a 42V electrical system standard was proposed....

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