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Tuesday, July 22, 2014

More Magnets and Machinery...

In the last tech article on magnets and machines, I described how any piece of iron bearing metal can be made magnetic and can act just the same as any other magnet simply by wrapping that chunk of metal with insulated wire and applying an electric current to it.  Lets explore more of the capabilities of these wonderful devices, electromagnets, and what they can do for us.  

Alternators and generators are machines that transform mechanical energy into electrical energy.  They do this by spinning a magnet inside of multiple coils of wire. 

OK- time to backtrack?  Cool, back to basics. So one of the fundamentals of physics, and more specifically, electromagnetism, is that a moving magnet can induce an electric current in a wire.  When a magnet is passed over even a single strand of wire, the magnetic field knocks electrons loose from the atoms of the metal and pushes them into the next atom.  This bumping of electrons from one atom to the next one near it is the transference of energy from the magnet to the wire.  

Electrons move from one atomic cloud to the next and we call that electric current: the flow of electrons in a conductor.  That electronic flow is what we use to do various types of work in toasters and microwaves, electric tools and computers, cell phones and satellites. Creating that electron flow in a wire is now considered basic physics, but 150 years ago, it was unheard of and unknown to most people.  Experimenters like Maxwell, Faraday, Edison, Tesla and a myriad of others all contributed to our knowledge of how electric current could be created and utilized. 
Most of the electricity that powers our homes and businesses comes from the burning of coal or natural gas, or from nuclear plants, but they all do it the same way- heat water, boil it to steam under high pressure, then release the pressure and allow the steam to expand and cool as it moves through the turbine.  As the superheated steam passes through the turbine unit, it cools and transfers its energy to the turbine blades attached to the shaft, then to a generator/ alternator.  As the steam passes through the turbine,  most of the energy in the compressed superheated steam gets used to spin the turbine at very high speeds.  The turbine is connected via a common shaft to the generator or alternator head usually.

In a car, the alternator is spun at high speeds by a belt on a small pulley driven from the crankshaft pulley.  Usually these days a large, flat belt (serpentine belt) is responsible for turning the alternator in a car along with all the other accessories that need spun (A/C, power steering, water pump...) Regardless of how they are spun, an alternator is an interesting piece of equipment.   Inside an alternator, there is is the inner core (rotor) anchored directly to the spinning shaft.  This rotor is simply a coil of wire that is charged with a small electric current to become a magnet.  That magnetic coil in the rotor has ends and center made of iron, (steel) and thusly as current is applied to the coil in the rotor, the magnetic flux in the rotor core increases proportionally to the current flow.  These steel ends are brought around to the sides of the rotor to create a series of alternating North and South magnetic poles around the circumference of the rotor.  It is the constantly changing magnetic flux, switching rapidly from North to South that induces a current tin the stator coils. 

Controlling an alternator to put out specific voltage or current is simple in some ways.  A separate, or integrated voltage regulator controls output power by varying the small current that flows through the rotor.  Surrounding the rotor are the stator coils that are excited as the magnetic rotor spins inside them.  This creates a tremendous voltage and current in the stator with only a small current flowing through the rotor.  Its the input current that controls the output current.  For this reason, this design of alternator has become the standard for almost all equipment that must produce electrical power.  

So, again, heres to magnets and the ability to create all sorts of machines using them.  Magnets can be used to make speakers that spread sound through the room, or they can be used for detecting the position of something tiny and in need of perfect calibration.  Magnets are everywhere, and where they are not, we can make them using steel and wire to create electromagnets.  These electromagnets can be easily controlled with tiny amounts of power, thus the output of an alternator is also easy to adjust and control.  

Heres to long lived machines and healthy, happy people too,

             Again soon, MW

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