Leyden Jar, Electric Charge, Galvanic Cell, Voltaic Pile, Anions, Cations, Daniell Cell, Zinc-Carbon Battery and Alkaline Battery

Posted by PITHOCRATES - December 25th, 2013

Technology 101

(Originally published December 19th, 2012)

Luigi Galvani made a Dead Frog’s Leg Twitch when he hit it with the Electric Discharge Shock from a Leyden Jar

The field of electricity took off with friction generators.  Dragging something across another substance to produce an electrical charge.  Like sliding out of your car on a dry winter day.  Producing an electric discharge shock just before your hand touches the metal door to close it.  Atoms in materials are electrically neutral.  There are an equal number of positive particles (protons) and negative particles (electrons).  Friction can transfer some of those electrons from one surface to another.  Leaving one surface with a net positive charge.  And the other with a net negative charge.  These charges equalize after that electric discharge shock.  Returning the atoms in these materials to an electrically neutral state.

Further exploration of static electric charge led to the development of the Leyden jar.  A precursor to the modern capacitor.  A glass jar with metal foil on the inside and outside of a glass bottle.  The foil sheets act as plates.  The glass as a dielectric.  An electrode attached to one plate received an electric charge from a friction generator.  The other plate was grounded.  The dielectric helped the plates hold an electric charge.  Benjamin Franklin did a lot of experiments with the Leyden jar.  He noted how multiple Leyden jars could hold a greater charge.  Commenting that it was like a battery of cannons.  Giving us the word battery for an electrical storage device.

Luigi Galvani made a dead frog’s leg twitch when he zapped it with the electric discharge shock from a Leyden jar.  Furthering his experiments Galvani found that he could reproduce the twitching by placing the frog’s leg between two different types of metals.  Creating a galvanic cell.  Which created an electric current.  Alessandro Volta recreated this experiment while substituting the frog tissue with cardboard soaked in salt water (an electrolyte).  Creating the voltaic cell.  Piling one voltaic cell onto another created a Voltaic Pile.  Or as we call it today, a battery.

A Daniell Cell created a Current by Stripping away Electrons from one Electrode and Recombining them on Another

What Galvani and Volta discovered was a chemical reaction that caused an electric current.  The Voltaic Pile, though, had a limited life.  To improve on it John F. Daniell added a second electrolyte.  Creating the Daniell Cell.  Which extended the life of a battery charge.  Allowing it to do useful work.  Becoming the first commercially successful battery.  Powering our first telegraphs and telephones.  Even finding their way into our homes operating our doorbells for a century or so before Nikola Tesla brought alternating current electric power to our homes.

The chemical reaction in a Daniell Cell created an electric current by stripping away electrons from one metal electrode in a solution (anode oxidation).  And recombining electrons onto another electrode of a different metal in a different solution (cathode reduction).  Each electrode is in an electrolyte solution.  In a copper-zinc Daniell Cell the anode is typically in a solution of zinc sulfate.  And the cathode is in a copper sulfate solution.  A salt bridge or porous membrane connects the different electrolytes.  When an electric load is connected across the ‘battery’ electrodes it completes the electrochemical system.

Each electrolyte contains ions.  Atoms with a net positive or negative charge.  Positive ions are cations.  Negative ions are anions.  The cathode attracts cations.  Where they combine with free electrons to return to a neutral state.  The anode attracts anions.   Where they give up their extra electrons to return to a neutral state.  This chemical activity dissolves the zinc electrode.  And deposits copper on the copper electrode.  (This electrolysis is the basis for the metal plating industry.)  It is the dissolving of the anode that gives up electrons that travel from one electrode through the electric load to the other electrode.  Doing work for us.  By lighting our flashlights.  Or powering our portable radio.  When the anode dissolves to the point that it cannot give up anymore electrons the chemical reaction stops.  And we have to replace our batteries.

An Alkaline Battery will produce more Useable Power and have a longer Shelf Life than a Zinc-Carbon Battery

Of course, the zinc-carbon batteries we use for our flashlights and radios are not wet cells.  They’re dry cells.  Instead of an electrolyte solution the common battery is made up of dry components.  The zinc anode is the battery casing.  Just inside the battery zinc casing is a paper layer impregnated with a moist paste of acidic ammonium chloride.  This separates the zinc can from a mixture of graphite powder and manganese (IV) oxide (pyrolusite).  In the center of the battery is a carbon rod.  The zinc casing is the negative electrode (anode) and the carbon rod is the positive electrode (the cathode).  The chemical reactions are the
same as they are with the wet cell.  The zinc casing (the anode) becomes thinner over time.  When holes begin to appear the battery will leak creating a sticky mess.  As you no doubt experienced when taking an old set of batteries out of a flashlight that hasn’t been used in years.

An alkaline battery looks similar to a zinc-carbon battery.  But there are many differences.  Instead of an acidic ammonium chloride electrolyte an alkaline battery uses an alkaline potassium hydroxide electrolyte.  The little nub (positive terminal) on top of the battery does not connect to a carbon rod in the center of the battery.  It connects to the outer casing.  Inside this casing is a mixture of graphite powder and manganese (IV) oxide (pyrolusite).  Then a barrier to keep the anode and cathode materials from coming into contact with each other.  But lets ions pass through.  On the other side of the barrier is the anode.  A gel of the alkaline potassium hydroxide electrolyte containing a dispersion of zinc powder.  In the middle of the battery is a metal rod that acts as a current pickup that connects to the bottom of the battery (the negative terminal).

Alkaline batteries are the most popular batteries today.  Because they have a higher energy density than a zinc-carbon battery.  Meaning that an alkaline battery will produce more useable power than a comparable sized zinc-carbon battery.  And they have a longer shelf life.  But with these benefits comes costs.  They can leak a caustic potassium hydroxide.  An irritant to your eyes and skin.  As well as your respiratory system.  As they age they can produce hydrogen gas.  Which can rupture the casing.  If a battery leaks potassium carbonate (a crystalline structure) can grow.  If this crystalline structure reaches the copper tracks of a circuit board it will oxidize the copper and metallic components.  Damaging electronic devices.  But the benefits clearly outweigh the risks.  As about 80% of all batteries sold in the U.S. are alkaline batteries.

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Leyden Jar, Electric Charge, Galvanic Cell, Voltaic Pile, Anions, Cations, Daniell Cell, Zinc-Carbon Battery and Alkaline Battery

Posted by PITHOCRATES - October 2nd, 2013

Technology 101

(Originally published December 19th, 2012)

Luigi Galvani made a Dead Frog’s Leg Twitch when he hit it with the Electric Discharge Shock from a Leyden Jar

The field of electricity took off with friction generators.  Dragging something across another substance to produce an electrical charge.  Like sliding out of your car on a dry winter day.  Producing an electric discharge shock just before your hand touches the metal door to close it.  Atoms in materials are electrically neutral.  There are an equal number of positive particles (protons) and negative particles (electrons).  Friction can transfer some of those electrons from one surface to another.  Leaving one surface with a net positive charge.  And the other with a net negative charge.  These charges equalize after that electric discharge shock.  Returning the atoms in these materials to an electrically neutral state.

Further exploration of static electric charge led to the development of the Leyden jar.  A precursor to the modern capacitor.  A glass jar with metal foil on the inside and outside of a glass bottle.  The foil sheets act as plates.  The glass as a dielectric.  An electrode attached to one plate received an electric charge from a friction generator.  The other plate was grounded.  The dielectric helped the plates hold an electric charge.  Benjamin Franklin did a lot of experiments with the Leyden jar.  He noted how multiple Leyden jars could hold a greater charge.  Commenting that it was like a battery of cannons.  Giving us the word battery for an electrical storage device.

Luigi Galvani made a dead frog’s leg twitch when he zapped it with the electric discharge shock from a Leyden jar.  Furthering his experiments Galvani found that he could reproduce the twitching by placing the frog’s leg between two different types of metals.  Creating a galvanic cell.  Which created an electric current.  Alessandro Volta recreated this experiment while substituting the frog tissue with cardboard soaked in salt water (an electrolyte).  Creating the voltaic cell.  Piling one voltaic cell onto another created a Voltaic Pile.  Or as we call it today, a battery.

A Daniell Cell created a Current by Stripping away Electrons from one Electrode and Recombining them on Another

What Galvani and Volta discovered was a chemical reaction that caused an electric current.  The Voltaic Pile, though, had a limited life.  To improve on it John F. Daniell added a second electrolyte.  Creating the Daniell Cell.  Which extended the life of a battery charge.  Allowing it to do useful work.  Becoming the first commercially successful battery.  Powering our first telegraphs and telephones.  Even finding their way into our homes operating our doorbells for a century or so before Nikola Tesla brought alternating current electric power to our homes.

The chemical reaction in a Daniell Cell created an electric current by stripping away electrons from one metal electrode in a solution (anode oxidation).  And recombining electrons onto another electrode of a different metal in a different solution (cathode reduction).  Each electrode is in an electrolyte solution.  In a copper-zinc Daniell Cell the anode is typically in a solution of zinc sulfate.  And the cathode is in a copper sulfate solution.  A salt bridge or porous membrane connects the different electrolytes.  When an electric load is connected across the ‘battery’ electrodes it completes the electrochemical system.

Each electrolyte contains ions.  Atoms with a net positive or negative charge.  Positive ions are cations.  Negative ions are anions.  The cathode attracts cations.  Where they combine with free electrons to return to a neutral state.  The anode attracts anions.   Where they give up their extra electrons to return to a neutral state.  This chemical activity dissolves the zinc electrode.  And deposits copper on the copper electrode.  (This electrolysis is the basis for the metal plating industry.)  It is the dissolving of the anode that gives up electrons that travel from one electrode through the electric load to the other electrode.  Doing work for us.  By lighting our flashlights.  Or powering our portable radio.  When the anode dissolves to the point that it cannot give up anymore electrons the chemical reaction stops.  And we have to replace our batteries.

An Alkaline Battery will produce more Useable Power and have a longer Shelf Life than a Zinc-Carbon Battery

Of course, the zinc-carbon batteries we use for our flashlights and radios are not wet cells.  They’re dry cells.  Instead of an electrolyte solution the common battery is made up of dry components.  The zinc anode is the battery casing.  Just inside the battery zinc casing is a paper layer impregnated with a moist paste of acidic ammonium chloride.  This separates the zinc can from a mixture of graphite powder and manganese (IV) oxide (pyrolusite).  In the center of the battery is a carbon rod.  The zinc casing is the negative electrode (anode) and the carbon rod is the positive electrode (the cathode).  The chemical reactions are the
same as they are with the wet cell.  The zinc casing (the anode) becomes thinner over time.  When holes begin to appear the battery will leak creating a sticky mess.  As you no doubt experienced when taking an old set of batteries out of a flashlight that hasn’t been used in years.

An alkaline battery looks similar to a zinc-carbon battery.  But there are many differences.  Instead of an acidic ammonium chloride electrolyte an alkaline battery uses an alkaline potassium hydroxide electrolyte.  The little nub (positive terminal) on top of the battery does not connect to a carbon rod in the center of the battery.  It connects to the outer casing.  Inside this casing is a mixture of graphite powder and manganese (IV) oxide (pyrolusite).  Then a barrier to keep the anode and cathode materials from coming into contact with each other.  But lets ions pass through.  On the other side of the barrier is the anode.  A gel of the alkaline potassium hydroxide electrolyte containing a dispersion of zinc powder.  In the middle of the battery is a metal rod that acts as a current pickup that connects to the bottom of the battery (the negative terminal).

Alkaline batteries are the most popular batteries today.  Because they have a higher energy density than a zinc-carbon battery.  Meaning that an alkaline battery will produce more useable power than a comparable sized zinc-carbon battery.  And they have a longer shelf life.  But with these benefits comes costs.  They can leak a caustic potassium hydroxide.  An irritant to your eyes and skin.  As well as your respiratory system.  As they age they can produce hydrogen gas.  Which can rupture the casing.  If a battery leaks potassium carbonate (a crystalline structure) can grow.  If this crystalline structure reaches the copper tracks of a circuit board it will oxidize the copper and metallic components.  Damaging electronic devices.  But the benefits clearly outweigh the risks.  As about 80% of all batteries sold in the U.S. are alkaline batteries.

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Heart Attacks and Defibrillators

Posted by PITHOCRATES - May 29th, 2013

Technology 101

Moving Electrons from one Atom to another creates a Positively and a Negatively Charged Atom

Too much humidity can make one uncomfortable.  It can labor your breathing.  Make you sweat so much that you stick to everything.  Making it feel hotter than it is (it’s not the heat; it’s the humidity).  And play havoc with well-coiffed ladies.  As excessive humidity can straighten the finest curl.  That’s why we like the spring and fall.  When there are warm days without the humidity.  Winters, on the other hand, are just too cold.  And uncomfortable humidity-wise.  They’re not too humid.  But too dry.  Giving us dried and cracked skin.  Bloody noses.  And painful electrical shocks.  As anyone can attest to who has slid out of a car only to get a big static spark when they pushed the door close.

What causes that static electric spark?  When you slide your buttocks over the car seat to get out of the car you are charging a capacitor.  By stripping electrons away from atoms.  Leaving atoms with fewer electrons than protons.  Giving them a positive charge.  And atoms with more electrons than protons.  Giving them a negative charge.  Atoms prefer to be electrical neutral.  Which is why when we reach for that metal door those excess electrons jump the air-gap as soon as they can.  So both atoms can return to a neutral state.  Until the next time we drag our buttocks across the seat.

These electric discharges can be painful.  And annoying as they scare the bejesus out of you when you’re not expecting it.  But this is not all that capacitors do.  As it turns out this charging ability has a lot of uses.  They are in pretty much every piece of electrical and electronic equipment we use.  We use them to condition power.  For power factor correction.  Signal processing.  Noise filters.  Tuned circuits (as used in a radio dial to tune in a station).  And energy storage.  Which is what we do when we drag ourselves across a car seat.  We’re storing energy that we discharge later.  In a car it just annoys us.  But it can act like a temporary battery when we change the batteries in something with a volatile memory.  So we don’t lose the songs on our MP3 player when we change the batteries.  And the energy they store can even save lives.

A Defibrillator sends an Electric Charge through an Irregularly Beating Heart to Shock it back into Rhythm

In the movie The Matrix the machines took over the world.  And used humans as batteries to power their machines.  Because a human is a little like an electrical battery.  It creates electricity that operates the human body.  For the human body is controlled by electrical impulses sent along our nervous system.  These electrical impulses even make our hearts pump.  The heart itself is ‘wired’ to transmit this pulse in a delayed mode to the various tissue in the heart.  First a pulse contracts the two top chambers (atria).  This contraction empties the blood they hold into the two bottom chambers (ventricles).  Then after a delay that same pulse contracts the ventricles.  Pushing the blood out and through the body.  When a doctor looks at an EKG he or she can see how that pulse propagates through the heart.  And determine if it’s healthy (showing a normal sinus rhythm).  Or if there was some cardiac event that has altered the normal sinus rhythm.

If a heart doesn’t have a normal sinus rhythm it can lead to cardiac arrest (i.e., a heart attack).  An arrhythmia (irregular heartbeat) can be a fast heartbeat.  A slow heartbeat.  Or it may be an irregular heartbeat.  Which is due to abnormal electrical activity in the heart.  And can lead to ventricular fibrillation.  Where the muscles don’t contract in a coordinated fashion with the proper delays propagating through the heart tissues to pump the blood.  But instead contract without this coordination.  Causing the heart muscles to quiver instead.  If this continues more than a few seconds the heart may stop.  With an EKG showing a flat line.  With no blood flowing organs begin shutting down.  Causing irreversible damage.  And if a normal sinus rhythm isn’t restored within 90 seconds once a person goes into v-fib the chance of survival from this cardiac event are pretty much zero.

In the movies and on television when a patient goes into v-fib they sometimes show the patient flat-lining when they rush in the crash cart.  They rub gel on the paddles of a defibrillator.  Yell ‘clear’ and shock the patient.  Sometimes with the patient jerking wildly from the jolt from the paddles.  They may do this a couple of times until they hear the flat-line begin beeping again in a sinus rhythm.  It doesn’t really happen like that, though.  If a person is flat-lining a jolt from a defibrillator won’t bring them back.  Some medicine shot into the heart and chest compressions might.  But not an electric shock.  The use of a defibrillator sends an electric charge through a heart beating with an irregular rhythm to shock it back into a normal rhythm.  Sort of like banging on an electronic device to get it working properly again.  With the physical shock perhaps jiggling a loose component back into connection with something.  It can sometimes make the device work again.  But it won’t make it work if the cord is unplugged or if the batteries had been removed.

Portable Defibrillators have a Charged Battery that Charges a Capacitor

Early defibrillators were AC devices that plugged into a wall outlet.  They had a big transformer to step up the voltage.  But they were big and bulky and difficult to move around in a crowded room.  And they didn’t work that well.  Rarely pulling a patient out of v-fib.  And sometimes damaged the heart tissue as much as the heart attack.  In 1959 the AC defibrillator was replaced with one using charged capacitors.  This is the type we see in the movies and on television.  And use in real life.

If a patient goes into cardiac arrest they set the charge level for the given arrhythmia.  As the capacitors charge the person who will use it removes the paddles while someone else applies an electrically conducting gel to the paddles.  The person then places the paddles on the patient with force to ensure a good electrical connection.  And waits for the unit to finish charging.  Once charged anyone working on the patient breaks any contact they have with the patient so they won’t get shocked, too.  When everyone one and everything is clear the person will focus on the EKG for the appropriate point in the rhythm to press a button that discharges the capacitors.  Causing the stored energy to flow from one paddle to the other through the heart.  To reset the arrhythmia into a normal sinus rhythm.

Time is critical in surviving a heart attack.  So using a defibrillator as soon as possible increased a person’s chances of surviving from a heart attack.  Making defibrillators portable allowed paramedics to use them in the field.  Before they got the patient to a hospital.  These portable units have a charged battery that charges a capacitor.  Electronics and computer controls even allow ordinary people to use an automated external defibrillator (AED).  You will see AEDs in crowded areas like airports, shopping malls, casinos, etc.  Anywhere a large concentration of elderly men (the most likely to suffer cardiac arrest) may congregate.  This device often triggers a security alarm when removed to alert first responders.  Someone who witnesses a person suffering a heart attack can follow automated voice instructions from the AED and hook it up on the patient.  The AED will analyze the arrhythmia.  Set the appropriate charge level.  But usually requires someone to press a button for the shock.  To give everyone a chance to get clear from the person before the capacitor discharges its energy.  Because if they are in contact with that body when that charge hits it they may have more than a bad hair day afterwards.  Perhaps even sending their own heart into arrhythmia.  As this shock will be nothing like the one they get after sliding out of a car on a dry winter’s day.

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Lead–Acid Battery, Nickel–Cadmium Battery (NiCd), Nickel–Metal Hydride Battery (NiMH) and Lithium-Ion Battery

Posted by PITHOCRATES - January 9th, 2013

Technology 101

The Chemical Reactions in a Zinc-Carbon Battery are One Way

A battery uses chemistry to make electricity.  An electric current is a flow of electrons that can do useful work.  The chemical reaction inside a battery creates that flow of electrons to produce an electric current.  In a common zinc-carbon battery, for example, a zinc electrode dissolves in an electrolyte.  As it does atoms release free electrons and become positive ions (cations) in the electrolyte.  Giving this solution a positive charge.  At the same time a carbon electrode is in a different electrolyte solution.  One filled with negative ions (anions).  Giving this solution a negative charge.

With no electrical load attached to the battery these electrodes and electrolytes are in equilibrium.  When we attach an external circuit across the battery terminals they provide a pathway for those free electrons.  As the free electrons travel through the external circuit the cations and anions travel through a porous membrane from one electrolyte to the other.  The positive cations (atoms with room for an additional electron) flow towards the carbon electrode.  And combine with the free electrons on the surface of the carbon electrode and become electrically neutral.

We can stop this chemical reaction.  Say by turning a flashlight or a portable radio off.  But we can’t reverse it.  This is a one-way chemical reaction that eventually dissolves away the anode.  A Zinc-carbon battery is inexpensive.  The amount of battery life we get out of it more than offsets the price.  And they’re easy to change.  But sometimes an application calls for a battery that isn’t easy to change.  Like a car battery.  Imagine having to change that a few times a year when it ran down.  No, that would be far too inconvenient.  Difficult.  And costly.  So we don’t.  Instead, we recharge car batteries.

The Chemical Reactions in a Lead-Acid Battery are Reversible allowing these batteries to be Recharged

A car battery is a lead-acid battery.  Each cell of a lead-acid battery has a positive electrode (i.e., plate) of lead dioxide.  A negative electrode of lead.  And an electrolyte of a sulfuric acid-water solution containing sulfate ions.  The lead chemically reacts with the sulfate ions to produce lead sulfate on the negative electrode while producing positive ions.  The lead dioxide chemically reacts with the sulfuric acid to produce lead sulfate on the positive electrode while giving up free electrons.

When we attach an external circuit to the battery (such as starting a car) the free electrons leave the positive electrode, travel through the external circuit and return to the battery.  Where they combine with those positive ions.  Lead sulfate forms on both electrodes.  These reactions consume the sulfuric acid in the electrolyte and leave mostly water behind.  Reducing the available charge in the battery.  But unlike zinc-carbon batteries these chemical reactions are reversible.  After a car starts, for example, the alternator provides the electric power needs of the car.  While applying a charging voltage to the battery.  This voltage will ionize the water in the battery which will break down the lead sulfate.  Deposit lead oxide back onto the positive electrode.  And deposit lead back onto the negative electrode.  Giving you a charged battery for the next time you need to start your engine.

A lead acid battery can provide a strong current to spin an internal combustion engine.  Which takes a lot of energy to fight the compression of the pistons.  And it can work in some very cold temperatures.  But it’s big and heavy.  And works best in things bigger and heavier.  Like cars.  Trucks.  Trains.  And ships.  But they don’t work well in things that are smaller and lighter.  Like cordless power tools.  Cell phones.  And laptop computers.  Things where battery weight is an important issue.  Requiring an alternative to the lead-acid battery.  One of the earliest rechargeable battery alternatives was the nickel–cadmium battery.  Or NiCad battery.

The Chemical Reactions produce Heat in a Lithium Ion Battery and can Catch Fire or Explode

The nickel–cadmium battery works like every other battery.  With chemical reactions that produce electrons.  And chemical reactions that consumes electrons.  The NiCad battery uses nickel (III) oxide-hydroxide for the positive electrode.  Cadmium for the negative electrode.  And potassium hydroxide as the electrolyte.  A NiCad battery may look like a zinc-carbon battery.  But the electrodes are different.  Instead of the zinc canister and a carbon rod the electrodes in a NiCad battery are long strips.  One is placed onto the other with a separator in between.  Then rolled up like a jelly-roll.

NiCad batteries have a memory effect.  If they were recharged without being fully discharged the battery ‘remembers’ the amount of charge it took to recharge the partially discharged battery.  So even if you fully discharged the battery it would only recharge it as if you partially discharged it.  Reducing the battery capacity over time.  The nickel–metal hydride battery (NiMH) eliminated this problem.  And improved on the NiCad.  Giving it 2-3 times the capacity of a NiCad battery.  NiCad and NiMH batteries are very similar.  They use the same positive electrode.  But instead of the highly toxic cadmium NiMH batteries use a mixture of a rare earth metal mixed with another metal.

Today battery technology has evolved into the lithium-ion battery.  Where the positive electrode is a compound containing lithium.  The negative electrode is typically graphite.  The electrolyte is a lithium salt.  Lithium ions travel between the electrodes through the electrolyte.  And electrons flow between the electrodes via the external circuit.  They have a greater capacity, no memory effect and hold their charge for a long time when not being used.  Making the lithium ion battery ideal for cell phones and other consumer electronics.  These chemical reactions produce heat, though.  And can catch fire or explode.  Trying to prevent this from happening increases their manufacturing costs, making them expensive batteries.  So expensive that people will buy cheaper generic brands.  Cheaper because they are not built to the same quality standards of the more expensive ones.  And are more prone to catching fire or exploding.

Something to think about when you feel the heat of your cell phone after a long conversation.  Only use a battery recommended by the manufacturer.  Even if it costs a small fortune.  It may be expensive.  But probably not as expensive as your monthly airtime charges.  So don’t skimp when it comes to lithium ion batteries.  For those cheap ones do have a tendency to catch fire.  Or explode.

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Leyden Jar, Electric Charge, Galvanic Cell, Voltaic Pile, Anions, Cations, Daniell Cell, Zinc-Carbon Battery and Alkaline Battery

Posted by PITHOCRATES - December 19th, 2012

Technology 101

Luigi Galvani made a Dead Frog’s Leg Twitch when he hit it with the Electric Discharge Shock from a Leyden Jar

The field of electricity took off with friction generators.  Dragging something across another substance to produce an electrical charge.  Like sliding out of your car on a dry winter day.  Producing an electric discharge shock just before your hand touches the metal door to close it.  Atoms in materials are electrically neutral.  There are an equal number of positive particles (protons) and negative particles (electrons).  Friction can transfer some of those electrons from one surface to another.  Leaving one surface with a net positive charge.  And the other with a net negative charge.  These charges equalize after that electric discharge shock.  Returning the atoms in these materials to an electrically neutral state.

Further exploration of static electric charge led to the development of the Leyden jar.  A precursor to the modern capacitor.  A glass jar with metal foil on the inside and outside of a glass bottle.  The foil sheets act as plates.  The glass as a dielectric.  An electrode attached to one plate received an electric charge from a friction generator.  The other plate was grounded.  The dielectric helped the plates hold an electric charge.  Benjamin Franklin did a lot of experiments with the Leyden jar.  He noted how multiple Leyden jars could hold a greater charge.  Commenting that it was like a battery of cannons.  Giving us the word battery for an electrical storage device.

Luigi Galvani made a dead frog’s leg twitch when he zapped it with the electric discharge shock from a Leyden jar.  Furthering his experiments Galvani found that he could reproduce the twitching by placing the frog’s leg between two different types of metals.  Creating a galvanic cell.  Which created an electric current.  Alessandro Volta recreated this experiment while substituting the frog tissue with cardboard soaked in salt water (an electrolyte).  Creating the voltaic cell.  Piling one voltaic cell onto another created a Voltaic Pile.  Or as we call it today, a battery.

A Daniell Cell created a Current by Stripping away Electrons from one Electrode and Recombining them on Another

What Galvani and Volta discovered was a chemical reaction that caused an electric current.  The Voltaic Pile, though, had a limited life.  To improve on it John F. Daniell added a second electrolyte.  Creating the Daniell Cell.  Which extended the life of a battery charge.  Allowing it to do useful work.  Becoming the first commercially successful battery.  Powering our first telegraphs and telephones.  Even finding their way into our homes operating our doorbells for a century or so before Nikola Tesla brought alternating current electric power to our homes.

The chemical reaction in a Daniell Cell created an electric current by stripping away electrons from one metal electrode in a solution (anode oxidation).  And recombining electrons onto another electrode of a different metal in a different solution (cathode reduction).  Each electrode is in an electrolyte solution.  In a copper-zinc Daniell Cell the anode is typically in a solution of zinc sulfate.  And the cathode is in a copper sulfate solution.  A salt bridge or porous membrane connects the different electrolytes.  When an electric load is connected across the ‘battery’ electrodes it completes the electrochemical system.

Each electrolyte contains ions.  Atoms with a net positive or negative charge.  Positive ions are cations.  Negative ions are anions.  The cathode attracts cations.  Where they combine with free electrons to return to a neutral state.  The anode attracts anions.   Where they give up their extra electrons to return to a neutral state.  This chemical activity dissolves the zinc electrode.  And deposits copper on the copper electrode.  (This electrolysis is the basis for the metal plating industry.)  It is the dissolving of the anode that gives up electrons that travel from one electrode through the electric load to the other electrode.  Doing work for us.  By lighting our flashlights.  Or powering our portable radio.  When the anode dissolves to the point that it cannot give up anymore electrons the chemical reaction stops.  And we have to replace our batteries.

An Alkaline Battery will produce more Useable Power and have a longer Shelf Life than a Zinc-Carbon Battery

Of course, the zinc-carbon batteries we use for our flashlights and radios are not wet cells.  They’re dry cells.  Instead of an electrolyte solution the common battery is made up of dry components.  The zinc anode is the battery casing.  Just inside the battery zinc casing is a paper layer impregnated with a moist paste of acidic ammonium chloride.  This separates the zinc can from a mixture of graphite powder and manganese (IV) oxide (pyrolusite).  In the center of the battery is a carbon rod.  The zinc casing is the negative electrode (anode) and the carbon rod is the positive electrode (the cathode).  The chemical reactions are the same as they are with the wet cell.  The zinc casing (the anode) becomes thinner over time.  When holes begin to appear the battery will leak creating a sticky mess.  As you no doubt experienced when taking an old set of batteries out of a flashlight that hasn’t been used in years.

An alkaline battery looks similar to a zinc-carbon battery.  But there are many differences.  Instead of an acidic ammonium chloride electrolyte an alkaline battery uses an alkaline potassium hydroxide electrolyte.  The little nub (positive terminal) on top of the battery does not connect to a carbon rod in the center of the battery.  It connects to the outer casing.  Inside this casing is a mixture of graphite powder and manganese (IV) oxide (pyrolusite).  Then a barrier to keep the anode and cathode materials from coming into contact with each other.  But lets ions pass through.  On the other side of the barrier is the anode.  A gel of the alkaline potassium hydroxide electrolyte containing a dispersion of zinc powder.  In the middle of the battery is a metal rod that acts as a current pickup that connects to the bottom of the battery (the negative terminal).

Alkaline batteries are the most popular batteries today.  Because they have a higher energy density than a zinc-carbon battery.  Meaning that an alkaline battery will produce more useable power than a comparable sized zinc-carbon battery.  And they have a longer shelf life.  But with these benefits comes costs.  They can leak a caustic potassium hydroxide.  An irritant to your eyes and skin.  As well as your respiratory system.  As they age they can produce hydrogen gas.  Which can rupture the casing.  If a battery leaks potassium carbonate (a crystalline structure) can grow.  If this crystalline structure reaches the copper tracks of a circuit board it will oxidize the copper and metallic components.  Damaging electronic devices.  But the benefits clearly outweigh the risks.  As about 80% of all batteries sold in the U.S. are alkaline batteries.

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Electric Grid, Voltage, Current, Power, Phase Conductor, Neutral Conductor, 3-Phase Power, Transmission Towers and Corona Discharge

Posted by PITHOCRATES - August 15th, 2012

Technology 101

The Electric Grid is the Highways and Byways for Electric Power from the Power Plant to our Homes

Even our gasoline-powered cars operate on electricity.  The very thing that ignites the air-fuel mixture is an electric spark.  Pushed across an air-gap by a high voltage.  Because that’s something that high voltages do.  Push electrons with such great force that they can actually leave a conductor and travel through the air to another conductor.  Something we don’t want to happen most of the time.  Unless it’s in a spark plug in our gasoline engine.  Or in some movie prop in a cheap science fiction movie.

No.  When we use high voltage to push electrons through a conductor the last thing we want to happen is for the electrons to leave that conductor.  Because we spend a pretty penny to push those electrons out of a power plant.  And if we push the electrons out of the conductor they won’t do much work for us.  Which is the whole point of putting electricity into the electric grid.  To do work for us.

The electric grid.  What exactly is it?  The highways and byways for electric power.  Power plants produce electric power.  And send it to our homes.  As well as our businesses.  Power is the product of voltage and current.  In our homes something we plug into a 120V outlet that draws 8 amps of current consumes 960 watts.  Which is pretty big for a house.  But negligible for a power plant generator producing current at 20,000 volts.  For at 20,000 volts a generator only has to produce 0.48 amps (20,000 X 0.48 = 960).  Or about 6% of the current at 120V.

Between our Homes and the Power Plant we can Change that Current by Changing the Voltage

Current is money.  Just as time is money.  In fact current used over time helps to determine your electric bill.  Where the utility charges you for kilowatt hours (voltage X current X time).  (This would actually give you watt-hours.  You need to divide by 1000 to get kilowatt hours.)  The electric service to your house is a constant voltage.  So it’s the amount of current you use that determines your electric bill.  The more current you use the greater the power you use.  Because in the power equation (voltage X current) voltage is constant while current increases.

Current travels in conductors.  The size of the conductor determines a lot of costs.  Think of automobile traffic.  Areas that have high traffic volumes between them may have a very expensive 8-lane Interstate expressway interconnecting them.  Whereas a lone farmer living in the ‘middle of nowhere’ may only have a much less expensive dirt road leading to his or her home.  And so it is with the electric grid.  Large consumers of electric power need an Interstate expressway.  To move a lot of current.  Which is what actually spins our electrical meters.  Current.  However, between our homes and the power plant we can change that current.  By changing the voltage.  Thereby reducing the cost of that electric power Interstate expressway.

The current flowing through our electric grid is an alternating current.  It leaves the power plant.  Travels in the conductors for about 1/120 of a second.  Then reverses direction and heads back to the power plant.  And reverses again in another 1/120 of a second.  One complete cycle (travel in both directions) takes 1/60 of a second.  And there are 60 of these complete cycles per second.  Hence the alternating current.  If you’re wondering how this back and forth motion in a wire can do any work just think of a steam locomotive.  Or a gasoline engine.  Where a reciprocating (back and forth) motion is converted into rotational motion that can drive a steam locomotive.  Or an automobile.

The Voltages of our Electric Grid balance the Cost Savings (Smaller Wires) with the Higher Costs (Larger Towers)

An electric circuit needs two conductors.  When current is flowing away from the power plant in one it is flowing back to the power plant in the other.  As the current changes direction is has to stop first.  And when it stops flowing the current is zero.  Using the power formula this means there are zero watts twice a cycle.  Or 120 times a second.  Which isn’t very efficient.  However, if you bring two other sets of conductors to the work load and time the current in them properly you can remove these zero-power moments.  You send the first current out in one set of conductors and wait 1/3 of a cycle.  Then you send the second current out in the second set of conductors and wait another 1/3 cycle.  Then you send the third current out in the third set of conductors.  Which guarantees that when a current is slowing to stop to reverse direction there are other currents moving faster towards their peak currents in the other conductors.  Making 3-phase power more efficient than single-phase power.  And the choice for all large consumers of electric power.

Anyone who has ever done any electrical wiring in their home knows you can share neutral conductors.  Meaning more than one circuit coming from your electrical panel can share the return path back to the panel.  If you’ve ever been shocked while working on a circuit you switched off in your panel you have a shared neutral conductor.  Even though you switched off the circuit you were working on another circuit sharing that neutral was still switched on and placing a current on that shared neutral.  Which is what shocked you.  So if we can share neutral conductors we don’t need a total of 6 conductors as noted above.  We only need 4.  Because each circuit leaving the power plant (i.e., phase conductor) can share a common neutral conductor on its way back to the power plant.  But the interesting thing about 3-phase power is that you don’t even need this neutral conductor.  Because in a balanced 3-phase circuit (equal current per phase) there is no current in this neutral conductor.  So it’s not needed as all the back and forth current movement happens in the phase conductors.

Electric power travels in feeders that include three conductors per feeder.  If you look at overhead power lines you will notice they all come in sets of threes when they get upstream of the final transformer that feeds your house.  The lines running along your backyard will have three conductors across the top of the poles.  As they move back to the power plant they pass through additional transformers that increase their voltage (and reduce their current).  And the electric transmission towers get bigger.  With some having two sets of 3-conductor feeders.  The higher the voltage the higher off the ground they have to be.  And the farther apart the phase conductors have to be so the high voltage doesn’t cause an arc to jump the ‘air gap’ between phase conductors.  As you move further away from your home back towards the power plant the voltage will step up to values like 2.4kV (or 2,400 volts), 4.8kV and13.2kV that will typically take you back to a substation.  And then from these substations the big power lines head back towards the power plant.  On even bigger towers.  At voltages of 115kV, 138kV, 230kV, 345kv, 500kV and as high as 765kV.  When they approach the power plant they step down the voltage to match the voltage produced by its generators.

They select the voltages of our electric grid to balance the cost savings (smaller wires) with the higher costs (larger towers taking up more land).  If they increase the voltage so high that they can use very thin and inexpensive conductors the towers required to transmit that voltage safely may be so costly that they exceed the cost savings of the thinner conductors.  So there is an economic limit on voltage levels  As well as other considerations of very high voltages (such as corona discharge where high voltages create such a power magnetic field around the conductors that it may ionize the air around it causing a sizzling sound and a fuzzy blue glow around the cable.  Not to mention causing radio interference.  As well as creating some smog-causing pollutants like ozone and nitrogen oxides.)

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Neutrons, Electrons, Electric Current, Nuclear Power, Nuclear Chain Reaction, Residual Decay Heat and Pressurized Water Reactor

Posted by PITHOCRATES - July 18th, 2012

Technology 101

We create about Half of our Electric Power by Burning Coal to Boil Water into Steam

An atom consists of a nucleus made up of protons and neutrons.  And electrons orbiting around the nucleus.  Protons have a positive charge.  Electrons have a negative charge.  Neutrons have a neutral charge.  In chemistry and electricity the electrons are key.  When different atoms come together they form chemical bonds.  By sharing some of those electrons orbiting their nuclei.  In metals free electrons roam around the metal lattice of the crystalline solid they’re in.  If we apply a voltage across this metal these free electrons begin to flow.  Creating an electric current.  The greater the voltage the greater the current.  And the greater the work it can do.  It can power a television set.  Keep your food from spoiling in a refrigerator.  Even make your summers comfortable by running your air conditioner. 

We use electric power to do work for us.  Power is the product of voltage and current.  The higher each is the more work this power can do for us.  In a direct current (DC) system the free electrons have to make a complete path from the power source (an electric generator) through the wiring to the work load and back again to the power source.  But generating the power at the voltage of the workload required high currents.  Thick wires.  And a lot of power plants because you could only make wires so thick before they were too heavy to work with.  Alternating current (AC) solved this problem.  By using transformers at each end of the distribution path to step up and then step down the voltage.  Allowing us to transmit lower currents at higher voltages which required thinner wires.  And AC didn’t need to return to the power plant.  It was more like a steam locomotive that converted the back and forth motion of the steam engine into rotational power.  AC power plants generated a back and forth current in the wires.  And electrical loads are able to take this back and forth motion and convert it into useful electrical power.

Even though AC power allows us to transmit lower currents we still need to move a lot of these free electrons.  And we do this with massive electric generators.  Where another power source spins these generators.  This generator spins an electric field through another set of windings to induce an electrical current.  Sort of how transformers work.  This electrical current goes out to the switchyard.  And on to our homes.  Simple, really.  The difficult part is creating that rotational motion to spin the generator.  We create about half of our electric power by burning coal to boil water into steam.  This steam expands against the vanes of a steam turbine causing it to spin.  But that’s not the only heat engine we use to make steam.

To Shut Down a Nuclear Reactor takes the Full Insertion of the Control Rods and Continuously Pumping Cooling Water through the Core

We use another part of the atom to generate heat.  Which boils water into steam.  That we use to spin a steam turbine.  The neutron.  Nuclear power plants use uranium for fuel.  It is the heaviest naturally occurring element.  The density of its nucleus determines an element’s weight.  The more protons and neutrons in it the heavier it is.  Without getting into too much physics we basically get heat when we bombard these heavy nuclei with neutrons.  When a nucleus splits apart it throws off a few spare neutrons which can split other nuclei.  And so on.  Creating a nuclear chain reaction.  It’s the actual splitting of these nuclei that generates heat.  And from there it’s just boiling water into steam to spin a steam turbine coupled to a generator.

Continuous atom splitting creates a lot of heat.  So much heat that it can melt down the core.  Which would be a bad thing.  So we move an array of neutron absorbers into and out of the core to control this chain reaction.  So in the core of a nuclear reactor we have uranium fuel pellets loaded into vertical fuel rods.  There are spaces in between these fuel rods for control rods (made out of carbon or boron) to move in and out of the core.  When we fully insert the control rods they will shut down the nuclear chain reaction by absorbing those free neutrons.  However there is a lot of residual heat (i.e., decay heat) that can cause the core to melt if we don’t remove it with continuous cooling water pumped through the core. 

So to shut down a nuclear reactor it takes both the full insertion of the control rods.  And continuously pumping cooling water through the core for days after shutting down the reactor.  Even spent fuel rods have to spend a decade or two in a spent fuel pool.  To dissipate this residual decay heat.  (This residual decay heat caused the trouble at Fukushima in Japan after their earthquake/tsunami.  The reactor survived the earthquake.  But the tsunami submerged the electrical gear that powered the cooling pumps.  Preventing them from cooling the core to remove this residual decay heat.  Leading to the partial core meltdowns.)

Nuclear Power is one of the most Reliable and Cleanest Sources of Power that leaves no Carbon Footprint

There is more than one nuclear reactor design.  But more than half in the U.S. are the Pressurized Water Reactor (PWR) type.  It’s also the kind they had at Three Mile Island.  Which saw America’s worst nuclear accident.  The PWR is the classic nuclear power plant that all people fear.  The tall hyperboloid cooling towers.  And the short cylindrical containment buildings with a dome on top housing the reactor.  The reactor itself is inside a humongous steel pressure vessel.  For pressure is key in a PWR.  The cooling water of the reactor is under very high pressure.  Keeping the water from boiling even though it reaches temperatures as high as 600 degrees Fahrenheit (water boils into steam at 212 degrees Fahrenheit under normal atmospheric pressure).  This is the primary loop.

The superheated water in the primary loop then flows through a heat exchanger.  Where it heats water in another loop of pumped water.  The secondary loop.  The hot water in the primary loop boils the water in the secondary loop into steam.  As it boils the water in the secondary loop it loses some of its own heat.  So it can return to the reactor core to remove more of its heat.  To prevent it from overheating.  The steam in the secondary loop drives the steam turbine.  The steam then flows from the turbine to a condenser and changes back into water.  The cooling water for the condenser is what goes to the cooling tower.  Making those scary looking cooling towers the least dangerous part of the power plant.

The PWR is one of the safest nuclear reactors.  The primary cooling loop is the only loop exposed to radiation.  The problem at Three Mile Island resulted from a stuck pressure relief valve.  That opened to vent high pressure during an event that caused the control rods to drop in and shut down the nuclear chain reaction.  So while they stopped the chain reaction the residual decay heat continued to cook the core.  But there was no feedback from the valve to the control room showing that it was still open after everyone thought it was closed.  So as cooling water entered the core it just boiled away.  Uncovering the core.  And causing part of it to melt.  Other problems with valves and gages did not identify this problem.  As some of the fuel melted it reacted with the steam producing hydrogen gas.  Fearing an explosion they vented some of this radioactive gas into the atmosphere.  But not much.  But it was enough to effectively shut down the U.S. nuclear power industry. 

A pity, really.  For if we had pursued nuclear power these past decades we may have found ways to make it safer.  Neither wind power nor solar power is a practical substitution for fossil-fuel generated electricity.  Yet we pour billions into these industries in hopes that we can advance them to a point when they can be more than a novelty.  But we have turned away from one of the most reliable and cleanest sources of power (when things work properly).  Using neutrons to move electrons.  Taking complete control of the atom to our make our lives better.  And to keep our environment clean.  And cool.  For there is no carbon footprint with nuclear power.

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Silicon, Semiconductor, LED, Photon, Photovoltaic Effect, Photocell, Solar Panel, Converter, Battery and Solar Power Plant

Posted by PITHOCRATES - July 4th, 2012

Technology 101

A Photocell basically works like a Light Emitting Diode (LED) in Reverse

Solar power is based on the same technology that that gave us the electronic world.  Silicon.  That special material in the periodic table that has four electrons in its valence (i.e., outer most) shell.  And four holes that can accept an electron.  Allowing it to form a perfect silicon crystal.  When these silicon atoms come together their four valence electrons form covalent bonds with the holes in neighboring silicon atoms.  These silicon atoms share their valence electrons so that each silicon atom now has a full valence shell of eight electrons (with four of their own electrons and four shared electrons).  Making that perfect crystal structure.  Which is pretty much useless in the world of semiconductors.  Because you need free electrons to conduct electricity.

When we add impurities (called ‘doping’) to silicon is where the magic starts.  If we add a little bit of an element with five electrons in its valence shell we introduce free electrons into the silicon crystal.  Giving it a negative charge.  If we instead add a little bit of an element with 3 electrons in its valence shell we introduce extra holes looking for an electron to fill it.  Giving it a positive charge.  When we bring the positive (P) and the negative (N) materials together they from a P-N junction.  The free electrons cross the junction to fill the nearby holes.  Creating a neutrally charged depletion zone between the P and the N material.  This is a diode.  If we apply a forward biased voltage (positive battery terminal to the P side and the negative battery terminal to the N side) across this junction current will flow.  Like charges repel each other.  The negative charge pushes the free electrons on the N side of the junction towards the junction.  And the positive charge pushes the holes on the P side of the junction towards the junction.  Where they meet.  With free electrons filling available holes causing current to flow.  A reverse bias does the reverse.  Pulls the holes and electrons away from the junction so they can’t combine and cause current to flow.

It takes energy to move an electron out of its ‘hole’.  And when an electron combines with a hole it emits energy.  Typically this energy is not in a visible wavelength so we see nothing.  However, with the proper use of materials we can shift this wave length into the visible spectrum.  So we can see light.  Or photons.  This is the principle behind the light emitting diode.  Or LED.  An electric current through a P-N junction causes electrons to leave their holes and then recombine with holes.  And when they recombine they give off a photon in the visible spectrum of light.  Which is what we see.  A photocell basically works the other way.  Instead of using voltage and current to create photons we use photons from the sun to create voltage and current.

A Solar Array that could Produce 12,000 Watts under Ideal Conditions may only Produce 2,400 Watts in Reality

When we use the sun to bump electrons free from their shells we call this the photovoltaic (PV) effect.  This produces a small direct current (DC) at a low voltage.  A PV cell (or solar cell) then is basically a battery when hit with sunlight.  Electric power is the product of voltage and current.  So a small DC current and a low voltage won’t power much.  So like batteries in a flashlight we have to connect solar cells together to increase the available power.  So we connect solar cells into modules and modules into arrays.  Or what we commonly call solar panels.  Small panels can power small loads.  Like emergency telephones along the highway that are rarely used.  To channel buoys that can charge a battery during the day to power a light at night.  And, of course, the electronics on our spacecraft.  Where PV cells are very useful as there are no utility lines that run into space.

These work well for small loads.  Especially DC loads.  But it gets a little complicated for AC loads.  The kind we have in our homes.  A typical 1,000 square foot home may have a 100 amp electric service at 240 volts.  Let’s assume that at any given time there could be as much as half of that service (50 amps) in use at any one time.  That’s 12,000 watts.  Assuming a solar panel array generates about 10 watts per square foot that means this house would need approximately 1,200 square feet of solar panels (such as a 60 foot by 20 foot array or a 40 foot by 30 foot array).  But it’s not quite that simple.

The sun doesn’t shine all of the time.  The capacity factor (the percentage of actual power produced divided by the total possible it could produce under the ideal conditions) is only about 15-20%.  Meaning that a 1,200 square foot solar array that could produce 12,000 watts under ideal conditions may only produce 2,400 watts (at a 20% capacity factor).  Dividing this by 120 volts gives you 20 amps.  Or approximately the size of a single circuit in your electrical panel.  Which won’t power a lot.  And it sure won’t turn on your air conditioner.  Which means you’re probably not going to be able to disconnect from the electric grid by adding solar panels to your house.  You may reduce the amount of electric power you buy from your utility but it will come at a pretty steep cost.

Solar Power Plants can be Costly to Build and Maintain even if the Fuel is Free 

Everything in your house that uses electricity either plugs into a standard 120V electrical outlet, a special purpose 240V outlet (such as an electric stove) or is hard-wired to a 240V circuit (such as your central air conditioner).  All of these circuits go back to your electrical panel.  Which is wired to a 240V AC electrical service.  A lot of electronic devices actually operate on DC power but even these still plug into an AC outlet.  Inside these devices there is a power supply that converts the AC power into DC power.  So you’ll need to convert all that DC power generated by solar panels into useable AC power with a converter.  Which is costly.  And reduces the efficiency of the solar panels.  Because when you convert energy you always end up with less than you started with.  The electronics in the converters will heat up and dissipate some of that generated electric power as heat.  If you want to use any of this power when the sun isn’t shining you’ll need a battery to store that energy.  Another costly device.  Another place to lose some of that generated electric power.  And something else to fail.

We typically build large scale solar power plants in the middle of nowhere so there is nothing to shade these solar panel arrays.  From sun up to sun down they are in the sunlight.  They even turn and track the sun as it rises overhead, travels across the sky and sets.  To maximize the amount of sunlight hitting these panels.  Of course the larger the installation the larger the maintenance.  And the panels have to be clean.  That means washing these arrays to keep them dirt and bird poop free.  Some of the biggest plants in service today have about 200 MW of installed solar arrays.  One of the largest is in India.  Charanka Solar Park.  When completed it will have 500 MW of PV arrays on approximately 7.7 square miles of land.  With a generous capacity factor of 30% that comes to 150 MW.  Or about 19 MW/square mile.  The coal-fired Robert W. Scherer Electric Generating Plant in Georgia, on the other hand, generates 3,520 MW on approximately 18.75 square miles.  At a capacity factor of about 90% for coal that comes to about 3,168 MW.  Or about 169 MW/square mile.  About 9 times more power generated per square mile of land used.

 So you can see the reason why we use so much coal to generate our electric power.  Because coal is a highly concentrated source of fuel.  The energy it releases creates a lot of reliable electricity.  Day or night.  Summer or winter.  A large coal-fired electric generating facility needs a lot of real estate but the plants themselves don’t.  Unlike a solar plant.  Where the only way to generate more power is to cover more land with PV solar panels.  To generate, convert and store as much electric power as possible.  All with electronic equipment full of semiconductors that don’t operate well in extreme temperatures (which is why our electronics have vents, heat sinks and cooling fans).  So the ideal conditions to produce electricity are not the ideal conditions for the semiconductors making it all work.  Causing performance and maintenance issues.  Which makes these plants very costly.  Even if the fuel is free. 

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Silicon, Semiconductor, Electrons, Holes, PN Junction, Diode, LED, Photon, 7-Segment LED and Full-Color Flat Panel LED Displays

Posted by PITHOCRATES - May 30th, 2012

Technology 101

Applying a Voltage across a PN junction to Create a Forward Bias Pushes Electrons and Holes towards the Junction

There’s gold in them thar Hills.  And silicon in the valley.  California has been a fountain of wealth.  Much of which they built from two materials located on the periodic table.  Atomic number 79.  Gold.  Or ‘Au’ as it appears on the periodic table.  And atomic number 14.  Silicon.  Or ‘Si’ as it appears on the periodic table.  Both of these metals proved to be valuable.  One by its scarcity.  One by what we could do with it.  For it was anything but scarce.  Silicon is the second most common element behind only oxygen.  But this commonly found material proved to be a greater font of wealth for California.  For it fueled the semiconductor industry.  For when we doped it with impurities we produced negatively (N-type) and positively (P-type) charged material.  Bringing the N and the P together gave us the PN junction.  Giving us the diode, transistor and integrated circuit.

The miracle of semiconductors occurs at the atomic level.  Down to the electrons orbiting the atom’s nucleus.  The nucleus contains an equal number of positively charged protons and neutrally charged neutrons.  The number of protons gives us the atomic number.  Changing the number of neutrons gives us isotopes.  Radioactive material has more protons than neutrons.  Uranium-235 is an isotope.  The stuff that made the atomic bomb dropped on Hiroshima.  Electrons orbit the nucleus.  In discrete energy levels.  The orbits closest to the nucleus have the lowest energy levels.  The orbits father away from the nucleus have higher energy levels.  Most of these orbits are ‘full’ of electrons.  The outer electron shell when ‘full’ is inert.  An outer shell that isn’t ‘full’ or has extra electrons is active.  And can chemically react.  Forming molecules.  When chemicals come into contact with each other and form molecules it is these electrons in the outer orbits (or valence electrons) that move into and out of the orbits of the different chemicals.  That is, the different elements share these valence electrons.

This is what we do when we dope silicon with impurities.  We either remove electrons from the valence shell to create a net positive charge.  Or we add electrons to the valence shell to create a net negative charge.  Giving us P-type and N-type material.  At the PN junction the N-type material loses its excess electrons to the P-type material across the junction as the empty holes in the valence shell attract the excess electrons.  As electrons leave the valence shells in the N-type material they leave holes in the valence shell where they once were.  Or, in the world of electronics, as electrons flow one way holes flow the other.  When we apply a voltage across a PN junction to create a forward bias (negative voltage applied to N-type and positive voltage applied to P-type) we push electrons and holes towards the junction.  If the forward bias is great enough they will continue all the way through the junction and into the material on the far side.  Where electrons will combine with excess holes.  And holes will combine with excess electrons.  Creating an electric current.  If we apply a voltage to create a reverse bias we will pull electrons and holes away from the PN junction.  And there will be no electrical current. We call such a PN device a diode.  A very important and indispensible device in electronics.

Placing Seven LEDs into a Figure-Eight Pattern created the Seven-Segment LED

Now back to those discrete energy levels.  There is another useful property we get when electrons move between these energy levels.  Electrons absorb energy when they move to a higher energy level.  And emit energy when they move to a lower energy level.  We make use of this property in fluorescent lighting.  A charged plasma field in a fluorescent lamp excites a small amount of mercury in the lamp.  As electrons fall into lower orbits in the mercury atoms they release invisible short-wave ultraviolet radiation.  The phosphor coating on the inside of the lamp absorbs this radiation and fluoresces.  Creating visible light.  By using different materials, though, we could see the energy (a photon) emitted by an electron falling into a lower energy level.  We have been able to move the wavelength of this photon into the visible spectrum.  The first commercial application to convert these photons into visible light was a device that gave us a red light.  That device was that important and indispensible PN-junction.  The diode.  And the use of different materials other than silicon moved these photons into the visible spectrum.  Giving us the light-emitting diode.  Or LED.

The first LEDs were only red.  Then we developed other colors using different materials.  Shifting the wavelength of the photon through all colors of the visible spectrum.  Being low-power devices, though, the intensity of light emitted was limited.  So an LED required careful mechanical construction and optics.  To direct the light out of the material forming the PN junction.  With a reflector behind the junction.  And a lens above.  To aim and diffuse the light.  And to prevent it from reflecting back into the material where it may be dissipated as heat.  Early use of LEDs was for indicator lights.  The low power consumption meant little heat was generated as with an incandescent lamp.  Which worked well in the temperature sensitive computer world.  Placing 7 LEDs into a figure-eight pattern created the seven-segment LED display.  With a rectangular shaped piece of translucent plastic above each LED you could see a bar of light for each light emitting diode.  Creating a forward bias on certain bars in the seven-segment display created the numbers we saw on our first calculators and digital watches.

An LED could produce a similar radiation like in the fluorescent lamp.  Using that radiation to fluoresce a phosphor coating inside a lamp to produce white light.  Similar to the fluorescence lamp.  Only while using less power.  Mixing the emitted light from red, green and blue (RGB) LEDs also produced white light.  Further improvements allowed us to emit whiter and brighter lights.  Allowing brighter lamps that consumed less power than the compact fluorescent lamps which were energy saving alternatives to the incandescent lamps.  With the lower power consumption of LEDs creating less heat we expanded the lifespan of lighting sources made from LEDs.  Using them to increase the service life in lamps inconvenient to change.  Like in traffic signal lights over busy intersections.  To the taillights in tractor trailers.  Where anytime spent not hauling freight was lost revenue.

We made Full-Color Flat Panel Displays from LEDs by combining Red, Green and Blue LEDs into Full-Color Pixel Clusters

The market didn’t demand these developments in semiconductors or LEDs.  For the most part the market didn’t even know this technology existed.  But the entrepreneurs gathering in Silicon Valley did.  They had some great ideas of what they could do with this new technology.  All they needed was the capital to bring these ideas to market.  It was risky.  The technology was good.  But could they use it to make useful things at affordable prices?  And would the people be so enamored with the things they built that they would buy them?  There were just too many unknowns for conservative bankers to take a risk.  But thanks to venture capitalists those entrepreneurs got the capital they needed.  Brought their ideas to market.  Created Silicon Valley.  And the modern world we now take for granted.

They continue to advance this technology.  Creating full-color flat panel displays.  By combining red, green and blue LEDs into full-color pixel clusters.  Which, unlike an LCD flat panel display, does not need a backlight as they produce their own light.  So these panels are thinner and use less power than LCD displays.  Making them ideal for the displays in our cellular devices for they allow more battery life between charges.  They also have wide viewing angles.  People looking at these displays from near perpendicular viewing angles see nearly the same quality of picture as those viewing directly in front.  Making them ideal for use in stadiums.  The video replays you see on that mammoth flat panel display in the new Dallas Cowboy stadium is an LED flat panel display.

All of this from joining two differently-charged semiconductor materials together.  Creating that all important and indispensible PN junction.  The foundation for every electronic device.  And of Silicon Valley itself.

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Sound Waves, Phonograph, Stylus, Piezoelectric & Magnetic Cartridges, Thermionic Emission, Vacuum Tube, PN-Junction, Transistor and Amplifier

Posted by PITHOCRATES - May 2nd, 2012

Technology 101

The First Phonographs used a Stylus attached to a Diaphragm to Vibrate the Air and a Horn for Amplification 

Sound is vibration.  Sound waves we hear are vibrations in the air.  A plucked guitar string vibrates.  It transfers that vibration to the soundboard on the guitar body.  The vibration of the soundboard vibrates the air inside the guitar body.  Amplifying it.  And shaping it.  Giving it a rich and resonant sound.  Creating music.  And we can reverse this process.  Taking these vibrations from the air.  And putting them into a piece of wax.  Via a vibrating needle.  Or stylus.  Cutting wavy grooves into wax.  And then we can even reverse this process.  By dragging a stylus through those same wavy groves.  Causing the stylus to vibrate.  And if we transfer those vibrations to the air we can hear those sound waves.  And listen to the music they make.

The first phonographs could reproduce sound.  But they didn’t sound very good.  The first phonographs were purely mechanical.  A stylus vibrated a diaphragm.  The diaphragm vibrated the air.  And a horn attached to that diaphragm was the only amplification.  Sort of like cupping your hands around your mouth when shouting.  Which reinforced and concentrated the sound waves.  Making them louder in the direction you were facing.  Which is how these early phonographs worked.  But the quality of the sound was terrible.  And played at only one volume.  Low.

Electric circuits changed the way we listen to music.  Because we could amplify those low volumes.  By changing the vibrations created from those wavy grooves into an electrical signal.  The first phonographs used a piezoelectric cartridge.  Which the stylus attached to.  The piezoelectric cartridge converted a mechanical pressure (the needle vibrating in the wavy groove) into electricity.  Later phonographs used a magnetic cartridge.  Which did the same thing only using a varying magnetic field.  The vibration of the needle moved a magnet or a coil through a magnetic field.  Thus inducing a current in a coil.  Then all you needed was an amplifier and a loudspeaker to make sweet music.

Small Changes in the Control Grid Voltage of a Vacuum Tube make Larger Changes in the Plate Voltage

The first amplifiers used vacuum tubes.  Things that once filled our televisions and stereo systems.  Back in the old days.  Up until about the Seventies.  A vacuum tube operated on the principle of thermionic emission.  Which basically means if you heat a metal filament it will ‘boil off’ electrons.  The basic vacuum tube used for amplification consisted of a cathode and an anode.  Or filament and plate.  And a control grid in between.  Sealed in, of course, a vacuum.  Creating the triode.  The cathode (filament) and anode (plate) created an electric field when connected to a large power source.  The cathode is negative.  And the anode is positive.  When negatively charged electrons are ‘boiled off’ of the cathode the positive anode attracts them.  The greater the heat the greater the thermionic emission.  And the greater the current flow from cathode to anode.  Unless we change the electric field to inhibit the flow of current.  Which is the purpose of the control grid.

Small changes in the control grid voltage will make changes in the large current flowing from cathode to anode.  That is, the larger current replicates the smaller signal applied to the control grid.  This allows the triode to take the low voltage from a phonograph cartridge and amplify it to a higher voltage with enough power to drive a loudspeaker.  Which is similar to diaphragm and horn on the first phonographs.  Only the amplified electric signal moves a lot more air.  And better materials and construction create a better quality sound.  Amplifiers with vacuum tubes make beautiful music.  High-end audio equipment still uses them to this day.  Including almost all electric guitar amps.  So if they have the highest quality why don’t we use them elsewhere?  Because of thermionic emission.  And the heat required to ‘boil off’ those electrons.

Vacuum tubes worked well when plugged into line power.  Such as a radio in a house.  But they don’t work well on batteries.  Because it takes a lot of electric power to heat those filaments.  And you need pretty big batteries to get that kind of electric power.  Like a car battery.  But even a car battery didn’t let you listen to music for long when parked with the engine off.  Because those tubes drained that battery pretty fast.  So there were limitations in using vacuum tubes.  They draw a lot of power.  Produce a lot of heat.  And tend to be pieces of furniture in your house because of their physical size.

Small Changes in the Base Current of a Transistor is Replicated in the Larger Collector-Emitter Current

The transistor changed that.  Making music more portable.  Thanks to semiconductors.  Material with special electric properties.  Based on the amount of electrons in the atoms making up this material.  Atoms with extra electrons make material with a negative charge (N-material).  Atoms missing some electrons make material with a positive charge (P-material).  When you put these materials together the N and the P attract each other.  Electrons cross the junction and fill in the holes that were missing electrons.  And the ‘holes’ cross the junction and fill in the spaces where there were excess electrons.  (When an electron moved, say, from right to left it made a hole and filled a hole.  It made a hole where it once was.  And it filled a hole where it now is.  So it looks like the hole moved from left to right when the electron moved from right to left.)  Neutralizing the N-material and the P-material.  But creating a charged region around the junction.  And it’s this electron flow and hole flow that make these PN junctions work.  When you add a third material you get a transistor.  Made up of three parts (NPN or PNP).  Emitter, base, and collector.

To get the electrons and holes flowing you start applying voltages across the junctions.  A large current will flow from the collector to the emitter.  Similar to the current flow in a tube from cathode to anode.  And a small base current will change that current flow.  Just like the control grid in a vacuum tube.  Small changes in the base current will make similar changes in the larger collector-emitter current.  Just like in a vacuum tube, the larger current replicates the smaller signal applied to the ‘control’.  Or base.  This allows the transistor to take the low-level signal from a phonograph cartridge and amplify it to a higher level.  Just like a vacuum tube.  Only with a fraction of the electric power.  Because there are no filaments to heat. 

Low power consumption and the small physical size allowed much smaller amplifiers.  And amplifiers that everyday batteries could power.  Creating new ways to listen to music.  From the pocket-size transistor radio.  To the bigger stereo boombox.  To the iPod.  Where the basic principle of how we listen to music hasn’t changed.  Just how we vibrate the air that makes that music has.

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