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AC Current

In another section, current was defined as motion of the electrons caused by a difference in potential or voltage. In the several sections, a battery was the source of direct current. It should be noted for that case, electron motion was only in one direction. When electronic flow is in one direction,  by definition this is known as direct current (DC).

When the source of voltage alternates in a positive and negative direction, it causes the electrons to flow in two directions in a cyclical fashion. In other words the voltage source which could be a generator at the power company will cause the current or electron flow to go along your wiring  first in one direction and then in another direction in a cyclical fashion like 60 Hertz or 60 cycles per second. In this situation the power generator is the source and the electrical devices in your house are refered to as the load. Ref: Figures below.

 

Alternating Current (ac) Waveform

 The sinusoidal waveform below represents your house ac current whereupon ONE CYCLE is equal to 1/60 second along the TIME LINE. In other words, 60 cycles would take place every second. The Cycle Rate used to be called 60 cycles per second or 60 Hertz. Notice that the current changes direction from Plus to Minus during each cycle. The Frequency is also known as the Cycle Rate. (Frequency can take values from near zero to the GHz region, which is in the billions). A quick reminder 0 Hz is actually dc resulting in a straight-line waveform versus time.

 

 

 

It should be noted that the Lionel O gauge trains operate via an alternating current variable transformer power pack, with exception of those that are Digital Command and Control (DCC) compatible.

AC Current can be measured by putting an AC Current meter in series with the load or by using an AC Clamp-On meter which clamps to the external wiring of interest without interupting the circuit.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Resistors in Series and in Parallel

There are two simple forms of electric circuits; the series circuit provides a single conducting path, and the parallel circuit provides more than one. A battery and a single lamp  is an example of the simple circuit. If a second lamp  is added in series the circuit would appear as follows:

 

 

 

Example of Simple Series Circuit

Kirchoff’s Second Law).   Both lamps share the same current.   Another interesting observation, if one of the lamps burns out, the other lamp will also go out because the burnt lamp has now opened the circuit. Another observation, if the lamp specification calls for 12 volts, the 6 volts across each lamp will reduce the illumination. Hence, this circuit as applied to Model train layouts is not very desirable.

Note:  When the switch is closed the 12 volt battery will light both lamps, however each lamp will be dimmer because the ½ of the 12 v battery voltage will appear across each lamp assuming the lamps are identical.

Example of Simple Parallel Circuit

Note:  When the switch is closed the 12 volt battery will light both lamps, however each lamp will be glow with the same intensity because the 12 v battery voltage will appear across each lamp.

 The current from the Battery must be split between Lamp1 and Lamp 2. (Kirchoff’s First Law) Therefore, the Battery must supply twice the current as that supplied in the previous example (series circuit) to the rest of the circuit. This circuit can be a limitation, if your dc source cannot supply the current.

Another interesting observation, if one of the lamps burns out, the other lamp will not go out because the burnt lamp has not interrupted the current going to the other lamp. This application is appropriate for Model Train Layouts.

Resistors In Series

In the following sketch two resistors are in series. Let’s find the total resistance.


Total Value of the Resistance = R1 + R2 in Ohms

Resistors In Parallel

In the following sketch two resistors are in parallel. Let’s find the total resistance.

Total Value of the Resistance = 1/R1 + 1/R2 in Ohms

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics


In general, the following vendors are recommended for any of the above electronic components:

Radio Shack (Local Store or on-line at  www.radioshack.com)

Futurlec at  www.futurlec.com

DeMar Electronics at  www.demarelectronics.com/

Kirchoff’s Laws

Kirchofff’s First Law states that the sum of the currents entering and leaving a node is equal to zero.  Let us evaluate a simple circuit comprised of two resistors R1 and R2 connected in parallel with a +12 vdc battery.   In the following circuit there are 3 currents associated with node (point A).

 

Let’s evaluate node (pointA) in the above figure. The current entering node A is labeled I (Total).

The current leaving node A and passing through R1 is labeled I (1). 

The current leaving node A and passing through R2 is labeled I (2).

Let’s also define currents entering the node as positive and those leaving the node as negative.

Applying Kirchoff’s First Law we can write: I (Total) – I(1)-I(2) = zero or I (Total) = I (1) + I (2)

Kirchoff’s Second Law states that the sum of the voltages around a loop is equal to zero.  Let us evaluate a simple circuit comprised of two resistors R1 and R2 connected in resistors with a  battery.  In the following circuit there are 3 voltages associated with the loop which starts and ends at the battery.

Let’s evaluate the voltage loop in the above figure.

The voltage at the battery is labeled E.

The voltage across R1 is labeled V1.

The voltage across R2 is labeled V2.

The voltage polarities reflect current flowing from + to -. We can then write the following equation:

E – V1 -V2 = zero  or E = V1 +V2

Observe that if  I apply Ohm’s Law (V = IR)  we can also write E = IR1 + IR2

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

In general, the folowing vendors are recommended for any of the above electronic components:

Radio Shack (Local Store or on-line at  www.radioshack.com)

Futurlec at  www.futurlec.com

DeMar Electronics at  www.demarelectronics.com/

Ohm’s Law

RELATIONSHIP BETWEEN VOLTAGE, CURRENT, AND RESISTANCE

The three aforementioned quantities are related in the following equation (Ohm’s Law):

 Voltage  = Current times Resistance

                              or

                        V = IR

 Whereupon  V = Voltage; I = Current; and R = Resistance

 Simple Circuit Example:

 

 

In the above circuit when the Toggle Switch is open as shown, the 12 volt lamp cannot light and the battery cannot put out any current because there is an infinite resistance to Electrical current flow (open circuit). 

Applying the formula: V=IR or R=V/I 

R= +12v /0 current gives us an Infinite value for Resistance in ohms = Open Circuit

When the Toggle Switch is closed, the Lamp presents a finite resistance to electron flow, but because the lamp contains a filament, the filament will begin to glow as current passes through it.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Electrical Voltage

 

 

ELECTRICAL VOLTAGE (Potential) – It takes an electric field, or another way of putting it, a difference in potential to cause electrons which are negatively charged to be attracted to be attracted to a positively charged body. That Potential difference is commonly called Voltage.

 ELECTRICAL CURRENT – The motion of the electrons is known as the Electrical Current. It is analogous to water running through a pipe. The Electrical Potential is analogous to a water tower which contains the stored water in the form of potential mechanical energy. Electrical Current is measured in Amperes (AMPS).

RESISTANCE – As the word implies, the medium (wire)  in which the electrons flow provide a certain amount of Resistance.   This would be analogous to the diameter of the water pipe. Electrical RESISTANCE  is measured in Ohms.

Ohm’s Law is the equation which relates the voltage, current and resistance in a circuit.

Voltage is measured using a voltmeter, Current is measured with an ammeter, and Resistance with an ohmeter.

Combination meters are known as VOM’s or Volt Ohm Meters.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Electrical Charge

 

 

ELECTRICAL CHARGE – The ancient Greeks discovered what might be called the first electrical experiment. It was noticed that when a piece of amber when rubbed with a cloth, the amber was able to attract small pieces of near-by straw or feathers. Today, we understand that the amber became charged with electricity, and the attraction between the amber and the other material (straw, feathers) is referred to as Static Electricity. The word Electricity is derived from electron, the Greek word for amber.

            Later in the sixteenth century, it was found that many other substances other than amber can be charged in the same way. For example, a glass rod rubbed with silk can also produce an electrical charge on the rod. A hard-rubber rod rubbed with fur also picks up an electrical charge. Then in the eighteenth century, Benjamin Franklin was able to prove by experimentation that the glass rod actually had a positive charge and the rubber rod had a negative charge. He was also able to prove that like charges (either 2 positives or 2 negatives) repel each other and that unlike charges (1 positive and 1 negative attract each other).  For the purpose of simplicity, details of  Franklin’s experiment have not been provided.

BASIC STRUCTURE OF THE ATOM –  It  should be noted that an atom is comprised of a nucleus which is made up of only protons which are positively charged and neutrons which have no charge. The nucleus is at the center of the atom. Surrounding the nucleus are the electrons, which orbit around the nucleus, that are negatively charged. In a normally uncharged atom, the number of positively charged protons equals the number of electrons. 

PRODUCTION OF ELECTRIC CHARGE – It is possible in some materials to disturb this equality as was achieved by rubbing the amber with the cloth or the glass rod rubbed with silk. In the case or the glass rod rubbed with silk, the glass rod becomes positive because it loses electrons while the silk gains these electrons and becomes negatively charged to an equal extent.

Other Examples of Electric Charge Production: Shuffling of your feet on a woolen carpet, in dry weather passing your comb through your hair.

ELECTRICAL FIELD – The region around the charged item is known as the electric field of  force, or more simply the Electric Field, because any other charge located in that electric field experiences either a force of attraction or repulsion.  The Electric Field phenomenon is the fundamental  theory behind the operation of electric motors used in Model train locomotives in addition to many other motors used for thousands applications.

If you wish to acquire a better understanding of Electronics Theory, I suggest you go to  the following  link: Electronics

Electronics

 

Over the past decade the Model Railroad Hobby has changed drastically in the way that the train and it associated accessories operate.  The purpose of this section is to explain to the hobbyist some basic electronics theory that will be of interest, without inundating the reader with too much complexity.

It will begin with some basic theory followed by definitions of electrical variables followed by some detailed applications to the Model Train Hobby.  Specifically the theory and operation and application of the following components to Model Train Layouts are discussed: Diodes,Light Emitting Diodes (LED’s),Zener Diodes,  and sample Zener applications.

A discussion of Digital Command and Control (DCC) as well as Computer Control techniques are also included.

If you wish to acquire a better understanding of Electronics Theory, I suggest you highlight the underlined topic areas in the sequential order as listed below:

(1) Electrical Charge

(2) Electrical Voltage

(3) Ohms Law

(4) Definition of  Power

(5) AC Current

(6) Resistors in Series and in Parallel

(7) Kirchoff’s Laws

(8) Capacitor

(9) Capacitors in Series and Parallel Circuits

(10) Diodes

(11) Zener Diode

(12) Inductance

(13) Transformers

(14) Digital Command Control (DCC) for Model Trains

(15) DCC combined with Computer Control

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