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Some basic definitions, equations and analogies of electricity.

[edit] Definitions

[edit] Equations

P=IV

Power=Current*Voltage

look familiar see P=Q*H*e/k

V=IR

Volts=Current*Resistance

I=V/R might be more edifying since current is usually the result of pressure acting on resistance.

This only applies to ohmic circuits, those circuits which display a linear relationship between current and voltage (i.e. the resistance does not change based upon current or voltage).

[edit] Analogies

The following animated analogy has much information to go along with it. This analogy is a combination of many analogies, and although has the problems endemic to all models, I feel that it is quite good. Please leave feedback, questions and lambastings on the discussion tab above. Look for an update in February 2007.

For each example, ask yourself:

• How fast will the battery run out?
• How fast will the virgin margaritas be made?
• And most importantly why?

If you would like to do math to support these analogies, use:

• Feet = volts
• GPM = amps
• Each blender has a resistance of 6 Feet/GPM = 6 ohms

[edit] 1 Tank 1 Blender

• This is the test case (datum).

[edit] 1 Tank 2 Series Blenders

Notice that:

• The flow is 1/2 the speed of our test case.
• The two blenders in series are each going 1/4th the speed of our test case.

[edit] 1 Tank 2 Parallel Blenders

Notice that:

• Each blender is at the same speed as our test case.
• The flow from the tank is twice as fast as our test case.

[edit] 2 Parallel Tanks 1 Blender

Notice that:

• The blender is the same speed as our test case.
• The flow from each tank is half as fast as our test case.

[edit] 2 Series Tanks 1 Blender

Notice that:

• The blender is 4 times the speed as our test case.
• The total flow is twice the speed as our test case.

[edit] Background Essentials

(This is information transferred from the Rural Electrification Systems page which needs to be integrated with this page).
These are all key words or terms that anyone proceeding through this work should be familliar with:

Electrical circuit, Ohm's Law, Heat, Magnetism, Light, Parallel circuit, Series circuits, Matter, Electron, Orbits, Nucleus, Atoms, Electric charge, Proton, Current, Generator, Amperes, Ammeter, Direct current, Pulsating (DC) current, Alternating Current, Voltage, Resistance, Power, Energy, Heat, Light, Electromagnetism, Induced Voltage, Meter, Voltmeters, Wattmeters, Multimeter, Voltage Drop.

The total Resistance of a Parallel circuit decreases with an increase in the number of devices operated. This is apparent since an increase in the number of paths for current results in a decrease in total resistance. Remember: The total Resistance of a parallel circuit is always smaller than the smallest resistor of that circuit. The total Resistance can be found by applying the correct voltage to the circuit and measuring the total current taken. The total Resistance is then determined by applying Ohm's Law.

Resistance of circuit = (Voltage/Current)

The total circuit resistance can be found by an application of the following formula which applies to any parallel circuit. This formula is known as the Reciprocal Formula.

Series-parallel circuits

Fig. 1.12

The total resistance of Circuit A can be figured by parts. The two 10 ohm loads in parallel, considered alone have a resistance of 5 ohms. Thus circuit A is equivalent to two 5 ohm resistances in-series, or a total resistance of 5 + 5 = 10 ohms.

The total resistance of Circuit B can also be figured in parts. It is two series circuits which are in parallel to each other. It is the equivalent of tm, 25 ohm resistances in parallel. Thus the total resistance is: 25 = 12.5 ohms.

The most common series parallel circuit is the control of several loads by one switch. The switch is in series with parallel loads.

[edit] ALTERNATING CURRENT PRINCIPLES

An alternating current can be generated by rotating a coil magnetic field. The voltages induced as the coil makes one revolution are shown in Fig. 1.14. The part of the graph below axis indicates voltage in the opposite direction.

Fig. 1.14

Cycle

Effective Values

Apparent power

[edit] POWER FACTOR

In AC circuits, especially circuits that have large motor loads, the Apparent power is not always the same as the Effective power, as measured with a wattmeter. The effective power is often less than the Apparent power. To measure the amount that these differ we define the term power factor:

To measure the power factor of a circuit, measure the effective power with an AC wattmeter, measure the current with an AC ammeter, and measure the voltage with an AC' Voltmeter.

It is desirable to have as high a power factor as possible. A low power factor means larger conductors are needed to supply the same Power. Power factor can be corrected by installing capacitors into the system. They use no power but correct the power factor. Let the engineer in charge of the project decide when Capacitors are needed and let him decide upon the size needed. Capacitors store power. They are dangerous even when disconnected. Handle with extreme care and always with the terminals connected together.

[edit] AC MOTORS

There are many ways to build AC motors. However, they all operate on the same principle. In all AC motors an AC Voltage is applied to stationary coils, which produce a varying magnetic field that changes at a speed proportional to the frequency of the current. The rotating coil rotates in an effort to line up with this changing field.

[edit] SINGLE PHASE AC

All the material about alternating current so far has been concerned with, single phase AC. The voltage reaches a maximum twice during each cycle (once in each direction). Therefore an AC motor receives two "pushes" each cycle.

[edit] THREE PHASE AC

A lawnmower engine has one cylinder. An automobile engine has six or eight. The automobile engine receives six or eight pushes per revolution compared to the single push of the lawnmower engine. It would be convenient if an electric motor could receive more pushes per revolution. This happens with three phase AC. A generator is so constructed that it generates three alternating voltages, but they reach their maximum values at different times. A three phase motor has three coils which each connect to a different "phase" of the three phase generator. Thus the motor is getting six pushes (two pushes from each phase) in the same period of time that a single phase motor gets only two pushes.

The advantage of generating three phase power is single phase power can also be obtained by connecting the circuit to a single phase, rather than all three. Also, three phase motors are more efficient, simpler, less expensive to buy and run. There are two ways to connect loads to a three phase generator. In Fig. 1.15 and Fig. 1.16 the generators are the same, the diagrams show the three coils which have voltage induced in them by a rotating electromagnet. In the diagrams the arrangement of the coils is different but only for convenience in drawing. The coils each generate 120 V. The voltages obtained with each type of connection are indicated.

Delta Connection- The delta connection of a three phase generator, which resembles the Greek letter A (Delta), is shown in Fig. 1.15.

Fig. 1.16 shows the same generator connected similar to the letter Y. This connection is sometimes referred to as a star connection.

Fig. 1.15 Fig. 1.16

[edit] TRANSFORMERS

A moving magnetic field generates an electric current in a conductor, and an alternating current flowing in a conductor produces an alternating magnetic field. These two effects can be combined in a circuit such a3 Fig. 1.17.

Fig. 1.17

One coil has a current flowing 3n it. It is an AC current that sets up an alternating magnetic field around the coil. If another coil is placed next to it, there will be an alternating current induced in it by the magnetic field. The first coil is the primary, the second coil is the secondary, and the combination is called a transformer. Most commercial transformers appear as, shown in Fig. 1.18.

Fig. 1.18

Transformers can change voltage. If there are twice as many loops in the coil of the secondary as there are loops in the primary, the voltage in the secondary will be twice the voltage of the primary. This ratio is called the turns ratio, or voltage ratio. A transformer which will change the voltage from 1,000 V. to 100 V. is called a step down transformer. A transformer that would raise the voltage would k called a step up transformer.

[edit] Links

http

//www.batteryfaq.org/

Everything you every wanted to know about Lead Acid batteries.

Car and Deep Cycle Battery FAQ

http

//hyperphysics.phy-astr.gsu.edu/hbase/electric/dccircon.html#c1

Fantastic site on physics in general. Easy to understand, but accurate information on DC Circuits.

HyperPhysics - DC Circuits

http

//library.thinkquest.org/10796/ch11/ch11.htm

Some easy to follow basic theory.

Lesson 3: Electricity - Colegio Franklin Delano Roosevelt

http

//science.howstuffworks.com/electricity.htm

Some more information on electricity. Not wrot with error like at least one of their other pages.

How Stuff Works - Electricity

http

//cnx.org/content/m1000/latest/

Understanding current

[edit] See also

• Low voltage connection basics
• Power and energy basics