Order Klein Electricians' Tools Online --

Order Greenlee Electricians' Tools Online --

Order Ridgid Electricians' Tools Online --

There is every reason for an electrician to become knowledgeable in the vast field of electronics. At one time the emblems of his (almost all electricians were men) trade were the soldering iron and friction tape. Today he or she confronts a vast array of computer controlled equipment and even a hairdryer is likely to contain a printed circuit. For those electricians who have not ventured into the world of electronics, we will be making available starting on this page a series of electronics tutorials which will assume no prior knowledge of the field and progressively address more complex topics.

Georg Simon Ohm first introduced what is now called Ohm's Law in 1827. There is nothing mystical about Ohm's Law Wheel. It is a circular tabulation of formulas, which could also be expressed like this:

E = RxI

E = P/I

E = Square root of PxR

R = E/I

R = E squared / P

R = P/I squared

I = Square root of P/R

I = P/E

I = E/R

P = E squared / R

P = R x I squared

P = E x I

Actually, all these formulas can be derived by knowing just these two:

E = IxR

P = E x I

E is volts. (It actually stands for electromotive force)

R is ohms. (It stands for resistance)

I is current, expressed in amps. It is the most fundamental of these concepts, because one amp has been defined as a certain definite very high number of electrons passing a given point in one second.

E and R are derivative of I. One volt is the amount of electromotive force required to force one amp to flow through one ohm of resistance.

Basic electronic troubleshooting involves primarily taking measurements with a DVOM (digital volt ohm milliammeter). With this instrument Amperage measurements cannot be taken on current over a certain very low level. An ammeter is in series with the current flow and the full amount of current flows through it. An ammeter has very low impedance. A voltmeter has high impedance and is placed across the item being measured. A minute amount of current flows through it.

When you turn on a high impedance voltmeter, you will see a low voltage value displayed, and it will drift in a random fashion. This is called "phantom voltage" and it doesn't mean anything. When you touch the probes to a voltage source the meter will quickly stabilize and the correct voltage will be displayed.

Higher levels of amperage can be measured using a clamp-on ammeter. This instrument is quite accurate and is very useful when repairing all sorts of appliances, motors and other electrical equipment. You just open the jaws of the meter and insert one conductor. If both circuit conductors are inserted as in a jacketed cable, the current flows, since they are going in opposite directions, will cancel and the meter will read zero. To take a reading on a cord and plug connected appliance, make up a short extension cord. Make a six inch slit in the outer jacket and pull out a current-carrying conductor so that a reading may be taken on the current that is flowing through it.

Ohm's Law is applicable in both DC and AC circuits. A resister is a component manufactured to present a definite unchanging resistance in DC or AC circuits. (At high frequencies, the resister will have an unintended capacitive and inductive component, which will alter its opposition to the flow of current. At the 60-Herz frequency that is standard in the United States and the 50-Herz frequency in many other parts of the world, these effects are minimal and do not have to be figured in.)

In the course of ordinary electrical work, many pieces of equipment behave as resistances. Heating elements, light bulbs and long runs of wire are examples.

When two or more resistive loads are in series, the total resistance is found by adding all loads. If the loads are not equal, they will have different voltages across them.

Some of the Ohm's Law derivatives are very important while others are rarely used. Why would you want to find voltage given current and resistance? Generally the voltage supplying a piece of equipment is known at the outset or can be measured easily.

One of the commonly used formulas is P = R X I squared. It gives the loss in heat dissipation of a resistive load.

Another important and often used formula is I = P/E. In order to size out a circuit in accordance with the National Electric Code, you have to know amps. Amperage is the unknown which you have to solve for when you are given the wattage and of course voltage of a piece of equipment. In the denominator go any other mitigating factors such as efficiency, power factor and 1.73 for a three-phase circuit.

An important fact to understand is the difference between cold resistance and hot resistance. A resistive load will become lighter (that is it will have a higher resistance) once it gets to an elevated operating temperature. A lightbulb will read artificially lower resistance measured with a meter than in actual operation. Sometimes lights on a circuit will be seen to dim momentarily when an additional bulb is switched on. Much equipment draws more current while it is moving from a lower (or zero) energy state to a higher one. This is particularly true of a motor as it gains speed under load.

We have considered resistive loads in series -- to find the total resistance, just add them. What about resisters in parallel? The calculation is a bit more complex. If you think of a resistance as opposition to current flow, it is easy to see that two or more resistive loads in parallel will be less of a bottleneck than just one of these. In fact, the total resistance is given by this formula:

1/total resistance = 1/R#1 + 1/R#2 + 1/R#3 . . .

This formula works when the resisters are not all the same value. It also works when they are all the same value, but in that case a simpler formula is possible:

Total resistance = (R#1 X R#2)/ (R#1 + R#2)

Combination circuits made up of series and parallel elements are not difficult to figure if you take a methodical approach. There are two basic forms, with more complex variations.

The first scenario is series resisters in parallel.

The second scenario is parallel resisters in series.

In the first case, figure the series elements and then treat the subtotals as single resistances and solve for two parallel resistive loads.

In the second instance, figure the parallel elements and then treat the subtotals as single resistances and solve for two series resistive loads.

For information on analyzing more complex DC networks, please refer to Electronic Theorems.

When America was first powered up, a great controversy erupted over what type of electricity was to be used, AC (alternating current) or DC (direct current). Engaged in this debate were Thomas Edison and George Westinghouse, who was allied with the highly eccentric but brilliant innovator Nikola Tesla. In the end, the Westinghouse-Tesla team won, and today it is AC that is primarily used in the United States.

Direct current (DC), while simpler and more fundamental than alternating current (AC), is in someways less useful. DC is the flow of electricity in one direction, generally at a fixed rate. Early researchers were mistaken about the direction of flow and incorrectly labelled positive and negative poles. When the true state of affairs was ascertained, rather than switching terminology with regard to poles, electrons were arbitrarily declared to carry a negative charge and an electrode that had a shortage of electrons was considered positive.

From their experience with dry cells in flashlights and toys, many children at an early age become familiar with simple DC circuits. They observe that both poles have to be connected for current to flow and that the flow of electricity is in some ways like the flow of water in a pipe in that there has to be a complete circuit for a load to become energized.

AC is a little more complex, but the fundamental mechanics is the same with the additional concept of frequency or periodicity added to the pictures.

In the case of AC, the poles reverse, usually aat a fixed rate. This is largely due to the nature of the source, a rotary electromechanical generator.

Both systems have their advantages. AC can be changed (rectified) to DC easily by placing a diode in series with the voltage source and load. DC can be less easily converted to AC by means of a rotary inverter or solid state circuitry. DC is needed to charge batteries and to power most solid state equipment such as found in amplifiers, computers and the like. All of these have power supplies which incorporate diode rectification, which produces pulsating DC, and filtering capacitors which smooth out the ripples to produce more or less pure DC like what is available at the terminals of a battery.

Unrectified AC cannot be used to charge a battery -- for every half cycle that would charge the battery, the other half cycle would discharge it. So it is more difficult to store AC than DC. Another advantage in DC is for arc welding. It produces a better weld. DC welders, powered with utility AC, incorporate large rectifiers.

But AC has one decisive advantage, it can be stepped up or down to any voltage with not too much loss. Just feed the available voltage into a transformer and another voltage is available at the output terminals, that voltage dependent upon the windings ratio. Later, when we get to the topic of inductance, we shall see how a transformer works.

To be continued . . .

HOME | Best Web Host | Question of the Week | Archived Questions | More Archived Questions | Articles | Electrical Deficiencies | Electricians Tools | Online computers | Cybercorner | Electrician's License | Electronics Tutorials | Electricians' worksaving ideas | Electronic Theorems | Satellite Dish | Digital Cameras and Equipment | HTML Color Chart | Links |