E lectronics
1 like1,018 views
1. Electrical circuits require a complete current path from a power source to loads and back in order to function. 2. There are three main types of circuits - series, parallel and series-parallel - which differ based on how the components such as the power source, conductors, loads and protective devices are connected. 3. Ohm's Law defines the relationship between voltage, current and resistance and is useful for troubleshooting circuits.
E lectronics
- 1. ELECTRICAL CIRCUITS Electrical Circuits A complete path, or circuit, is needed before current path if too much current flows. Too much voltage can cause a current flow through current is called an overload, which could resistances to perform work. damage conductors and working devices. A list of five things to look for in any circuit: There are several types of circuits, but all require the same basic components. A power source 1. Source of Voltage (battery or alternator) produces voltage, or 2. Protection Device electrical potential. Conductors (wires, printed circuit boards) provide a path for current flow. 3. Load Working devices, or loads (lamps, motors), 4. Control change the electrical energy into another form of energy to perform work. Control devices 5. Ground (switches, relays) turn the current flow on and off. And, protection devices (fuses, circuit We will be identifying these items when we look at breakers) interrupt the Automotive Circuits a little later in this book. Page 1 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 2. ELECTRICAL CIRCUITS Types Of Circuits There are three basic types of circuits: series, parallel, and series-parallel. The type of circuit is determined by how the power source, conductors, loads, and control or protective devices are connected. SERIES CIRCUIT A series circuit is the simplest circuit. The conductors, control and protection devices, loads, and power source are connected with only one path for current. The resistance of each device can be different. The same amount of current will flow through each. The voltage across each will be different. If the path is broken, no current flows. PARALLEL CIRCUIT A parallel circuit has more than one path for current flow. The same voltage is applied across each branch. If the load resistance in each branch is the same, the current in each branch will be the same. If the load resistance in each branch is different, the current in each branch will be different. If one branch is broken, current will continue flowing to the other branches. SERIES-PARALLEL CIRCUIT A series-parallel circuit has some components in series and others in parallel. The power source and control or protection devices are usually in series; the loads are usually in parallel. The same current flows in the series portion, different currents in the parallel portion. The same voltage is applied to parallel devices, different voltages to series devices. If the series portion is broken, current stops flowing in the entire circuit. If a parallel branch is broken, current continues flowing in the series portion and the remaining branches. Page 2 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 3. ELECTRICAL CIRCUITS SERIES CIRCUITS In a series circuit, current has only one path. All voltage on the other side of the load. The drop or the circuit components are connected so that the loss in voltage is proportional to the amount of same amount of current flows through each. The resistance. The higher the resistance, the higher circuit must have continuity. If a wire is the voltage drop. disconnected or broken, current stops flowing. If one load is open, none of the loads will work. When troubleshooting, then, you can see that more resistance will reduce current and less resistance Use of Ohm's Law will increase current. Low voltage would also reduce current and high voltage would increase Applying Ohm's Law to series circuits is easy. current. Reduced current will affect component Simply add up the load resistances and divide the operation (dim lamps, slow motors). But, increased total resistance into the available voltage to find the current will also affect component operation (early current. The voltage drops across the load failure, blown fuses). And, of course, no current at resistances are then found by multiplying the all would mean that the entire circuit would not current by each load resistance. For calculation operate. There are electrical faults that can cause examples, see page 6 in the Ohms law section. such problems and knowing the relationship Voltage drop is the difference in voltage between voltage, current, and resistance will help (pressure) on one side of a load compared to the to identify the cause of the problem. Page 3 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 4. ELECTRICAL CIRCUITS PARALLEL CIRCUITS In a parallel circuit, current can flow through more the smallest load resistance. This makes sense than one path from and to the power source. The because current can flow through more than one circuit loads are connected in parallel legs, or path. Also, remember that the voltage drop across branches, across a power source. The points each branch will be the same because the source where the current paths split and rejoin are called voltage is applied to each branch. For examples of junctions. The separate current paths are called how to calculate parallel resistance, see page 6. branch circuits or shunt circuits. Each branch operates independent of the others. If one load When troubleshooting a parallel circuit, the loss of opens, the others continue operating. one or more legs will reduce current because the number of paths is reduced. The addition of one or Use of Ohm's Law more legs will increase current because the number of paths is increased. Current can also be Applying Ohm's Law to parallel circuits is a bit reduced by low source voltage or by resistance in more difficult than with series circuits. The reason the path before the branches. And, current can be is that the branch resistances must be combined to increased by high source voltage or by one or find an equivalent resistance. Just remember that more legs being bypassed. High resistance in one the total resistance in a parallel circuit is less than leg would affect component operation only in that leg. Page 4 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 5. ELECTRICAL CIRCUITS SERIES-PARALLEL CIRCUITS In a series-parallel circuit, current flows through The total resistance is then divided into the source the series portion of the circuit and then splits to voltage to find current. Voltage drop across series flow through the parallel branches of the circuit. loads is current times resistance. Current in Some components are wired in series, others in branches is voltage divided by resistance. For parallel. Most automotive circuits are series- calculation examples, see page 6. parallel, and the same relationship between voltage, current, and resistance exists. When troubleshooting a series-parallel circuit, problems in the series portion can shut down the Use of Ohm's Law entire circuit while a problem in one leg of the parallel portion may or may not affect the entire Applying Ohm's Law to series-parallel circuits is a circuit, depending on the problem. Very high matter of simply combining the rules seen for resistance in one leg would reduce total circuit series circuits and parallel circuits. First, calculate current, but increase current in other legs. Very the equivalent resistance of the parallel loads and low resistance in one leg would increase total add it to the resistances of the loads in series. circuit current and possibly have the effect of bypassing other legs. Page 5 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 6. ELECTRICAL CIRCUITS Ohm's Law sample circuits. Current found by dividing voltage by resistance. This can be very helpful when Fast, accurate electrical troubleshooting is easy diagnosing electrical problems: when you know how voltage, current, and resistance are related. Ohm's Law explains the • When the resistance stays the same ... current relationship: goes up as voltage goes up, and current goes down as voltage goes down. A discharged battery • Current (amps) equals voltage (volts) divided by has low voltage which reduces current. Some resistance (ohms) ... I = E ÷ R. devices may fail to operate (slow motor speed). An unregulated alternator may produce too much • Voltage (volts) equals current (amps) times voltage which increases current. Some devices resistance (ohms) ... E = I X R. may fail early (burned-out lamps). • Resistance (ohms) equals voltage (volts) divided • When the voltage stays the same ... current goes by current (amps) ... R ÷ E = 1. up as resistance goes down, and current goes down as resistance goes up. Bypassed devices USING OHM'S LAW reduce resistance, causing high current. Loose connections increase resistance, causing low current. The effects of different voltages and different resistances on current flow can be seen in the Page 6 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 7. ELECTRICAL CIRCUITS SAMPLE CALCULATIONS Ohm's law includes these two ideas: Here are some basic formulas you will find helpful 1. In a circuit, if resistance is constant, current in solving more complex electrical problems. They varies directly with voltage. provide the knowledge required for confidence and thorough understanding of basic electricity. Now what this means is that if you take a component with a fixed resistance, say a light bulb, The following abbreviations are used in the and double the voltage you double the current formulas: flowing through it. Anyone who has hooked a six- volt bulb to a twelve-volt circuit has experienced E = VOLTS this. But it wasn't "too many volts" that burned out I = AMPS the bulb, it was too much current. More about that R = OHMS later. P = WATTS 2. In a circuit, if voltage is constant, current varies • Ohm's Law inversely with resistance. Scientifically stated, it says: "The intensity Of the This second idea states that when resistance goes current in amperes in any electrical circuit is equal up, current goes down. That's why corroded to the difference in potential in volts across the connectors cause very dim lights - not enough circuit divided by the resistance in ohms of the current. circuit." Simply put it means that current is equal to volts divided by ohms, or expressed as a formula, • Watts the law becomes: A watt is an electrical measurement of power or I=E/R work. It directly relates to horsepower. In fact, in the Sl metric standards that most of the world or it can be written: uses, engine power is given in watts or kilowatts. E=IXR Electrical power is easily calculated by the formula: This is important because if you know any two of P=EXI the quantities, the third may be found by applying the equation. For instance, a halogen high-beam headlight is rated or 5 amps of current. Figuring 12 volts in the system, we could write: P=EXI P = 12 X 5 P = 60 watts Page 7 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 8. ELECTRICAL CIRCUITS RESISTANCE That becomes: The effect of individual resistors on the total resistance of a circuit depends on whether the circuit is series or parallel. Which becomes: Series Circuits In a series circuit, the total resistance is equal to the sum of the individual resistors: So there is a little more than one-half ohm resistance in the circuit. You can see that the more SERIES: resistors in parallel, the less the resistance. total R = R1 + R2 + R3 + In fact, the total resistance is always less than the smallest resistor. This is why a fuse will blow if That is the basis of the concept of voltage drop. you add too many circuits to the fuse. There are so For example, if you had a circuit with three loads in many paths for the current to follow that the total series (a bulb, resistor, and corroded ground) you resistance of the circuit is very low. That means would add the three together to get total the current is very high - so high that the fuse can resistance. And, of course, the voltage would no longer handle the load. drop across each load according to its value. B. For two resistors: Parallel Circuits Parallel circuits are a different story. In a parallel circuit, there are three ways to find total For a 3 ohm and a 5 ohm resistor that would be: resistance. Method A works in all cases. Method B works only if there are two branches, equal or not. Method C works only if the branches are of equal resistance. A. The total resistance is equal to one over the C. For several identical resistors, divide the value sum of the reciprocals of the individual of one resistor by the number of resistors, or: resistors. That sounds confusing, but looking at the formula will make it clearer: PARALLEL: Where R1 is the value of one resistor and n is the number of resistors. So if you had three 4 ohm resistors in parallel it would be: n example will make it even clearer. Suppose there is a circuit with three resistors in parallel: 4 ohms, 2 ohms, and 1 ohm. The formula would look like this: Page 8 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 9. ELECTRICAL CIRCUITS Page 9 © Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
- 10. ELECTRICAL CIRCUITS ASSIGNMENT NAME: 1. Draw and label the parts of a Series Circuit and a Parallel Circuit. 2. Explain the characteristics of “Voltage” and how it differs between a Series Circuit and a Parallel Circuit. 3. Explain the characteristics of “Current” and how it differs between a Series Circuit and a Parallel Circuit. 4. Explain the characteristics of “Resistance” and how it differs between a Series Circuit and a Parallel Circuit.