1. Electricity

2. TYPES OF CIRCUITS Individual electrical circuits normally combine one or more resistance or load devices. The design of the automotive electrical circuit will determine which type of circuit is used. There are two basic types of circuits: Series Circuit Parallel Circuit * #21

3. SERIES CIRCUITS A series circuit is the simplest circuit. The conductors, control and protection devices, loads, and power source are connected with only one path to ground for current flow. 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 and no part of the circuit works. Christmas tree lights are a good example; when one light goes out the entire string stops working. #’s 22,23,24,&25

4. A simplified series circuit is made up of three elements: 1. A source (power supply) 2. Resistors which use the electrical energy and are commonly referred to as loads. 3. Ideal conductors (wires), with no assumed resistance, to connect the elements in the series. # 26

5. Other elements such as switches and fuses can be added to the circuit.

6. Opening or breaking a series circuit such as this at any point in its path causes the circuit to “open” or stop operating. This is because the basic requirement for the circuit to operate as a continuous closed loop path is no longer met. If any device on the circuit fails, the entire circuit will fail. Some Christmas lights are a good example of this failure. #’s 27 & 28

8. SERIES CIRCUITS A Series Circuit has only one path to ground, so electrons must go through each component to get back to ground. All loads are placed in series. Therefore: 1.An open in the circuit will disable the entire circuit. 2. The voltage divides (shared) between the loads. 3. The current flow is the same throughout the circuit. 4. The resistance of each load can be different.

9. The value of current, I, is always the same at any point in a series circuit. The total resistance,(RO), is equal to the sum of all resistances (R1 + R2 + R3 +.......) #29

10. Resistance R0 (a combination of resistances R1 and R2, which are connected in series in the circuit as illustrated) and current I flowing in this circuit can be determined as follows:

11. Consider a simple series circuit consisting of a 120 volt outlet as the source, a switch, and a 60 watt light bulb. When the switch is open (turned off), the light bulb cannot operate since the circuit is not complete. When the switch is closed (turned on), the light bulb operates since the current can flow through the circuit.

12. If two light bulbs are connected to the circuit in series, the Resistance of the circuit doubles. The current flow is now half of what it was when only one lamp was in the circuit as before. The voltage across each lamp is not only 60 volts due to the reduced current flow. Each bulb is operating at only one-half its intended Voltage, which reduces the brightness. # 30

13. If we add a third 60-watt bulb to the circuit, then each Bulb will receive a third of the total circuit voltage, or 40 watts. Each bulb will produce even less light than before Because we continue to add more resistance to the circuit each time we add a bulb.

14. A parallel circuit has more than one path for current flow. The same voltage is applied across each branch. If one branch is broken, current will continue flowing to the other branches 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. # 31

16. PARALLEL CIRCUITS A Parallel Circuit has multiple paths or branches to ground. Therefore: 1.In the event of an open in the circuit in one of the branches, current will continue to flow through the remaining branches. 2. Each branch receives source voltage. 3. Current flow through each branch can be different. 4. The resistance of each branch can be different. #’s 32, 33, & 34

17. Household Circuits In a home, many appliances draw current from the same circuit. If more appliances are connected, more current will flow through the wires. As the amount of current increases, so does the amount of heating in the wires. If the wire gets too hot, the insulation can melt and the bare wires can cause a fire. To protect against overheating, all household circuits contain either a fuse or a circuit breaker. # 35

18. An electrical fuse Contains a piece of Metal that melts if the Current becomes too High. When it melts, it causes A break in the circuit, Stopping the flow of current Through the overloaded Circuit. To fix this, you Must replace the blown Fuse with a new one.

19. A circuit breaker is another guard against Overheating a wire. A circuit breaker contains a Piece of metal that bends when it gets hot. The bending causes a switch to flip and open the Circuit. # 36