Electrical Fundamentals

Module 1

Grading policy • Participation 10 marks

– Preparation, Promptness, Level of Engagement, Behavior• HWs 10 marks

– 2 HWs• Quizzes 10 marks

– 2 quizzes & SWQ• Practical 30 marks

– Lab activities and Practical exam • IAT competency exams (practical and knowledge ) 40

marks

Preparation marks

• Print the modules and cover it and bring it to every class with you• Calculator • Stationary • Lab cout

Participation Marks

• Promptness: On time or Late• Level of Engagement• Behavior

Objectives

• Electrical Circuit Components• Power supplies – Types of power supplies – Functions of power supplies

• Close circuit / open circuit • Switches– Parts – Manually operated switches: Knife Switch, push

button and selector switch

Electrical Circuit ComponentsHow many elements do you see ? Input device, what do you think it do? Output device / Load. Give example of other loads How the elements are connected ?What does generate the electric current ?Which device allow the current to flow ?

Power supplies• Power supply are used in

electrical systems to modify the power supplied from the power company (e.g. from the wall socket) to a form that is needed for the application.

• One feature power supplies are usually designed to do, is provide a constant current or constant voltage output. This is called regulation.

Power Supply

constant current power supply

the same current level regardlessof the demand placed on it by the load.

However, the voltage variesaccording to the size of the load.

Application: Limited

constant voltage power supplies

They maintain a constant voltage output, regardless of the load.

Here, the current varies instead of the voltage.

Application: Widely used

Constant voltage power supply

DC Voltage

AC voltage

Function Generator

The T7017 power supply

DC Power Supply, Battery

• A battery depends on chemical reaction to produce electricity. It does not require an external source of power.

• However, most constant voltage supplies, require an external AC power source.

Functions of Power supplies

• Regulating voltage or current (providing constant voltage or constant current)

• Reducing voltage levels• Changing AC to DC• Providing over current protection.

Closed circuit Open circuit

Switches

• The two main components of a manual switch– Operator (lever)– Contacts

• Switches use two types of contacts:– Normally Open (N.O.) – Normally Closed (N.C.)

Switches

• Switch operators are:– Manually-operated - The operator is activated by

a person.• Knife switch• Pushbutton switch• Selector switch

– Automatically-operated - The operator is activated by a machine

Knife Switch

• Single-pole double-throw (SPDT) :one set of contacts

• Double-pole double-throw (DPDT) knife switch: two sets of contacts.

What is the difference ?

Pushbutton Switch

Selector Switch

Recap

• Electrical Circuit Components• Power supplies – Types of power supplies – Functions of power supplies

• Close circuit / open circuit • Switches

Just a minute! Yesterday you

said x equals two

Class warm up

• Electrical Circuit Components• Power supplies – Types of power supplies – Functions of power supplies

• Close circuit / open circuit • Switches– Parts – Manually operated switches: Knife Switch, push

button and selector switch

Objectives

• Lab activity 2, testing different kinds of switches

• Output devices

Activity 2-Part 1

Activity 2-Part 2

Activity 2-Part 3

Output Devices

• Lamp• Resistor• Buzzer• Solenoid• Motor

Lamp

• A lamp contains a resistive element inside a glass bulb. The bulb is filled with a gas. When current flows through the element, the element heats up and excites the gas. This produces the light that we see

Resistor

• A resistor limits the flow of electrical current.• It is one of the most commonly used

components in an electrical circuit. • Resistors are often used with motors to

suppress the surge of current and allow the current to the motor to be gradually increased.

• A resistor is made of a material that does not allow current to easily flow through ex. carbon.

Buzzer

• When electricity is applied to a buzzer, it causes a vibration to occur inside the buzzer’s housing. This vibration is what causes the buzzing noise.

Solenoid• A solenoid produces linear mechanical motion from

electrical energy.

• Solenoids are used to – operate flippers in pinball machines

– operate fluid power valves

– turn motors on and off

Solenoid• Solenoid consist of – armature (plunger)– C Frame (coil)

• The solenoid has an armature or plunger that moves in a linear motion when electrical current is applied to its electrical coil

Motor

• A motor is the output device that produces rotary mechanical motion, ex. a fan

motor of a fan

Activity 3

Recap

• What are the output devices

High current • High current can damage electrical components.• High current occur for two reasons:

1. many loads are connected to the circuit

2. A short circuit

Short circuit

• A short circuit is a direct path with little or no resistance created between the positive and negative terminals of the power supply

• Since current flows through the path with least resistance, it will take this path.

Short Circuit

Circuit protection

• Devices used to protect electrical components from high current: Fuse Circuit Breaker

The Fuse Operation

A fuse is used to protect the circuit components from high current.

The fuse must be replaced each time an overload or short circuit condition occurs.

Fuses are used in applications where a problem rarely occurs, ex. car’s light

• Fuses are rated for a maximum current value. • If the maximum current value is exceeded, the fuse

blows to protect the components of the circuit.

What is the current ratings

for the following fuses ?

Fuse rating

• When the current flow exceeds the rated value of the fuse, the wire or foil strip melts and opens the circuit (the fuse is blown).

Testing the continuity of the fuse

Continuity

• If the fuse is good, it has continuity (like a wire)

• If a fuse is blown, it has no continuity.

Fuses• Many electrical devices have fuses.

• Fuses are easy to replace.

• Fuse are low cost. One fuse cost 0.25 DHS per fuse.

• Special care needs to be taken to make sure that the properly rated fuse is installed to provide the needed protection.

Say it in a simple words…

Circuit Breakers

– Circuit breaker is used to protect the circuit components from high current.

– Just as a fuse blows, a circuit breaker opens or trips when an excessive current is present.

– The circuit breaker can be reset and used again.

Circuit breakers are used where overloads commonly occur

Ex. power supply and your house wiring

Testing the continuity of the circuit breaker

• If the breaker is tripped, it has no continuity

• if the breaker is reset, it has continuity

Circuit breaker

• Circuit breakers are either – thermally-triggered tripped due to heat caused by excessive current– magnetically-triggered tripped due to the strength of the magnetic field

created by excessive current.

• In some cases a circuit breaker is combination of both

• Circuit breakers can have different types of reset switches

• Some have lever type resets, while some have pushbutton resets.

• Most newer homes and businesses use circuit breakers in their electrical control pannel

• control panels. electrical control panels.

Is it lever type or push button type?When this circuit breaker will trip?

Activity 4

Wait for about 30 seconds to see if the circuit breaker “trips” off.

Repeat step 2 and observe the circuit breaker’s operation.

I=24/25 = 0.96 A

I= 1.25 A

I=24/10 = 2.4 A

• Measure continuity of the circuit breaker • Replace the 10 ohm resistor with a 25 ohm

resistor.

Activity 4

Recap

• High current • Short circuit • Circuit protection: Fuse and circuit breaker• Fuse rating • Fuse operation• Testing the continuity of the fuse • Circuit breaker