AC and DC Loads and Load Sizing for JSS 1

Class: JSS 1
Term: First Term
Week: 6
Age: 12 years
Duration: 45 minutes
Subject: Solar PV Installation and Maintenance
Curriculum Theme: Solar Photovoltaics System for Electricity Generation
Focal competence: Demonstrate the knowledge of Solar Photovoltaics System and safety precautions
Key competencies/values: Communication; Collaboration; ICT and Digital Competencies
Skills:

• Using name plates of appliances, functions or power source to determine their category of load

Previous Lesson: Difference the two
Topic: Electrical Appliances Power Load/Loads Sizing: Ac And Dc Loads
Subject Matter: AC and DC Loads, Load Sizing

Specific Objectives

By the end of the lesson, pupils/students should be able to:

Cognitive Domain

• Explain electrical loads.
• State the characteristics of types of electrical loads.
• Explain AC and DC loads.
• Identify the categories of load based on the type and the function of the appliance.
• Explain the difference in shock risk between AC and DC at comparable specified conditions.

Affective Domain

• Appreciate the importance of correctly identifying electrical loads for safety.
• Collaborate with peers to identify different types of electrical appliances.

Psychomotor Domain

• Extract relevant data from appliance nameplates.
• Categorise appliances as either AC or DC loads.

Reference Materials

The following resources were used in planning this lesson:

• 2025 Revised 9 Years Basic Education Curriculum
• Relevant State Unified Scheme of Work
• Approved curriculum resource/material
• The HeadTeacher Scheme of work

Instructional Materials

The teacher will teach this lesson with the aid of:

• Various electrical appliances (e.g., fan, light bulb, radio, phone charger, laptop)
• Pictures of different electrical appliances
• Appliance nameplates (actual or printed examples)
• Chart showing examples of AC and DC loads

Rationale for the Lesson

This lesson is important because understanding electrical loads, particularly AC and DC types, is fundamental for designing and installing effective solar PV systems. It helps students recognise how different appliances consume power and the necessary information to size a solar system correctly, while also highlighting critical safety aspects of electrical currents.

Prerequisite/Previous Knowledge

Students should have basic knowledge of electricity and simple electrical circuits from their previous science lessons.

Lesson Content/Board Summary

Electrical Appliances Power Load/Loads Sizing: AC And DC Loads

Electrical Loads

An electrical load is any component or device that consumes electric power. It converts electrical energy into other forms of energy such as light, heat, or mechanical work. Examples include light bulbs, fans, refrigerators, and mobile phones.

Types of Electrical Loads

Electrical loads can be broadly categorised based on the type of electric current they use:

1. Alternating Current (AC) Loads: These are appliances that operate on alternating current, where the electric charge periodically reverses direction. Most household appliances in Nigeria run on AC power.
2. Direct Current (DC) Loads: These are appliances that operate on direct current, where the electric charge flows in only one direction. Many portable electronic devices and appliances directly powered by batteries or solar panels are DC loads.

Characteristics of AC and DC Loads

1. AC Loads:
   1. Typically used in homes and offices, powered by the national grid.
   2. Can be transmitted over long distances with less energy loss.
   3. Examples: Televisions, refrigerators, electric irons, washing machines, ceiling fans.
2. DC Loads:
   1. Common in battery-powered devices and solar PV systems.
   2. Voltage is constant and current flows in one direction.
   3. Examples: Mobile phones, laptops, LED lights (when directly powered by battery/solar), car batteries, solar charge controllers.

Identifying Load Categories Using Appliance Nameplates

An appliance nameplate is a label usually found on the back or bottom of an electrical device. It provides important information about the appliance, including:

1. Voltage (V): The electrical potential difference required for the appliance to operate. It often specifies AC (e.g., 220-240V AC) or DC (e.g., 12V DC).
2. Current (A): The amount of electrical flow the appliance draws.
3. Power (W or VA): The rate at which the appliance consumes electrical energy.
4. Frequency (Hz): For AC appliances, this indicates the number of cycles per second (e.g., 50 Hz or 60 Hz). DC appliances do not have a frequency.

By checking the voltage and frequency on the nameplate, one can determine if an appliance is an AC or DC load.

Load Sizing

Load sizing is the process of calculating the total electrical power consumed by all appliances that will be connected to a power system (like a solar PV system). This calculation helps determine the appropriate size of components needed for the system, such as solar panels, batteries, and inverters. To size loads, you need to identify all appliances, their power ratings (from nameplates), and how many hours they will be used per day.

Electrical Shock Risk: AC vs. DC

Both AC and DC currents can cause electrical shock and be dangerous. However, at comparable specified conditions (e.g., same voltage and current levels), AC is generally considered more dangerous than DC for the following reasons:

1. Muscle Contraction: AC current can cause involuntary muscle contraction, making it difficult for a person to let go of a live conductor. DC current often causes a single convulsive contraction, which might throw a person away from the source.
2. Threshold for Perception and Let-Go: The threshold for feeling an AC shock and the “let-go” current (the maximum current at which a person can still release the conductor) are lower for AC than for DC. This means AC can be felt at lower levels and is harder to escape.
3. Heart Fibrillation: AC current is more effective at inducing ventricular fibrillation (irregular heartbeat) in the human heart, which can be fatal.

Teaching Methods/Instructional Techniques

Discussion, Demonstration, Guided Practice, Question and Answer, Explanation, Observation, Practical Activity

Instructional Procedures

Step 1: Introduction

Time: 5 minutes

Teaching Skill: Engaging/Questioning

Teacher’s Activity: The teacher greets the students and asks them to name some electrical appliances they use daily at home. The teacher then asks what makes these appliances work.

Pupils’ Activity: Pupils respond by naming appliances like fans, TVs, phones, and state that electricity makes them work.

Learning Point: Daily appliance usage

Step 2: Explanation of Electrical Loads

Time: 7 minutes

Teaching Skill: Explanation/Discussion

Teacher’s Activity: The teacher explains what an electrical load is, using the appliances named by students as examples. The teacher guides students to explain electrical loads in their own words.

Pupils’ Activity: Students listen, ask questions, and attempt to explain electrical loads.

Learning Point: Meaning of electrical loads

Step 3: Introduction to AC and DC Loads

Time: 8 minutes

Teaching Skill: Explanation/Demonstration

Teacher’s Activity: The teacher introduces the two main types of electrical current: Alternating Current (AC) and Direct Current (DC). Using examples and pictures, the teacher explains that appliances are designed to use either AC or DC. The teacher explains AC and DC loads.

Pupils’ Activity: Students observe the examples, listen to the explanation, and differentiate between AC and DC loads.

Learning Point: AC and DC loads

Step 4: Characteristics of AC and DC Loads

Time: 7 minutes

Teaching Skill: Guided Discussion

Teacher’s Activity: The teacher guides students to state the characteristics of AC and DC loads, providing further examples for each type. The teacher highlights where each type of current is typically found (e.g., grid for AC, batteries/solar for DC).

Pupils’ Activity: Students contribute characteristics and examples of AC and DC loads.

Learning Point: Load characteristics identified

Step 5: Identifying Load Categories and Nameplates

Time: 6 minutes

Teaching Skill: Practical Demonstration

Teacher’s Activity: The teacher shows students actual appliances or pictures of their nameplates. The teacher demonstrates how to locate and identify relevant data (voltage, current, power, frequency) on the nameplates to determine if an appliance is an AC or DC load.

Pupils’ Activity: Students observe the nameplates and identify key information. They categorise appliances as AC or DC.

Learning Point: Nameplate data extraction

Step 6: Electrical Shock Risk Comparison

Time: 5 minutes

Teaching Skill: Explanation/Safety Awareness

Teacher’s Activity: The teacher explains the curriculum-stated difference in shock risk between AC and DC at comparable conditions, emphasising why AC is generally considered more dangerous due to its effect on the human body.

Pupils’ Activity: Students listen attentively and ask questions about electrical safety.

Learning Point: AC/DC shock risk

Step 7: Evaluation/Review

Time: 5 minutes

Teaching Skill: Questioning/Assessment

Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. What is an electrical load?
2. Mention two types of electrical loads.
3. How can you tell if an appliance is an AC or DC load?
4. Why is AC generally considered more dangerous than DC at the same voltage?

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Load types understood

Step 8: Note-Taking

Time: 4 minutes

Teaching Skill: Guided Writing

Teacher’s Activity: The teacher guides pupils/students to copy the essential Board Summary notes on AC and DC loads into their notebooks.

Pupils’ Activity: Pupils/students copy the notes carefully into their notebooks.

Learning Point: Board summary recording

Step 9: Conclusion

Time: 1 minute

Teaching Skill: Summarising

Teacher’s Activity: The teacher briefly reminds students that understanding AC and DC loads is crucial for working with solar PV systems and for ensuring safety. The teacher thanks the students for their participation.

Pupils’ Activity: Students listen and prepare for the next lesson.

Learning Point: Lesson consolidated

Continuous Assessment/Further Study

Type: Homework

Instruction: In your notebook, complete the following tasks:

1. List five electrical appliances found in your home and state whether each is an AC or DC load.
2. For two of the appliances you listed, write down the voltage and power rating from their nameplates.
3. Explain in your own words why it is important to know if an appliance is AC or DC when planning a solar power system.

Lesson Keywords

• Electrical Load – A device that consumes electric power.
• Alternating Current (AC) – Electric current that periodically reverses direction.
• Direct Current (DC) – Electric current that flows in only one direction.
• Nameplate – A label on an appliance showing its electrical specifications.
• Voltage – The electrical potential difference.
• Power – The rate at which electrical energy is consumed (measured in Watts).
• Load Sizing – Calculating total power consumption for system design.

Differentiation

For weaker learners: Provide pre-labelled pictures of AC and DC appliances for easier identification. Focus on identifying only voltage and AC/DC on nameplates. Use simpler language for explaining shock risk.

For faster learners: Challenge them to calculate the current drawn by a given appliance if its power and voltage are known. Ask them to research specific examples of appliances that can operate on both AC and DC (e.g., laptops with adapters).

Suggested Lesson Videos

For further understanding, search on YouTube for: “AC and DC loads for solar JSS 1” or “Difference between AC and DC current for beginners”.

Teacher Guide for Using This Lesson Plan

Before the lesson, gather a variety of actual electrical appliances or clear pictures of them, along with visible nameplates. Start by engaging students with familiar examples of appliances. Clearly explain the concepts of AC and DC loads, using the characteristics to help students differentiate. When demonstrating nameplates, guide students step-by-step to extract relevant data. Emphasise the practical application of this knowledge in solar PV installation and reinforce the safety aspects of working with electricity. Allow students to copy the Board Summary notes after the main teaching and evaluation to ensure they have accurate information for future reference.