Source: https://mokxi.com/teachers/plans/transformers-in-practice Lesson plan # Transformers in practice lesson plan The iron box between the wall and your project, measured: turns ratio, VA ratings, center taps, regulation under load, isolation, and the 24 V control transformer in every furnace. 7 chapters, 7 lessons, about 5 hours, no board. Every lesson runs in the browser, with nothing to install. Start a class from this course The unit ## Objectives and materials ### By the end, students can - Volts down, amps up, and why DC gets nothing through. - Half load, full load and overload on a 12 VA transformer. - Two halves and two diodes make full-wave DC. - Why a 12 V transformer reads 13 V, and what a brownout adds. - A floating secondary, and what it does not protect against. - R, C, W and G, the VA budget, Class 2 and the fuse. - A 24 VAC control supply with a regulated 12 V rail. ### Materials for the whole unit - Capacitor - Diode x 2 - Filament lamp - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 3 - Resistor x 2 - Signal generator - Voltage regulator Every part is already on the simulator’s bench, so there is nothing to buy or hand out. The counts are the most any one lesson uses, if you build it on real breadboards too. Chapter 1. About 40 min ## Turns ratio Volts down, amps up, and why DC gets nothing through. Lesson | Time | What students do Turns ratio: volts down, amps up Two coils on one iron core: the turns ratio sets the volts, the amps trade the other way, and DC gets nothing through at all. | 40 min - Run it and read the secondary - The primary barely sips - Predict: half the mains - Volts down means amps up - Predict: a 24 V transformer - DC gets nothing through ### Materials - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 2 - Resistor - Signal generator ### Check for understanding Each student finishes "Turns ratio: volts down, amps up" on their own, without opening the hints. The simulator checks 6 of its 6 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "DC gets nothing through". Chapter 2. About 40 min ## VA rating Half load, full load and overload on a 12 VA transformer. Lesson | Time | What students do VA rating: how much it can give Volts times amps is the number on the label. Load a 12 VA transformer to half, to full and past it, and watch the volts sag and the copper heat. | 40 min - Half load - Read the VA - Full load - Predict: overload it - Sag and heat - Design with a margin ### Materials - Mains transformer, 230 V or 120 V to 12 V - Multimeter - Resistor - Signal generator ### Check for understanding Each student finishes "VA rating: how much it can give" on their own, without opening the hints. The simulator checks 6 of its 6 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Design with a margin". Chapter 3. About 50 min ## Center taps Two halves and two diodes make full-wave DC. Lesson | Time | What students do Center taps and full-wave DC A tap in the middle of the secondary gives two equal halves: with two diodes, a full-wave rectifier with half the ripple of one. | 50 min - Two halves - Half-wave DC - Measure the ripple - Wire the other half - Full-wave DC - Predict: the ripple - End to end ### Materials - Capacitor - Diode x 2 - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 3 - Resistor - Signal generator ### Check for understanding Each student finishes "Center taps and full-wave DC" on their own, without opening the hints. The simulator checks 7 of its 7 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "End to end". Chapter 4. About 40 min ## Regulation under load Why a 12 V transformer reads 13 V, and what a brownout adds. Lesson | Time | What students do Regulation under load Why a 12 V transformer reads 13 V on the bench: no-load versus full-load voltage, regulation as a percentage, and what a brownout adds. | 40 min - Light load - Too bright - Full load - The lamp settles - Predict: half load - Brownout ### Materials - Filament lamp - Mains transformer, 230 V or 120 V to 12 V - Multimeter - Resistor - Signal generator ### Check for understanding Each student finishes "Regulation under load" on their own, without opening the hints. The simulator checks 6 of its 6 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Brownout". Chapter 5. About 40 min ## Isolation A floating secondary, and what it does not protect against. Lesson | Time | What students do Isolation: the secondary floats No wire joins the windings, so a floating secondary has no path to earth. What that protects you from, and what it never does. | 40 min - A secondary with no reference - Touch one side - Predict: ground the secondary - Now S1 has a voltage to earth - Predict: a 24 V secondary - What isolation does not do ### Materials - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 2 - Resistor x 2 - Signal generator ### Check for understanding Each student finishes "Isolation: the secondary floats" on their own, without opening the hints. The simulator checks 6 of its 6 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "What isolation does not do". Chapter 6. About 40 min ## 24 V control transformers R, C, W and G, the VA budget, Class 2 and the fuse. Lesson | Time | What students do 24 V control transformers The transformer in every furnace and air handler: R and C, the thermostat's W and G, a VA budget, and the fuse on the secondary. | 40 min - R and C - Call for heat - Fan on too - Predict: blow the VA budget - The sag on the R wire - Class 2 and the fuse ### Materials - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 2 - Resistor x 2 - Signal generator ### Check for understanding Each student finishes "24 V control transformers" on their own, without opening the hints. The simulator checks 6 of its 6 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Class 2 and the fuse". Chapter 7. About 50 min ## Boss project A 24 VAC control supply with a regulated 12 V rail. Lesson | Time | What students do Boss: a 24 VAC control supply One 24 V transformer runs a thermostat loop and a regulated 12 V DC rail: center tap, full-wave, VA budget and regulation in one build you then change. | 50 min - Run the supply - The 12 V rail - The display lights - Call for heat - Your change: a two-stage valve - Still in spec - Write up your supply ### Materials - Capacitor - Diode x 2 - Filament lamp - Mains transformer, 230 V or 120 V to 12 V - Multimeter x 2 - Resistor - Signal generator - Voltage regulator ### Check for understanding Each student finishes "Boss: a 24 VAC control supply" on their own, without opening the hints. The simulator checks 7 of its 7 steps as they go. Then ask each one to explain, in a sentence or two, the last thing it asked of them: "Write up your supply". Your class ## Teach this unit as a class Start a class from this course and its 7 lessons are assigned in one go, in order. Students join with a six-character code or printed login cards, and each one’s work comes back to you. The class tools are free for 30 days for one class of up to 20 students, with no card. The lessons themselves are free either way. Start a class from this course See the demo class More units ## Other lesson plans Electronics basics 20 lessons, about 10 h. Embedded on the Arduino Uno 16 lessons, about 12 h. Embedded on the ESP32-C3 13 lessons, about 11 h. Embedded on the Raspberry Pi Pico 7 lessons, about 6 h. Build your own fight stick 5 lessons, about 4 h. Embedded on the STM32F411 6 lessons, about 6 h. C++ on a board 13 lessons, about 10 h. Digital logic and memory 4 lessons, about 4 h. Interactive devices on the Uno 9 lessons, about 8 h. From gates to a computer 23 lessons, about 16 h. Build a claw machine 8 lessons, about 6 h. Every unit All the courses as ready-made units, on the teachers page.