Introduction: 120W Induction Cooktop

For our university course Design engineering for physicists we had to make a setup for a practical experiment a secondary school teacher could do. Therefore we decided to build an induction cooktop, which would be able to bake an egg.

The induction cooktop can be found in the photo above, in this setup you can only turn the cooktop on/off. The way you can do this is by turning the power supply on/off. An induction-compatible pan can be placed on top of the tile and when turned on the induction cooktop will start to generate heat in the pan (very slowly).

The slow speed is caused due to the specifications of the induction cooktop, since we had to follow some safety limitations. The relevant safety guidelines for this project are listed below:

  • The maximum power we could use was 120W consisting out of:
  • A maximum current of 5 A.
  • A maximum voltage of 24V.
  • The maximum temperature any part of the system could reach was 50°C / 122°F.
  • The use of glass is not permitted.

It could be possible to upgrade this induction cooktop to meet your own standards, however keep in mind that these guidelines we used are for safety. We advice you not to use different values for your current and/or voltage if you do not know whether your circuit and you can handle it safely.

This project has been done by Hugo Bemer, Merel Vooijs and Hidde van Zoggel, we had help from older Applied Science students and of course the three Makerspace makertiers Ron, Tom and Diederik.

Supplies


You will need the following supplies in order to replicate this build:

Casing:

  • 1x ceramic bathroom tile (180x180x5mm).
  • 2x metal bars (5x3x1cm).
  • 1x plywood plank (600x450x6mm).
  • 1x plywood plank (450x300x6mm).
  • 1x cylinder PVC (length: 10cm, R=2.5cm)

Electronics:

  • 1x Arduino Uno (https://www.arduino.cc/).
  • 1x Breadboard.
  • 1x 12V computer fan (120x120mm).
  • 1x LM35 temperature sensor.
  • 1x Arduino relay module
  • 1x Copper wire (~1m R=0.5mm).
  • 1x Copper wire (~8m R=0.25mm).
  • 2x 470Ω resistances.
  • 2x 10kΩ resistances.
  • 2x IRL540 MOSFETs.
  • 4x IN5408 diodes.
  • 1x 0.56µF capacitor.
  • 1x 0.39µF capacitor.
  • Breadboard wires.
  • Electrical wires.

Tools:

  • 1x 2A, 20V DC PSU (We used a CPX400A DUAL 60V 20A, here you can alter the current/voltage).
  • Soldering iron and solder.
  • Pliers.
  • Sanding paper.
  • Woodglue (if the case won't click well).
  • Lasercutter.

Skills:

Note: If you are not comfortable with one or more of these skills, look up more tutorials and keep trying!

Software:

Step 1: Lasercutting

The coil to produce heat in the pan is different from traditional coils. This will be a flat coil in the shape of a spiral, therefore it is difficult to be made with a machine, so you can do it by hand.

In order to make the coil, you need to make a holder for the coil, after that you can click the copper coilwire (R = 0.25mm) into the holder. You have to cut out a circle (R = 8.5cm) for the coil holder. In the circle, you have to engrave a spiral with a thickness and engraving depth of 0.5mm. The coil has to have 50 windings and a fan spread of 1. At the start, middle and the end of the coil there should be a hole cut in order to allow the wire passing through the back of the holder. When pressing in the wire, when you reached the hole in the middle, you need to allow a little u-bend wire to pass through the hole. After the u-bend, the wire should continue to be pressed in the engravings.

One important thing that we noticed: our lasercutter had issues with registering the line width of the spiral function in inkscape. We solved this problem by using 2 spirals, but 1 flipped around. Space between these spirals can then be filled with the paintbucket. We listed our coilholder in this step, watch out, we didn't lasercut a hole in the middle, so you still have to do that on your own!


The other thing that has to be lasercut is the case of the induction plate, you will need to lasercut a box (25x25x15cm) but you dont need the top of the box. A great tool to create your own lasercut boxes without having to use woodglue is Makercase (https://en.makercase.com/#/). You will still need to add holes in the sides in order to let wires in and out, install the 2 metal bars and give the fan access to fresh air. The holes for the metal bars should be 3cm wide and 1cm high, they should be apart by 16cm measured from the inner edges of the holes.

Again, we listed our case design below. Watch out, we didn't lasercut a fan-hole and holes for the metal bars, so you still have to do that on your own!

Both the coilholder and the case can be cut from the 2 plywood planks, so both designs should be merged into the same .svg file.

Attachments

Step 2: Cooling System

The cooling system can be made using the Arduino Uno, breadboard, breadboard cables, temperature sensor and arduino relay module. You can use the schematic drawing in order to install the arduino and the relay module. Instead of using a lamp which is displayed in the schematic, you should use the fan.

After that, these steps have to be followed to install the LM35 temperature sensor:

  • VCC (Positive) pin of LM35 -> 3.3V pin of Arduino
  • GND (Ground) pin of LM35 -> GND pin of Arduino
  • OUT pin of LM35 -> Analog input pin (e.g., A0) of Arduino

Then, the code for the Arduino has to be made so the fan goes on at 35°C. We listed the code that we used, however you can also choose to do it yourselves. Code:


// Pin connections

const int temperaturePin = A0; // Analog pin to read the LM35 temperature sensor

const int relayPin = 9;       // Pin connected to the relay module


// Temperature thresholds

const int maxTemperature = 50; // Maximum temperature in degrees Celsius


void setup() {

 pinMode(relayPin, OUTPUT);  // Set the relay pin as an output

 Serial.begin(9600);         // Initialize serial communication

}


void loop() {

 // Read the temperature from the LM35 sensor

 int sensorValue = analogRead(temperaturePin);


 // Convert the sensor value to temperature in degrees Celsius

 float voltage = (sensorValue / 1024.0) * 5.0;

 float temperature = voltage * 100;


 // Print the temperature on the serial monitor

 Serial.print("Temperature: ");

 Serial.print(temperature);

 Serial.println(" °C");


 // Check if temperature exceeds the threshold

 if (temperature > maxTemperature) {

   digitalWrite(relayPin, HIGH); // Activate the relay to turn on the fan

 } else {

   digitalWrite(relayPin, LOW);  // Deactivate the relay to turn off the fan

 }


 delay(1000); // Wait for a second before reading the temperature again

}

Step 3: Electric Circuit

The next step in the process is building the electric circuit. The schematic for the electric circuit can be found above. When we talk about connecting, we mean soldering the connections.

You first have to make an inductor with the ~1m wire and the PVC cylinder. You do this by circeling 5 windings of the copper wire around the PVC cylinder. Then leave a little bit of straight wire at the ends, so it can be connected to the rest of the circuit and then cut the wire with the pliers.

After that it is important to use the sanding paper to scratch the ends of the inductor and the 3 ends of the heating coil. By scratching the ends of the copper wire you remove the coating at that place, so the wire connects better when soldering.

Next, connect the u-bend from the middle of the coilwire of the heating coil to one of the ends of the inductor. After that, using electrical wire, connect the center end of the coil to 1 of the pins on the 0.56µF capacitor and connect the outside end of the spiral to the other pin on the 0.56µF capacitor.

Now, again using electrical wire, connect 1 of the pins on the 0.56µF capacitor to 1 of the pins on the 0.39µF capacitor and then connect the other 2 pins with each other. Now, connect 1 of the pins on the 0.39µF capacitor to the drain of 1 of the MOSFETs. Now, connect the 2nd pin of the 0.39µF capacitor to the drain of the other MOSFET.

After that connect a 10k resistor to both MOSFETs from the drain pin to the ground pin. Connect 2 diodes to the circuit. One from the drain of one mosfet to the ground of the other mosfet with the negative side to the drain. The other diode in reverse.

The other two diodes need to be connected between the positive power source and the inductor. Each need to be connected from that point to one of the wires before the capacitor facing the MOSFETs. Both MOSFETs also need to be connect from source to source because that is where the ground will be attached.

At last connect two 470Ω resistors from both diodes to a joint point with the inductor. This is where the positive pole of the power source will be attached.

Step 4: Combining All Parts

This is the finalizing step of the build, here we put everything into the case. First, start with clicking the plywood case parts into each other. If you have used Makercase to make these parts, then they shouldn't be able to move. If the plates aren't connected well, then you should glue them together using wood glue.

Next, install the fan on the outside of the case, make sure the circuit is placed so it doesn't take up too much space. Then, use ductape to install the heating coil directly under the bathroom tile. Keep the electric circuit away from the cooling circuit, because if they connect, they might cause a short circuit.

Now, you can place the tile with the coil on top of the 2 metal bars, it should be fine that it moves, however if you please you can use ductape to make it rigid.

And that's it! Congratulations with making your own induction cooktop!