Simple Induction Heater Circuit

This article shows you how to build a circuit that uses magnetism to heat up iron objects.

This is called induction heating.

WARNING: Building circuits with high voltage and currents can be dangerous.

Only do this with adult supervision and proper safety gear.

This project is not recommended for beginners.

What is a Induction Heater Circuit:

An electrical gadget called an induction heater circuit uses the electromagnetic induction principle to produce heat in a specific region.

Usually, a high frequency magnetic field is used to create eddy currents in conductive materials, such metal objects, which causes the material to heat up quickly.

Applications for induction warmers include kitchen appliances, research experimentation and metal hardening.

Circuit Working:

Parts List:

Induction Heater Working Principle:

An induction heater employs a high frequency magnetic field to induce eddy currents in iron or ferromagnetic metals.

This process restricts the movement of electrons within the metal, resulting in the development of eddy currents and subsequent heating.

The heat generated is directly proportional to the square of the current I² multiplied by the resistance R of the metal considering iron in this context.

The resistivity of iron is 97 nΩ*m emphasizing the need for optimized designs utilizing ferrite materials instead of traditional iron stamped transformers in high frequency switching applications.

Formula:

Below formula explains how resistance, current and heat generation interact in an object, like as an iron.

It is an example of Joules Law, an essential electrical concept.

Heat = I² × R (Iron)

where,

• Heat: This is the quantity of thermal energy that the iron produces, it is commonly expressed in calories (cal) or joules J.
• I2: This stands for the square of the irons current flow, expressed in amperes A, the square represents the fact that the heat produced rises in direct proportion to the square of the stream.
• Put more simply, the creation of heat will double with a doubling of the current.
• R: This is the irons heating elements, electrical resistance, expressed in ohms Ω.
• Resistance causes electrical energy to be converted into thermal energy by obstructing the passage of current.

How the formula works:

The heating element of the iron conducts electricity when it is plugged in and turned on.

Because of the high resistance material used to make it, this element provides a lot of resistance to the passage of electricity.

Electrical energy is converted by this opposition into thermal energy, which is what we experience as heat.

Zero Voltage Switching Technology:

The discussed induction heater circuits exploit ZVS technology for triggering the MOSFETs

ZVS ensures minimal device heating enhancing the overall efficiency of the operation.

The circuit are inherently self resonant automatically aligning with the resonant frequency of the attached coil and capacitor, resembling a tank circuit.

Utilizing Oscillator:

The circuit incorporates a Royer oscillator known for its simplicity and self resonant operating principle.

The functioning involves a sequential turn on of MOSFETs, where one initiates conduction before the other due to inherent variations in electronic device specifications.

ZVS Technology and Its Advantages:

ZVS or Zero Voltage Switching ensures safe MOSFET activation with minimal or zero current at their drains.

This property reduces the need for large heatsinks enabling the circuit to handle substantial loads of up to 1 kVA efficiently.

The resonant frequency of the circuit is directly dependent on the inductance L1 and capacitance C1 values, as calculated by the formula:

Formula:

f = 1 / 2π × √L × C​

where,

• f: This is the circuits resonance frequency, expressed in hertz Hz.
• The frequency at which the circuit oscillates most naturally and with the largest amplitude is known as the resonant frequency.
• 2π: is the product of twice the mathematical constant pi (about equivalent to 3.14159).
• It typically appears in computations involving oscillations and other periodic processes.
• L: This is the inductors measured inductance in henries H for the LC circuit.
• By producing a voltage, inductors resist variations in current.
• C: This is the capacitance expressed in farads F, of the capacitor in the LC circuit.
• In an electrostatic field, capacitors store electrical energy.
• √: The square root is represented by this symbol.

How the formula functions:

Consider a swing set, comparable to the swings length is the inductance L, and the weight of the person seated on it is equivalent to the capacitance C.

You may modify the swings inherent frequency of oscillation by varying these variables.

In essence, the formula says that the square root of the product of capacitance C and inductance L determines the resonant frequency of the LC circuit in an inverse manner.

Component Specifications:

Recommended MOSFETs, such as the IRF540 rated at 110V and 33A can be used for the induction heater circuits.

While heatsinks may be employed the design ensures that heat generation is within manageable limits.

Adequately rated N channel MOSFETs can also be used without specific restrictions.

Inductor and Tank Circuit:

The inductor associated with the main heater coil acts as a choke preventing high frequency content entry into the power supply and restricting current to safe limits.

Its value should be significantly higher than the work coil typically around 2mH, constructed with high gauge wires to handle high currents safely.

The tank circuit, comprising C1and L1 is designed for high resonant frequency latching and must be rated to withstand high current and heat magnitudes.

Powerful Induction Heater Design:

The first design introduced is an efficient ZVS induction concept based on the Mazzilli driver theory.

Featuring a single work coil and two current limiter coils, this design eliminates the need for a center tap, ensuring effective and rapid heating of large loads through a full bridge push pull action.

Power Output:

The power output of this design can reach up to 1200 watts with an input voltage of 48V and current up to 25A.

This level of power is demonstrated by the ability to melt a 1 cm thick bolt within a minute when the system is in operation.

The module for this design is readily available online making it accessible at a reasonable cost.

How to Build:

Constructing a high frequency induction heater using ZVS technology involves assembling the necessary components and following process.

Prepare the Inductor :

• Wind a center tapped coil with high gauge wires.
• Aim for a value around 2mH.

Assemble the Tank Circuit :

• Connect the metalized PP capacitor e.g. 330nF 400V in parallel with the inductor L1.

Build the Oscillator:

• Set up the Royer oscillator using resistors and capacitors ensuring proper values for reliable operation.

Connect MOSFETs:

• Connect the IRF540 MOSFETs or other selected N channel MOSFETs to the circuit.
• Ensure proper placement and connections.

Integrate Schottky Diodes:

• Connect Schottky diodes across the gates sources of each MOSFET to discharge gate capacitance during non conducting states facilitating quick switching.

Incorporate Fast Recovery Diodes:

• Connect fast recovery or high speed switching diodes as needed in the circuit.

Verify Connections:

• Double check all connections ensuring that there are no loose wires or incorrect placements.

Power Supply Connection:

• Connect the power supply to the circuit, ensuring it meets the specified voltage and current requirements.

Testing:

• Power on the circuit and observe its behavior.
• Check for oscillation at the resonant frequency and ensure that the components are not overheating.

Adjustments:

• Fine tune the circuit if necessary adjusting components for optimal performance.

Load Connection:

• Connect the load e.g. a work coil to the circuit and observe the heating effect.
• Exercise caution and follow safety guidelines when testing with loads.

Conclusion:

Building electronic circuits requires knowledge of electronics and soldering skills.

If you are not familiar with these consider seeking assistance from someone with experience or consulting detailed circuit diagrams and guides.

Ensure safety precautions are followed, and always power off the circuit when making adjustments.

References

Induction heater

PMW control of a 5-12v ZVS induction heater?