3kW Induction Heater Build

WARNING!

This induction heater produces hundreds of volts across its output. DO NOT touch the circuit OR workcoil while powered on! Or you risk being electrocuted! Once the power is switched off, the capacitor bank instantly discharges and the circuit is safe to work on.

Downloads:

Circuit Schematic

PCB Gerber Files

Watch Build Video

Specifications:

PCB Size: 86 x 284mm

Input voltage: 40~65VDC

Max input current: 50A

Max power consumption: 3,250watts

Assembling the PCB

You’ll find all the components & their specifications listed below. You can download a detailed schematic to identify what component goes where on the PCB.

PCB Components:

C1~14 – 330nF 600VAC Capacitors

C15, C16 – 2.2uF 100V Ceramic Capacitors

D1, D2 - 12V 5W Zener Diode

D3, D4 – FR307 Fast Diode

D5 – 5mm LED

D6 - SB5H100 200A 100V Schottky Diode

L1, L2 – 60uH 25A Custom made inductors (watch video)

R1, R3 – 150R 5W Metal Oxide Resistor

R2, R4 – 1K 5W Metal Oxide Resistor

R5, R6 – 10K 1/2W Metal Oxide Resistor

R7 – 4.7K 1/2W Metal Oxide Resistor

R8, R9, R10, R11 – 18R 1/2W Metal Oxide Resistor

Q1, Q2, Q3, Q4 - IRFP4668PBF MOSFET

Bolstering the PCB traces

The traces on the PCB that are exposed on the underside need to be bolstered by either cutting out copper busbars from a sheet of copper (1.5mm or thicker) Or by using 14AWG, 2.5mm core electrical cable, soldered to the PCB traces. I used the latter method in the build video, and although it’s not very aesthetically pleasing. It’s proven to work without any issues

Workcoil Design

The workcoil is the business end of all induction heaters. When it comes to designing a workcoil several design elements should be taken into account. This is an area where I’d admit, I’m still learning myself, so I don’t consider my advice on this topic to be all that helpful. But, a good starting point is to have a workcoil with 6 turns of 3/8” copper tubing to make the workcoil.
The internal diameter should be around 10~20mm larger than the piece of metal you’re intending to heat.
Using a workcoil that has a much larger diameter than the piece of metal you’re heating, will reduce performance & lead to longer heat times.

The air gap between turns has a significant role in determining the input current consumption and power output. Increasing the air gap also increases input current consumption. And the opposite is also true, smaller airgap = lower input current consumption. Calculating the correct air gap on paper before you construct your workcoil is very doable however, it's also possible to use a trial & error method. Start by keeping the windings tight (around 2mm air gap), operate the induction heater, and monitor the current consumption, if you wish to increase the current, then gently spread the winding further apart to increase the airgap. You can repeat this process until you achieve your ideal power input/output. (Don't forget to have the induction heater OFF while making alterations to the workcoil)

A company called ‘Ambrell’ published a 28-page guide around workcoil design. You can request a free copy of their guide by using this link Click Here (They do ask for your name & email, but it’s 100% free)

Cooling

During normal operation, the MOSFET heatsinks & capacitors will get hot! You will need to use a fan to blow air over the components to keep the temperatures at acceptable levels.

For runtime more than 30 secs or so, the workcoil will get very hot. I’d highly recommend cooling the workcoil by continually pumping water through it.

Printed Circuit Board

Order your own custom printed circuit board using the files below:

Download PCB Gerber Files

Inductors

I made my own custom inductors for this project. I used a total of 4x T157-26 Inductor Toroid Rings. Each inductor has 2 toroid rings stacked on top of one another. I have found this to be the most cost-effective solution for this project. A total of 16 turns of 2mm (12AWG) magnet wire is wrapped around the toroids to produce an inductor with approximately 60uH of inductance.

You can customize the inductance by adding or subtracting turns around the toroids. If you’re heating smaller pieces of metal, to maximize power output from the induction heater into the piece of metal you’re heating, you may want to consider lowering the inductance to around 30~40uH. Similarly, the inverse is true. If you’re heating large pieces of metal & your induction heater is drawing more current than the maximum allowed (50A) Then increasing the inductance to 60~200uH will bring the input current down to a safe level.

If you’re using 2x T157-26 stacked together, below is a cheat sheet to quickly customize the inductance.

Number of turns for inductance:

36uH = 13 Turns

60uH = 16 Turns

100uH = 21 Turns

150uH = 26 Turns

200uH = 30 Turns

Alternatively, you can use this calculator to help you customize the inductance

Components:

4x T157-26 Inductor Toroid Ring

· Size: 40x24x15mm

· Material: Iron Powder