1.4kW Induction Heater

Resources:

Build & demo video: Click here

Coil form tool Download STL file

PCB Gerber files Download gerbers

Schematic Download Schematic

Details:

Voltage input: 12~48VDC

Current input: up to 30A (@48VDC)

Peak power input: 1,400watts

The Circuit

This induction heater is based on the popular "Royer induction heater" schematic. I believe this is the original post/author? Click here

Changes made to the design include:

• Higher rated MOSFETs

• Bigger Zener diodes

• RC filter on the Gates

• Flyback Diode (D8)

• Gate resistors to limit ringing (R8, R9)

In short, all of the changes help to improve the durability of the induction heater. It has been reported with the original design, often the MOSFET gate's would be damaged from flyback after extended use. To be fair, I haven't tested the circuit without my additions so I can't confirm or deny this. Gate resistors have to be added as ringing was quite a problem without them. The ringing would cause the MOSFETs to become quite hot & this can lead to premature failure. With the addition of a pair of 18R gate resistors. The ringing was reduced to an acceptable level.

Components:

2x Wakefield-Vette, 694-50 Heatsink Click here

2x IRFP4668PBF MOSFETs Click Here

10x WIMA, MKP1J034706B00KB00, 470nF, 630VAC Capacitor Click here

2x 2.2uF Ceramic 100v Capacitor Click here

2x FR307 Fast Diode Click here

2x 47R, 5w Metal Oxide resistor Click here

2x 470R, 5w Metal Oxide resistor Click here

2x 12v, 5w Zener Diode Click here

1x SB5H100 Schottky Diode Click here

2x 100uH, 15A inductor Click here (see below for details)

2x 10k, 1/2w resistor

1x 4.7k, 1/2w resistor

2x 18ohm 1/2w resistor

1x 5mm LED of your choice (power indicator LED)

The inductors

For the inductors, I opted to wind my own. Options for this size are somewhat limited & it was cheaper to make my own anyhow. If you don't wish to make your own, then alternatively you can buy them from banggood Click here

Toroid details:

Size: 42x22x17mm

Material: Iron Powder, HY2

Color Code: Yellow/White

For the wire, I used 1.25mm (16AWG) enamel insulated copper wire. Each toroid used approx 1.6m (63inch) of wire. This length of wire yields 30~32 turns around the toroid giving an approx inductance of 100uH.

Tinning the high current traces

Located on the underside of the PCB is several exposed traces that should be tinned with PLENTY of solder after all the components have been installed. These traces carry very high current that pulses through the work coil. Failure to adequately bolster these traces with copious amounts of solder will result in the solder melting off the PCB, which will result in the trace burning out, which in turn blows up one of the MOSFETs (not that I'd have done anything like that :P )

I'd recommend laying down some fairly heavy copper wire on top of the traces & solder it in place just to be on the safe side.

The Coil

This is the work coil. I made my coil from 3/8" copper tubing (the type used for aircon, fridges.etc) It's pretty inexpensive & easy to find at most hardware stores or aircon shops. The inside diameter of my coil is 70mm to accommodate almost anything I'd need to heat.

The coils consist of 6 & 1/2 turns. The amount of turns does play a role in determining the resonating frequency (and also power output/consumption). If you know what you are doing & are willing to experiment with different coils, then go for it. Otherwise, I'd suggest making a coil with 6~8 turns.

If you watched my build video, then you'll have seen me 3D print a form tool, used to wrap the copper around to form the coil into a spiral. Strictly speaking, It's not essential however, it does produce a nice uniform coil. You can download the STL file Here

Performance

With a 48V power input and a 140mm PC fan blowing air over the heatsinks & caps. Temperatures were quite acceptable at 80c (176f) for the MOSFETs, the capacitors were about the same. And the inductors never felt even slightly warm. I think for higher input voltages (above 48VDC) You'd have to start considering spacing the caps further apart for better cooling & depending on how far you push the envelope.... maybe water cooling the MOSFETs & work coil.

Will it melt Aluminum?

The original author demonstrates his induction heater melting an aluminum heatsink. I've attempted to melt alloy in my induction heater and it failed to do so. I'm not exactly sure why he was able to melt alloy and I was not but, I do wonder if he is tuning up his power input to achieve this? He seems to indicate this in his post. It's also possible different alloy's melt easier than others so perhaps this is something I'll explore later.

What would it take to make this induction heater more powerful?

In truth, the components used could probably handle 60V (just monitor the peak voltage across the caps & make sure to stay within their max voltage rating). However, at higher power levels, you certainly need to bolster the high current traces on the PCB to prevent failure. Keeping the caps & MOSFETs within temperate limits could also be a challenge. Perhaps water-cooling would be a viable solution? In any case, it's certainly possible for this circuit to handle higher voltage than 48VDC if appropriate measures are implemented.