## Chinese 1800 Watt Induction Heater – Horizontal Oven Heat Insulation Test

Test with using regular mineral wool for house insulation, to insulated the work coil in order to achieve higher steel temperatures. Here is another try, …

## Chinese 1800 Watt Induction Heater – Heat Insulation Test

Test with using regular mineral wool for house insulation, to insulated the work coil in order to achieve higher steel temperatures.

## 2200 Watt server power supply for induction heating

A new 2200 Watt power supply made from server power supplies, and with steady cameras 🙂 Test of it in a long induction heater run …

## Unboxing a Chinese 1800 Watt Induction heater

I finally got around to get the IH out of the box and repair it, here is part 1 of a series of videos on …

# Snubber capacitor calculator

Here you can calculate the snubber capacitance that is needed to keep transient voltages below the maximum allowed value. Stray inductance is the inductance in the primary circuit of the inverter. If the stray inductance is not known, the two estimates can be used, high estimate for cable/wire primaries or long distances. Low estimate for copper busbar and short distances.

Switch between the input fields to automatically calculate the values.

 Stray inductance nH Peak current A Max transient voltage V DC bus voltage V Results Snubber capacitance uF High inductance estimate uF Low inductance estimate uF

Formulas used

Calculated snubber capacitance = Stray inductance * Peak current^2 / (maximum allowed transient voltage – DC bus voltage)^2

Snubber capacitance is given in Farad, stray indutance is given in Henry and voltage in Volt.

Estimated high inductance snubber capacitance = Peak current / 100

Estimated low inductance snubber capacitance = (Peak current / 100) * 0.5

## TL494 flyback driver

It took some years and someone recently bumping up my old thread about this project for me to write up a article, find the pictures, …

# TL494 flyback driver

Published on: Jun 14, 2013. Updated on: Nov 28, 2017.

## Introduction

I wanted to design a versatile driver circuit that could drive a half- or full-bridge of MOSFETs or IGBTs through a gate drive transformer (GDT). This should make a driver that is able to run flyback transformers found in CRT TV sets and computer monitors.

The TL494 IC is designed for maintaining all the functions needed in a switching mode power supply using pulse width modulation (PWM). The output transistors can be run in either single ended mode or push-pull. The pulse width is normally controlled through a feedback signal in the power supply, but for this project we want to control it manually, this is done differently in almost all schematics found.

## Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

## Considerations

Flyback transformers from a CRT TV are typically driven at 15 kHz and flyback transformers from computer monitors are typically driven between 30 to 150 kHz.

The TL494 IC uses a 5% dead time to insure proper switching and at frequencies over 150 kHz this minimum dead time is higher.

The design goals for this project will be a driver with a variable duty cycle from 0% to 45% and a variable frequency from 50 kHz to 150 kHz.

This should make for a efficient driver and one that works out of the audible spectrum. In order to design with components at hand, the frequency span is not going so low as 15 kHz.

## Specifications

 Voltage supply IRFP250N: 0 VAC to 120 VAC Frequency span 38 kHz to 150 kHz. Duty cycle span 0% to 43%

## Construction

25th May 2009

The breadboard prototype is ready to be tested, the tape is to hold the timing capacitor in place since the legs on it was too short.

In the first oscilloscope shot we see the output waveform without pull up resistors, it is about 38 kHz at 43% duty cycle.

In the second oscilloscope shot we see the output waveform without pull up resistors, it is about 38 kHz at 5-7% duty cycle.

In the third oscilloscope shot we see the output waveform without pull up resistors, it is about 150 kHz at 43% duty cycle.

27th May 2009

PCBs was made for both the driver and half-bridge section. The full bridge rectifier used here in the pictures is only rated for a mere 4 A. This is not enough for running a flyback with low input voltage and high duty cycle. A 25 A bridge with heat sink should be used to ensure some overhead.

## Test

29th May 2009

In the oscilloscope shot we see the waveform of the primary side of the GDT driving a MOSFET half-bridge. To test the circuit I first used a old half-bridge I had from an earlier project.

The sturdiness of this new driver shines through when I killed a flyback transformer due to over-voltage on the secondary side. Corona glow can be seen in the center towards the ferrite core.

## Conclusion

This universal inverter makes it possible to adjust the output voltage and current exactly to ones needs. It makes a great and much more sturdy flyback driver than many simple drivers with just a single transistor, which is of course no surprise as it implements its own control IC, MOSFET driver ICs and a half-bridge of MOSFETs.

For a final constant voltage or current power supply it will not work, as there is no feedback adjusting the pulse width to a certain load.

# Royer induction heater

Published 18. January 2013. Updated 21. March 2019.

## Introduction

The Mazilli ZVS flyback driver is well-known throughout the high voltage community for its simplicity and ability to deliver 20-50 kV at high currents for a flyback transformer.

About one and a half year ago, Marko from 4hv.org gave the circuit a comeback with it converted to a simple induction heater.

I build the circuit as a proof of concept model in order to show it to my father that would like to start doing black smith work on small knifes.

To explore all my induction heaters, including the Chinese 1800 Watt induction heater, check out my youtube playlist for all induction heater related projects: https://www.youtube.com/watch?v=N1tg3mQL7lQ&list=PLw4xMO1xCMSUOj19zUmFE2-a2lcFBuzX_

## Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

## Considerations

The MOSFETs used need a voltage rating about 4 times higher than the supply voltage and a on-resistance below 150 mΩ. In ZVS operation the switches see a voltage that is π times input voltage, so 4 times rating of input voltage leaves some head room for playing it safe.

If supply voltage gets over 40 VDC, consider using resistors between 470R-800R for the gates. Supply voltage needs to be minimum 12 VDC, lower than 470R gate resistors can be used in that case, if supply voltage dips under 10 VDC, there is a risk of MOSFETs failing from overheating by working only in the linear region or short circuit if one of them stops switching.

Supply voltage should not exceed 60 VDC, as this is very close to 200 VDC across the MOSFET. The internal construction of MOSFETs with a higher voltage rating makes them unsuitable for use in a self oscillating circuit like this Royer oscillator.

A MMC is made from 27 capacitors to avoid excessive heating in a single capacitor. The capacitors will still heat as massive current flows between the tank and work coil. To get a good result, a large tank capacitance is needed, if a capacitance lower than 4 uF is used, results might be disappointing. It is strongly advised to use a capacitor with made from polypropylene (MKP) or similar that can handle large RMS currents, it might even be necessary to water cool the capacitor too. A MMC as the one I use here can only withstand short run times and will even then heat up.

The value of the inductors are advised to be between 45 to 200 uH and depending on core material the number of turns varies a lot, use a LCR meter to check the values.

Water cooling of the work coil is a must! Even at just small runs with moderate power input as the ones I have conducted, the work coil would take damage from heat.

## Specifications

 Voltage supply 35 VDC smoothed with 40000 uF MMC 3 uF from 9 in parallel strings of 3x 2 275 VAC MKP X2 capacitors in series. Power consumption 650 Watt. Best result Between red hot and white hot M10x20mm bolt

## Construction

17th January 2013

I succeeded in putting the entire setup together from parts I have salvaged from old equipment, only the MOSFETs was bought new and used before.

The transformer takes 230 VAC in for 32 VAC out, properly around 700 VA transformer estimated from the core size. It is rectified with a 25 A bridge rectifier smoothed with 40000 uF capacitance from four electrolytic capacitors 70 VDC / 10000 uF each.

The inductors are made from ferrite transformer cores from old power supplies. 14 turns of 1,5 mm^2 gave approximately 130 uH inductance.

Two IRFP250N MOSFETs mounted on each their fairly small heat sink, but big enough for the circuit to run for a couple of minutes and only get a little above hand warm. The heat sinks are glued together with a piece of acrylic plastic in-between to insure electrical isolation between the two heat sinks.

The work coil is made from 5 turns of 8 mm copper tubing, giving approximately 0,477 uH. The MMC consists of 9 parallel strings of 3 in series Rifa 1 uF / 275 VAC MKP X2 capacitors for 3 uF. This gives a resonant frequency calculated to about 133 kHz.

Measurements during a run of heating a M10x20 mm bolt at 33 VDC in, 260 VAC at 2.5 A input into transformer.

Resonant frequency is measured to 106 kHz. The measured frequency is different from the calculated as the work piece will influence on the coils electromagnetic properties.

In the following oscilloscope screenshot:

Yellow: Inverter current, here measured to 10 Ampere.

Blue: Inverter voltage, here measured to 100 Volt.

In the following oscilloscope screenshot:

Yellow: Tank current, here measured to 200 Ampere.

Blue: Tank voltage, here measured to 100 Volt.

Three pieces of metal heated to what is possible with input voltage of 35 VDC.

## Conclusion

A good and reliable oscillator as long as supply voltage is kept within safe area of operation for the MOSFETs and only short run times are used unless there is used good components and water cooling on work coil, MOSFETs and capacitors.

Further improvements in use as a heater / melter would be a higher supply voltage.

# Kaizer SSTC III

## Introduction

The idea was to build a very small and compact Tesla coil as a gift for my mother that works in various science classes for the lower grades in public school.

This driver circuit is very similar to the one used in Kaizer SSTC I. This time I have made a PCB containing both driver circuit and bridge.

## Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

## Considerations

I knew this would get claustrophobic with so little space for a complete interrupter, driver and bridge.

Using the enclosure as the heat sink is the reason why a low break rate is chosen, to avoid excessive heating.

## Specifications

 Bridge 2x IRFP460 MOSFETs in a half bridge configuration Bridge supply 230VAC directly from the wall, 4A rectifier bridge and 330uF smoothing capacitor Primary coil Rev 1: 55 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings.Rev 2: 80 mm diameter, 1.38 mm diameter isolated copper wire, 10 windings. Secondary coil Rev 1: 50 mm diameter, 200 mm long, 1430 windings, 0.127 mm enamelled copper wire.Rev 2: 75 mm diameter, 165 mm long, 1500 windings, 0.1 mm enamelled copper wire. Resonant frequency Rev 1: Self tuning at around 470kHz.Rev 2: Self tuning at around 180 kHz. Topload Rev 1: Made of two bottoms from beer cans, 65mm diameter and 30mm in height.Rev 2: 45 x 152 mm turned aluminium toroid. Input power Interrupted mode: ?W at 230VAC input voltage. Spark length Rev 1: up to 140 mm long sparks.Rev 2: up to 250 mm long sparks.

## Schematic and PCB files

PCB file for ExpressPCB

## Construction

21st July 2009

I designed a compact single sided PCB that contains both driver and bridge section on a mere 65 x 75mm board. Here is newly etched board, traces are a bit shaky as I have drawn them all by hand.

The MOSFETs uses the enclosure as a heat sink, I sanded down the paint for metal contact and use pads to isolate between MOSFETs and enclosure.

BPS is kept low, but can be varied from 4 to 20 BPS, to avoid excessive heating as the enclosure is not an optimal heat sink.

In the bottom of the following picture you can see the bridge rectifier mounted to the enclosure and the input filter for 230VAC in. The red wires lead to the 330uF/400V smoothing capacitor and the 100nF/1600V Rifa capacitor is the DC blocking capacitor in the primary circuit.

The coil is connected directly to 230VAC without any kind of voltage regulation and also requires a external 12VDC supply for the driver.

Antenna and primary coil connections are temporary solutions for the sake of demonstrating the Tesla coil in working order. A fold out antenna from a small radio or such will be added later. Some kind of support with banana jacks with a secondary and primary coil mounted on will be added, to avoid wrong phasing of the primary coil.

Here the complete setup is size compared to a 330ml beer can

## Sparks

Here is one of the more spectacular spark pictures I have taken, in my eyes it looks like a demon waving its arms over the head which also have a distinct face with glowing eyes and a open mouth, or maybe I am just seeing things from inhaling too much ozone 😀

24th July 2009

I borrowed a expensive macro lens for my Canon 350D camera and took some pictures with great details of the sparks, very sharp pictures!

## Revision 2

1st August 2009

Doing a short demonstration I adjusted the antenna with my hand while the coil was running, this resulted in unstable oscillations and the bridge was short circuited. I am now replacing the destroyed MOSFETs and here I can feel the disadvantage of servicing on a compact design.

A new secondary coil is in the making, it is wider, shorter and have half the resonant frequency of the first. It will be fitted nicely on a piece of acrylic for a complete look.

19th August 2009

The new secondary is finished, it took me about 8 days to do the winding as it is very intensive to wind with such a thin wire. Keeping the wire tight, windings close to each other, not pulling the wire too hard from the spool, watch for jams and overlaps and it all have to be done with a bright light very close to get a good view.

It uses the topload from my VTTC I, a 45 x 152 mm aluminium toroid, with this it have a new resonant frequency around 180 kHz.

Top of secondary was filled with epoxy to insulate the brass bolt from the inside of the secondary and the bottom earth connection is fastened with a nylon bolt.

It is all fitted onto a piece of acrylic with additional protection around the primary connections so it no longer possible to touch any conducting part of the primary circuit.

## Audio modulation

I use a audio modulator made by the user Reaching (Martin Ebbefeld) from 4hv.org.

For sound input I use a cheap children’s keyboard from a toy store, its far from perfect for the job, especially because its waveform is highly distorted and its not clean tones but seems to involve a lot of modulation inside it to simulate different instruments. But its cheap and expendable.

Watch the film and look at the schematics for more about the audio modulation.

## Conclusion

I am very satisfied with the final result, that I got to fit everything and use the enclosure as a heat sink turned out real good. Heating is not a problem with run times at about 2-3 minutes which is also the durations its been built to be demonstrated for.

Enclosure dimensions are 125W x 80D x 50H mm.

Revision 2 looks even better, performs better but was also a lot of work to wind the new secondary with such a thin wire.

Revision 1

Revision 2

# Mazilli ZVS flyback driver

## Introduction

The Mazilli ZVS flyback driver is well-known throughout the high voltage community for its simplicity and ability to deliver 20-50 kV at high currents for a flyback transformer.

I build this circuit almost a year ago on a vero board, but it kept blowing the thin traces due to high currents flowing. I eventually put the project in a box and forgot all about it.

Inspired by the point to point soldered designs Myke from the 4hv.org forums often uses, I tried to make something in that manner, not as pretty as his work though.

## Safety

WARNING!: Working with electricity is dangerous, all information found on my site is for educational purpose and I accept no responsibility for others actions using the information found on this site.

## Considerations

The MOSFETs used need a voltage rating about 4 times higher than the supply voltage and a on-resistance below 150 mΩ

5 + 5 primary windings are suitable for voltages between 10 to 40 VDC, at higher voltages additional windings will be needed. Experiment with the number of windings to improve performance. Too few windings will result in excessive heating and too many will result in reduced power output.

A MMC is made from 6 capacitors to avoid excessive heating in a single capacitor.

This driver will push as much power as it can, so be sure to use flyback transformers that can handle the abuse if you want it to live.

## Specifications

 Voltage supply 35 VDC from a rewound microwave oven transformer. MMC 0.66 uF from series string of 3x 2 275VAC MKP X2 capacitors in parallel . Power consumption 400 Watt. Longest arc 100 – 110 mm long white arcs

## Construction

15th may 2009

I have now rebuild the driver using 2.5mm² / 14AWG wire for a good current ability, larger heat sinks and a MMC to avoid as much heating as possible.

## Sparks

16th may 2009

I found 4 different flyback transformers from my collection, among these are a 1980’s Bang & Ollufsen television flyback. A small flyback from a photocopier. A  flyback from a 1990’s portable television, it is without screen and focus resistor networks. A flyback with rectifier tube from a black & white 1950’s television.

The pictures with long arcs about the size of  100 – 110 mm was made with the 1980’s Bang & Ollufsen flyback transformer.

## Conclusion

It was well worth it to rebuild this driver. It can now handle long run times with little heating despite pushing out around 400 Watt  of power!