Just some thoughts from me.

It's directly mains powered, that's very dangerous and isolation should be handled with care.
The designer has a non water cooled working coil, what's an absolute no go.
It's a rather big physical build and I wouldn't prefer it.
Power adjust is only possible with the working coil geometry and the matching inductance.
I personally don't like these capacitor banks made of hundreds of caps, get some real ones, which are at least air cooled.
The power of that thing is around 1.5 kW so it's nothing special.

You can adjust your power with the magnetic field, since the frequency changes are rather small.
The higher the magnetic field at the workpiece, the higher the possible wattage.

The bigger the current through the coil, the bigger the magnetic field.
The current depends on the frequency and the supply voltage, a voltage between 40-100V is what I'm using in my heater.
Since this build has an isolation transformer other values may be better.

You can change the coil geometry to adjust the power.
With more windings and less distance between workpiece and coil you get more power.

Changing the coil will change the frequency, so I'm not sure how preferable that would be for this circuit.

My final heater is in nearly ready to be show able, so if you aren't in a rush and have a week time, you can take a look at mine. It's around 4-8 kW at 30-130V and is electrical more simple, it just needs some good coolers.

Hi everyone,

Last week I finished my own ZSV heater circuit.
After some many cooling problems and my first self made water coolers it worked great.
The circuit from Jörg Rehrmann works fantastic with no issues.
The capacitor from Eectech has 4.0µF 400Vrsm 700Arms and don't get that warm.
For cooling I have two of the Chinese water pumps in parallel, of course watercooled (they get really hot after some time) with a 30 litre canister.
With pancake coils the circulated water is around 30 °C warmer than the supply water.
With my nice case I can touch most of the heater without shocking my self.
I confirmed 5kW at 50A and 100V at the input. The water cooled IGBT are getting up to 80°C at 50 A, that's OK, not great but solid.
I plan to make some more professional water coolers and upgrade the pumps, the cooler the system runs, the more efficient it gets.

For me the 650V IGBT are more than enough and it was the right decision to not use the not so suitable 1200V IGBT.
The stainless steel is glowing at 1150 °C and was melting from behind. 

Good thing that my multimeter can handle these frequencies, after making a new coil it's always interesting how the inductance is.

As I said earlier I had some ringing Problem with the IXTH62N65, because of there really slow body diode (typ. at 25°C 445ns).
As a comparison, the IRFP260N (typ. at 25°C 268ns) there's also some ringing but it's not consistent and gets better with heavy load.
I also tested some FGH80N60 (typ. at 25°C 61ns).

The FGH80N60 worked just fine but they got really hot.
So I ordered some IKW50N65 (typ. at 25°C 52ns) which should be fast and cool enough. I'm not sure how the relative slow turn off delay time will matter, but I'll see.

The next step for 200V input voltage would be some good capacitors, but there are the next problems.
With these high frequencies and "high" voltages of the standard 2000W heater model, the capacitors are already at there current rating with only 50V input.
So that's not a long term solution. Other similar capacitor like the used MKPH-R or Dawncap aren't that suitable. If the overall capacitance is too low the frequency rises, which is a bad thing for the slower IGBT. If the capacitance per capacitor is too high, the currents are way above the ratings.
So more small capacitors would be the way to go, but these won't fit more than four on the original board.
I could make a new board/circuit, but the start/stop routine works really good and I want to keep it (no need for turning off the big PSU...).

With 4 capacitors which cost 15 to 25 € I can also go with some seriously big stuff like this:
http://www.eectech.store/cs-30122-solid-state-high-frequency-film-capacitor-12uf-500vac-p0319.html
Which can handle the voltage, current and frequency. It's even smaller than 4 big film caps. With some cutting at the PCB it will fit nicely.

However, my previously statement with the 6mm copper pipe isn't true in that case and a10mm pipe is probably more suitable.
Since I have two units, I put 4 originals caps on the IRFP260N unit with 6mm; 1/4" connectors and the second one with the new cap, IKW50N65 and 10mm; 3/8" connectors.

That should power things up. The oscillating current should increase with the higher capacitance which lead to a smaller working coil, which should be better for screws and non crucible stuff, which I use it for.

There's also a mains powered updated version of this circuit:
http://www.joretronik.de/Oszillatoren/Oszillatoren.html
This can't hang up at start up and can't fail like the royer.
Since my PSU is limited somewhere to 4kw-6kw I don't see a need to go higher up in voltages/complexity right now.
I'm not that firm with high energy stuff at that high frequency. For a proper circuit you would need a start/stop routine, over current protection, a relay and so on.
I try to get this thing working, build a housing and that's it, since i have seen many "super big" induction heater projects which never finished...

Hello everyone,

I got around to test the new arrived heating unit. It came with a different coil (4 instead of 6 windings).  I have to correct my thought about the current limiting potentiometer. It's a bit strange, you can limit the current and you can trim the shunt resistor.Therefore, a real current meter is a have to. Maybe it's some sort of current limiting in the first 50% and shunt tuning with max current at the last 50% or something.

Here are the results from some testing:
Coil with 6 windings, 50 mm high, 45mm inner diameter
with no workpiece:
In 24,4V 45W; Out 74V peak on the caps
In 38V 90W; Out 112V peak on the caps
In 50V 185W; Out 152V peak on the caps
In 60V 250W; Out 188V peak on the caps
The voltage over the caps are pretty much spot on the PI times input voltage. Due to the higher oscillating current, the power loss increases also.

Heating up a workpiece:
Steel bolt 22mm diameter and 60 mm high
In 52V, used power 1600W at beginning, 2100W peak and 700W at around 900°C.

I maybe solder a copper pipe direct at the capacitor connection to cool them with the water too. A cooled heat sink for the mosfets would be great to, since the get a little bit warm at high currents.

The used resistor is a 5.1 Ohm, so I updated the schematics, the simulation is much more stable now.

The µC stands for microcontroller.
I didn't bother to track the all the way back to it.
Of course this isn't the whole schematic since there is also an lcd display.

https://www.banggood.com/2000W-ZVS-Induction-Heating-Module-Board-Flyback-Driver-Heater-Good-Heat-Dissipation-With-Coil-Pump-Power-Adapter-Kit-p-1464491.html?cur_warehouse=CN

5V worth arguing? Rule of thumb is 4 times.

I finished the circuit for the unit.

Printing on the Board:

2000W Rated Power
input voltage DC24V- DC70V
maximum input current <48A
ZVS2000S High frequency induction heating
8300515

As far as I can tell, the controller checks for a mosfet fault before switching the relay on.
Voltage, current a temperature are always checked.
You can add an extra external switch for short heating applications.
There's a potentiometer to limit the max current.

The controller does NOT know if the circuit is oscillating or not, but you can check your setup with a low current setting. In case something went wrong, the unit should open the relay faster, that's handy before start working with different coils/voltages or after a repair for obvious reasons.

If the coil inductance is way too high/low, it can detect a mosfet fault.
The components with an "X" are unknown.

Due to the applied voltage of 100V, the mosfets, transistors, optocoupler and the resistor "R15" blew up. This resistor is crucial for the proper working. I have to wait for the new one board to get the value to repair it properly.
If I had removed the heat sink, the mosfets were most likely also got damaged and since there was no information available.
I wanted to know, how high I can get with the input voltage.

The measured current from the unit was way too high, I shortened the shunt and adjusted the value with some extra tin.
With that method you can also increase the maximum power output relative simple.

The optocoupler for the fan/pumpe is always on.

Just a quick response from my side.

The higher the resistance of the material, the better it is for heating it. Steel for example, it starts with 60% power than rises to 100% due to increasing electrical resistance and goes down to let's say 40%. These are just estimations, based on my analogue 80a current meter.

So getting up with the temperature is for non magnetic materials in theory better. That would at least explain the overall low power consumption for these relatively high voltage.

For a steel crucible, I can say the following. The normal steel will get destroyed from the air/oxygen and the aluminium, starting at 700°C/1292°F. For example a 2mm thick steel crucible will be destroyed after around 10h to 20h completely unusable at 900°C. Steel with 25% Cr, 20% Ni will withstand the oxygen in this temperature but will still be "eaten" by the aluminium. There are some coatings which slow the process like "3M Bornitride Suspension WP"

http://technical-ceramics.3mdeutschland.de/en/products/3m-release-agents-and-lubricants.html#c880

Cost in Germany around 40€ for 1 litre.
They also have other coatings. But they only slow down the process. They are likely to crack and there is the crap happening again....

For controlling the real power of a ZVS Circuit, you can basically only lower the input voltage, for all the other stuff you have to change components on the board.

Best regards Robert