Just asking, where are you living now? Denmark? I ask in case I need to buy something and you can ship to my relatives in France.

On the other hand, are these ferrite cores good to make chokes in Royer IH? Does their performance are the same as toroid cores? I'm not good with these things myself (and magnetism in general), so while we are at it, can you explain the functionality of each of these cores?

I have a small question regarding the toroidal cores for the two chokes in the driver.

I just read a few articles on the net and I found out that the mix in the core can affect the performance of the chokes. And you can determine the freq band that the core can work based on its paint color. I'd like to know more about this, in case if it is true.

I'm having two green cores, but they are quite small so I'm thinking of purchasing something bigger, so that I can use bigger wire.

Hi guys,

Not so relevant to our usual high voltage stuffs, I'd like to consult you about etching PCB via chemical process (which is cheap!)

Though I'm not really good with chemistry, luckily for PCB etching it is not about organic chemistry (yay).

I am using Copper (II) Chloride solution by using Hydrochloric Acid taking copper directly from the board, with hydrogen peroxide as oxidizer. As you know, CuCl2 takes copper from the board to become Cupric Chloride. This solution can be reusable by bubbling air (oxygen) into the solution with more Hydrochloric Acid, turning CuCl back to CuCl2.

However, the etching speed is really slow. It took me 10 hours to clear up around 9 cm² of copper, which is so darn long. I even had to heat the solution up but it did not speed up much. On the copper tracks that needs removing, it turns dark-colored and it seems that I have to rub them off to speed up the etching (I suspect this is copper oxide that is resulted from copper and peroxide, but it is strange as it isn't solved by acid). It is very time-consuming and inconvenient. Even worse, the longer I leave the PCB in, the chemicals will start to attack the part that I don't want to be removed.

I don't etch PCB much, but I sometimes have to do it, so I need to improve my solution for my future usage. Some DIY sites don't have much information to solve this problem for me; their etching speed doesn't look this long.

Anyone here can help me with this problem?

First off- if anything fails in this driver - it would be a good idea to check all other components too. Your transformer is probably fine. Just make sure your Zenner diodes arent shorted and that your ultrafast diodes are ok. Next step would be mosfet replacement. Then you can test tank cap - charge it up to 30v and see if it starts to discharge quickly. If it can hold its charge (and its capacitance always reads the same) then its good.

Alright , It may be that your frequency is inappropriate for your switches or if your driver isn't working at all anymore your zenner/fast diodes have blown. If that is the case your FETs will also be damaged. a multimeter on diode test can quickly ensure that everything is working and not shorted out.  If it only works with one coil, then i would check that it is not pushing the frequency up too far.

I see you have ~80Khz resonance - Thats not bad. Sometimes a bad cap can start to blow up mosfets. What size is your capacitor and how much capacitance does it have ?

As for the first try on the new coil, I burnt through 3 FETs and a few diodes. Most of the rest were still safe, but to be sure, I replaced all diodes and the remaining MOSFET as well.

With the second try, it is still not oscillating, but everything still looks okay (I did a quick measurement of resistance between important nodes and compared the values before and after the test). Within 5 seconds running, I checked that the source voltage dropped to approx 7.5V from 18V (before it was 15.7V), drawing approx 20A of current. I assumed that the problem lies in CLC filter, notably the capacitor banks could not hold the voltage high enough during the startup, so it fails to oscillate. I used 17 electrolytic capacitors of 1kV-1mF (though they aren't at good quality: most of them are 750µF and 900µF), creating two banks of around 7mF for the CLC filter. I'm planning to buy even more capacitors as well.

Tank cap is 16x0.22µF MKV cap and I measured 4.33µF (I assumed one cap got disconnected from the bank, I'll resolder the joints later). Since with this tank cap I was able to make the circuit oscillates and the capacitance didn't drop so much, I think it is still working. Though, I'll need better cap if I'm aiming for 2kW heating output.

I HAVE REWORKED THE CIRCUIT PLEASE CLICK ON THIS LINK TO HEAD TO THE NEWEST CIRCUIT: https://highvoltageforum.net/index.php?topic=46.msg540#msg540

Hi guys,

First time coming here, though I have been in Kaizerpowerelectronics blog before.

Since it will be pointless to make another thread just for the same induction heater, I'm borrowing kamelryttarn's thread to post about my machine. If you don't mind, that is (I'll do another thread if you do mind).

First of all I have to thanks Mads for his advice on using multiple pairs of MOSFETS to deal with high-power circuit. I have made a prototype, and it worked out well:


However, the consumption rate is bad. Even at no load, it consumed approx. 16A for 15.7V input (dropped from 18V). When I put a screwdriver in, the input current rose to  17.47A. Putting in a piece of stainless steel (3x6 cm²) it became 24A. Basically, the wasted energy into heat is just too big.

I assumed that the soldered joints and copper traces burn out a lot of energy, so I decided to redo the circuit (simpler, and wider traces for high-load). Also, getting a bigger work coil.

But for this time, it does not oscillate. I fried 3/4 MOSFETs when it failed to oscillate, and had to redo the circuit (again). Still no oscillation. Just in case, I only make the newest circuit to run under voltage for around a few seconds to observe the problem.

It seems that the input voltage has dropped very low, around 7.5V (from 18V) at 20A consumption. Something must happen badly with the power supply, so I'm posting it all here as well.

The transformer is one I wound by myself. It is very big (enough to be put inside a computer case) and personally I think it can support at least 2kW:

Little final touch:


Assembled with rectifier diodes. You can see below the two square components (the bridge rectifiers) that can deal 1kV-50A each. I used two so that it can work well to 100A (I'm using the transformer at 40A as my aim, btw). To protect the transformer I also added a 20A anti-leakage circuit breaker for the primary coil.


Basically I'm confident that my transformer can support a lot of current even for 18V secondary. I'm, however, doubting the filter I used.

I'm using capacitor-input filter (pi-filter with 1 capacitor bank + 1 coil + 1 capacitor bank) to increase the filtering efficiency. You can see the big-ass coil of 48mH underneath the capacitor bank (actually two banks of around 7000µF each I combined on one circuit board).


I assume that with bigger coil the circuit will need stronger power spike to start up, and with that it overloaded the filter. Do you think that it is the case with mine?

EDIT: To OP: Where did you buy (or find) the choke? I'm trying to find a big one like that but it is hard to get one. If you bought it, how much did it cost? And btw, you are using the two chokes in the induction heater, or they are for the power supply?