This design based on modified Royer/Mazzeli circuit
CAUTION THIS PROJECT USES HIGH VOLTAGES AND CURRENTS THAT CAN SERIOUSLY INJURE AND POSSIBLY CAUSE DEATH!
Induction heaters are an invaluable tool to have in the shop, from rehardening chisel tips , drill bits, blades, loosening rusted bolts, to smelting gold. They give you the ability to precisely heat a localized area without flame and or damage to entire work piece
After a lot of research I decided to build a small , powerful , induction heater rather than buy. I was amazed at how simple, cheap , and quick it was to design and build and would like to pass it on.
I'll leave the theory, and 3rd order math out, and keep this a nuts and bolts project. This IH is the combination of several different designs and built to meet my needs .
Total cost under $30 US
Total time to design and build under 2 hours
I would like to point out I'm not a "techy" I'm more at home with a hammer and a wrench, so my descriptions may not be tech correct. One last bit of information, I built this without having oscillascope , inductance meter, only a simple multimeter.
The entire tool consists of small fountain pump, power supply capable of 24-36 vdc@20+ amps, rubber hose, mosfets + gate driver circuit, and tank circuit ( capacitor bank & work coil).
Let's start with the tank circuit
Tank circuit consists of the work coil (5/16 copper tubing ) wrapped aroung 1 1/2 pipe forming 5 turns and capacitor bank.
The capacitor bank is in parallel with work coil so each capacitor see all the voltage and current flowing in the coil you can purchase very expensive purpose built caps or use multiple common caps. I used 250vac MKP x2 series caps (28 @0.33uf) I don't recommend using any caps except for the MPK or FPK. The sparks and light show is impressive if your cap bank fails. Your total capacitance needed depends on the frequency you want.
Next is mosfets a driver circuit
Mosfets You want mosfets with a voltage high enough to support supply power x π + safety margin. So at 40vdc you would want 150v absolute minimum 200v ideal, and high current rating (determines power ). Here is one other critical factor for MOSFET choice, they have to have an rds/on of 25 mill ohm or less any higher and circuit tends to latch up causing another spectacular light show. The IRFP260n seems to work best@ 200v 50 amp and RDS/on 0.014. And depending on your tool needs only 2 or for higher power 2 sets of 2 paralleled.
The driver circuit consists of 2 470 ohm resistors (2watt min.) 2 10 ohm resistors , 2 12v zener diodes (1watt min.), 2 ultra fast diodes(400v min.), and 2 hand wound inductors, I used the yellow/green inductors from a couple of old PC power supplies and rewound with #18 magnet wire. Also need 1 perf board/ breadboard size based on your needs, solder, and some wire. That's it!!
A few bits of info keep all wires as short as possible, reduces chance of "noise" in the circuit, make sure PCB traces are thick enough to handle the current, I did all the calculations needed the hard way helped with understanding of the tool, my advice use the calculators simulators available free online (not kidding about 3rd. Order math). And as far as building the circuit that's really up to your needs, attached is the basic circuit schematics, straight forward and simple easily adapted to your needs. Pics and schemo. next
If you would like plans used in this design and more in depth explanations I will have that available end of week
Due to time constraints complete tool build will be posted in segments