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Royer induction heater

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StevenRS

Thu Jan 29 2015, 06:48PM

Registered Member #54367 Joined: Wed Jan 28 2015, 05:39PM
Location:
Posts: 5

So, I decided to jump on the induction heating bandwagon finally. I actually *need* one to quickly heat up a thin steel band, 1" wide and .015" thick so I can quench it as I draw it through the heater. This is the schematic I've come up with, with modifications to deal with my particular PSU.

Be74d50ed6

I already have all the parts, and have tested discrete elements of it. Before I hook it all up, does anyone have any concerns/criticisms? I could replace the mosfet that switches the circuit on once the cap is charged with a relay, but it should only dissipate about 10 watts.

I also am thinking about adding a simple overcurrent protection circuit to it, but not sure about the best way to do that. Ideally I would like to detect a latchup and switch it off via the capacitor charge detector mosfet.

What I would really like is a way to drive the mosfet gates down faster, because it looks like the vast majority of their dissipation happens because they both enter linear operation simultaneously, with once switching off and the other on. I wonder if a slightly asymmetrical design could make sure one switches faster than the other and reduce dissipation while preventing latchup without blowing everything to pieces. Will experiment, and post pictures soon.

Also, if anyone wants it I attached the spice schematic I've been playing with. I changed the filter cap's value to 1000Âµ so the simulation starts in a reasonable amount of time, otherwise it takes AGES to start oscillating (It does, though). You will need to place the two files for the fast diodes and irfp260's into your LTspice top dir for it to run.

]royer_induction_heater.zip[/file]

hen918

Fri Jan 30 2015, 04:27PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Are you sure this will be powerful enough?
You may need to double up on the MOSFETs and I would make the coupling inductors out of ferrite cored pipe, and the cap banks out of many, many, small caps(I like polypropylene tubular audio caps 0.1uf)
You'll have to tune it to get close coupling with your work-piece.

Good luck! (I've made Royer oscillator type IHs and never got them very efficient.)

Experimentonomen

Sat Jan 31 2015, 12:53PM

Registered Member #941 Joined: Sun Aug 05 2007, 10:09AM
Location: in a swedish junk pile
Posts: 497

You might wanna look into Neon John's "ROY" circuit which is a improved version of the royer/mazzilli circuit.

hen918

Sat Jan 31 2015, 02:39PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Experimentonomen wrote ...

You might wanna look into Neon John's "ROY" circuit which is a improved version of the royer/mazzilli circuit.

Please note that the "ROY" circuit is designed for rectified 110v AC not 240v AC

StevenRS

Sat Jan 31 2015, 04:32PM

Registered Member #54367 Joined: Wed Jan 28 2015, 05:39PM
Location:
Posts: 5

Forgot to mention that my cap is made of I think 18 or 19 polypropylene film caps, soldered directly to a chunk of bus bar.

I'm going to assemble it today, we will see how it goes!

mister_rf

Sun Feb 01 2015, 04:42PM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

Hi, I was able to test this Royer Oscillator design.

Instead of IRFP260N I have used the IXFK140N30P MOSFET transistors. No additional circuits for latch-up protection, just a small switch to connect the power to the gates after the main power on. Main capacitor =4.4uF, made from a bunch of 20 polypropylene film caps, the 940C series. The power supply used for the test provide 50V and the current up to 40-50 amps. I used to measure the current by a small 0.1 ohm shunt resistor.
For the no load condition, I=6-7 amps and on load the current rise up to 30 amps. Please see the attached video.

Claude

Mon Feb 02 2015, 02:40AM

Registered Member #3379 Joined: Mon Nov 01 2010, 06:34AM
Location: Sydney, Australia
Posts: 24

Hello I am able to obtain a large quantity of wima 0.1uf MKC capacitors. I am wondering if these will be ok for a small induction heater project as they are metallised polycarbonate.

Mads Barnkob

Mon Feb 02 2015, 06:33AM

Registered Member #1403 Joined: Tue Mar 18 2008, 06:05PM
Location: Denmark, Odense C
Posts: 1968

mister_rf wrote ...

No additional circuits for latch-up protection, just a small switch to connect the power to the gates after the main power on.

You need it the other way around. Without power on the gate, you have no idea if they are open, closed or somewhere in between.

mister_rf

Mon Feb 02 2015, 09:16AM

Registered Member #4465 Joined: Wed Apr 18 2012, 08:37AM
Location: Bucharest, Romania
Posts: 145

I need to give all details about the schematics I have used for.
Thatâ€™s the one including some additional resistors and diodes:

hen918

Mon Feb 02 2015, 09:25PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

I would advise pulling both gates down via diodes to turn it off. works very well and means that the MOSFETs do all of the switching, which they are very good at!
btw this was Uzzor's idea, not mine

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