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Royer induction heater

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Marko

Sat Aug 13 2011, 11:48PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi guys

I remember a while ago some members complaining they can't find an easy to build and yet powerful enough IH to play with. This has been done before and I just reiterated it in my own way, built in one afternoon to see if it would work. To keep short here are some of the most important hints:

- The circuit is the very same as ZVS mazilli flyback driver (along with zeners and 470 ohm resistors), except it uses two inductors going from V+ to each end of the coil instead of one going to center of the coil.

- Use water cooling. Your mosfet drains are electrically connected to each end of the coil and you can use this as an opportunity to cool them too without investing in big heatsinks. I soldered some pieces of copper to loose ends of the copper pipe and bolted mosfets to them - not the best waterblocks in existence but worked more than well enough.

- Use a MMC of many parallel FKP caps for your tank cap. If you want to push a lot of power you'll need a lot of capacitance. I used 16 * 270nF, total over 4uF. The MMC has to handle very large current so you can't save there.

- Don't push your supply voltage, 50-60V would be ideal along with IRFP260's. I used up to 30V and could push over 600 watts and melt aluminum and ignite steel coins quite fast. If I used bigger mosfets like IRFP260's and 60V input, I could do likely over 2kW. This would ruin the caps very quickly though as they get very hot and were a limiting factor in my design. If you want an industrial power IH prepare to buy hundreds of small caps of a conduction cooled cap (both might turn out costing about the same).

Here is a video for now showing melting a brass coin, melting/burning up a steel coin and melting a piece of aluminum heatsink (shown uncut), along with some additional aluminum re-melting.

It was fun and I'm thinking about building a bigger version, with an unique water-cooled MMC. I don't have a proper power source though, I feel sorry killing my only MOT to rewind it. I'll post schematics (if required at all?) after some interest shows up.

*Some pics and a schemo*

jnbrex

Sun Aug 14 2011, 02:10AM

Registered Member #3950 Joined: Wed Jun 15 2011, 12:45AM
Location:
Posts: 51

That thing is awesome! Some schematics would be great too. That is a very interesting project, but I think it looks a little too complicated for my novice soldering skills...

On another note, does the copper pipe that is the heater get hot? I thought that induction heaters worked through eddy currents produced on the object to be heated and didn't actually heat up themselves.

radhoo

Sun Aug 14 2011, 07:43AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

looks and works great!

a few months ago I built something similar, schematics and photos here:

Conundrum

Sun Aug 14 2011, 12:46PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Its a shame you can't buy cheap magnetic solder (yet!)
Something like this would be great for emergency repairs etc and for people who aren't allowed to use a conventional soldering iron for safety reasons.

-A

Gabriel35

Wed Aug 17 2011, 02:33AM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Incredible!
How do you got so much power from a simple Royer oscillator? I'm very very interested on the schematic *-*
I got some nice IGBT's and 30vDC Supplys here, and I can't wait to try this scheme out!
Can IGBT's be used instead of mosfets?
I have here a pair of IRFPG40 4.3A @ 1000v
and a Pair of IRFZ48N 64A @ 55v

Can some of them be used?
It's really the same mazilli's driver only with two inductors and strong caps?

Thank you!!

Dr. ISOTOP

Wed Aug 17 2011, 03:13AM

Registered Member #2919 Joined: Fri Jun 11 2010, 06:30PM
Location: Cambridge, MA
Posts: 652

Conundrum wrote ...

Its a shame you can't buy cheap magnetic solder (yet!)
Something like this would be great for emergency repairs etc and for people who aren't allowed to use a conventional soldering iron for safety reasons.

-A

Induction heaters will melt normal solder. It's a common misconception that they only heat ferrous objects.

Gabriel35

Wed Aug 17 2011, 12:52PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Can you post some photos of your circuit too?

Thank you!
I can't wait to buy some mosfets and try it out!

Marko

Wed Aug 17 2011, 01:12PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Gabriel35 wrote ...

Incredible!
How do you got so much power from a simple Royer oscillator? I'm very very interested on the schematic *-*
I got some nice IGBT's and 30vDC Supplys here, and I can't wait to try this scheme out!
Can IGBT's be used instead of mosfets?
I have here a pair of IRFPG40 4.3A @ 1000v
and a Pair of IRFZ48N 64A @ 55v

Can some of them be used?
It's really the same mazilli's driver only with two inductors and strong caps?

Thank you!!

Yes it is, and if you wanted you could even center-tap the coil and use a single inductor if you wished. Another advantage of this would be that you could drive the water supply through both ends of the coil and having it exit through the center tap, removing the temperature difference that would normally be experienced between mosfets cooled with same water flow. But this didn't really matter at this power level and used only a tiny fraction of possible flow rate, so you can do as you wish I guess.

Regarding switches, I would still best recommend IRFP260's and a rewound MOT for the power supply.

Those IRFG40 high voltage mosfets are pretty useless for this circuit, you want low voltage mosfets with ON resistance of 50m ohms or less which is important for keeping the circuit stable. IGBT's, especially 1200V ones have high voltage drop which may again result in the circuit ceasing to oscillate and shorting out the power supply. You can try them but at your own risk, and they will probably not be as efficient as mosfets at such low voltages.

IRFZ44/48 or whatever are another extreme, with them you would be limited to like a 12-15V supply (car battery)? providing tens of amps, and you would have to put a step up transformer between your driver and the tank circuit, or use a 4x larger tank cap than I did which would be impractical.

The radhoo's schematic which uses the transformer is wrong, the tank cap should go after the transformer and not before it by the way.

Gabriel35

Wed Aug 17 2011, 02:36PM

Registered Member #2310 Joined: Wed Aug 19 2009, 08:04PM
Location: Santa Catarina - Brazil
Posts: 169

Ok!
So the secret of the huge power of the classic Royer Oscillator isn't the two inductors?

I have here a bank of 32x 0.068uF @ 630v - P612 w722 EPCOS Model (P6XX MKP capacitor)
Resulting a capacitance of 2.176uF. I can buy those IRFP260's and try it out!
I've experienced with Royer Oscillator a long time ago using two IRFP250 and a 36v Supply. But it was so weak, It was just capable of making a screwdriver redhot. I think that I still don't know what is the BIG difference between this circuit and the classic ones, like the one I've tryed... It is pretty incredible the power amout that you achieved on that video =O
What about the number of turns and diameter of work coil? are them important variables?
About the water? It's just to maintain the whole thing as cool as possible or it affects the Pratical Power of the circuit?

The capacitors? Can i use the ones mentioned? Do I need more capacitance?
I have a transformer here that is 24v. Rectified and with 8x 470uF capacitors it results in 36vDC, this tranformer is capable of 10~15amps. Can I use it?

About the Zeners, I plan to use 1N5349B 5w.
And the Fast Rectifiers, BYT11-1000
The 470 Ohm 5w Resistors, OK
And the 10K 0.5w too. =D

EDIT: I've found some IRF540N's here...VDSS = 100V RDS(on) = 44mÎ© ID = 33A... Can I use them with 36vDC?

Thank you, and nice pics too!

Forty

Wed Aug 17 2011, 04:00PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

ah the pictures certainly help. I can close the paused youtube video tab now lol. I wonder how the dual inductor scheme would work with driving a flyback.
I imagine you formed your work coil around a pipe. Did you fill it with sand or anneal it to help with even bending? I've got the tubing sitting here, I just don't want to screw it all up by bending it improperly.
what do you guys think about fairchild's fdp2552

for zvs circuits like this? or should I finally give in and buy the proper irf's?

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