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induction heating levetation

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IamSmooth

Mon Jan 18 2010, 06:34PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

can I combine two schottkys in parallel? I found a through hole at 30A. If I use two then it is 60A.

Is this ok, or should I use the 65A on that I found?

IamSmooth

Mon Jan 18 2010, 11:44PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

Here are two more videos of me levitating copper and another levitating and melting copper. I plan on putting a tutorial page at the end of my current induction heater tutorial on how to construct the levitating coil, and what considerations need to be given for the topic. I just need to do a little more experimenting with different coils before I write everything down for others to read.

Enjoy.

Levitating and melting copper
Levitating a small piece of copper

teravolt

Tue Jan 19 2010, 05:45AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

hello IamSmooth, that is a cool vid and I am working on a setup my self. Is the coil that you are useing a loop that has counter field or wound back on its self? my setup is kind of baried in my other projects and it is based on your tutorial with a cuple of improvements with the water flow. I haven't even found the resonant freq yet and just finished the caps sunday and I would like to try your exieiment if my heater works. NB

Steve Conner

Tue Jan 19 2010, 10:34AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Iamsmooth: The datasheet for a dual schottky ought to specify whether it's OK to use the two diodes in parallel. For most devices it's not a problem. Just watch out for the ones that have the anode of one diode connected to the cathode of the other! These are intended for bridge rectifiers and it's physically impossible to parallel them.

The surface mount ones aren't a problem, they can be easily mounted with an ordinary soldering iron. I do it all the time at work.

Can you tell us the number and type of capacitors you used in your work circuit? And the operating frequency, if you haven't mentioned it already. Melting copper is about the hardest thing you can do with an induction heater. The caps must be pretty good if they can stand it for more than a few minutes, though I'm sure water cooling through the leads helps.

IamSmooth

Tue Jan 19 2010, 02:29PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

Steve - I used 20 capacitors of this

They are rated for 14A. I used 20 for 4.4uf and 300A. They are sandwiched between to copper bars 3/16" thick with copper cooling tubing running alongside them. Depending on my coil Fres has been between 65 and 90kHz. The aluminum and copper were done at about 80kHz. The water I am using has chunks of ice in it from outside, and is near 32F.

With the series configuration and the step-down coupling transformer, my inverter is seeing 20-30A.

Teravolt - I will have pictures and diagrams up soon showing the levitating coil I am using. Right now I am trying to get the right configuration to levitate a chunk of copper. Higher density metals are problematic to maintain in the field when the melt.

The coil is a tight conical helix, starting small and expanding as you go up. Then, you bow the copper tubing backwards to form 2-3 turns of an anti-coil. This is the bucking plate that will prevent the metal from popping out. It creates a "null" zone where the metal will float. The widest turn in this coil I have used is 1" diameter.

Adrenaline

Tue Jan 19 2010, 02:34PM

Registered Member #235 Joined: Wed Feb 22 2006, 04:59PM
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Posts: 80

IamSmooth wrote ...

This isn't a big problem, as I have the heat station for it. I want to have some headroom above 30A. Do you know of any through-hole style for +40A schottkys?

I guess the MUR1560s are a good choice using a pair for the free-wheeling diodes.

Here is a dual Schottky diode that you could cut in half for 2 , 30v 250A diodes.
BGMicro

Edit:
Here is a link to the datasheet.
MicroSemi

GeordieBoy

Tue Jan 19 2010, 02:49PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

> Melting copper is about the hardest thing you can do with an induction heater. The caps must be pretty good if they can stand it for more than a few minutes, though I'm sure water cooling through the leads helps.

Agreed. Copper is non-magnetic and a good electrical conductor, both of which make it more challanging than other metals to heat efficiently by induction. It is easy to see that the whole process is not very efficient if there is 2-3kW of power going in and you can only just melt a tiny piece of metal over a long duration. Something else somewhere in the system must be dissipating quite a bit of power.

Regarding the workpiece rotating in the field: Something like a metal disk or a small section of tube will try to align itself with the magnetic field. This minimises its area that is cut by the field lines and the current induced into it. For instance if you place a metal coin in the work coil it will heat most efficiently when lied flat, but the reaction force will try to make it stand on edge in the work coil. If it does stand on end the heating effect is greatly reduced. Mechanically constraining it can keep it in the horizontal position where the heating effect is greatest.

-Richie,

IamSmooth

Tue Jan 19 2010, 03:33PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
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Posts: 1567

The workcoil is dissapating a lot of heat. Richie, you are right about it trying to push it out. If you all notice when I push the copper tubing just a little deeper it heats until almost ready to melt. If I push it more it melts almost instantly. One of the problems I have right now while working out getting a chunk of copper to levitate is it starts to melt before I can poke it high enough into the field. I need a strong field to levitate it, but this field will heat it to melting within a few seconds.

Different metals behave differently in the levitating field, based on the density, surface area, and how close it sits to the coils. A nice sphere would work best, but the last time I checked, I don't have metal spheres lying around my house.

IamSmooth

Wed Jan 20 2010, 10:58PM

Registered Member #190 Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567

The tutorial for making a levitation coil for induction heating is complete. You can read it here.

I have been able to boil aluminum, steel and copper with my induction heater. I have not found a good way to contain the metal. Quartz glass worked great for heating, but cracked on coiling as some metal was stuck to the side. Ceramic is touchy, and I seem to not be patient enough to heat it over 1/2 an hour so it does not crack.

I have been able to levitate solid aluminum. I can levitate hollowed pieces of steel and copper. I don't seem to have the power to levitate solid pieces. It must take a lot more than 2.5kw.

Although you can come up with variations of the design, the coil I present has worked well for me with various sizes of metals.

IntraWinding

Thu Jan 21 2010, 02:25PM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

Could you melt something and then, while keeping it levitated, reduce power to solidify it into a smooth rounded shape?
Non contact melting is good for melting super pure materials in a vacuum as it avoids contamination from any container.

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