Stable eddy current induction levitation of aluminum disk

Aluminum disk floats stably on an alternating magnetic field. Induction heating of disk boils water and even makes tiny spots glow red when the current is concentrated.
For 60Hz levitation using microwave oven transformers:

This is a flat coil much like an induction cook-top, except that the inner half of the coil is wound in one direction and the outer half in the other direction. This concentrates the magnetic field half-way out, making a stable pocket to float the aluminum disk.

The coil is 18 turns, 11 on the inner part and 7 on the outer part. ID is 50mm with 5mm thick ferrite disk inside that, 11 clockwise-wound turns to 117mm diameter, a ring of 5mm thick ferrite pieces, then the winding continues CCW for 7 turns from 137mm to 180mm final outside diameter. There's another layer of 5mm thick ferrites under the entire coil assembly. Total inductance is 32.8uH. The ferrites are 3F36 material, tiled and/or cut from 65 x 51mm rectangle blocks (meant for use in wireless phone... chargers). The drive circuit is resonant. The coil current is about 45A RMS at about 200V RMS at 23KHz. A somewhat lower frequency would be a bit more efficient, but I wanted to keep it above audible range. The drive is a single FET in a flyback style circuit. At 23KHz, the coil needed to be litz wire, which is home-made 380 strands of 35AWG wire. (My small prototypes for coil-geometry optimization used a low-voltage full-bridge in series with the resonant circuit, rather than a flyback FET in parallel. Either one can work.)

After completing this unit, I was regretting not starting with an induction cook-top, as that might have been less work. Besides changing the coil (reversing direction after using half the wire - a bit more than half the diameter), the iron-pan detector would need to be defeated. The remaining question is if the cook-top's electronics function correctly without the load of an iron pan. It might need to be powered from a lower line voltage, such as buying a 220V cook-top and using it at 120V. The internal low-voltage supply for the control electronics might have a problem at lower line voltage, or might not. It would take some experimenting.

[OMNI_INFINITY]

Thanks!👍🏻 That's the only modern edition of the college of london videos levitator I have seen on youtube thus far

[Guishan_Lingyou]

Very cool project. I bet it was a lot of work. Thanks for sharing.

[D_Printing]

Magnetic frequency change. Lower magnetic to higher heat, infrared and light

[Triffgits]

Hi, I realize it's been some years but in your initial planning had you thought about a lower current version of this? Would it be possible to use a different frequency or higher voltage AC at lower current and through thinner wire in the coils to generate the field for less power?

[daddydisla]

Hey, just wondering, can this induction levitation device be made out of a portable induction cooktop by simply changing the coil?

Thanks for reading,
Ed

[eriepolytechnic]

Hey Dave, I am looking to build something like this for an experiment in acoustics. I like the idea of using the 220 induction cook top. Currently, search for a good candidate.

[Viperlover-cwqx]

What would it take to turn it the other way and have it lift itself and the power supply over the aluminum? I'm assuming the aluminum would have to be thick and so would the copper coil, plus you'd have to push a ton of power through it. It has to technically be possible though right?

[billycassanova]

It could push the projectile faster than gun powder does, and without any sound at all.
Or it could be placed under the road for a floating car or floating skateboard in a skateboard park.

[venture_lab]

What’s the relationship between lift distance and weight relative to current and frequency?

[wdwadindwatri]

interesting, the magnetic force muffles the ringing sound. i guess it's the force that keeps it floating is muffling the vibrations, I only wonder how does it look on molecular level? the same as drops on the water?

[Ninetwoeightnine]

Hi Dave, I found the video really interesting. Thanks for posting it. I am interested in keeping a mild steel metal disc in a concentric position. I wondered if you could share your coil geometry, ID OD, number of layers etc? Also what ferrite you are using below the coil? Also an idea for you (if it's needed) for improved cooling would be to use thermally conductive glue on both sides of the ferrite. Just an idea to decrease the thermal resistance from the warm copper coil to the aluminium heatsink.
Lastly, I've been experimenting with electromagnetic Halbach Array designs, with the aim to make a single sided AC magnetic field. I wondered if you've every tried it. Or had any thoughts or ideas on that topic. Kind regards David

[SpotterDeer]

Floating pan? Who wants to make one work for food?

[theinel]

How does the respons on smaller like 1or 2mm size of aluminium?

[OMNI_INFINITY]

Some photos of the build would certainly be appreciated! Surprised that it seems to say the SAME wire is coiled one way and then reversed halfway through the winding so that it makes a second coil in opposite direction in the inner circumference of the first winding. Had originally assumed it was 2 wire coils with one nested inside the other with AC 180 out of phase in second coil. But then thought 2 wire coils with one reverse direction winding. But then saw ONE wire seemingly coiled in both directions...that was surprising! Didn't know one wire could make 2 opposite magnetic fields in that kind of configuration. So basically it levitates without flying off because 2 magnetic fields in opposite directions generate 2 other magnetic fields in opposite directions from the eddy current loops in the aluminum and thus the aluminum plate is pushed AND pulled by the coils simultaneously? If so, is it necessary to make the push coil have more windings than the pull coil? Oh, and the ferromagnetic pieces are there basically to strengthen the fields, right? Thanks in advance for explaining and thanks again for posting that video!👍🏻
Saw now that the coils are flat. Wow, want to make one of those and a piezo lighter dipole antenna transmitter/receiver combo ASAP! Tried flipping that levitator on a large piece of aluminum to try making it move around on the aluminum plane with rotation of coils?

[---ulin]

hacksmith is doing this to make a hoverboard

[OMNI_INFINITY]

Assume that is a "MOSFET" and not a jfet. Would an IGBT be better for that?

[artolauri]

* Nyt jos koskaan on hyvä aika laittaa Arto Lauri Youtube kanava tilaten. Niin itselle, kuin kavereille kanssa.

[floriandelmas]

Hi Dave,
Just a simple question, is it a simple full or half bridge plugged to the coil, or is there some resonating caps?
How do you chose the drive frequency?
Regards,

Flo

[davyponte]

45A rms 220 V them u wanna say us it works at 9, 9KW??? 😮

[eduardobarros]

It's sad that it generates such amount of heat with the current materials we know to work with this setup. We need to develop something that doesn't lose as much energy to heat but gets a lot of force generated. It would serve really well for machines that need to avoid contact as much as possible.