Can spinning magnets fry an egg? You bet they can! Let’s see how a simple array of magnets can generate eddy currents in a conductive frying pan, heating it up enough to cook an egg.
The setup is quite simple. Simply take a motor that can spin quickly and handle a decent amount of load (we used an old treadmill motor), bolt it to the underside of a table, mount a disc with the magnet array onto the shaft, and spin away! You'll also need some sort of tabletop to put the pan onto.
-1 motor w/ controls (we used an old treadmill motor)
-Wooden or plastic disc
-Several neodymium magnets
-Solid aluminum or copper pan
Step 1: Creat Magnet Array
The first step is to create the magnet array on the spinning portion of the stove top. We found a large, wooden disc at a local craft store. This was perfect for our array of magnet.
We laid out a template for placing the magnets, to make sure they were spaced evenly. We planned on using 10 1.5" x 1/2" x 1/4" countersunk magnets. The K&J part number is BX884DCS.
The outer diameter of the magnet array was about 5.5"...we figured this would mimic a smaller stove burner.
Centering the template on the disc, we screwed the magnets in place, making sure to alternate the polarities. The alternating poles is what induces the eddy currents in the pan, creating heat!
Then we drilled out a center hole in the disc. This is where the nut would sit that screws onto the motor shaft.
Step 2: Mount Motor
The treadmill motor we found was perfect for this, because it came with a bracket that we could use to mount it. We drilled a hole through our table, and bolted the motor to the underside of the table.
We found it easier to flip the table over to mount the motor, so that we didn't have to hold it up while bolting it.
We fastened the electronics to a wooden board under the table, to keep them out of the way.
Also, we salvaged the controls for the treadmill motor and kept them hooked up so we could have variable speed control. We didn't have to do any additional wiring, just kept it as is!
You could use many different types of motors for this. We spun our disc at around 1600 RPM. The eddy currents create some resistance, so you'll need to choose a motor that can handle the additional load.
Step 3: Mount the Disc to Motor
This step is simple enough...mount the disc to the motor shaft. Our treadmill motor shaft has left-handed threads, so we had to go out and buy left-handed nuts. You might need a few washers to keep the disc from scraping against the table top.
Step 4: Create "stove Top"
You'll need something to keep the aluminum/copper pan very close to the spinning magnets, but without touching them. The closer the pan is, the stronger the eddy currents, the more heat that will be produced.
We used some scrap wood to get the right height and a 1/4" thick lexan sheet. The lexan was only about 1/16" away from the magnet surface, so in total the magnets were only 5/16" away from the pan.
Step 5: Testing and Troubleshooting
Check out the video to see the whole setup and the testing/troubleshooting we went through with the project.
Initially, we only used one layer of magnets with a large aluminum pan. However, we could only get this setup to reach about 120°F.
So we doubled up the magnets (20 total) and used a smaller, thicker aluminum pan. With this setup, we were able to get the pan up to around 212°F, which is boiling water temperature! It's max temperature topped off around 240°F, which is enough to fry an egg and slowly cook things, but not nearly as hot as a regular stove.
Step 6: Cook Away!
Ultimately, we were able to fry an egg with our DIY induction stove. We definitely won't be winning any design awards, but it was a fun way to demonstrate how eddy currents can create heat.
You can buy induction stoves for your home, but they work a bit differently. They don't use permanent magnets--they basically use AC current flowing through coils to heat up steel or cast iron pans. They are pretty neat, but you are limited to only using steel or cast iron pans.