induction

38 Articles

DIY Induction Heater Draws 1.4 KW And Gets Metal Hot

November 29, 2020 by 16 Comments

Induction heaters can make conductive objects incredibly hot by generating eddy currents within the metal. They’re used in a wide variety of industrial processes, from furnaces to welders and even heat treatments. [Schematix] whipped up his own design, and put it through its paces on the bench.

The build in question is a fairly compact design, roughly shoebox-sized when fitted with its six-turn coil. Running off anything from 12 V to 48 V, the heater put out at a massive 1.4 kW in testing. At this power level, the high current draw led the power traces to heat up enough to melt solder, and eventually burn out. [Schematix] plans to rebuild the heater with added copper wiring along these traces to support the higher power levels without failure.

The heater is able to quickly heat ferrous metals, though was not able to meaningfully dump power into aluminium under testing. This is unsurprising, as non-ferrous metals primarily undergo only Joule heating from induction, forgoing the hysteresis portion of heat transfer due to being non-magnetic. However, modification to the design could improve performance for those eager to work with non-ferrous materials.

We’ve seen a few induction heaters before, for purposes as varied as soldering and casting. Video after the break.

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A Clock From An Electricity Meter

October 29, 2020 by 4 Comments

Electric utilities across the world have been transitioning their meters from the induction analog style with a distinctive spinning disc to digital “smart” meters which aren’t as aesthetically pleasing but do have a lot of benefits for utilities and customers alike. For one, meter readers don’t need to visit each meter every month because they are all networked together and can download usage data remotely. For another, it means a lot of analog meters are now available for projects such as this clock from [Monta].

The analog meters worked by passing any electricity used through a small induction motor which spun at a rate proportional to the amount of energy passing through it. This small motor spun a set of dials via gearing in order to keep track of the energy usage in the home or business. To run the clock, [Monta] connected a stepper motor with a custom transmission to those dials for the clock face because it wasn’t possible to spin the induction motor fast enough to drive the dials. An Arduino controls that stepper motor, but can’t simply drive the system in a linear fashion because it needs to skip a large portion of the “minutes” dials every hour. A similar problem arises for the “hours” dials, but a little bit of extra code solves this problem as well.

Once the actual clock is finished, [Monta] put some finishing touches on it such as backlighting in the glass cover and a second motor to spin the induction motor wheel to make the meter look like it’s running. It’s a well-polished build that makes excellent use of some antique hardware, much like one of his other builds we’ve seen which draws its power from a Stirling engine.

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Simple Induction Heater Helps With Homebrew Shrink-Fitting

October 26, 2020 by 14 Comments

Machinists have a lot of neat shop tricks, but one especially interesting one is shrink-fitting tools. Shrink-fitting achieves an interference fit between tool and holder by creating a temperature difference between the two before assembly. Once everything returns to temperature, the two parts may as well be welded together.

The easiest way to shrink-fit machine tooling is with induction heating, and commercial rigs exist for doing the job. But [Roetz 4.0] decided to build his own shrink-fitting heater, and the results are pretty impressive. The induction heater itself is very simple — a 48 volt, 20 amp power supply, an off-the-shelf zero-voltage switching (ZVS) driver, and a heavy copper coil. When the coil is powered up, any metal within is quickly and evenly heated by virtue of the strong magnetic flux in the coil.

To use the shrinker, [Roetz 4.0] starts with a scrupulously clean tool holder, bored slightly undersized for the desired tool. Inside the coil, the steel tool holder quickly heats to a lovely deep brown color, meaning it has gotten up to the requisite 250-300°C. The tool is quickly dropped into the now-expanded bore, which quickly shrinks back around it. The advantage of this method over a collet or a chuck is clear in the video below: practically zero runout, and the tool is easily released after another run through the heater.

You say you’ve got no need for shrink-fitting tools? How about stuck bolts? Induction heaters work great there too.

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The Easiest Way To Put Your Doorbell On The Internet

June 1, 2020 by 39 Comments

Thanks to low-cost WiFi enabled microcontrollers such as the ESP8266 and ESP32, it’s never been a better time to roll your own smart home system. But that doesn’t mean it isn’t daunting for new players. If you’re looking for an easy first project, putting your old school doorbell on the Internet of Things is a great start, but even here there’s some debate about how to proceed.

Most people stumble when they get to the point where they have to connect their low-voltage microcontroller up to the relatively beefy transformer that drives a standard doorbell. We’ve seen a number of clever methods to make this connection safely, but this tip from [AnotherMaker] is probably the easiest and safest way you’re likely to come across.

His solution only requires an inductive current sensor, which can be had for less than $1 from the usual overseas suppliers. One leg of the doorbell circuit is passed through the center of this sensor, and the sensor itself is connected up to your microcontroller of choice (here, and ESP32). The rest is software, which [AnotherMaker] explains in the video after the break. With the addition of a little debounce code, your microcontroller can reliably determine when somebody is out there jabbing the bell button; what you do with this information after that is up to you.

If you’re worried this method is too easy you could always try it with an optocoupler, or maybe convert the low-voltage AC to something your microcontroller can handle.

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Set Your Nuts (and Bolts) Free With This Induction Heater

May 22, 2019 by 36 Comments

[Amon] built an induction heater to break stuck bolts loose. If you work on cars, machines, or anything big and metal, sooner or later you’re going to run into stuck nuts and bolts. Getting them unstuck usually involves penetrating oil, heat from a torch, and cheater bars. Heat usually works well, as heating the bolt makes the metal expand, helping it to break free. Torches aren’t exactly precision instruments though, and things can get interesting using one in tight spaces.

Fire isn’t the only way to heat a bolt through. Electricity can do the job as well. But why use a heating coil when you can grab an induction heater. Mechanics have had induction heaters in their toolboxes now for a few years, under names such as Bolt Buster or Mini Ductor. These devices cost several hundred dollars. However, you can purchase a 1000 watt induction heater from the usual sources for around $30. These are open frame Zero Voltage Switching (ZVS) power supplies, with uninsulated copper coils.

[Amon] bought one of these induction heaters, along with a beefy 24V, 40 amp switch mode supply to power it. He built the two into a plastic enclosure. A relay energizes the induction heater, so it isn’t always running. The key to this build is the handle. Rather than mount the induction coil directly on the supply, [Amon] ran two extension wires to a 3d printed gun style handle. This keeps the bulky part of the heater away from the work. The copper tube coil was re-shaped to better work with the gun. Some fiberglass sleeve keeps everything insulated, even at extreme temperatures.

The result is a very useful heater, ready to bust loose some bolts. We’ve seen homebuilt ZVS supplies powering induction coils before. It will be interesting to see how well these commercial units hold up.

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Cooking Eggs With Magnets In Motion

November 2, 2018 by 71 Comments

It’s probably always going to be easier to just find some dry wood and make a cooking fire, but if you’re ever in a real bind and just happen to have a bunch of magnets and a treadmill motor, this DIY induction cooktop could be your key to a hot breakfast.

For those not familiar with them, induction cooktops are a real thing. The idea stretches all the way back to the turn of the last century, and involves using a strong magnetic field to induce eddy currents in the metal of a cooking vessel. As [K&J Magnetics] explains, the eddy currents are induced in a conductor by changing magnetic fields nearby. The currents create their own magnetic field which opposes the magnetic field that created it. The resulting current flows through the conductor, heating it up. For their cooktop, they chose to spin a bunch of powerful neodymium magnets with alternating polarity using an old treadmill motor. The first try heated up enough to just barely cook an egg. Adding more magnets resulted in more heat, but the breakthrough came with a smaller pan. The video below shows the cooktop in action.

It’s worth noting that commercial induction cooktops use coils and a high-frequency alternating current instead or rotating magnets. They also are notoriously fussy about cookware, too. So, kudos to [K&J] for finding success with such an expedient build. As a next step, we’d love to see the permanent magnets replaced with small coils that can be electrically commutated, perhaps with a brushless motor controller. Continue reading “Cooking Eggs With Magnets In Motion” →

Is Your Wireless Charger Working?

November 25, 2017 by 3 Comments

It’s that time of year at which the Christmas lights are coming out of storage, isn’t it. Some modern seasonal rituals: untangling half a mile of fairy lights, and replacing a pile of CR2032 cells in LED candles.

[RobBest] had a solution to the latter, owning a set of nifty rechargeable LED candles that came with their own wireless charger. Sadly the charger wasn’t working quite as intended, as the indicator light to show when it had finished its cycle was always on. How could he indicate that the induction system was in operation?

His answer was to take a non-functioning candle and strip it down to expose its induction pick-up coil. He could have simply hooked it up to an LED for a quick result, but since the device in question was a candle it made sense to give it a candle effect. A PIC microcontroller was therefore pressed into service to drive the LED with its PWM output, giving a pleasing flickering effect.

You don’t have to own a set of electronic candles to have a go at wireless charging. Instead you could try a trip to IKEA.