Keep Coffee Warm Through Induction Heating

Transformers have an obvious use for increasing or decreasing the voltage in AC systems, but they have many other esoteric uses as well. Electric motors and generators are functionally similar and can be modeled as if they are transformers, but the truly interesting applications are outside these industrial settings. Wireless charging is essentially an air-core transformer that allows power to flow through otherwise empty space, and induction cooking uses a similar principle to induce current flow in pots and pans. And, in this case, coffee mugs.

[Sajjad]’s project is an effort to keep his coffee warm while it sits on his desk. To build this special transformer he places his mug inside a coil of thick wire which is connected to a square wave generator. A capacitor sits in parallel with the coil of wire which allows the device to achieve resonance at a specific tuned frequency. Once at that frequency, the coil of wire efficiently generates eddy currents in the metal part of the coffee mug and heats the coffee with a minimum of input energy.

While this project doesn’t work for ceramic mugs, [Sajjad] does demonstrate it with a metal spoon in the mug. While it doesn’t heat up to levels high enough to melt solder, it works to keep coffee warm in a pinch if a metal mug isn’t available. He also plans to upgrade it so it takes up slightly less space on his desk. For now, though, it can easily keep his mug of coffee hot while it sits on his test bench.

Thanks to [Jerry] for the tip!

13 thoughts on “Keep Coffee Warm Through Induction Heating

  1. I remember my father in the early 70s coming home with his latest creation from work and getting my mum to test boiling milk in an iron saucepan. Very easy to control the heat with the potentiometer. Made quite a loud buzzing, probably wouldn’t pass any modern safety tests, and we couldn’t watch the TV, but hey, a prototype induction stove and we were really impressed. Nowadays I have a consumer grade induction hob in the kitchen, easy to use and it’s quiet and I can watch TV.
    Just don’t run it when there are people who have pacemakers around.

  2. Wow, 300W just to heat a mug?
    Why not use a 100W resistor mounted on a plate of aluminum? I use those to heat up pcbs with large ground planes when soldering. About 25W is enough to increase the temperature of the pcb to 100 deg. Centigrade.

    1. Well. Surplus Space Lasers from United States Space Force could be a solution.

      Just take a Bodum insulated glass mug (they are truly great!) or a clone (cheaper and same greatness), install the laser into the ceiling (looks more tidy), route some bell wire to the next three-phase switch box and voila. Instantly reheated coffee.

  3. While the project is awesome you should keep in mind that those cheap thermal cups from China are made with really poor grade stainless steel. At Warsaw Military University of Technology we’ve tested hot water stored in them for 20 minutes. Those cups exhibited dangerously elevated hexavalent chromium levels compared to water from the same kettle but stored in a glass.

    1. Thanks for the warning. Do you have a link?

      And while we’re on the subject, also watch out for cheap “brass” plumbing fittings. There’s often a lot of lead in them.

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