What Can We Learn From A Cheap Induction Cooktop?

Sometimes tearing down a cheap appliance is more interesting that tearing down an expensive one. A lot of the best engineering happens when cost is an issue. You may not solve the problem well, but you can solve it well enough for a discount shelf.

[openschemes] purchased a 1.8kW induction hot plate at a low price off Amazon. The reasons for the discount soon became apparent. The worst of which was a fully intolerable amount of high frequency switching noise. Wanting to know how it worked, he took it apart.

After he had it apart on his desk, he deciphered the circuit, and wrote about it clearly. As usual with extremely cheap electronics, some clever hacks were employed. The single micro-controller was used for monitoring, and generated a PWM signal that was instantly converted to DC through some filters. All the switching was done the old fashioned way, which explained why the hotplate seemed so brainless to [openschemes] when he first turned it on.

Lastly, he did some work on manually controlling the cooktop for whatever reason. The good news? He managed to figure out how to control it. Unfortunately he also destroyed his unit in the process, via a misapplication of 1200 volts. A fitting end, and we learned a lot!

Thanks [David Balfour] for the tip!

16 thoughts on “What Can We Learn From A Cheap Induction Cooktop?

  1. Bonus points for their delicious sense of humour, understandable even for us (folks from overseas with limited knowledge of english language). The “Fig 4 – Inside the Base. Are belong to us” one tore me apart :-)

  2. A few years ago I bought a “high end” induction hot-plate to supplement the stove in my apartment which only had one larger burner. The noise was atrocious, I’d guesstimate in up around the 17kHz range. I suppose if i were a back-line audio tech for a thrash metal band and didn’t have any hearing above 8kHz anymore, it’d have been fine. For me it was like someone was poking a knife in my ear.

    1. Hard thing being able to hear high frequencies. I bought a Belkin USB power supply that can make 2.3A for ~35€ for a small router. Whenever I start the wifi on the router, the power supply start whistling and I find it very annoying. I’m the only one hearing it, and only with my left hear but god it is annoying ! I switched for a 10€ power supply, 2.4A, no problems.

  3. Article says
    “The 8uF is the input cap located right after the bridge rectifier. They run this thing almost like a PFC so he eats a LOT of ripple at 60Hz.”

    But it is not. That sounds like a standard bridge rectifier followed by a smoothing capacitor. Non-sine bad PF and all.

    The ferrites are probably not there to increase the inductance without a pan present, as the experimenter notices the inductance goes down with a pan sitting on it. More likely the ferrite rods are there to prevent the field from extending below the unit and heating up silverware in the drawer underneath the unit. And secondarily increasing the inductance.

    1. I must correct myself, later in the analysis it is shown that the 8uF capacitor is insufficient to stay charged and in fact likely just removes some of the switching noise. On page 5, it is clear that the coil draws current spikes the entire 60Hz cycle.

      I just realized that this teardown is from 2010!

  4. I wonder if they ever got anywhere with it. As noted, it’s not isolated so bad for exposed coil. However, either an output transformer (the frequency is right on the edge of air vs iron core) or an isolating input transformer would help to protect the operator. I’d probably consider the output as I suspect you’d want to go to a much lower turn coil for metalworking and added water cooling.

  5. A lot of things could account for the price difference, including capacity, features, recognized name brand, materials and labor costs, etc. Give the model numbers of both and then we can compare them. Thank you.

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