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Induction hob

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Wow! An actual electronics question in cooking  :-DD

OK, so we (that is, I, but hopefully there won't be an argument) are looking at a portable induction hob. Reason: to see how it goes and maybe upscale to a full 4-hob panel. A browse of Amazon and John Lewis (a UK shop with good rep, usually sells quality kit) shows many such single-hob products all very similar.

Now, my understanding is that induction is better than gas or electric (plates - I know induction is electric!) is that the heat is more instant and controllable. All the ones I have seen in this price range, which is <£100 and typically <£55, don't have the fine control. They have steps, such that you pick 1 of 10 power levels, say, or similar temperature settings (although the temperature appears to be quite, ah, loose).

OK, I can go with that but it seems that at the two lowest levels the PWM is very slow. Slow enough that on boiling a pan you can see the water bubble, then not bubble, then bubble, not bubble. This is how my partner's folks' halogen  hob works normally, and it's horrible - no-one likes cooking on that. Anyway, I am wondering why all the different brands are subject to this low-power stuttering.

Am I making a mistake in going for one of these to discover the delights of induction?

Induction normally does PWM of the actual oscillator, no real power control is possible with the cheap self oscillating designs they normally use, and thus at low settings they implement pretty coarse PWM to get low average power, and also to avoid harmonics being impressed on the mains, so the drive has to be an integral number of full mains cycles, and thus the low PWM frequency. Hard to do single pulse control that way, better to have a longer time, say 10s total, and average over that.

Yes the single plate ones all are pretty much the same electronics inside, similar controls for power as well, and thus similar characteristics. Only a few power levels as well, some have more, some have less, but pretty much only a full stove will have any form of temperature feedback, simply because of the very poor coupling between the pot and the glass top, deliberate though it is, and also because your sensor wiring will also have massive common mode voltage in it. About the only feedback is detecting pot size on the built in types, using a few separate drivers, and sensing the open circuit voltage and current on them, so as to detect pot size, and presence on the top every cycle, so that the power can be turned off before it destroys the oscillators.


--- Quote ---so the drive has to be an integral number of full mains cycles, and thus the low PWM frequency
--- End quote ---

Ah! That explains it perfectly, thanks  :-+

Update: finally acquired a Lidl (aka Silvercrest) induction hob for £29, perhaps the cheapest available without going to Ebay used. Lidl have removed the advert in the UK but I found this: https://www.lidl.de/p/silvercrest-induktionskochplatte-sikp-2200-b1/p100354554

Anyway, I was pretty impressed. I put a pan on it with oil in, set to 180C and then got some garlic out of the pantry. When I turned around the thing was already smoking! On our electric hob you'd be waiting several minutes for that. So, pushing on I turned it down to 140C and did the onions, and at that temperature they were on the verge of burning but not quite there. And stayed like that. I couldn't manage to do that on the electric hob without fiddling with the control all the time.

For soup, I could set it to simmer and it would jolly well stay simmering. No setting the control to 2 then 3 then 2, the frequency depending on whether the door is open or not. So I like this and can see a full stove top in the future.

One thing though: I am told it makes an awful racket. I initially thought that was the cooling fan, but thinking about it the kettle makes a racket as well, even when it's just started and not yet boiling. Is the noise an unavoidable part of the process?

Doesn't induction cooking require pans with a "diamagnetic base" to facilitate eddy currents?


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