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Other Communities => Cooking => Topic started by: PlainName on May 19, 2022, 09:15:34 am

Title: Induction hob
Post by: PlainName on May 19, 2022, 09:15:34 am
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?
Title: Re: Induction hob
Post by: SeanB on May 19, 2022, 12:34:57 pm
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.
Title: Re: Induction hob
Post by: PlainName on May 19, 2022, 12:45:12 pm
so the drive has to be an integral number of full mains cycles, and thus the low PWM frequency

Ah! That explains it perfectly, thanks  :-+