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Induction hob

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PlainName:

--- Quote from: Alti on February 03, 2023, 04:41:00 am ---
--- Quote from: PlainName on May 19, 2022, 09:15:34 am ---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.
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More instant than resitive heaters - yes, if same powers are considered and low quantity of food is prepared. If you want to compare 2kW inductive and 3kW resistive, the higher the quantity/mass, the less of an advantage inductive heating has.

--- End quote ---

I am thinking that, like with microwaves, the energy is going into the internals of the target rather than being conducted from the outside. So instead of waiting for the heat to work it's way up through the heating element and then the pan base, it's starting off in the base.


--- Quote ---Controllable - depends on the definition. Both are open loop. The resistive heaters usually use infinite switches and come with infinite step count. Inductive - usually 10 steps 0-9.

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Similarly, there is no thermal inertia from the cooker. Turn off the power and the temperature should start dropping straight away. With the resistive heater, even though the element will start to cool, it is still imparting energy to the pan and will increase the thermal mass.

PlainName:

--- Quote ---Aside from needing suitable cookware I can't see a downside.
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Fragility. You wouldn't want to be banging your wok against the glass like they do in the YouTube 'Asian streetfood' videos. And the glass is easily marked, and it's slippery. You can get silicone disks to go under the pans to counter the marking and slipperiness, so maybe that's the answer, but it's amazing how much you bang pans on the stove without realising.

Marco:

--- Quote from: Alti on February 03, 2023, 04:41:00 am ---Controllable - depends on the definition. Both are open loop.

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There are hobs with temperature sensors for closed loop control, but if you want a smooth surface and not mess about with external probes they need to work through the glass and with pans made from wildly different materials, so I wouldn't 100% rely on it working all the time.

For portable hobs Xiaomi/Tokit has one with a nub which contacts the pan for temperature control, but it's a smart device and you can only do temp control through your mobile phone for some obscure reason.

Alti:

--- Quote from: PlainName on February 03, 2023, 01:24:57 pm ---
--- Quote from: Alti on February 03, 2023, 04:41:00 am ---(..)If you want to compare 2kW inductive and 3kW resistive, the higher the quantity/mass, the less of an advantage inductive heating has.
--- End quote ---
I am thinking that, like with microwaves, the energy is going into the internals of the target rather than being conducted from the outside. So instead of waiting for the heat to work it's way up through the heating element and then the pan base, it's starting off in the base.
--- End quote ---

BTW, 2kW in case of induction is 2kW input. It has some drop in efficiency, lets say 5%. Are we comparing 1.9kW resistive with 2kW inductive for boiling 3 liters of soup or are we comparing 3kW resistive and 2kW inductive for boiling 1 spoon of oil?

I think it should be possible to estimate thermal inertia step response of ceramic glass + steel pot and when exactly it reaches 90% of setpoint of power. For sure this takes some time.
Boiling 1 liter of water 10oC-100oC requires 380kJ and that is 200s with 1.9kW delivered and no heat losses. As you can see - this is quite some time so either 1.9kW directly or 3kW through the glass and the answer is not that straightforward. Besides, you need to cut out power for resistive heater before water starts boiling (some experience needed, or controller) or this leads to losses.

Off the base with 2kW or with thermal inertia of ceramic glass with 3kW. Pot stays the same. The higher the quantity/mass, the less of an advantage inductive heating has. Those resistive ceramic heaters are rarely 2kW, maybe the smaller ones. The bigger the diameter the higher the powers these offer. And, you also need to have special pots with flat bottom for low thermal resistance. The cheapest crap that does not lay flush won't be fast.

PlainName:

--- Quote ---BTW, 2kW in case of induction is 2kW input. It has some drop in efficiency, lets say 5%. Are we comparing 1.9kW resistive with 2kW inductive for boiling 3 liters of soup or are we comparing 3kW resistive and 2kW inductive for boiling 1 spoon of oil?
--- End quote ---

Sorry, I don't have a clue. The only reason I know the induction hob is 2KW is because it says so in the manual (and is part of the name). I didn't buy it because it was rated thus - I would have got it had it been 1.8kW or 3kW. As to the traditional resistive hob... there are two sizes: big hot ones and small not so hot ones. That's the sum of my knowledge, I'm afraid :)

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