Rick's b.log - entry 2024/09/21

Autumn Equinox

🔓 New fear unlocked.

Silvercrest SIKP 2200 B1 Induction Hob

For many a year, my cooking has been with the following things:

• A microwave oven.
• A camping stove.
• A multicooker (like a smart rice cooker with extras).
• A mini-cooker.
• A smart rice maker (sometimes).
• A pressure cooker (rarely).

The top four are the main things, roughly in order of frequency of use.

The microwave needs replacing, it's old and starting to rust, but I'm keeping it going as the microwaves that I see in the supermarket are all 700W unless it's an expensive model that does 900W or more. While a 700W is perfectly usable, it will take longer, and for pretty much all of my life that has had microwaves in it, they've been 800W models, so I know the timing. Plus, you know, I'm impatient. It's not as if you're swapping a bad 2kW model for an improved 700W model like with vacuum cleaners. You're either dumping 800W into the food, or 700W for slightly longer. Either way, I can't imagine the energy required to heat food is, in the long run, going to be any different. What's different is the time it takes.

The oven... was replaced several years ago. If I can say anything to you, I will say that don't ever buy a mini-oven with a single piece of glass as a door. Insist upon a model that has a double-pane door. That keeps a more even temperature inside, as best a mini-oven can, rather than having one side of the box leaking a lot of heat away from the oven.

The gas stove is rusty. It has seen many years of use. A few less now that some tasks have been moved over to the multicooker, but still, there are some things that are less trouble heated in a saucepan.

Here is a really badly drawn diagram of using gas to heat up some water.

The theory of operation is as simple as when we were using bashed metal on open fires. There's a heat source. Put the item to be heated over top, then wait. Heat rises, it'll rise up into the item which will itself heat up.

The problem is that while cooking like this is convenient, it isn't particularly efficient. Let's look at this image again, this time adding in an even more poorly drawn representation of where the heat is.

As you can see, while the majority of the heat will be transferred into the item, in this case the water, there is a large amount lost around the sides.
This wasn't a problem back in þe olde dayes because the fire also served the purpose of heating the room and its occupants, so heat loss was not a problem.
It was also not a problem in the slightly less olden days as fuel was dirt cheap and used with reckless abandon.
These days? Everything is a lot more expensive and it's pretty well known what effects we are having on our environment. So, even though the heat loss around my pan may be insignificant, I'm not the only person on the planet using a gas cooker. A lot of insignificant starts to get quite significant.

Now, you might say, if gas is inefficient, why not use an electric cooker instead? Well, it's a valid question but I can shoot it down on three accounts:

• There's a lot less control with an electric ring. It's either on or off. With gas, you can adjust the flame to any arbitrary setting between barely-lit and maximum.
• One of the main reasons that I won't go near electric is that there is a large lag in between when you turn the element down, and when it begins to cool. Like, say, pasta water about to boil over. With gas, knock the knob back and the results are immediate.
• And, the big one: It's still inefficient. You are still throwing heat underneath something in order to transfer it into the item you're intending to heat. As you might have noticed from the shiny foil underneath the elements, they don't radiate heat up, they radiate in all directions. The foil is to reflect that heat up, but again quite a bit gets lost.

The problem, you see, is that we are using a heat source to heat a pan to heat the contents within.

There is, actually, a better way.

Those of you who enjoyed physics class will be aware of something called a transformer. This is a large coil of wire around an iron core, which is itself surrounded by a possibly larger coil of wire. What happens is that electricity is dumped into the first coil. As it is AC (transformers don't work with DC), the back and forth of the electricity waveform creates magnetic fields in the iron core, which in turn induces energy in the second coil of wire. How this works is a combination of science and magic. Actually, magnetic fields shove electrons around, though the reason why is liable to be one of those freaky quantum mechanics things, so let's just say "magic" as it is so much simpler to type. Either way, it's a known-known and careful adjustment of the coils (how many times wound around the core) has made electrical things work for us for about eighty-odd years.
Granted, most power supplies these days are switch mode as they're a lot smaller and even more efficient than a big transformer, but hey, even those have a little transformer inside. Transformers also made the high voltages that got the big old glass-tube televisions working. Or the spark plugs in petrol engines. Or, indeed, the very electricity we are using - how do you think the 11kV supply from the overhead wires ends up as 230V in your sockets?
[note: electricity distribution networks use a variety of voltages; the three-wires-on-a-pole is often something like 11/18/22kV, while the big pylons could be something like 400kV]

Perhaps surprisingly, induction cookers use a process that is similar. There is a coil mounted under a cooking surface, often a glass plate, and electricity is dumped into the coil with a waveform that's something like 30-50kHz. This creates an electromagnetic field. When a suitable cooking implement that is magnetically-friendly is placed close to the coil, in other words placed upon the cooking surface, the electromagnetic field induces large eddy currents (closed loops of magetically induced current) in the base of the cooking implement.
The coil has many turns, while the saucepan, frying pan, etc effectively forms a single shorted turn.
Yes - we have just turned a cooker/pot into a rudimentary transformer. You won't get electrocuted from it as many-to-one not only steps down the voltage, and steps up the current, but by vertue of forming a single shorted turn, there are no 'ends' to carry any current between them. It's all happening by way of eddy currents within the metal. Since there is nowhere for all of this energy to go, it does what we usually don't want to happen - it heats up. A lot. But since it's a saucepan, heating up is the intended function.

Here's another lousy drawing. I'll make it bigger so you can see the arrows better. They represent the magnetic fields. And, of course, we have wibbly intestines rather than a coil as, well, it's a representation.

This brings us to the modern era, when no longer should we say "Now we're cooking with gas!" but rather "Now we're cooking with magnetically induced eddy currents!". Hmm, doesn't quite have the same ring to it, does it?

However, as you can see, we've effectively removed a step in the process. No longer do we have to heat the cooking implement, it itself becomes the heat source, and thus is able to transfer the heat directly into whatever it is we're cooking. Much more efficient.

A new induction cooker

Induction cooker (banana for scale).

The box says:

• Touch controls
• 60-240°C
• Ten levels of power and temperature
• 2 metre cord
• 2200W

The controls

Control panel.

From left to right, top row:

• Child lock - locks the unit off, or to its most recent settings. Bizarre, because to lock or unlock, you just need to press it for three seconds, so it'll only defeat a very young or stupid child...but may confuse a fair few adults. ☺
• Delay timer - you can set the timer (default 30 minutes, can set up to 24 hours) and then select a cooking mode. When the timer expires, the cooker turns on and begins to cook. Which seems incredibly reckless to me...
  Also used to adjust the cooking time whilst cooking is in progress.
• Minus - turn the power level or temperature down. Minimum is 200W or 60°C.
• Display - an LED by °C or P or the clock symbol indicates whether the display is showing temperature or power or remaining time.
  In standby it will say -H- if the cooking surface is hotter than 60°C (which means "don't touch"), or -L- if it is lower (which means "fondle freely").
• Plus - turn the power level or temperature up. Maximum is 2000W (which is shown as level 10 or L10) or 240°C.
• M - toggle selection between temperature and power. If the cooker is not heating, this also starts the heating. The defaults are L05 (1000W) or 120°C.
• On/Off - hold for three seconds to turn on, simple touch to turn off.

Now for the bottom row:

• Keep warm / Reheat - continuous moderate heating, will keep the food at 60°C for up to two hours.
• Teapot! - keeps the power level constant and high (2000W) for boiling water. Defaults to 20 minutes of heating.
• Soup - the cooker adjusts the power level to prepare soups in a complicated cycle.
• Milk - heats up to 60°C for up to 20 minutes.
• Simmer - (no, it's not a frying pan) This brings the food to a boil and then simmers (<95°C = 2000W; >=1000W).
• Stew - Continual heating with moderate (600W) power, for up to two hours.
• Deep fry - for high temperature heating, heats to 180°C.
• Boost - This will switch to the full 2200W power for thirty seconds, before switching back to the previous settings. So while it says 2200W on the box, it can only do this in 30 second blasts.

First test

Boiling water.

It took just a smidgen over two minutes to bring the water up to a boil.
For comparison, a kettle rated 2200W took one minute and fifty three seconds, while the gas stove took a positively sedate three minutes and twenty four seconds.

First use

Not this time. Halfway through the first round of toast the chicken in white sauce was already up to cooking temperature. I had set the cooker to heat to 80°C and it seemed to be "not quite boiling", which was okay, if perhaps a tad on the high side. I stirred frequently as I wasn't really familiar enough with the product to knock the power back a little.
The meal was made, however, and the induction cooker impressed me with how speedily it heated.

Ratings and options

The temperature levels are 60, 80, 100, 120, 140, 160, 180, 200, 220, and 240°C.

The device weighs 2.1kg, and measures 31cm by 27cm with a height of 6.3cm (from the booklet, I didn't measure it).

It accepts cookware from 10cm to 22cm diameter.

It's electric consumption per kilogram, as I mentioned in the video, is the meaningless gibberish of 185.4 Wh/kg.

Second test - sixty degrees using the milk programme

As I was holding the themometer and resting my hand on the side of the saucepan because I'm lazy, I could feel the vibrations as the magnetic field kicked in and switched off. It was on for four seconds in every ten. So (2000W ÷ 10) × 4 means it was running at around 800W equivalent for a fairly gentle heating. It wasn't particularly fast, but on the other hand you shouldn't end up with that nasty milk scorching.

As the temperature passed sixty, the device stepped down to heating for two seconds in every ten, so we're down to ~400W equivalent. But it kept heating.

It wasn't until the temperature was just below 70°C that the cooker backed off, to keep the water heated to around 68-69°.

Heating water to 60°C.

Third test - hitting eighty

Anyway, it started. Power was dumped, water was heated. When it got to about 82°C, the cooker started making a bizarre pulsing sort of noise, I'm just going to guess it was running at half power, like quarter second on, quarter second off.
The temperature kept rising.

In a test I did last night, the temperature rose up to 96°C before dropping down, the cooker clicked off for a moment, before coming back on to hold steady around 91-92°C.
In today's test, it was better, it went up to 88°C and stayed pretty much there. I'm not sure why the difference in behaviour.

Suffice to say, it appears as though the temperature seems to be reading about 10°C out. I don't know how it actually senses, as the glass is warm but not overly hot after two minutes of heating to 80°C (actually ~88°C).

I'm not sure how much I'd be inclined to trust the 180°C for deep frying, but then how accurate are the so-called "semi-pro" deep fryers that cost forty euros? There is some headroom here as the boiling point of oil is around 200°C, the smoking point is higher, and the flashpoint is around 315°C. Obviously it depends upon the type of oil.
The Maillard reaction happens between 140-160°C, which is why oil is usually heated to around 180°C (it is hotter because you're often frying frozen food).

A bad point

That being said, I'm not sure what they could replace it with. It has to be something impervious to electromagnetic fields and it needs to be, for the users, something that's easy to manage. Maybe textured and rougher glass would hold better? But at the cost of being hell to clean...

I'll throw in here an extra point, although it isn't a problem for me [spoilers: yes, it is!].

A look inside... sort of

Looking up from underneath, we can see the coil.

Induction coil (looking up from underneath).

Looking further up one can see the interface board running under the controls.

Control panel underside.

Given the position of that IC, I'm going to guess it's something like a 1628 LED driver, but given that it is working with capacitive inputs, probably more likely something like a CAP1114. But you get the idea.

Just visible on the other side, and not worth taking a picture of, is the edge of a large heatsink. This will be where the power electronics and the control system are located. And it is likely to be running a Zilog S3 8 bit microcontroller, specifically the S3F84B8. This offers a SAM88 Z8-compatible CPU core (it's similar to the Z80, but not the same nor a derivative, it was first made in 1979 to go alongside the Z80), 8K Flash, 272 bytes of RAM, 78 CISC instructions, 17 vectored interrupts, a 1 channel 10 bit PWM, an 8 bit basic timer, an 8 bit timer/counter with PWM mode, and a 16 bit timer, plus a 10 bit SAR ADC, 4 comparators, 1 op-amp, and either an internal 8MHz oscillator or up to 10MHz external.
Why do I think it is this chip? Well, the datasheet says "The S3F84B8 MCU is designed specifically for induction heating cookers and related applications.".
Of course there are other chips available, this was the first one Google found me.

The effective cooking area

In reality, the maximum effective size is about 16cm, because the coil inside is smaller than the larger ring printed on the glass.

Let's see what happens if I shine a light up from underneath.

How big is the heating coil?

As you can see, the heating coil is visible for about the inner two thirds of the outer circle. Beyond that point, nothing.

I did want to demonstrate why this is important using my frying pan to show you a heated ring smaller than the pan base, but this is when I discover that my habitual frying pan is made of aluminium. Induction hob says NO.

Don't worry, tonight's stir-fry isn't ruined. I have another one that is smaller but deeper. And this one has a stupidly thick base, it's like almost a centimetre thick. Smack a burglar across the bonce with this one, you'll be looking at homicide.
And... it boils the water marginally faster, one minute and fifty seven seconds.

Just for the sake of it, I decided to see what would happen if I put 500ml of cold water into that pan with the epic base and keep prodding the Boost button for the full 2200W experience. In other words, racing the kettle.

Let's crank this right up to eleven.

The result? One minute and forty four seconds. Whoo-yeah.

You'll note, also, that there's a paper towel underneath. As the cooking surface doesn't get especially hot (depends on what/how you're cooking, but certainly there's no flame or red-hot element involved) it ought to be possible to put a piece of paper towel down to catch bits that might tumble overboard and be a pain in the arse to clean up... though less of a pain than burned into enamel like a regular stove.

Some more electrical-porn

Bzzt-zap!

Looking at a little slit between the coil and the glass top, we can see the temperature sensor cemented to the glass.

Sensing the temperature.

Focus beyond that, it is possible to see the springs of the capacitive controls.

Sensing the fleshy appendages.

Your comments:

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jgh, 22nd September 2024, 20:47

Yes, glass surface hobs. I can picture myself smashing them within days of purchase by dropping something on it.    What would be useful is if you keep a note of your electricity and gas bills to see how they change with the transition to electric cooking. Electricity is more expensive that gas, but if you usage is more than, mmm, 8-ish times more efficient it can end up cheaper.

A tree-dwelling mammal, 23rd September 2024, 01:00

I currently have a 5-burner gas hob in my kitchen that I had fitted (to replace the really nasty enclosed radiant electric one) when I first moved in. I'd already decided that if I could get gas to the kitchen I'd have a gas hob, but if not then I'd install a halogen one. Turns out that getting gas to the kitchen was pretty trivial as there was a gas pipe running along the landing (to the combi boiler) directly above the kitchen.    However, that was in 2006. Having now installed solar PV, if I did need to replace the gas hob, I'd be fitting an induction hob. 90% of my pans will work on it.    As for keeping it clean, it's probably about the same as a halogen hob (which you can no longer get as they've been replaced by induction). Maybe slightly easier as the surface itself doesn't heat up. Definitely easier than keeping a gas hob clean, it requires a weekly strip-down and deep clean, with all the burner components being put through the dishwasher after being sprayed with industrial strength cleaner and degreaser.    That said, gas is completely controllable. You turn it off and it's off immediately, no lag. (Rick - is halogen the same? I'd have thought so, but there may be a lag?)    Of course the other down side to gas is that you have to turn the extractor on when you're using the hob. Otherwise you end up with a condensation problem and a build-up of fumes.

C Ferris, 23rd September 2024, 10:13

Seems that in the Supermarkets - the electric baby fan cookers are stacked high.  Seems they use a kettle element - plus fan.

A tree-dwelling mammal, 25th September 2024, 12:24

Also, are you aware that the 450K PNG file with the spider at the top of the page doesn't have any cache headers set? Which means it has to download on every page fetch?    Might be a server configuration issue, or might be that you're not setting / mis-setting the Cache-Control header in your script?

Rick, 25th September 2024, 14:53

Most likely a case of not setting. I'll look and see what the script is doing when I find myself a rounded tuit.

Zerosquare, 25th September 2024, 15:10

Wait, giant spiders? Did I type heyrick.au by mistake instead of heyrick.eu?

Rick, 26th September 2024, 18:50

Okay, I've added a cache-control header, timeout of 1 day...

A tree-dwelling mammal, 28th September 2024, 11:28

Just checked it - fixed now. Document inspector on Firefox reports the image as "cached", and more to the point you don't see it reloading every time you flick back to the page!

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