What happens if you suddenly remove the pot from an induction cooker when on? - Page 1
Forum section: electronics / projects

author: Sourav
author_rank: Newbie
timestamp: August 15, 2025, 07:21:30 pm
content: Hi,I'm curious about what happens if you suddenly remove the pan from an induction cooker when it's running.The images are of two different induction cooker circuits, they're identical but the control circuitry is different (one has buttons, the other has touch, etc.)DetailsCoil: 100µH coil with a DCR of 82.5 mΩ.A tank capacitor is connected in parallel with the coil. The circuit is driven at resonance around 29 kHz.The tank capacitor is a:600 VAC / 1200 VDC rated0.3 µFMetallized polypropylene self-healing (MKP-SH)Designed for resonant and pulsed applications with dv/dt rating of 500 V/µsHas extremely low ESR at 10 kHz - 100 kHz; below the measurement limit of my LCR meters (<0.00 Ω, likely in the hundreds of micro-ohms range)Made by CG-Elec or sometimes BM, and has no capacitance reduction after 8 years of continuous operationThe switching device is a 25N120 IGBT rated for 1200 V maximum.Also, there are no TVS diodes or varistors on the IGBT to clamp surge voltages. There is only an inductor after the full-wave bridge rectifier to suppress the 29 kHz fundamental and harmonics from leaking back to the mains supply.BehaviorWhen there is no ferromagnetic pan on top of the induction cooker, it will not start and shows E0 on the seven-segment display.If it is running and the pan is suddenly removed, it continues to pulse for perhaps half a second before shutting down.When unloaded, the MCU runs the coil in short pulses to detect if cookware is present. My oscilloscope showed about 350 V oscillation, but for a much shorter duration when the cooktop is absent.The cooker's manual asks not to remove the pan when it's under operation.My questionMy intuition says: If you suddenly remove the pan while it is running, the very high Q-factor of the L-C tank becomes unloaded, which can cause a large back-EMF. The MCU turns it off, but it takes some time as mentioned above. If it runs for half a second without the pan, won't this cause under-damped LC oscillations of much higher voltage than the IGBT is designed to withstand?The steel pan naturally damps the oscillation through eddy current losses, but without it the tank is essentially unloaded.So, what actually happens in that short unloaded period, and is there a real risk of damaging the IGBT (through backEMF and HV oscillations) in this scenario?Please don't write silly answers like "just don't remove the pan, it's dangerous," etc. This question is theoretical and I want to precisely know what happens electrically when you suddenly remove the pan.Similar Question:https://www.eevblog.com/forum/projects/induction-hob-what-is-the-effect-of-suddenly-removing-the-pan/

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 16, 2025, 04:25:53 am
content: A full energy pot removal is clearly going to be a stress test, but consider* You cannot actually remove a pot instantly, relative to 29KHz there are many switching cycles to catch the reduced coupling.* There will be fast HW based protection that reduces duty quickly* My understanding is the 'better designed' induction drivers use two power devices in half bridge, which is naturally more tolerant of this situation.

author: antenna
author_rank: Frequent Contributor
timestamp: August 16, 2025, 05:19:55 am
content: I'm going to guess that the removal of the pot will cause an increase in circuit Q and could potentially over-volt the driving mosfet. I've always assumed that's how automotive induction heaters from amazon burn out (besides ignoring the duty cycle and running until the coil melts).

author: Psi
author_rank: Super Contributor
timestamp: August 16, 2025, 05:23:36 am
content: It should obviously be engineered to handle this without problems.Doesnt mean it is, especially cheaper ones.

author: wofritz
author_rank: Contributor
timestamp: August 16, 2025, 07:50:55 am
content: Quote from: Psi on August 16, 2025, 05:23:36 amReal life data point: My AEG (don't know the exact model) displays a fault state when you remove the pot and recovers automatically when you put it back.

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2025, 08:14:15 am
content: Quote from: Psi on August 16, 2025, 05:23:36 amEven the very cheapest induction stoves detect it and handle it properly. I have several <$50 induction hotplates from Aldi, and they handle it perfectly. You can’t really get any cheaper than those. The same basic product, with trivial variations to the front panel design, are sold under countless brand names.(As an aside, those things are legit impressive, giving 2kW of power into a single burner for the 230V models. They look like toys, but handle like real stovetops. I’ve been using one as my primary stove for years now, because I prefer cooking on it instead of the regular glasstop electric stove built into my countertop.)

author: Psi
author_rank: Super Contributor
timestamp: August 16, 2025, 09:26:03 am
content: by 'handle it without problems' I was more meaning that it should not slowly cause damage that ultimately leads to failure after x years.Obviously there's not going to be many induction cookers that fail the first time you yank a pot off them, if any.

author: Tation
author_rank: Regular Contributor
timestamp: August 16, 2025, 09:40:41 am
content: When the pot is on, there's a high power consumption. When it is off, power consumption is much lower, as there's no place for the energy to go. Can measure AC current consumption at the transient of removing the pot?Simply a guess, as I haven't studied it.

author: Psi
author_rank: Super Contributor
timestamp: August 16, 2025, 09:45:22 am
content: They all detect removal of the load/pan and switch to a pulsed 'load check' mode until the load is back.The main question is if they detect and switch fast enough not to cause any long term damage.

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2025, 09:47:04 am
content: Quote from: Psi on August 16, 2025, 09:26:03 amAs I said:Quote from: tooki on August 16, 2025, 08:14:15 amIt’s probably going on 10 years old at this point. It’s seen multiple active pot removals per day for years now, so thousands and thousands of times.And it’s literally, like, the cheapest one you can get.I think that counts as “handles it without problems” without long-term damage.

author: Psi
author_rank: Super Contributor
timestamp: August 16, 2025, 09:49:37 am
content: Quote from: tooki on August 16, 2025, 09:47:04 amA sample size of 1 doesnt prove anything, induction cooktops failing due to bad design is definitely a thing.

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2025, 09:51:27 am
content: Quote from: Psi on August 16, 2025, 09:49:37 amIf there were a design flaw that meant they couldn’t handle pot removal without self-destructing, then there’s no way it could make it anywhere near this far. Your question wasn’t about the reliability of induction stoves, but whether cheap ones contain the detection circuitry. This certainly proves they do.Not to mention that millions and millions of people use induction stoves. If removing pots killed them, we’d know about it.

author: Psi
author_rank: Super Contributor
timestamp: August 16, 2025, 10:22:04 am
content: Quote from: tooki on August 16, 2025, 09:51:27 amI never asked or implied that cheap ones don't have the detection/shutdown circuity.I questioned if they were all engineered properly to handle removal. They need a shutdown system, or the energy will go into the driver. But a badly engineered removal circuit means it wasn't properly engineered. It's really hard on the driver in the time before it detects pan removal and shuts off, and companies don't always want to spec the best parts or the best shutdown systems.

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2025, 10:49:21 am
content: Quote from: Psi on August 16, 2025, 10:22:04 amSure. But I would (and do) argue that the relatively high reliability of induction cookers of all price ranges suggests that this is not a widespread problem. If it were, we’d know about it, since there are so many of them in use. (Consider how in contrast, the shorter lifespans of modern washing machines, refrigerators, etc. are well-known.)This doesn’t mean there will be zero failures. Non-induction stoves fail, too. But I’ve neither seen nor heard any evidence that induction stoves are unreliable, neither in general, nor specific to cheaper models.

author: Psi
author_rank: Super Contributor
timestamp: August 16, 2025, 10:57:10 am
content: Quote from: tooki on August 16, 2025, 10:49:21 amI thought we did know that cheaper induction cookers tend to have some reliability problems. At least that has always been what I've heard from people. Not cheap cookers failing left and right, just a general trend that cheaper inductive cookers tended to have a larger number of issues, or shorter lifespan, than a typical kitchen appliance does.

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2025, 11:29:20 am
content: Quote from: Psi on August 16, 2025, 10:57:10 amI’m sure they’re less reliable than traditional resistive cookers. But not so much that one could call them inherently unreliable. (And with resistive cookers getting so much hotter underneath the glass, the now ubiquitous electronic user interface controls might actually be worse off in a resistive cooker than an induction one!)Of the many people I know with induction, only one has had trouble of any kind, and that’s with a Samsung model that has been fickle about pan detection from day 1. So either a design or manufacturing flaw, but not a reliability issue. (It struggles to detect smaller pans that are well beyond the minimum pan size, and sometimes fails even with larger pans. It affects all the burners, so I suspect a design flaw more than manufacturing.)I tried actively searching* (in two languages) for reports on induction cooker reliability problems and came up dry; I can’t find any evidence that they are more failure-prone than other stove types.*as much as doing actual web searches is possible anymore, since the engines focus so much on shopping and AI crap.

author: PlainName
author_rank: Super Contributor
timestamp: August 16, 2025, 01:51:49 pm
content: QuoteIf they were not, wouldn't there be something in the instructions about not removing a pan whilst powered, or similar?

author: Simmed
author_rank: Frequent Contributor
timestamp: August 16, 2025, 03:23:04 pm
content: my $50 cooker lets out a beep and stopsit resumes when i put the pot back

author: TimFox
author_rank: Super Contributor
timestamp: August 16, 2025, 04:05:13 pm
content: Quote from: Psi on August 16, 2025, 09:49:37 amWhat is your proof that induction cooktop failure due to bad design “is a thing”?Obviously, bad design is always possible, but is it prevalent?Before the internet, we had “urban legends”, often spread by fax machines during that primitive era, that cited “FOAF”, friend of a friend, as the source.

author: radiolistener
author_rank: Super Contributor
timestamp: August 16, 2025, 06:02:13 pm
content: When you remove the pan from a running induction cooker, the losses in the LC tank circuit drop sharply - the ferromagnetic cookware adds significant damping through eddy currents and magnetic losses. Without it, the tank becomes high-Q, and the energy pumped into it each cycle starts accumulating, which results in a rising oscillation amplitude of both voltage and current.Although the growth is not unlimited - it is ultimately constrained by internal losses (coil resistance, capacitor ESR, driver limitations), the new steady-state amplitude without the load can still exceed the safe operating limits of the switching device. If the protection circuitry or control algorithm does not cut the drive quickly enough, the voltage across the tank capacitor and the IGBT can exceed its maximum Vce rating, leading to avalanche breakdown of the IGBT. This is a destructive failure that will require replacing the IGBT.In most modern cookers, the microcontroller detects the missing load within a few tens or hundreds of milliseconds and stops the oscillation, so the risk is low, but with very cheap or poorly designed units, this risk is real.It’s also worth noting that the main drawback of many low-cost induction cookers is not so much possible IGBT breakdown when cookware is removed, but rather their crude power control method. Instead of smoothly adjusting the drive amplitude or frequency, they often use burst-mode on/off cycling at full power. As a result:- at “medium” heat, water may either erupt in violent bursts, splashing everything around, or fail to boil at all - there is no middle level,- when simmering or frying, food may either burn quickly or fail to reach cooking temperature - there is no middle level.For boiling water, this is not a big problem, but for more delicate cooking requiring constant temperature, these cookers can be inconvenient or even impossible to use.For this reason, such cookers are unsuitable for preparing soups, vegetables, meat, or any other dishes that require low but steady heat.

author: Simmed
author_rank: Frequent Contributor
timestamp: August 16, 2025, 07:18:49 pm
content: Quote from: radiolistener on August 16, 2025, 06:02:13 pmin some ways what you said is truefor small thermal mass or the heating is very highwhen sudden burst pumps heat into a mass, it needs time for temperature risemy cheapie cooker appears to do it in 800w bursts at low modethe time duration is roughly 1s on, 4s offi have many pots in many sizesa few of them have inductive basesthicker base = high thermal massthe pot i estimate the weight around 0.8kgif assuming most of the mass is in the base plate (spec heat 500J/kg/K)the 2s burst will add about maybe +3C (not counting losses)so the heavy pot to me is like slower and predictable ?but my other light weight pot is not soi think it maybe shoots +20 every burst, the metal is so thinand because of that, i like to use it to do quick boil or fry

author: Sourav
author_rank: Newbie
timestamp: August 16, 2025, 07:55:03 pm
content: Quote from: tooki on August 16, 2025, 09:51:27 amYes, millions of people do use induction cookers. Just a few hours back, I passed by the local repair market and saw a huge stack of damaged units, probably 40 to 50 piled up for repair. I sometimes repair these for neighbours (and myself) for free, and most of the time the failure is the IGBT possibly due to overheat. Sometimes the controller dies, and in those cases the repairmen here usually replace the entire board with a cheap Chinese ready made one (about Rs. 480, roughly USD 5.50). Of course, another possible reason for this kind of damage is that the unit is operating in what might be considered an IPC-6011 Class 3 environment (hot, humid (sometimes RH >= 90%), and possibly polluted kitchen), even though the boards might never actually qualified for that level of reliability, especially the Chinese ones!An old man told me a few weeks back that his cooker exploded violently after such a sketchy local repair, likely because those Chinese boards use a sketchy slow blow glass fuse (T 10A L). Unlike ceramic fuses, these can shatter into pieces and make quite a bang.In most cases the users are not technical. If their cooker dies right after they remove a pot, they will not know the reason and certainly won't be posting scope shots on EEVblog! That makes me think the danger here could be very real...

author: kite31
author_rank: Regular Contributor
timestamp: August 16, 2025, 10:40:11 pm
content: This thread seems to be drifting into general confirmation that cheap goods may compromise on quality, more than analysing how the control circuits work, or how effectively.I have used induction cooktops since 2011, the current one since 2017 (new house). If it explodes, I promise to let you know.

author: Psi
author_rank: Super Contributor
timestamp: August 17, 2025, 12:26:13 am
content: Quote from: TimFox on August 16, 2025, 04:05:13 pmI don't have any proof, it was just something I thought was common knowledge in the industry based on what I've heard from others. I'm ok being wrong if that is the case. It's not a hill I want to die on.

author: jh15
author_rank: Frequent Contributor
timestamp: August 17, 2025, 12:33:29 am
content: Wish we in USA had 240v countertop receptacles.At one time there was a big stink about the RFI from the then new induction cooktop ranges, and the FCC kept them off the market. Not sure how long... years, days...

author: antenna
author_rank: Frequent Contributor
timestamp: August 17, 2025, 02:36:58 am
content: Quote from: jh15 on August 17, 2025, 12:33:29 amjust move your neutral over to your other hot rail and swap your US outlets for the euro ones so nobody mistakenly uses them with 120v stuff.

author: jh15
author_rank: Frequent Contributor
timestamp: August 17, 2025, 11:33:53 am
content: But the GFCI's will not like that.

author: tooki
author_rank: Super Contributor
timestamp: August 17, 2025, 01:08:20 pm
content: Quote from: radiolistener on August 16, 2025, 06:02:13 pmWhile you are mostly correct about the technical implementation, you are wildly exaggerating the extent of the problem. (And don’t forget that resistive electric stoves work the same way. Actually worse, because they only have a single actual power level.)The cheap induction cookers I have use two “native” output power levels (1000W and 2000W), so they absolutely do have a true medium heat. They pulse the two power levels to get any of the other possible power settings (the 200, 400, 600, and 800W settings pulse between 0W and 1000W, while the 1200, 1400, 1600, and 1800W settings pulse between the 1000W and 2000W levels).Indeed, for very small pots of thick liquids, this can boil over sometimes. In particular, if you use high heat to bring it to a boil and then drop down to, say, 200W to simmer, then it can initially boil over. (In my cheap induction cookers, because their PWM cycles begin with the “ON” half, and changing the power setting always starts the cycle over, lowering the setting means you always cause it to immediately add heat, even though you may not want that. So sometimes I just pull the pan off the burner for a second.)However, as long as you use pans with reasonably thick bottoms (= large thermal mass) this really isn’t an issue. And once you get beyond very small pans (I’d say ~ 1.5 liter and up) it simply isn’t a problem, because the mass of the pan and of the food within it are enough to smooth out the pulses of heat.I’ll also point out that the consequences of something boiling over on induction are way less than on resistive electric: since the burner itself generates no heat, food doesn’t burn onto the glass. At lower heat levels (for example, the 200W setting I use for cooking rice), you can even just put a paper towel or a piece of baking parchment between the burner and the pan, making cleanup super easy.

author: tooki
author_rank: Super Contributor
timestamp: August 17, 2025, 01:12:17 pm
content: Quote from: jh15 on August 17, 2025, 12:33:29 amWhat for? In kitchens with an electric range, you have the 240V receptacle for that, and nothing else in a kitchen would really benefit very much.

author: BadeBhaiya
author_rank: Regular Contributor
timestamp: August 17, 2025, 01:15:26 pm
content: I always thought these induction stoves relied on changing their switching frequency to be always at resonance so that no matter what kind of pot you put on them they can change the frequency until resonance is observed. Intuitively I don't think these can work at a constant frequency because when we put a pot on a stove, its coupled to the coil, hence changing its inductance, and hence the resonant frequency. Because of the distance between the coil and the pot, I don't believe its a large inductance difference (and hence not a large resonant frequency difference either) but it must be present.The best thing about these resonant circuits is that the current being switched is actually not very large at all, a few amps at most but the resonance causes a MASSIVE current to jump around between the coil and the capacitor. I'm not from a power electronics background so this was incredible to me.

author: BadeBhaiya
author_rank: Regular Contributor
timestamp: August 17, 2025, 01:20:34 pm
content: Quote from: radiolistener on August 16, 2025, 06:02:13 pmI once had a cute little moka pot for making coffee. It made me many a cup of delicious coffee. One day in a hurry I put it on my induction stove instead of gas stove to heat it. Within a minute, it blew up, launching itself in the air with such force that it hit the ceiling, spilling coffee everywhere in the kitchen. Fortunately I was not burnt too badly. The pot hit he ceiling with such force, it deformed itself and had to be thrown out later. Thankfully I was not directly on top of the moka pot while it was brewing (I often like to look at the coffee dripping down the "chimney" thing)It still escapes me how the landlord didn't notice the obvious, massive coffee stain on the ceiling. Not that I'm complaining, I though my deposit was gone for sure.

author: grumpydoc
author_rank: Super Contributor
timestamp: August 17, 2025, 01:29:58 pm
content: Quote from: tooki on August 17, 2025, 01:08:20 pmOut of interest - I've had two Indesit units and noticed that when set to lower power levels there is considerable length of time between "on" pulses, some seconds at the lower settings which means a constant simmer is difficult to achieve. Is this normal, why have such a low "PWM" frequency?

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 17, 2025, 01:35:08 pm
content: Quote from: BadeBhaiya on August 17, 2025, 01:15:26 pmYeah, the method by which the inverter is controlled is critical to answering questions like this. In particular, the following aspects need to be answered:1. Inverter frequency. Does is always track the resonant frequency of the load? Is it constant?2. Is the inverter voltage fed or current fed?3. Is the tank circuit series or parallel?4. Does the controller have some inner feedback loop for regulating/limiting current (either in the coil itself, or somewhere else)?For example, if the answers are:1. Variable, always tracks the resonant frequency.2. Voltage fed3. Series4. NoThen the circuit will draw far more power without a pot than with a pot (and that power will just heat the coil, perhaps until it glows yellow and then you have a more conventional electric stove!). Obviously not a good design!

author: tooki
author_rank: Super Contributor
timestamp: August 17, 2025, 03:46:45 pm
content: Quote from: grumpydoc on August 17, 2025, 01:29:58 pmIt’s normal, in that my cheapie units work the same way. I’m not sure why it can’t be faster, but presumably has something to do with cost-cutting.

author: DaJMasta
author_rank: Super Contributor
timestamp: August 17, 2025, 04:29:45 pm
content: Quote from: PCB.Wiz on August 16, 2025, 04:25:53 amI think this is really the critical point to be made, to get that big back EMF in the circuit the removal would have to happen on the order of a single oscillator cycle, and since even if you are batting the pan away with your hand, it's probably going to take 10+ms for the pan to get out of the effective coupling range of the burner, you've got hundreds of cycles of gradual collapse which render the spike near nonexistent and make sure most monitoring systems can detect that the pan is leaving.It would take something like blowing up the pan with high explosive yo start approaching time scales that could be a problem, in which case the back EMF is probably not a primary safety concern.

author: grumpydoc
author_rank: Super Contributor
timestamp: August 17, 2025, 04:31:31 pm
content: Quote from: tooki on August 17, 2025, 03:46:45 pmHmm, neither of the hobs was cheap - I presume then there is a reason other than cost cutting?

author: tooki
author_rank: Super Contributor
timestamp: August 17, 2025, 05:22:06 pm
content: Quote from: grumpydoc on August 17, 2025, 04:31:31 pmI dunno. I know that youcanmake induction that uses “linear” variable control. (My mom’s V-Zug for example.)

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2025, 05:47:02 pm
content: Quote from: DaJMasta on August 17, 2025, 04:29:45 pmyou can shoot the pan off your kitchen with a hypersonic railgun

author: TimFox
author_rank: Super Contributor
timestamp: August 17, 2025, 05:48:09 pm
content: Quote from: coppercone2 on August 17, 2025, 05:47:02 pmOr use the AR-15 you keep in the kitchen to protect your home from raccoons.

author: coppercone2
author_rank: Super Contributor
timestamp: August 17, 2025, 05:50:01 pm
content: actually there is a possibility there is some kind of digital averaging going on ? It may be multiple cycles.

author: hans
author_rank: Super Contributor
timestamp: August 17, 2025, 06:54:51 pm
content: Quote from: DaJMasta on August 17, 2025, 04:29:45 pmYep.Most inductive cooktops have quite a limited coupling range. Lifting a pot above the plate for just more than a few cms is often enough to turn it off (on both models I have used, 2-3cm is enough). Doing that <1ms means 2cm / 1ms = 20m/s, and 2cm/1ms^2 is already 2000G. Yet thats still a few dozen cycles to detect the motion.Even giving it 20ms is still around 5G. I doubt a human can generate more than 2-3Gs at any kind of mass.So I agree with the anecdotal proof set forth by @tooki (which I conform for 2 models, making it a sample size N=3). Even cheap induction stoves would need to have a reliable open-load detection to not spontaneously burst into flames, and it has to react within hundreds of cycles. Sounds like quite a reasonable specification to hit, even when some averaging gets involved.In other words, electronics is very fast, our senses are much slower, and any kind of human body movement is even slower than that.

author: Psi
author_rank: Super Contributor
timestamp: August 17, 2025, 10:04:45 pm
content: I don't think every manufacturer of cheap induction hobs actually did the calculations to figure out what the max speed a pot can be removed and then made sure to design it to handle a bit faster than that.

author: tooki
author_rank: Super Contributor
timestamp: August 18, 2025, 12:13:37 am
content: Quote from: Psi on August 17, 2025, 10:04:45 pmWhat evidence do you have for this, beyond your gut feeling? It seems to me like such a basic function that I can’t imagine theydon’tcalculate that.

author: Psi
author_rank: Super Contributor
timestamp: August 18, 2025, 01:21:44 am
content: Quote from: tooki on August 18, 2025, 12:13:37 amI said "think", it's my opinion.It's based on seeing how cheap electronics are usually created.For cheaper products it's a lot more about real-world testing of a prototype someone made (or copied) to see if it will last 'long enough'. It's less about doing the maths needed to confirm all parts are operating within their rated specs and all edge cases have been addressed. Cheaper stuff is sometimes just copied from existing products on the market with parts replaced as needed to reduce cost or due to availability. The time taken to do-the-math is often less than it should be.That's not to say all cheaper products are prone to failures, just that a higher percentage of them are, and induction hobs seem to me to have a suspiciously high failure rate. I come across dead ones a bit too often.

author: Tation
author_rank: Regular Contributor
timestamp: August 18, 2025, 06:31:17 am
content: Quote from: mtwieg on August 17, 2025, 01:35:08 pmThe more I think about this, the more interesting it seems.Some quick search reported that the relative permeability of stainless steel can be between 40 and more than 1000. So adding a pot may change the resonance frequency by a lot. Also, in the pot, seems reasonable to assume that eddy current losses dominate losses by hysteresis. In this regime, the reactance of the coil no longer varies linearly with frequency, but with the square root of frequency, and its phase is no longer 90º, but 45º, or slightly below it (if hysteresis losses are high), also modifying the resonance frequency of the tank.Thus... a more interesting problem than expected!

author: hans
author_rank: Super Contributor
timestamp: August 18, 2025, 08:20:45 am
content: Quote from: Psi on August 18, 2025, 01:21:44 amObviously. Maths only work if you can paint a certain scenario. In my example, I calculated for someone lifting it off.What if its knocked over by something else? Like a grocery bag being lifted and swayed over.Or what if someone had a spatula below the pot, and then used that for a seesaw motion. I also didn't calculate deacceleration/impulse forces for when a human punches/hits something like this.etc.Thats why I made my general statement about electronics behind so much quicker than humans. A 20kHz+ drive with say a 100Hz loop frequency will still be a few orders of magnitude faster than most human movements.

author: Assafl
author_rank: Frequent Contributor
timestamp: August 18, 2025, 01:48:31 pm
content: There is an assumption here that a microprocessor is responsible for managing the instantaneous control of the forward energy to the pot (vs the reflected energy that will burn the poor IGBT).Few comments on this assumption:Metcal MX500 is an induction soldering iron running at 13Mhz or so. Has no microprocessor. Detects reflected power using (I think) a transformer (T3) and detectors (diodes) that cuts the power from an LM2576HV version regulator when the reflected power increases. More here:https://colinoflynn.com/wp-content/uploads/2012/05/MX-500P-11.pdfThis happens immediately. For the Metcal the "pot" (the solder tip) "disappears" when Curie temp is reached. At that moment it ceases being ferromagnetic. It stays non-magnetic until the tip cools down a bit. So at that very moment the reflected waves sum up with the forward power and the transformer/detectors cuts the power to the oscillator FETS.So detecting VSWR using a transformer, a few diodes and a small capacitor prevents the soldering iron from destroying its own FETs.Now for cooktops. There are Curie metal pots and pans. They "disappear" almost instantly (albeit due to size and weight they probably "disappear" slower than the soldering tip which is tiny). They work really well. These will "appear" and "disappear" hundreds and thousands of times each cooking session. So the cooktop reacts equally fast. My bet is on increased voltage/reduced current in the coil directly into the power control feedback loop. Immediate.

author: Psi
author_rank: Super Contributor
timestamp: August 18, 2025, 10:32:26 pm
content: lol Curie temp pots. That's a new one. Would be nice if they gave the temp they limit at.If the temp seems usable I will have to try one. It does seem like a great way to prevent overheating when the water all evaporates.

author: johansen
author_rank: Super Contributor
timestamp: August 19, 2025, 01:46:30 am
content: As usual 90% of the replies are useless and do not answer the question even partially.Even cheap induction cook tops are going to have two methods to shut off the circuit:A voltage measurement on the tank voltageA current measurement on the IGBT current.Either of which can have hard and soft limits designed to shut off the circuit in less than 1 microsecond, which is on the order of 10 to 60 times the switching frequency.The reason the pan has to be so close to the coils is because the system is only able to transfer the heat with the help of the ferrite backing bars and the eddy currents induced with the help of a pan with a magnetic permeability of at least on the order of 100, which means the skin effect makes the current flow through a very thin layer of the steel or iron pan.You remove the pan, the frequency goes up (because its a cheap ZVS circuit, so does current, it shuts off.Its likely even if you instantaniously remove the pan you would have at least 2 entire switching cycles before you over volt the capacitor.in a regular induction heater with a non magnetic load where there is 10 times more energy stored in the tank capacitor than there is power flowing into the load, you have a lot longer time, on the order of ten switching cycles before the voltage and current increases 41%.

author: Assafl
author_rank: Frequent Contributor
timestamp: August 19, 2025, 09:19:58 am
content: Quote from: Psi on August 18, 2025, 10:32:26 pmI have one of these pots (from 2010 or so) - their Curie temp is 250C (according to Demeyere). And it seems a reasonable figure to me.It isn't as useful as one would think - but is good for one main purpose: searing steaks. You set it on the 1800W hob (or higher) and can sear steaks at full power.

author: Psi
author_rank: Super Contributor
timestamp: August 19, 2025, 10:07:16 am
content: Quote from: Assafl on August 19, 2025, 09:19:58 amI would be cool if they had a range of temps you could order. I'd totally be down for that. At least i would order it, i dunno if it would end up as useful as i'm imagining.

author: johansen
author_rank: Super Contributor
timestamp: August 19, 2025, 10:28:18 pm
content: Quote from: Psi on August 19, 2025, 10:07:16 amsome induction hot plates have a temperature sensor

author: Assafl
author_rank: Frequent Contributor
timestamp: August 20, 2025, 05:42:37 am
content: Quote from: johansen on August 19, 2025, 10:28:18 pmIn my experience not very accurate and has a very long lag (probably due to the ceran glass between the pot and the sensor). But YMMV.Not that ultra expensive Curie cookware is more useful. If temp is important (and it doesn't happen to be 250C) the only useful implement is a cooking thermometer (like a thermapen). And as many power settings as possible (or at least a logarithmic scale).

author: mtwieg
author_rank: Frequent Contributor
timestamp: August 20, 2025, 01:10:31 pm
content: Quote from: Tation on August 18, 2025, 06:31:17 amYes, the specific working principles behind these appliances is somewhat ill-defined. For example, it's generally known that ferromagnetic cookware is required to work with induction stoves. But it's unclear whether they generate most of their heat from eddy currents vs hysteresis (search google finds lots of contradictory explanations). Both seem plausible, as ferrous materials should yield a skin depth much less than the thickness of the cookware.Quote from: Assafl on August 18, 2025, 01:48:31 pmI'm no chef, but I would assume that having cookware which only heats to one temperature would be pretty annoying. But I guess a lot of EEs feel the same about Metcal too

author: Psi
author_rank: Super Contributor
timestamp: August 20, 2025, 01:39:02 pm
content: Quote from: mtwieg on August 20, 2025, 01:10:31 pmAs a general use pan sure, but as a special pan used to make a particular dish which is somewhat temp sensitive it might be quite useful.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 20, 2025, 06:02:51 pm
content: Dont forget the beer factor in sudden pot removals.Too much and you'll slosh boiling hot noodles on your belly.

author: tooki
author_rank: Super Contributor
timestamp: August 20, 2025, 09:21:35 pm
content: Quote from: johansen on August 19, 2025, 10:28:18 pmIncredibly, the super-cheap $50 ones basically all have it. (I use that regularly for deep-frying.) Yet most "real" induction stoves don't.

author: tooki
author_rank: Super Contributor
timestamp: August 20, 2025, 09:22:31 pm
content: Quote from: Assafl on August 20, 2025, 05:42:37 amYou can now get ones (even fairly inexpensive hotplates) with an external immersion probe to give true temperature control, at least for liquids and the like.

author: Psi
author_rank: Super Contributor
timestamp: August 20, 2025, 11:43:12 pm
content: Quote from: tooki on August 20, 2025, 09:22:31 pmBe cool if it had a feature to alarm/beep when the temp delta indicates that all the water has just boiled off.There's a few things I cook where I need to catch it the moment the water is gone and the temp starts to rise, as that is when it's ready to eat. Any longer and it starts to burn to the bottom of the pan.But I guess just setting a 105C limit would probably work ok. It would stop it burning atleast.

author: tooki
author_rank: Super Contributor
timestamp: August 22, 2025, 11:22:25 am
content: Quote from: Psi on August 20, 2025, 11:43:12 pmFYI, that’s exactly how rice cookers work. When the thermostat detects temperature trying to rise above ~100C, they switch from “cook” mode to the low-power “keep warm” mode.

author: PlainName
author_rank: Super Contributor
timestamp: August 22, 2025, 02:59:45 pm
content: And egg cookers, I am sure.Cheap ones, anyway. My slightly more expensive (but not much!) one does have an actual timer.