The ways that the power supplied to the hob and hence to the pan are limited for economy of production, and often involve schemes for turning power on and off rather than trying to regulate it by voltage. Another name for this is controlling the coil power duty cycle. This approach can be seen in many induction units at the low end of the power range. However, it is only noticeable if the time off is long relative to the thermal mass of the pan base.

I have a Revereware pan (thin skin -- no other base material) that has a very short thermal time constant, and below level 4 setting on my Frigidaire Gallery small hob the on/off action is visible in boiling water. (Level 4 is the 6th power level.) It is not noticeable for any of the more modern "induction ready" pans and pots that have thick bases.

Your data show this approach is used for level 9 and below, and is switching on and off over periods of seconds. This would be be quite noticeable on a thin based pan. A more refined approach would use tenths of seconds for the duty cycle periods and the effect would be difficult to spot. The user countermeasure is to use a thick based pan.

With respect to pan removal with the hob on, sensing of a pan is an important safety feature, however it need not make noise, and need not error out. My Gallery just flashes the power setting value, and it can flash for a while. I don't know the delay before the hob auto turns off; it is over a minute. If the pan is returned, the hob continues heating at its previous level.

Frigidaire is owned by Electrolux, which has been making induction cooktops in Europe since before they sold any in the USA (more than a decade ago). They probably have a pretty good sense by now of what the user interfaces should be to achieve customer satisfaction.

I don't know if they are available in the UK, but Cooktek has portable units for restaurant cooks to use in exposed dining room settings. My non-portable Cooktek induction wok hob has 22 levels and I don't recall any observable duty cycle operation. (This suggestion is based on the money-is-no-object point of view.)

I've owned this this Waring Pro ICT200 Induction Cooktop

1. While it does beep, it allows you to remove a pan from the cooktop for 30 seconds before shutting off.
2. I boiled some water and observed that it does not pulse while the water is boiling.
3. I tested the water temperature on the appliance's lowest setting. The temperature was 94C and held pretty steady, within one degree.

Thanks. Out of interest, what cookware did you use? Most importantly, is what material? 3 ply stainless steel is what i mainly own. Although my above video was using a thin steel wok which upon research, and what the commenter above you also suggested, maybe the problem i am having.

Unfortunately your hob isn't sold here in UK :(

Thanks.. a very insightful post with lots of good information. I used Le Creuset 3 ply stainless steel pans mainly. But in my above video, it was a thin steel wok which could be the problem then.

I will do further testing with some 3 ply steel pans and see if it's noticeable. I'll reheat yesterdays curry in a minute actually :)

@kaseki Okay so following from my last message to you. I have just reheated my curry, this time, using a 3 ply Le Creuset pan. Incidentally, I think they are the thickest of all the 3 ply brands at 3mm. The specialist induction cookware brands, seem to be 2.5mm. So Le Creuset should be perfect for the job.

Linked are two videos... one: https://streamable.com/krlsgh

Set to their default power 1000 (120c / 248f) this is the LOWEST it can go before it starts to need to cycle the heat on and off. And as I am sure you will agree, is far too hot for a lot of tasks. You'll see it boiling and spitting ferociously.

The second video: https://streamable.com/j9st1d

Is turned down to what I deem the best simmering power, which is 500 (80c / 176f) and as you will see, it cycles on and off. While on, it starts to boil crazily like the first video (which makes sense as power 1000 is the lowest it can go) and then turns off and slowly declines to almost still before coming back on.

My hope was that these "thick" pans would hold the heat so well, that the boil would remain consistent for a while even while off like you said it should be... but alas, it is more or less the same as my wok.

So, with all this evidence, do you think I could do better with a different hob brand? Maybe Tefal? or is this pretty much-expected behaviour across all hobs...

Thanks :)

I used the Calphalon Classic Stainless Steel 1 1/2-quart Sauce Pan for my test.

Some power cycle like that. Some don't. Mine has 100 power levels, and the duty cycle is computed over about 0.5 seconds. That is, 10% power would be 0.050 seconds on, 0.450sec off. It goes 'tic-tic-tic-tic'.

Joe: I can't suggest portable hobs among those available in the UK, or for that matter among the portable units sold in the USA. The "theinductionsite.com" might have more information.

It appears that even your thick pans cannot smooth out the 10-second period of your power waveform. Perhaps heavy cast iron might work, given the thermal time constant of its mass will be aided by its lower thermal conductivity (relative to other base materials).

Owners seem to like this JEROOP Induction Hob (Amazon UK) because it allows you to regulate it by temperature or wattage, the latter of which apparently allows you to maintain a simmer better. Search "simmer" in the product Q&A.

This VonShef Induction Hob also lets you regulate it by wattage. It's sold under the name "Cuisimax" in the US and people seem to like it.

Joe -- the pulsing you are seeing is pretty much endemic to lower-priced portable induction cookers (PICs).

The other name for what Kaseki called "duty cycle" is "pulse width modulation" (PWM). Microwave ovens use the same technique, switching power on and off at higher or lower frequency to simulate higher and lower power settings. The idea is that the heat averages out , although the average between the state of boiling and still water may not be the same as water at a more steady heat level. Having more power settings and/or settings targeted to temperature doesn't necessarily address the PWM frequency unless there is some kind of in-pan temperature probe. Induction units with in-pan probes are becoming available but still seem to be very expensive.

PICs can be built with high-frequency switching where the on-off switching happens so many times per second --- as Weed describes --- that the pulsing is rarely perceptible even with thin pans. Trouble is, the high frequency switching components are comparatively expensive. Using heavier pans (like the LeCrueset you mentioned) will help somewhat on better quality PICs and hobs but, as you are seeing, does not solve the pulsing problem when using the less expensive PICs like the one you apparently have.

If you were in the US, I would point you to the Century Life blogs site (link to their article on PICs). I don't know anything about the T-Fal you asked about but suspect that it is made either by Fagor or one of the Chinese factories to which many PIC brands sub-contract their production. Most, if not all of those, have the crude PWM electronics. The Century Life site recommends the Vollrath Mirage PICs for units that do not exhibit the boil-still-boil-still pattern. These are commercial units and, over here, the Vollrath units have been priced at about half-way between the lower-end PICS and what is usually charged here for the commercial-grade Cookteks that Kaseki and Weed have. Don't know if that will hold true in the UK but I believe that the Mirage units are available in the UK., at least from food service companies. You might try following up on that and seeing if searching on "Vollrath Mirage Induction" turns up some similar units from other brands which might be more favorably priced.

I've been researching portable induction cookers online, and what I discovered is the lowest continuous power level varies by brand. Yours is 1000 W which is at the higher end.

The Ikea Tilreda is 900 W. I have seen an expensive one at 500 W.

This info is fairly difficult to find in the manufacturers model data, as they often state power levels from 200 W to 2000 W, but not where the duty cycle starts.

If the Ikea Tilreda tries to maintain a 400 W (equivalent) from 900 W, then the duty cycle would be 44% on, 56% off.

But comparing your cooker at 400 W from 1000 W, the duty cycle is 40% on, 60% off.

The Ikea Tilreda doesn't seem much better, but compared to a model that has a lowest continuous power level of say 1100-1200 W, it would be.

Imagine a 500 W lowest continuous power level cooker trying to maintain 400 W. That's 80% on, 20% off. Much smoother power.

The next level up from consumer models is the hospitality models. They are much more expensive, and you have to be careful not to buy a 15 Amp model (in Aust. appliances up to 2400 W are 10 A). But I imagine those models have precise power control.

The built in cooktops for homes have better quality coils and electronics so they have finer power control.

I've never seen a detailed chart of the actual Watts and duty cycles before (your chart above).

This resurrected thread motivated me to test my Cooktek induction wok hob (with its provided stainless steel wok). This unit is rated at 3500W. I put about a pint of water in the wok and fired 'er up.

In the upper half of the power range there is no visible evidence of pulsing, either in boiling behavior or acoustic noise (barely perceptible hum from the unit). However, in the lower half of the range one can just hear pulsing (in an otherwise quiet room). Boiling doesn't show the effect, and in any case boiling stops in the lower part of the power range. The acoustic pulse rate is roughly 3 Hz (3 PPS). This value is approximate due to being at the margin of being too fast to be countable when trying to compare the mental count to a second kitchen timer.

So while the OP's device has a 10s period, the Cooktek is operating with 30 duty cycles over that same 10 seconds, such that the period is short enough that even a thin wok seems to average it out. To be sure of this below the setting where boiling stopped in my experiment, I would have to use a lower boiling point liquid -- closer to room temperature. Unfortunately, most that I can think of are flammable, the use of which might lead to a new recipe for bombe in Le Guide Culinaire.