The only time my burners aren't on consistently (Bosch) is when I have one of the paired burners on "boost". I think there's something wrong.

deleted

This post was edited by hvtech42 on Sun, Jan 4, 15 at 2:47

I have sometimes noticed that "pulsing" on our Thermador induction cooktop, and wondered about it. I can't say it happens all the time because often I'm not paying attention or perhaps just don't notice.

Mostly I observe it when there is less than a half-inch of water in the pot. No Power Boost engaged, nor other burners being used, either, when it happens. I wondered if it's a quirk of induction cooking.

sjhockeyfan, when you say you "think there is something wrong", are you talking about my cooktop or your cooktop. I think Ill call the guy who sold me the cooktop tomorrow and see what he says. He's worked at the appliance place for 20 years, so maybe he will have some insight on what exactly is going on with induction cooktops that cook in waves or pulses. I know lots of people on this site have inquired about it, but I have yet to see any information that solves the mystery. Thanks.

i meant yours i'll be interested to hear what he says .

I Googled this and found some other forums where people noticed their inductions pulsing, usually on a low temp setting and not much liquid in the pot (like ours). Nobody got an answer as to why this happens.

The pulsing is the induction unit turning on and off when you are not on high or power boost which are constant on, full power settings, thus enabling you to cook at a lower temperature. I think this is more noticable with induction because the high efficiency of induction heating only the magnetic metal of your pot does not have any residual heat of say a hot coil element to prevent much visible cooling between on off cycles. A heavy cast iron pot or fry pan has a lot of thermal mass and probably will not show water bubble or frying sizzle pulses. For fun and research I just tried a 7 or 8 inch cast iron fry pan with 1/2 inch of water at power 3, 5, and 7 and no pulsing visible but I HAVE seen pulsing at these power settings in regular lighter stainless steel induction pots just as you have.

I have never noticed my Electrolux induction range pulsing, even at lower settings. It seems like it can modulate without cycling.

I tried two stainless steel saucepans today, first an 8inch worn vintage single ply on the smallest hob on Electrolux slide-in range, 3/4 inch fresh cold tap water brought just to rapid boil then to medium heat (5) pulsing via the vigorous ring of bubbles very evident. Next a new 9 or 10 inch stainless-copper bottom sandwich Lagostina pan with both 3/4 inch and 1 1/2 inch water on second largest hob, unlike small pan no bubbles visible at 5med, at 5.5 and 6 a few scattered bubble points were visible but no obvious pulsing, at 7 more bubble generation but again no visible pulsing. I still like the idea of thermal mass accounting for this but hope Pillog, Herringmaven, and Kaseki will reply with their experience and and technical knowledge-even though I don't always understand all of Kaseki's technical replies, LOL.

I'm sorry, I don't know enough about this to say much. It doesn't sound like a problem, just an idiosyncrasy of the unit. Until you mentioned the bubbles coming on and off I thought you were talking about a sound. I've occasionally created a low pulsing sound on mine, but rarely. I do know that there are sounds that often happen when a clad pan with not much in it is turned on. The more solid the pan and more solid the content, the fewer the reports of odd sounds. I'm sure Gary is right that what you're observing is the element turning off and on. We do know some operate this way.

Recently, I managed to make my cooktop buzz. I had a what the heck moment. It was just a little butter in a thin carbon steel pan. Then I realized I'd smushed the butter with a stainless fork, and when the fork got low enough to be in the active field, it buzzed.

Induction is as weird as it is wonderful. :)

Having a Kenmore Electrolux Icon clone, I'll go with Gary's description for now.

It is within the design choices of the manufacturer to use a high enough frequency of power modulation (not to be confused with the induction field frequency) to hide the modulation within the thermal time constant of the most minimal pot, or equivalently in observability, make the modulation high enough frequency that the eye cannot spot it. (Cinema works at only 24 frames per second, for example.)

I suspect Electrolux had enough years of experience in Europe before introducing their cooktops to the US to determine what was necessary for acceptability to the widest audience.

Still, I have a truly minimalist pot (RevereWare with 400 series bottom that is likely less than .060 thick). I will try to remember to try it on a very low setting after it comes to a boil and see whether any modulation is detectable.

kas

When this happens on our Thermador, the pulsing bubbles are in a concentric circles shape. Since it is made by Bosch, and @sjhockeyfan's does it, then it would be a mfr. design.

I don't have an induction stove, just a single induction burner.

Mine cycles on and off at low temps. I first noticed this with porridge. When I turned down the temp to cook the oatmeal, bubbles will form and burst then nothing, then a few seconds later the porridge will bubble and burst again.

Your unit cycles on and off at low temperatures, as mine does.

With radiant stoves, you can see the burner cycle on and off, induction, there's nothing to see.

I boiled some eggs this morning and at the end of the designated boiling time (at a setting of 5.5), I turned down the hob into the lower settings. I had to choose a setting that was high enough to cause bubble formation because at the lowest settings the induced heat just conducted away. Settings between 3 and 4 would cause effects that could be easily observed.

It was evident that the power to the hob was modulating at a roughly 1-Hz rate. Hence my experience is not the same as Gary's and it is possible that my E'lux clone has a different circuit than his.

There are no noises associated with this modulation, and it occurs (for the particular pot and water level) at an energy input too low for bubbles to even detach from the pot bottom and potentially make noise at the surface. I don't consider this a defect; but rather a design choice that likely results from some trade-off that wouldn't be apparent to someone who doesn't design induction cooktops for a living. Perhaps switching at a higher frequency would induce additional circuit heating.

In any case, induction ready pots and pans have thicker bases with longer thermal time constants, so this effect may not be apparent with their use. Sometime I'll try a handy Emeril pan and see what happens.

kas

Cavimum, actually I meant that my Bosch does NOT pulsate, but I'm going to test it tonight.

Come to think of it, I'm wondering if the visibility of the pulsing is abnormal...

Well, only if you didn't remember to bring your glasses, pillog

Unsigned

Ok, so an update. I talked to my appliance guy, the guy thats worked in the field for 20 years. According to him, the cooktops will pulsate for a couple of reason. The first reason he said was temperature regulation. He basically said that the inductions cooktops create so much energy that they need to regulate temps by cycling on and off. The second thing he told me is that when you have multiple burners going, some of the burners will rob the other one of power. He described it as the cooktop not really having enough juice to run everything at once.
So I guess if he's right it seems like they have some kinks to work out with induction cooking. Though I believe the appliance salesman, what I would really like, is a Jenn-air rep to sit in my kitchen and explain exactly whats going on with the pulsing or cycling. I still feel its a little bit of a mystery and not completely sure if its by design or a flaw.

The only time one of my burners steals power from another burner is when one is on "boost".

"I still feel its a little bit of a mystery and not completely sure if its by design or a flaw."

IMO it just is what it is. Your appliance guy's explanation makes sense to me.
I still love this cooktop and would buy it all over again.

This post was edited by Cavimum on Wed, Jan 7, 15 at 21:21

I have a Bosch 800 induction cooktop. Overall I am satisfied with it, but it does have some quirks. When I got the new cooktop, I brought all new pots and pans. I mixed up all the better brands. I have Demeyere, All-Clad copper core, Staub, Le Crueset, Alessi, Ruffoni, and Mauviel. I have noticed pulsing only on the Mauviel pot. In fact things scorch in it. This does not happen with any of the other brands. Perhaps it is the stainless steel Mauviel uses or maybe the other ones hold the heat better and pulsing is not noticed. The Alessi is my pentola pasta pot and that one hums loudly on boost. The cooktop hums on boost with any pot but is much louder with that one.

It's going to depend on the manufacturer and the conditions. Power sharing between hobs could be involved as well.

My CookTek doesn't do this except in temperature mode, where it is set to maintain a given temperature.