Very high pitched squeal from induction hob, what could it be?

[niels007]

Hey guys,

We just got an expensive induction hob in our new kitchen. Its perfect!

Except the ear splitting very high (I think around 15khz) pitched sound that is...

I'm only a mechanical engineer.. What causes could there be for this to happen? The type of pan seems only to barely matter, it gets worse the more zones I turn on and the higher I turn up the heat. The noise being so high frequency seems to be quite directional, move my head in just the right (or wrong) spot and the sound gets much more noticeable.

 I found one similar case ( https://stellaculinary.com/forum/general-off-topic/cooking-equipment/trying-to-love-induction )

What could be going on? Wrong wiring? Coil whine? PWM stuff? Any ideas? Cooking is awesome on induction but this drives us nuts and is actually painful.

edit: this is pretty close to what I get, mine seems slightly higher pitched.

[abraxa]

Did you try other cookware? There are aluminium pots and pans around that have only small pieces of ferrous material in the bottom: http://www.beka-cookware.com/assets/products/images/13537204_Fluo_Frypan_20cm_Bottom.jpg
Such pots and pans cause a similar sound on my induction stove. I'd suggest cast iron for a test - it's perfect for induction.

[coppercone2]

I think what happens is the aluminum/stianless makes the coil look like a shorted turn so its either gonna blow up or go to a lower frequency (to avoid phase problems) which may be audible if it can do that

[T3sl4co1l]

Probably intrinsic to the device.

Inside, there are copper coils that deliver the power, surrounded by ferrite ceramic pole pieces.

The coils can vibrate due to magnetic deflection.  The ferrite can vibrate for this reason, as well as a material property (magnetostriction, a magnetic field <--> strain relationship).

There are also capacitors, which can vibrate for the same reason (except it's called electrostriction, and obviously, has to do with electric field instead), but that's not usually the culprit -- the above one is more common.

The operating frequency is typically low, for a variety of reasons (from electrical convenience to cost-effectiveness).  One would hope they put it above 20kHz (where most people can't hear it), but it seems you got doubly unlucky with a noisy and lower-frequency unit.

Incidentally, magnetostriction is a square-law phenomenon, meaning, if the excitation is a 20kHz sine wave, you'd expect it to sing at 40kHz (because sin^2 x ~= sin 2x).  The waveforms they are probably using, are too lopsided for this though, and you'll get some noise at the driven frequency anyway.

Tim

[niels007]

Digging up my old thread for the hordes of people dying to find out how I've been cooking the last couple of months.. 

It seems to come down to having a small pan, with not much in it like a bit of sauce or water for one cup of tea. Then the high pitched ear bleeding sound is most apparent.

So it seems to be pan vibration, which is less damped, or simply less 'moving mass' i.e. higher frequency, when the pan is nearly empty, that is the issue here!

I can live with the solution, make more sauce, tea or coffee, that isn't a bad thing.. :-)

[Zipdox]

Forgive my necropost. I also have an induction cooker with a similar problem. Mine whines periodically at 17kHz. I've attached a spectrogram made with my phone. 17kHz isn't a problem for most adults but my ears are pretty good. It appears to happen at higher power settings.

[Alex Eisenhut]

Depends on the material of the cookware, for me cast iron is quiet. I think its the dissimilar materials in steel cookware that somehow "magnetostrict" at different rates and so turn the cookware into a transducer. I guess. Beats me, really.

[T3sl4co1l]

Can also be plain old Lorentz force.  Which is higher for lower resistance materials.  And anything with less mass, means less stiffness or damping against the vibrations.

Tim