Induction Cooktop noisy when the lights are on?????

[magictolight.com]

We worked in a high end home in which we remodeled the kitchen this last year. We put in about 20 4" recessed lights with par lamps and low voltage undercabinet lighting, all on dimmers, lutron radio ra. We wired the owners new induction cook top. Now when the lights are on the cook top makes a high pitch buzzing noise, which is worse depending on the type of pan being used. Lights off, no or substantially reduced noise. Of course the manufacturer is giving the owner no explanation so who else would the owner turn to, the electrical contractor of course! Any insight would be much appreciated.

 

[realolman]

Alll I read that you said was lites on noise... lites off no noise.

does operating the dimmer have any effect on the sound? I mean does adjusting the lights from down low to bright have any effect on the sound. It sounds like it pretty much has to be the dimmer... but I guess you figured that out already. If you temporarily replaced the dimmer with a switch, would that affect the sound?
I wonder if removing some of the lamps would have any effect on the sound?

My glass topped range which is not induction makes the pans rock back and forth.... probably twice a second or so... very strange.

 

[realolman]

Mistake ... sorry.

 

[handy10]

Another question: does the cook top make a noise if there are no pans on the stove? Is there a noise if the cooktop is turned off? If the bottoms of the pans are not
perfectly flat, they may make more noise.

 

[magictolight.com]

The cooktop does change noise as the lights are dimmed down. We have several zones of lights in the kitchen and only the par 20 lamps over the stove cause this noise. Noise is from the cooktop when a pan is on it. Different pan different noise. Always amplified by the lights however. It's almost as though the pan is acting as a receiver and amplifier when the cooktop is on. I have not tried a different type lamp as yet but perhaps that is the next step. Par lamp speced by the architect. And of course this is a zone of 8 lamps among about 40 or so of the same exact fixture.

 

[realolman]

I think this problem is over my head, but I was glad to see it active again. I'll be very interested in seeing the outcome.

You're probably not going to modify the cooktop, and I doubt you're going to do some sort of exhaustive engineering analysis of the situation ...about all you can do is mess with the dimmer, the lights , or replace the cooktop.

If the noise is there when the dimmer is full on, I think I'd try to see if the noise was there with just a switch in place of the dimmer ( or the wires wire nutted together )

I think I'd try to remove lamps just to see what it effect, if any, it had. Apparently removing all of them in that circuit has an effect.

I can't remember what I'm about to say and very likely it has nothing to do with anything, but something rattles around my head about the amount of resistance in an inductive circuit.... is it the "Q" of a circuit?.... I don't know...

I just think you're going to have to experiment and see what seems to make a difference .

 

[jjkind]

Here's my nonexpert opinion.

I've never owned an induction cooktop, but a cursory search of the Internet led me to a site where someone suggested that the switching frequency for induction cooktops usually varies between 24-48kHz. This switching range should be outside of the audible range of humans and you should not hear anything from the switching power supply (humans can hear up to 20kHz).

In this case, however, you also have some low voltage lights? Do these low voltage lights have a switched mode power supply to convert the line current from AC to DC? Or do they use a step-down transformer and rectifier? (I'm guessing they use a SMPS as they are probably <100W?)

I'm assuming your induction cooktop requires a 240V circuit?

Here are a couple of theories:

1) A beat frequency in the audible range between the switching supplies, which may switch at slightly different frequencies. You can't hear each one independently, but perhaps when they are both on at the same time you hear a hum at the difference in their switching frequencies (my apologies to all previous physics teachers if I am misinterpreting this concept here!).

2) My other idea (slightly more complicated) is that perhaps your lights - more precisely the SMPS - is causing a voltage harmonic on one of your phases. Hold that idea, and let's look at the cooktop. I imagine that in the cooktop (again, stress that I've never pulled one of these things apart, so I'm guessing as to how they operate) uses some sort of AC-DC-AC conversion process to create the high frequency waveform that ultimately does your cooking. If this is the case, both phases are likely rectified as they come into the unit (using something like this full-wave rectifier - http://www.falstad.com/circuit/e-fullrect.html) and combined to create a relatively ripple-free DC waveform that can be chopped to the necessary high frequency.

Now, if one of your phases has a voltage harmonic, this harmonic could be passed through the rectifier (assuming no or filters not tuned to this frequency) and increase the ripple in your output waveform in the induction cooker, perhaps resulting in an audible hum.

Hmmm...that's the best I've got.

So if you do have a SMPS on your low voltage lights, I think the easiest thing to do would be to switch it out with a step-down transformer setup to see if this helps.

Here's a little reference I just pulled up on harmonics caused by SMPSs that seems useful: http://www.copperinfo.co.uk/power-quality/downloads/pqug/31-causes-and-effects.pdf

 

[jjkind]

@magictolight

My mistake - I just notice your response where you stated that the sound is changing as you change the dimmer settings. Since the dimmers are going to be pulse-width-modulating at one frequency, regardless of the dimmer setting, you've pretty much debunked my first idea.

Are any of these branch circuits run in parallel or perhaps even in the same conduit?

Jeremy

 

[realolman]

If it doesn't make noise without the dimmer, I'd try some other brand of dimmer or no dimmer.

What would you think about running those lights through a transformer?

 

[PetrosA]

Just a thought...

I suspect it has something to do with either the IR or UV output of the bulbs and that taking them off the dimmer won't stop the vibrations altogether. I would try blocking the light from the lamps one at a time with the cooktop on to see if just shielding the light makes a difference, and if so, which lamps are causing the issue (I would guess it's the ones aimed at the cooktop). If that checks out, I would look into getting bulbs with IR filters in them (if possible) or adding IR filters.

 

[magictolight.com]

The lights are a line voltage 120 volt par 20 halogen 50 watt flood lamp. We have several zones of light in and around the kitchen, but only the zone over the cook top seems to cause the noise to amplify. I had never thought that the lamp itself could broadcast an ir frequency and actually become audible at the cooktop. Also, the branch circuits did run through the garage in conduit, 2 or 3 3/4 emts as I recall. It is possible that the range circuit may have been included with a lighting circuit but that I have to verify.