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Author Topic: Do induction cooktops cause RFI?  (Read 10975 times)
WA2LJW
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Posts: 8




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« on: August 05, 2007, 04:18:24 PM »

We're about to update our kitchen. I've been investigating induction cooktops - they claim much higher efficiency than electric resistance or gas burners. What I cannot find so far is anything about whether they cause RFI. Google searches turn up lots of articles about potential issues for folks with cardiac pacemakers, but nothing so far about radio interference. Some manufacturers' sites allowed me to download manuals, all of which have the standard boilerplate about FCC compliance - that makes me a little nervous...

Does anyone have any information on this?

Thanks,

Jason
WA2LJW
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KE3WD
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Posts: 5688




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« Reply #1 on: August 05, 2007, 06:31:59 PM »

Perhaps you cannot find any references to RFI generated by induction cooktops because there simply isn't any?

I would expect the system to not be able to generate any RFI as it is working from 60Hz sine and working much like a common iron core transformer in that respect.  

However, if faced with the same problem, I'd get my hands on the schematic, service manual, whatever for the cooktop in question, examine that and then perhaps even call the mfr or service center with some questions before plunkin' down the money.  


Luck,

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KF7CG
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Posts: 1209




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« Reply #2 on: August 06, 2007, 09:27:20 AM »

You can't assume that the induction heating unit is operating at 60 Hz. Some induction heating devices and maybe some stoves operate in the 400 KHz Industrial, Scientific, and Medical (ISM) allocation. There are higher frequency allocations than this also. Most of the units using these frequencies have spurious emmissions limits. Items for home use should meet the Class B limits.

Note: Class A limits are higher and are for items primarily intended for a work environment. Hope this helps.

KF7CG
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KE3WD
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« Reply #3 on: August 06, 2007, 08:16:29 PM »

When I'm in the research mode of a project and look for information concerning something and don't find any, that is a big clue in and of itself.  
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NA0AA
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Posts: 1042




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« Reply #4 on: August 07, 2007, 10:13:11 AM »

Induction works by using a high intensity EM field to shake the metal molecules the same way a microwave does to H2O.

Look at it this way, you have upwards of 2.5 KW of input power, I cannot imagine it's completely clean, there's at least a hefty switching power supply in there somewhere.
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K7KBN
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Posts: 3541




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« Reply #5 on: August 07, 2007, 11:52:03 AM »

I haven't seen any household induction cooktops that operate at anything other than 60 Hz.  For 2500 watts at 240 volts, that's just over ten amperes.

At the shipyard where I used to work, the machine shop would get propeller shafts from icebreakers when they returned from the ice to this area (Puget Sound).  They'd chuck them up in a lathe and heat them to a nice cherry red.  As the shift electrician, I had to regulate things to maintain temperature - but it was all at 60 Hz.  LOTS of current, though.
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73
Pat K7KBN
CWO4 USNR Ret.
KE3WD
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Posts: 5688




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« Reply #6 on: August 07, 2007, 09:22:05 PM »

K7KBN sounds like someone who thinks and understands.  

Hams.  

Gotta love it.

Let's see, 2500W at 400KHz.  

The thing would have to have a box bigger than a Henry 3K sittin' next to it, considering the efficiency derate and all...

Okay, here comes the ham who will say that the power unit could be made MUCH smaller than that, but I'd bet it would still cost more than an Icom solid state 1KW linear does.  Lots more.  


Lesee, 240VAC switching power supply, capable of about 3000W output or so, then we need an exciter and an amplifier capable of handling the 2500W to the stovetop, well, in that scenario I guess there would indeed be bit of an RFI/EMI problem!  

But knowing how consumer appliances are really designed, I wouldn't be on all that being inside the doggone things at all.  

Here's some stuff from the installation manual of an induction cooktop:

"cooktop electrical characteristics are:

Operating voltage............ 240 V~ 60 Hz

Maximum power output........ 10800 W

Connect to ..... 240 V, 60 Hz, 2 Pole+G,

40 A (min) supply (3 conductors #8 AWG)"

"This unit has been tested and certified
under FCC CFR 47, Part 18, for
electromagnetic interference."

Guess which part of the tiele 47 CFR is not listed on Foxtrot Charlie's webpage?

http://wireless.fcc.gov/rules.html


"The users with heart pacemakers must
consult with the pacemaker manufacturer
prior to using this cooktop which
incorporates induction heating source."

One thing -- every one of these devices I've found any manner of information about on the web uses a digital control panel of some sort.  That might be the source of some EMI/RFI, although on a cooktop appliance I'd bet dimes to donuts that the thing is inside a sheet metal enclosure of some sort, that should at least help if they bypassed stuff properly inside the box.  

Still can't locate a schematic for one of these on line, but I'm betting some power Mosfets being used to control 60hz coils via the digital controller.  

Did find this design sheet about using this company's product to put together a nonisolated supply for displays and such on inductive cooktops and what it says in the .pdf file sheds a bit of light:

"Since the cooktop has conducted EMI filtering for the induction heating converter, this auxiliary supply requires no fuse or filter components."  

http://www.powerint.com/PDFFiles/di133.pdf

*****************

"Sunpentown
SR-1881 single element smoothtop portable induction cooktop in white or black.

110V / 1200W with touch controls

White - $135
Black - $140
"

http://www.inductionsystems.com/induction_cooktops.html

An Induction "hotplate" at a low price.  

Kinda puts the kibosh on anything other than 60Hz.  

Where's that guy who'll come along and say that maybe they do use 60Hz in the little hotplate but...

Right, my man.  You know you want to type it.  

***********************

The 90-95% efficiency is indeed enticing.  

Good luck with your installation and by all means come back and let us know your results!


KE3WD


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WA2LJW
Member

Posts: 8




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« Reply #7 on: August 09, 2007, 07:37:02 PM »

You're right... but I may have been framing the query wrong. I did find Class B FCC notices on websites for some cooktops.

Ever since my experience with my new Trane furnace, I guess I'm (unduly?) suspicious...


Jason
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WA2LJW
Member

Posts: 8




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« Reply #8 on: August 09, 2007, 07:39:29 PM »

Yup, the efficiency stat is compelling. What I do not know is how these gadgets modulate the heat output or if they work at 60Hz. I'm a bit suspicious that they may be the Light Dimmer From Hell.
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