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Induction Hobs

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ScottyUK

ScottyUK

Electrical
May 21, 2003
12,915
My wife recently bought a second-user induction hob. It has been working fine then this morning there was the brief hissing of an arc - probably HF - followed by a dull thump in the kitchen counter top tripping the MCB on that circuit and causing the RCD to clear the board. It got me thinking: what frequency do induction hobs typically use? I would have guessed it is a high 'audio' frequency - 5kHz up to maybe 50kHz. I'm startled by the price of spares too: like any tight-fisted engineer I am naturally intending to repair this if there aren't vapourised pieces of the power stage spread liberally over the inside of the unit, but I'm just curious about the frequency. If it is RF then I might be a little out of my area of experience!


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Scotty,
Found this on the web:
"IH cookers generate electromagnetic fields [in the frequency range of 100Hz and 18-23kHz ] when an electric current flows through coils under the top plate. Heat is created when the electromagnetic field reacts with the metallic pan atop the plate. (For the young, whose more sensitive hearing will be able to detect this level, cooking using an induction hob could well be accompanied by a rather unpleasant whine)."

That was after I had to look up "hob." Used mostly outside the US.

Take care,
Scott


In a hundred years, it isn't going to matter anyway.
 
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Good to know I am going deaf! I'll know a little more about what happened when I get the cover off tonight.

Thanks.
 
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Ok I know what happened, more-or-less: looks like a bit of wire or swarf bridged between the rivet attaching a TO-247 diode package to the heatsink assembly and the end of a big 3.3uF 400V metallised film capacitor causing an arcing fault. The cap has a fair bit of burn damage, plus there's a dead diode bridge, a relay which is toast, blown fuse and so on. Control stage looks ok as far as I can tell - nice design with opto-isolated gate drive. I think I was dead lucky that the IGBT inverter stage didn't get wiped out (fault was upstream of it).


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