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Author Topic: How does an induction hob cooker work?  (Read 7244 times)

chris

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How does an induction hob cooker work?
« on: 31/01/2010 11:26:30 »
How do induction hobs work, and do you need special saucepans to work on them?

Chris

graham.d

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How does an induction hob cooker work?
« Reply #1 on: 31/01/2010 11:50:02 »
The cooker has an electromagnets under each ring that produces an oscillating magnetic field. This heats up a metal saucepan by inducing eddy currents. They really work best on iron pans though as you get extra energy dissipated because of hysteresis losses from the magnetic field itself. Of course they don't heat up glass saucepans at all. Generally you have to use special pans. They are very efficient and safer than a normal hob though.

syhprum

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How does an induction hob cooker work?
« Reply #2 on: 31/01/2010 13:36:06 »
Do the electromagnets operate at power line frequency or is the frequency raised with semiconductor devices ?.
I see one problem, does not the electromagnetic field cause Aluminium saucepans to levitate ?

graham.d

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How does an induction hob cooker work?
« Reply #3 on: 31/01/2010 14:08:24 »
Hmm, I thought the frequency is higher than mains because another reason that iron pans are preferred is also to do with skin depth for the induction. But checking on the web seems to suggest that some can be as low as 100Hz and others in the region of 100kHz.

Good point about the levitation. That would be amusing. I wonder to they take steps to prevent that.

Geezer

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How does an induction hob cooker work?
« Reply #4 on: 01/02/2010 06:37:01 »
If they really operate on induction (by inducing current flow in the pan) I would have thought they might work with any good conductor, and aluminium and copper might actually be better than iron, but maybe a higher resistance actually helps to heat the pan up.

Either way, a ceramic pot won't be too effective, unless you add iron filings to your porridge.

syhprum

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How does an induction hob cooker work?
« Reply #5 on: 01/02/2010 09:25:27 »
I would think that if they worked at 50 or 100 Hz with an iron pan they would make a hell of a lot of noise and I shudder to think what effect several kW at 100kHz and its harmonics would have on AM broadcasts.

peppercorn

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How does an induction hob cooker work?
« Reply #6 on: 01/02/2010 12:17:26 »
The cooker has an electromagnets under each ring that produces an oscillating magnetic field. This heats up a metal saucepan by inducing eddy currents. They really work best on iron pans though as you get extra energy dissipated because of hysteresis losses from the magnetic field itself. Of course they don't heat up glass saucepans at all. Generally you have to use special pans. They are very efficient and safer than a normal hob though.
I can't see how this would be that efficient - compared to say a resistive element in iron plate.  You'd have to make sure there were no metal structures or object near the hob or they could get quite hot also.

chris

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How does an induction hob cooker work?
« Reply #7 on: 01/02/2010 14:04:53 »
Why should an aluminium pot levitate more than an iron one?

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syhprum

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How does an induction hob cooker work?
« Reply #8 on: 01/02/2010 15:41:36 »
There would be a similar levitating force on both but with the Iron pot it would be counteracted by the stronger attractive force.

chris

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How does an induction hob cooker work?
« Reply #9 on: 01/02/2010 18:09:52 »
Thanks, now I'm in the loop; and possibly the induction loop you could say!

Geezer

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How does an induction hob cooker work?
« Reply #10 on: 01/02/2010 18:24:17 »
The cooker has an electromagnets under each ring that produces an oscillating magnetic field. This heats up a metal saucepan by inducing eddy currents. They really work best on iron pans though as you get extra energy dissipated because of hysteresis losses from the magnetic field itself. Of course they don't heat up glass saucepans at all. Generally you have to use special pans. They are very efficient and safer than a normal hob though.
I can't see how this would be that efficient - compared to say a resistive element in iron plate.  You'd have to make sure there were no metal structures or object near the hob or they could get quite hot also.

Apparently they are quite a bit more efficient than conduction heating elements because most of the energy goes into heating the pot rather than the stove top. Steel and iron pots are better because of of their greater resistance than Al or Cu. The resistance essentially acts as a heating element within the pot itself.

BTW, should this topic not be in General Science or Technology?  ;D
« Last Edit: 01/02/2010 19:33:35 by Geezer »

peppercorn

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How does an induction hob cooker work?
« Reply #11 on: 02/02/2010 11:40:18 »
BTW, should this topic not be in General Science or Technology?  ;D

I had thought that as well :)

With hot plates it makes sense to turn them off a minute or two early, then the heat in the iron is doing the cooking.

syhprum

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How does an induction hob cooker work?
« Reply #12 on: 02/02/2010 20:23:13 »
Here are some technical details of an early cooker, I would expect modern designs to be quite similar but use fewer,larger transistors.

"In each of the electronics modules, the 240V, 60Hz domestic line power was converted to between 20V and 200V of continuously variable DC by a phase-controlled rectifier. That DC power was in turn converted to 27 kHz AC by two arrays of six paralleled Motorola automotive-ignition transistors in a half-bridge configuration driving a series-resonant LC oscillator, of which the inductor component was the induction-heating coil and its load, the cooking pan. That elegant circuit design, largely by Ray MacKenzie, successfully dealt with certain bothersome overload problems".


 

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