Raeburn to replace boiler/hob/oven

[Huge]

Wrongly, I'm afraid. My limited experience is that they're very good. They bear no resemblance to electric rings.

You may have to, yes.

They usually have a display that tells you they are hot.

[Tim Streater]

They work completely differently to the traditional heated electric ring.

They need iron or steel bases. The heating occurs in the *base* of the pan, not in the hob.

I've not had one (yet) but should they be hot (except for heat transferred downwards from the pan)? I thought that even when on they were supposed to be cool to the touch.

[polygonum]

Not very - at least compared with any other sort of hob. If you boil over a pan, the water might bubble a bit on the hob surface but as soon as you move the pan off the "burner", you can readily wipe up the spillage with a cloth and a little bit of care.

When there is no spillage you can wipe your hand across the surface without any problem - but don't leave your hand in one place for a long time.

[Huge]

Yes, I know, thanks.

Yes, I know, thanks.

No. They get hot through conduction from the hot pan base. The ones I've seen have an "H" that stays on until the surface is cool.

They are, unless they've had a hot pan sat on them for half an hour.

[Clive George]

Yes, sorry, might have made it clear that wasn't necessarily aimed at you :-)

[Tim Streater]

Yes I know *you* know. It didn't appear that friend Davey knew. Since he said "We ... regard induction as just another version of (rings)" I concluded that he didn't really know what an induction hob is. BICBW.

[Dave Liquorice]

Very much so. The biggest difference is that there is very little thermal mass, an induction ring will pass the "milk test", not other electric ring will there is way too much stored heat.

If your pans have magnetic bases, no.

They have an indicator. But they don't get anything like as hot as the pan supports of gas ring or any other electic ring. Something spilt onto the surface whilst cooking will dry out but not burn.

Might be worth getting one of the sub £30 portable single induction hot plates to play with. I did a while back and now use it in preference to the solid plate electic hob. It does what you tell it to, when your tell it.

[Davey]

OK.

[Davey]

As far as I know, we have a mixture of Stainless Steel, Aluminium and Copper for pan bases. None of which metals are known for being magnetic.

[Davey]

Correct. In fact, we have had very little exposure to them, having spent years living in American rented homes, none of which had induction hobs. And the last house, we bought, but it had a fully working electric range, so we didn't bother to look for anything new. You are never too old to learn.

[The Natural Philosopher]

induction heating doesn't need magnetic materials, though steel is.

And aluminium a teensy weensy bit IIRC

They work by being the secondary of a transformer buried under the hob, and it's the I squared R which heats them

all that is required is conductivity, so glass frying pans may not work

But you can slip a metal disk under those anyway.

[polygonum]

All the manufacturers of hobs and hobware say must be magnetic material. They suggest using a magnet to check. Pans made out of non-magnetic material have a layer of magnetic material buried within their structure.

Might be theoretically possible for them to work with non-magnetic materials but in reality I don't believe they do.

[The Natural Philosopher]

Mmm. I take it back. Seems they work on hysteresis heating.

Not induction.

[Huge]

This. I bought one, also, to see what they're like and use it in preference to gas in order to bring things to the boil, where it's *much* quicker. Being mega-cheap, it's not much good at simmering, so back to gas for that. The one in our rented house simmered perfectly well.

[Dave Liquorice]

Yep.

Our cheapo single induction hot plate refuses to work if it doesn't detect a magnetic pan. Beeps and displays "ERR", same if it's on and you take the pan away. After a couple/few tens of seconds of ERR it'll shutdown the hot plate.

Care to expand? Enquireing minds...

[Dave Liquorice]

Ours is not perfect at simmering but it's a damn sight better than the solid hot plate electic cooker, that *cannot* simmer. Even on "1" if you leave anything without stiring for more than 5 mins it will burn.

The cheapo induction on "1" is a bit more than a gentle simmer and things will stick after 5 mins but stick only they won't have burn't, the bottom of the pan just doesn't get hot enough. It also has a "temperature" mode, set that to 80 C and it's a "keep warm", I might try 100 C for a gentler simmer below "1" but I might have already tried that.

All sounds complicated but as the settings and controls behave in a consistent manner, ie set it to X it will do Y, irrespective of pan size or duration it has been on or since last change it is easy to pick up the settings you like.

Other electric hot plates are very inconsistent in use due to the high thermal mass. Pans can be fairly rapidly boiling 5 mins after you turned the ring off! And the crude ON OFF control means that if you look at a pan set for "simmer" (ha!) just before it's about to switch ON it looks too low or if you look just as it switches OFF too high. You simply can't just look at a a pan and say too high/low you need to look twice 30s to a minute apart.

[The Natural Philosopher]

Google it. eddy currents apparently

Oh. hang on eddy currents are pure conductor resistive stuff. Not magnetic hysterieis

That means the wiki ain't right ...the requirement for steel must be to do with flux concentration.

I'd be interested to know if you stick - say -a sheet of al foil on an induction hob, whether or not it gets hot.

Hmm.

So far research reveals that the mechanism is 'eddy currents' which don't need ferromagnetic stuff to work. And yet the same article in wiki insists that they do.

Vis:

"Eddy currents (also called Foucault currents[1]) are circular electric currents induced within conductors by a changing magnetic field in the conductor, due to Faraday's law of induction. Eddy currents flow in closed loops within conductors, in planes perpendicular to the magnetic field. They can be induced within nearby stationary conductors by a time-varying magnetic field created by an AC electromagnet or transformer, for example, or by relative motion between a magnet and a nearby conductor. The magnitude of the current in a given loop is proportional to the strength of the magnetic field, the area of the loop, and the rate of change of flux, and inversely proportional to the resistivity of the material."

See no mention of any need for the material to be magnetic, merely conductive.

Whereas in theh wiki on induction heating...

"In an induction cooker, a coil of copper wire is placed underneath the cooking pot. An alternating electric current flows through the coil, which produces an oscillating magnetic field. This field induces a magnetic flux with a resulting eddy current in the pot equivalent to the electric current in the coil. The eddy current in the metal pot produces resistive heating which heats the food. While the current in the coil is large, it is produced by standard household power supplies."

Ok so far so good. No mention of magnetic material - just conducting. This agrees with my general understanding of what induction heating is. Like the time I burnt my finger near an RF coil that had 25 watts flowing through it.

Then we have

"Cookware must be compatible with induction heating; glass and ceramics are unusable, as are solid copper or solid aluminum cookware for most models of cooker. Cookware must have a flat bottom since the magnetic field drops rapidly with distance from the surface"

Now why are they saying that al and cu wont work?

"For all models of induction cooktop, a cooking vessel must be made of a ferromagnetic metal such as cast iron or stainless steel or at least compounded with a steel inlay. "

I am wondering if this is in fact an urban myth, that has simply become received wisdom, and is actually WRONG?

Certainly the manufacturers say that iron/steel (not stainless steel) is necessary.

But as far as I can see the only effect iron would have is making a rather crap flux transfer efficiency slightly better by concentrating the flux.

I.e for the same reason you have an iron cored transformer - because you can build it smaller than an air cored one. But you dont *need* iron in a transformer.

[Huge]

Yep, it does. Just went and tried it.

So why don't Al pans work?

[Tim Streater]

Perhaps the notion is that they will, but not as well. Perhaps also there is the risk of damage to the coil in the ring? Poor impedance matching?

[The Natural Philosopher]

Well I suspect that actually they do.

I am beginning to think that the iron slab is more about making pots work BETTER.

And that the manufactures statements are there to (a) cover their arses and (b) ensure that only pots that are definitely designed with induction hobs in mind are used and (c) help boost sales of new pots. Preferably made in Germany ..