On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> As Boron said, avoid the older pieces with the smoke rings, intended for
> use on gas burners,

OK, I have to ask, why? As long as the cast iron is close enough to the surface to have the magnetic field induce eddy currents it should work, have you had some problem or is this just some FUD over a newfangled thing? According to everyone 20 years ago when I bought a house with a glass cooktop I would scratch or damage it by using cast iron pans. Well, the separate oven died 6 or 7 years ago, but that glass top is still fine and I use cast iron all the time.

So, what problem would using a cast iron pan with a rim on the bottom cause?

Bill Ranck
Blacksburg, VA

On Sat, 8 Nov 2014 10:35:11 -0800 (PST), "
> wrote:

> On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> > As Boron said, avoid the older pieces with the smoke rings, intended for
> > use on gas burners,
>
> OK, I have to ask, why? As long as the cast iron is close enough to the surface to have the magnetic field induce eddy currents it should work, have you had some problem or is this just some FUD over a newfangled thing? According to everyone 20 years ago when I bought a house with a glass cooktop I would scratch or damage it by using cast iron pans. Well, the separate oven died 6 or 7 years ago, but that glass top is still fine and I use cast iron all the time.
>
> So, what problem would using a cast iron pan with a rim on the bottom cause?
>
I think you need complete contact with the entire bottom of the pan
for induction to work as intended.


--
Avoid cutting yourself when slicing vegetables by getting someone else to hold them.

On Saturday, November 8, 2014 8:48:12 AM UTC-10, sf wrote:
> On Sat, 8 Nov 2014 10:35:11 -0800 (PST), "
> > wrote:
>
> > On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> > > As Boron said, avoid the older pieces with the smoke rings, intended for
> > > use on gas burners,
> >
> > OK, I have to ask, why? As long as the cast iron is close enough to the surface to have the magnetic field induce eddy currents it should work, have you had some problem or is this just some FUD over a newfangled thing? According to everyone 20 years ago when I bought a house with a glass cooktop I would scratch or damage it by using cast iron pans. Well, the separate oven died 6 or 7 years ago, but that glass top is still fine and I use cast iron all the time.
> >
> > So, what problem would using a cast iron pan with a rim on the bottom cause?
> >
> I think you need complete contact with the entire bottom of the pan
> for induction to work as intended.
>
>
> --
> Avoid cutting yourself when slicing vegetables by getting someone else to hold them.

Induction is the transference of energy through space so you do have some leeway as far as the contact range goes. I'm guessing I could put a plate between the cooking surface and the pan and it would still work. OTOH, doing that might cause some overheating of the induction coils and shut the burner off.

Anyway, my cast iron works just spiffy on the range because iron just sucks up magnetic fields. I don't like to use it much because a heavy pan with a rough surface just don't seem right on glass.

On 11/8/14, 1:35 PM, wrote:
> On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
>> As Boron said, avoid the older pieces with the smoke rings, intended for
>> use on gas burners,
>
> OK, I have to ask, why? As long as the cast iron is close enough to the
> surface to have the magnetic field induce eddy currents it should work....

From Wikipedia: "Cookware must have a flat bottom since the magnetic
field drops rapidly with distance from the surface."

It's an inverse square relationship.

> According to everyone 20 years ago when I bought a house with a glass cooktop
> I would scratch or damage it by using cast iron pans....

You could, if you shake or slide the pan around often while it's on the
cooktop. Especially if you have a current crappy Wagner with the rough
bottom.

> So, what problem would using a cast iron pan with a rim on the bottom cause?

Reduced heating due to the added distance between the coil and the pan;
potential aggravated scratching from all the weight focused on the
[perhaps rough] rim.

-- Larry

In article >, pltrgyst >
wrote:

> On 11/8/14, 1:35 PM, wrote:
> > On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> >> As Boron said, avoid the older pieces with the smoke rings, intended for
> >> use on gas burners,
> >
> > OK, I have to ask, why? As long as the cast iron is close enough to the
> > surface to have the magnetic field induce eddy currents it should work....

What you want to do is not just have *some* induction, but to maximize
it.

> From Wikipedia: "Cookware must have a flat bottom since the magnetic
> field drops rapidly with distance from the surface."
>
> It's an inverse square relationship.

I'm pretty sure it's an inverse cube relation (theoretically, which
real-world devices rarely are), which makes minimizing the spacing even
more important.

Isaac

On 11/10/2014 12:51 AM, isw wrote:
> In article >, pltrgyst >
> wrote:
>
>> On 11/8/14, 1:35 PM, wrote:
>>> On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
>>>> As Boron said, avoid the older pieces with the smoke rings, intended for
>>>> use on gas burners,
>>>
>>> OK, I have to ask, why? As long as the cast iron is close enough to the
>>> surface to have the magnetic field induce eddy currents it should work....
>
> What you want to do is not just have *some* induction, but to maximize
> it.
>
>> From Wikipedia: "Cookware must have a flat bottom since the magnetic
>> field drops rapidly with distance from the surface."
>>
>> It's an inverse square relationship.
>
> I'm pretty sure it's an inverse cube relation (theoretically, which
> real-world devices rarely are), which makes minimizing the spacing even
> more important.
>
> Isaac
>

I believe you are correct.

On 11/10/14, 1:45 AM, Travis McGee wrote:

>>> It's an inverse square relationship.
>>
>> I'm pretty sure it's an inverse cube relation (theoretically, which
>> real-world devices rarely are), which makes minimizing the spacing even
>> more important.
>
> I believe you are correct.

He is. My bad statement, sorry.

-- Larry

On Sunday, November 9, 2014 7:51:30 PM UTC-10, isw wrote:
> In article >, pltrgyst >
> wrote:
>
> > On 11/8/14, 1:35 PM, wrote:
> > > On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> > >> As Boron said, avoid the older pieces with the smoke rings, intended for
> > >> use on gas burners,
> > >
> > > OK, I have to ask, why? As long as the cast iron is close enough to the
> > > surface to have the magnetic field induce eddy currents it should work....
>
> What you want to do is not just have *some* induction, but to maximize
> it.
>
> > From Wikipedia: "Cookware must have a flat bottom since the magnetic
> > field drops rapidly with distance from the surface."
> >
> > It's an inverse square relationship.
>
> I'm pretty sure it's an inverse cube relation (theoretically, which
> real-world devices rarely are), which makes minimizing the spacing even
> more important.
>
> Isaac

In the real world, the raised rim on the bottom of my cast iron fry pan causes no problems. In fact, I like the idea of the bottom of the pan having an air gap between it and the glass surface. There's less heat transferred back to the glass.

"dsi1" > wrote in message
...
> On Sunday, November 9, 2014 7:51:30 PM UTC-10, isw wrote:
>> In article >, pltrgyst >
>> wrote:
>>
>> > On 11/8/14, 1:35 PM, wrote:
>> > > On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
>> > >> As Boron said, avoid the older pieces with the smoke rings, intended
>> > >> for
>> > >> use on gas burners,
>> > >
>> > > OK, I have to ask, why? As long as the cast iron is close enough to
>> > > the
>> > > surface to have the magnetic field induce eddy currents it should
>> > > work....
>>
>> What you want to do is not just have *some* induction, but to maximize
>> it.
>>
>> > From Wikipedia: "Cookware must have a flat bottom since the magnetic
>> > field drops rapidly with distance from the surface."
>> >
>> > It's an inverse square relationship.
>>
>> I'm pretty sure it's an inverse cube relation (theoretically, which
>> real-world devices rarely are), which makes minimizing the spacing even
>> more important.
>>
>> Isaac
>
> In the real world, the raised rim on the bottom of my cast iron fry pan
> causes no problems. In fact, I like the idea of the bottom of the pan
> having an air gap between it and the glass surface. There's less heat
> transferred back to the glass.

Would this help those who have problems with their pans not making full
contact with the hob:

'Induction hob converter'

http://www.coopersofstortford.co.uk/...FarKtAod4VcA_w

--
http://www.helpforheroes.org.uk/shop/

On 11/10/14, 5:30 AM, Ophelia wrote:
>
> Would this help those who have problems with their pans not making full
> contact with the hob:
>
> 'Induction hob converter'

Well no, because their pans won't make full contact with this disc either.

All these discs do is reduce the available heat by injecting another
contact surface into the equation. They're useful only if you want very
low heat for a delicate task, and your induction burner won't go that
low -- which is very, very rare.

-- Larry

On Monday, November 10, 2014 12:31:01 AM UTC-10, Ophelia wrote:
> "dsi1" <> wrote in message
> ...
> > On Sunday, November 9, 2014 7:51:30 PM UTC-10, isw wrote:
> >> In article >, pltrgyst >
> >> wrote:
> >>
> >> > On 11/8/14, 1:35 PM, wrote:
> >> > > On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> >> > >> As Boron said, avoid the older pieces with the smoke rings, intended
> >> > >> for
> >> > >> use on gas burners,
> >> > >
> >> > > OK, I have to ask, why? As long as the cast iron is close enough to
> >> > > the
> >> > > surface to have the magnetic field induce eddy currents it should
> >> > > work....
> >>
> >> What you want to do is not just have *some* induction, but to maximize
> >> it.
> >>
> >> > From Wikipedia: "Cookware must have a flat bottom since the magnetic
> >> > field drops rapidly with distance from the surface."
> >> >
> >> > It's an inverse square relationship.
> >>
> >> I'm pretty sure it's an inverse cube relation (theoretically, which
> >> real-world devices rarely are), which makes minimizing the spacing even
> >> more important.
> >>
> >> Isaac
> >
> > In the real world, the raised rim on the bottom of my cast iron fry pan
> > causes no problems. In fact, I like the idea of the bottom of the pan
> > having an air gap between it and the glass surface. There's less heat
> > transferred back to the glass.
>
> Would this help those who have problems with their pans not making full
> contact with the hob:
>
> 'Induction hob converter'
>
> http://www.coopersofstortford.co.uk/...FarKtAod4VcA_w
>
> --
> http://www.helpforheroes.org.uk/shop/

I think this full contact thing is overblown but the product might work fine if you want to use non-induction pans and don't mind a big drop in efficiency. If your pans are not flat you probably should be using a different pan. I did have a problem with my flat bottom wok bulging out a little and the pan not sitting flat. It still worked fine but was unstable. Putting a slight concave surface on the bottom made for a very stable wok. Glass surfaces really accentuate pans that have high points on the bottom.

In article >,
"Ophelia" > wrote:

> "dsi1" > wrote in message
> ...
> > On Sunday, November 9, 2014 7:51:30 PM UTC-10, isw wrote:
> >> In article >, pltrgyst >
> >> wrote:
> >>
> >> > On 11/8/14, 1:35 PM, wrote:
> >> > > On Saturday, November 8, 2014 11:07:34 AM UTC-5, pltrgyst wrote:
> >> > >> As Boron said, avoid the older pieces with the smoke rings, intended
> >> > >> for
> >> > >> use on gas burners,
> >> > >
> >> > > OK, I have to ask, why? As long as the cast iron is close enough to
> >> > > the
> >> > > surface to have the magnetic field induce eddy currents it should
> >> > > work....
> >>
> >> What you want to do is not just have *some* induction, but to maximize
> >> it.
> >>
> >> > From Wikipedia: "Cookware must have a flat bottom since the magnetic
> >> > field drops rapidly with distance from the surface."
> >> >
> >> > It's an inverse square relationship.
> >>
> >> I'm pretty sure it's an inverse cube relation (theoretically, which
> >> real-world devices rarely are), which makes minimizing the spacing even
> >> more important.
> >>
> >> Isaac
> >
> > In the real world, the raised rim on the bottom of my cast iron fry pan
> > causes no problems. In fact, I like the idea of the bottom of the pan
> > having an air gap between it and the glass surface. There's less heat
> > transferred back to the glass.
>
> Would this help those who have problems with their pans not making full
> contact with the hob:
>
> 'Induction hob converter'
>
> http://www.coopersofstortford.co.uk/...nduction-hob-c
> onverter-prodst09262i/?gclid=CIyZlI_q78ECFarKtAod4VcA_w

It turns a highly efficient induction unit into an ordinary "pan on a
hot metal plate" cooker. What's the point of that? Why not just use the
regular cooktop?

Isaac

On 11/10/14, 5:01 AM, dsi1 wrote:

>
> In the real world, the raised rim on the bottom of my cast iron fry pan
> causes no problems. In fact, I like the idea of the bottom of the pan
>having an air gap between it and the glass surface. There's less heat
> transferred back to the glass.

You might also note that manufacturers specifically warn against using
such cookware in the manuals for both induction and radiant glass cooktops.

-- Larry

On Monday, November 10, 2014 3:38:32 AM UTC-10, pltrgyst wrote:
> On 11/10/14, 5:01 AM, dsi1 wrote:
>
> >
> > In the real world, the raised rim on the bottom of my cast iron fry pan
> > causes no problems. In fact, I like the idea of the bottom of the pan
> >having an air gap between it and the glass surface. There's less heat
> > transferred back to the glass.
>
> You might also note that manufacturers specifically warn against using
> such cookware in the manuals for both induction and radiant glass cooktops.
>
> -- Larry

They want to cover their ass in case someone does something stupid. As it goes, my cast iron pan works fine on my range. The range is quite sensitive to overloading the induction coils i.e., if there's a problem with the transfer of energy to the pan i.e., if the pan is not made of suitable material, or is too far from the magnetic field, or is too small. My guess is that cast iron works great with induction and probably has the most efficient transfer of energy of any pan material. I won't use it because it's too heavy..

On Monday, November 10, 2014 8:38:32 AM UTC-5, pltrgyst wrote:
>
> You might also note that manufacturers specifically warn against using
> such cookware in the manuals for both induction and radiant glass cooktops.

Well, we're starting to go in circles here. That is one of the reasons I asked about *why*. According the manufacturers' recommendations I should have ruined my glass cooktop by using cast iron on it (and other things they advise against) but it's been over 20 years and it still works fine and hasn't cracked or been badly scratched or anything else. My question was specifically about induction, since I've found through empirical processes that the glass smooth top is not nearly as fragile as some would have me believe.

I did some Googling after posting and the idea of inverse square or cubed law is certainly something to think about. It doesn't apply to "near field" induction. Now, how far is near field at the wavelengths involved, I don't know and I don't feel like doing the math. I was hoping for someone with actual experience instead of the speculation most have been engaging in. I do believe one person said it works for them with their CI frying pan.

I suppose I should just buy one, or borrow one from my wife, and try it with my smooth bottomed vs. the one pan I have with a slight ring and see if there is any practical difference. If I do, I'll post results.

Bill Ranck
Blacksburg, VA

On Monday, November 10, 2014 12:51:30 AM UTC-5, isw wrote:
>
> I'm pretty sure it's an inverse cube relation (theoretically, which
> real-world devices rarely are), which makes minimizing the spacing even
> more important.
>
> Isaac

Inverse square law only refers to point sources. With extended
sources or different geometries it does not apply.

http://www.richardfisher.com

In article >,
Helpful person > wrote:

> On Monday, November 10, 2014 12:51:30 AM UTC-5, isw wrote:
> >
> > I'm pretty sure it's an inverse cube relation (theoretically, which
> > real-world devices rarely are), which makes minimizing the spacing even
> > more important.
> >
> > Isaac
>
> Inverse square law only refers to point sources. With extended
> sources or different geometries it does not apply.

Yup. And for magnetics, monopoles (which, AFAIK, are not yet being used
in induction cooktops.)

Isaac