OK, Aleph, and what sometimes happens at 3AM is that I miss stuff. I lost my infallibility back in 1969 and have been a human ever since. The explanation for that is only avaialble on a need-to-know basis, and nobody needs to know.

MrBill2 that's ok cuz I totally guarantee my reasons for missing stuff during _wee hours_ is way more embarrassing than yours (whatever they are)!

...only avaialble on a need-to-know basis, and nobody needs to know.

MrBill2 I say that's also philosophy MY generation and younger could totally benefit from for ALL things internet!

So we can be friendly from now on.

MrBill2 I totally agree abt us being friendly 2 each other going forward! But just so you know I also totally own blame! Cuz of {A} not reading subsequent posts and {B} overreacting with rude tone!

The closest that I ever came to intentional induction heating was in applying for a job at an induction heating company. I had studied the technology for two days but still they hired somebody else

MrBill2 I say don't let that bother you! My first experience with L-heating was totally accidental and also vry embarrassing! So cuz of _temporary lapse of reason_ I forgot implications of frequency and so used 2.25" steel tie bolt through aperture of huge Fe toroid combiner coil (which was part of my prototype for IEC fusor chain's PSU) so pwr level was abt 50kW with freq centered around 70kHz. So even though fastener ends were electrically isolated from each other, cross-sectional Foucault currents basically vaporized bolt with mini-explosion! So anyhow I still consider that important _epiphany_ for me cuz it showed me how theory (by which I mean _abstract knowledge_) definitely needs 2b complemented by real-life experience for rounded _education_!

 

MrBill2 that's ok cuz I totally guarantee my reasons for missing stuff during _wee hours_ is way more embarrassing than yours (whatever they are)!



MrBill2 I say that's also philosophy MY generation and younger could totally benefit from for ALL things internet!


MrBill2 I totally agree abt us being friendly 2 each other going forward! But just so you know I also totally own blame! Cuz of {A} not reading subsequent posts and {B} overreacting with rude tone!


MrBill2 I say don't let that bother you! My first experience with L-heating was totally accidental and also vry embarrassing! So cuz of _temporary lapse of reason_ I forgot implications of frequency and so used 2.25" steel tie bolt through aperture of huge Fe toroid combiner coil (which was part of my prototype for IEC fusor chain's PSU) so pwr level was abt 50kW with freq centered around 70kHz. So even though fastener ends were electrically isolated from each other, cross-sectional Foucault currents basically vaporized bolt with mini-explosion! So anyhow I still consider that important _epiphany_ for me cuz it showed me how theory (by which I mean _abstract knowledge_) definitely needs 2b complemented by real-life experience for rounded _education_!

Interesting about the ferrite toroid coil incident, because it has always been presented to me that they are "self shielding" and do not have much leakage flux fields. Of course 50kW is a lot of power and so even a small part of that is a whole lot. You have just provided a good addition to my understanding of a part of the real world that I had only seen from a distance. The closest I have come to that is a steel shaft in a 1kW powerstat variable transformer.

 

it has always been presented to me that they are "self shielding" and do not have much leakage flux fields.

MrBill2 ur totally right abt toroid inductors being self-shielding! Accident wasn't cuz of leakage at all (cuz fastener was through center)! But it was way too large diameter for operating freq (cuz of Foucault effect). Now being clear it wasn't simple shorted turn (cuz ends weren't electrically connected)! Heating was caused by Foucault currents which I totally neglected to consider when I physically built circuit!

So anyhow I have bad habit of calling toroid center hole _aperture_ instead of properly _foramen_ Sry if that's what caused confusion

 

MrBill2 ur totally right abt toroid inductors being self-shielding! Accident wasn't cuz of leakage at all (cuz fastener was through center)! But it was way too large diameter for operating freq (cuz of Foucault effect). Now being clear it wasn't simple shorted turn (cuz ends weren't electrically connected)! Heating was caused by Foucault currents which I totally neglected to consider when I physically built circuit!

So anyhow I have bad habit of calling toroid center hole _aperture_ instead of properly _foramen_ Sry if that's what caused confusion

What it tells me is that when using a donut core for a torroid coil at radio frequencies I need to avoid iron bolts and probably conductive bolts completely. That makes sense and it should be easy enough to do. Even though the exact mechanism of the field is not clear to me the means of avoiding the problem is obvious. And that hole certainly is the aperture of the assembly, at least when winding the thing.

 

I guess you could use your music system as induction heater???

Some amplifiers output 100's of watts . I guess it's just a case of making 2 coils of the right impedance to connect where the speakers usually go , and feeding in a sine wave?

This is unbelievable!

 

Interesting about the ferrite toroid coil incident, because it has always been presented to me that they are "self shielding" and do not have much leakage flux fields.

Heating was caused by Foucault currents which I totally neglected to consider when I physically built circui

What it tells me is that when using a donut core for a torroid coil at radio frequencies I need to avoid iron bolts and probably conductive bolts completely.

While the toroid coil has little outer magnetism it is very concentrated in the center. The magnetic concentration is one of the things that makes them more efficient than an E core transformer. I'm pretty sure a brass bolt through the center would work, being nonmagnetic, though most toroid mounting kits come with a nylon bolt and nut.

Aleph, never knew that Foucault current was the name for that.

 

Can you post this video?

What video??? I see no link or anything..

 

I know it can be non-intuitive 2 think on cuz skin effect makes it seem like magnetically induced currents would get less important with increasing freq but it's like convergent series settling to dominance of Foucault effect as frequency approaches infinity!

I'm pretty sure a brass bolt through the center would work, being nonmagnetic

Shortbus So it's not just abt hysteresis losses. But they're definitely the major issue on lower freqs! So being practical u can get away with almost anything at line freqs if vry small losses are tolerable but on higher freqs using non-metallic (not just non-magnetic) fastener goes from _good idea_ to _absolutely necessary_!

Aleph, never knew that Foucault current was the name for that.

Shortbus it's totally synonymous with _eddy current_ so whatever ur more comfortable with is totally sweet with me!

Now here's important point! When u think on direction of field in _foramen_ of toroidal coil (or really any magnetic transformer) it's easy to see how currents can be induced in closed axial conductor encircling form. So that's just regular _transformer action_. But transverse Foucault currents are also induced in the part of conductor inside foramen! So in transformer design that's why wire radius is a tradeoff between large enough to keep resistive losses to minimum vs small enough to keep Foucault effect losses acceptable!

Can you post this video?

Bentec How do u want me to image magnetic field? I'm fresh out of iron filings and I say they wouldn't be vry helpful imaging dynamic magnetic fields anyhow So my post is strictly _Theater of The Mind_

 

I know it can be non-intuitive 2 think on cuz skin effect makes it seem like magnetically induced currents would get less important with increasing freq but it's like convergent series settling to dominance of Foucault effect as frequency approaches infinity!


Shortbus So it's not just abt hysteresis losses. But they're definitely the major issue on lower freqs! So being practical u can get away with almost anything at line freqs if vry small losses are tolerable but on higher freqs using non-metallic (not just non-magnetic) fastener goes from _good idea_ to _absolutely necessary_!


Shortbus it's totally synonymous with _eddy current_ so whatever ur more comfortable with is totally sweet with me!

Now here's important point! When u think on direction of field in _foramen_ of toroidal coil (or really any magnetic transformer) it's easy to see how currents can be induced in closed axial conductor encircling form. So that's just regular _transformer action_. But transverse Foucault currents are also induced in the part of conductor inside foramen! So in transformer design that's why wire radius is a tradeoff between large enough to keep resistive losses to minimum vs small enough to keep Foucault effect losses acceptable!


Bentec How do u want me to image magnetic field? I'm fresh out of iron filings and I say they wouldn't be vry helpful imaging dynamic magnetic fields anyhow So my post is strictly _Theater of The Mind_

Magnetic fields are indeed very difficult to see, although they can be explored with a probe coil. BUT the currents mentioned would be much more difficult to investigate. So at some point it is safer to trust those who have seen the results. That is the motivation for non-metallic mounts for toroid coils .