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Making a Thomson Coil?
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Sarah Szabo
May 26, 2018, 3:18:58 AM5/26/18
to
I'm interested in making a Thompson's Coil after seeing my University's physics II (EM) professor demonstrate Faraday's Law to us using it. It seems like a fun device to demonstrate various principles of Electromagnetism to lay people (Induced Voltage by Faraday's Law, Resistive Heating, Electromagnetic Levitation (Of rings), Conductivity, etc).
I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
I'm also well set up for woodworking/steelworking equipment for making various components, although I have more of a specialization in woodwork for now. I also have been trying to get into electronics ever since taking the physics II class. I have multi-meters (Including a clamp on one), but don't really have a power supply yet, I also have a 30W Weller soldering iron, and I've wired up a few outlets/switches, as well as all the wiring I did in my Physics II labs.
Functionally, from what I've seen, a Thompson's Coil (Pictured Below)(Source: http://kossover.squarespace.com/journal/2012/5/1/improved-elihu-thomson-coil-jumping-ring.html), really just consists of a coil, with an insulated ferromagnetic iron core, such as this DIY Thompson's coil. I could copy this method outlined in the blog post of the person who made this Thompson's coil (He used the spool, with iron welding rods, which are used in TIG welding, if I'm not mistaken.), but I'm looking to make the best coil that I can, given the time and budget (Around $130-150) constraints, and I'm not sure if this is the design I should go with, hence my post here.
[​IMG]
Is this an acceptable design? Will it give good results for demonstrations? Will it run on 120V AC? What design choices would make it better?
More importantly, what inductor material would be optimal for this situation that I can realistically get my hands on? I was thinking of using the steel welding rods, but was advised by a retired particle physicist to use insulated floral wire. Are there any other substances that would be better?
What other optimizations could I make to make the project better? One consideration I was thinking about was thermal dissipation. It appears that it will overheat at some point due to thermal insulation and no cooling. That's alright for my application, as long as it doesn't overheat for about 30 seconds of use.
I'm guessing the limiting factor here is the inductance, and the higher the better, but I could be wrong, my understanding of inductance is rather limited.
I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
I'm also well set up for woodworking/steelworking equipment for making various components, although I have more of a specialization in woodwork for now. I also have been trying to get into electronics ever since taking the physics II class. I have multi-meters (Including a clamp on one), but don't really have a power supply yet, I also have a 30W Weller soldering iron, and I've wired up a few outlets/switches, as well as all the wiring I did in my Physics II labs.
Functionally, from what I've seen, a Thompson's Coil (Pictured Below)(Source: http://kossover.squarespace.com/journal/2012/5/1/improved-elihu-thomson-coil-jumping-ring.html), really just consists of a coil, with an insulated ferromagnetic iron core, such as this DIY Thompson's coil. I could copy this method outlined in the blog post of the person who made this Thompson's coil (He used the spool, with iron welding rods, which are used in TIG welding, if I'm not mistaken.), but I'm looking to make the best coil that I can, given the time and budget (Around $130-150) constraints, and I'm not sure if this is the design I should go with, hence my post here.
[​IMG]
Is this an acceptable design? Will it give good results for demonstrations? Will it run on 120V AC? What design choices would make it better?
More importantly, what inductor material would be optimal for this situation that I can realistically get my hands on? I was thinking of using the steel welding rods, but was advised by a retired particle physicist to use insulated floral wire. Are there any other substances that would be better?
What other optimizations could I make to make the project better? One consideration I was thinking about was thermal dissipation. It appears that it will overheat at some point due to thermal insulation and no cooling. That's alright for my application, as long as it doesn't overheat for about 30 seconds of use.
I'm guessing the limiting factor here is the inductance, and the higher the better, but I could be wrong, my understanding of inductance is rather limited.
bitrex
May 26, 2018, 10:27:25 AM5/26/18
to
On 05/26/2018 03:18 AM, Sarah Szabo wrote:
> I'm interested in making a Thompson's Coil after seeing my University's physics II (EM) professor demonstrate Faraday's Law to us using it. It seems like a fun device to demonstrate various principles of Electromagnetism to lay people (Induced Voltage by Faraday's Law, Resistive Heating, Electromagnetic Levitation (Of rings), Conductivity, etc).
>
> I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
>
> How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
It doesn't seem like a particularly amenable project as a first outing
> I'm interested in making a Thompson's Coil after seeing my University's physics II (EM) professor demonstrate Faraday's Law to us using it. It seems like a fun device to demonstrate various principles of Electromagnetism to lay people (Induced Voltage by Faraday's Law, Resistive Heating, Electromagnetic Levitation (Of rings), Conductivity, etc).
>
> I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
>
> How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
into electronics/electrical design. If you're not even sure if you would
need to use 120VAC wall power to meet the requirements of the device
you're considering building as you state further down I'd put it off at
least until I was confident I had the theory down to come to a
conclusion like that independently.
You may get more help from other people here but this group gets a fair
amount of questions on how to build things like stun guns, Tesla coils,
death rays, etc. from folks who don't seem to have had much time
learning which end of the soldering iron to hold and idk about other
people but I personally consider it a breach of engineering ethics to
give specific advice on projects like that to novices. Electronics/EM is
an exciting field and once you learn a bit it feels pretty awesome and
the tendency may be to want to "go big" but projects involving high
voltages and currents aren't to be fucked with on a whim, I would
consider carefully before continuing.
John Larkin
May 26, 2018, 10:30:45 AM5/26/18
to
On Sat, 26 May 2018 00:18:52 -0700 (PDT), Sarah Szabo
<physici...@gmail.com> wrote:
>I'm interested in making a Thompson's Coil after seeing my University's physics II (EM) professor demonstrate Faraday's Law to us using it. It seems like a fun device to demonstrate various principles of Electromagnetism to lay people (Induced Voltage by Faraday's Law, Resistive Heating, Electromagnetic Levitation (Of rings), Conductivity, etc).
>
>I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
>
>How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
>
>I'm also well set up for woodworking/steelworking equipment for making various components, although I have more of a specialization in woodwork for now. I also have been trying to get into electronics ever since taking the physics II class. I have multi-meters (Including a clamp on one), but don't really have a power supply yet, I also have a 30W Weller soldering iron, and I've wired up a few outlets/switches, as well as all the wiring I did in my Physics II labs.
>
>Functionally, from what I've seen, a Thompson's Coil (Pictured Below)(Source: http://kossover.squarespace.com/journal/2012/5/1/improved-elihu-thomson-coil-jumping-ring.html), really just consists of a coil, with an insulated ferromagnetic iron core, such as this DIY Thompson's coil. I could copy this method outlined in the blog post of the person who made this Thompson's coil (He used the spool, with iron welding rods, which are used in TIG welding, if I'm not mistaken.), but I'm looking to make the best coil that I can, given the time and budget (Around $130-150) constraints, and I'm not sure if this is the design I should go with, hence my post here.
>[?IMG]
<physici...@gmail.com> wrote:
>I'm interested in making a Thompson's Coil after seeing my University's physics II (EM) professor demonstrate Faraday's Law to us using it. It seems like a fun device to demonstrate various principles of Electromagnetism to lay people (Induced Voltage by Faraday's Law, Resistive Heating, Electromagnetic Levitation (Of rings), Conductivity, etc).
>
>I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
>
>How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
>
>I'm also well set up for woodworking/steelworking equipment for making various components, although I have more of a specialization in woodwork for now. I also have been trying to get into electronics ever since taking the physics II class. I have multi-meters (Including a clamp on one), but don't really have a power supply yet, I also have a 30W Weller soldering iron, and I've wired up a few outlets/switches, as well as all the wiring I did in my Physics II labs.
>
>Functionally, from what I've seen, a Thompson's Coil (Pictured Below)(Source: http://kossover.squarespace.com/journal/2012/5/1/improved-elihu-thomson-coil-jumping-ring.html), really just consists of a coil, with an insulated ferromagnetic iron core, such as this DIY Thompson's coil. I could copy this method outlined in the blog post of the person who made this Thompson's coil (He used the spool, with iron welding rods, which are used in TIG welding, if I'm not mistaken.), but I'm looking to make the best coil that I can, given the time and budget (Around $130-150) constraints, and I'm not sure if this is the design I should go with, hence my post here.
>Is this an acceptable design? Will it give good results for demonstrations? Will it run on 120V AC? What design choices would make it better?
>
>More importantly, what inductor material would be optimal for this situation that I can realistically get my hands on? I was thinking of using the steel welding rods, but was advised by a retired particle physicist to use insulated floral wire. Are there any other substances that would be better?
>
>What other optimizations could I make to make the project better? One consideration I was thinking about was thermal dissipation. It appears that it will overheat at some point due to thermal insulation and no cooling. That's alright for my application, as long as it doesn't overheat for about 30 seconds of use.
>
>I'm guessing the limiting factor here is the inductance, and the higher the better, but I could be wrong, my understanding of inductance is rather limited.
You'd essentialy be building a toy from plans. It wouldn't teach you
>
>More importantly, what inductor material would be optimal for this situation that I can realistically get my hands on? I was thinking of using the steel welding rods, but was advised by a retired particle physicist to use insulated floral wire. Are there any other substances that would be better?
>
>What other optimizations could I make to make the project better? One consideration I was thinking about was thermal dissipation. It appears that it will overheat at some point due to thermal insulation and no cooling. That's alright for my application, as long as it doesn't overheat for about 30 seconds of use.
>
>I'm guessing the limiting factor here is the inductance, and the higher the better, but I could be wrong, my understanding of inductance is rather limited.
much about inductance.
And where would you perform public demonstrations? I don't think that
"lay people" would learn anything either.
The answer to your technical questions is: do the math.
--
John Larkin Highland Technology, Inc
lunatic fringe electronics
Sarah Szabo
May 26, 2018, 1:12:08 PM5/26/18
to
> It doesn't seem like a particularly amenable project as a first outing
> into electronics/electrical design. If you're not even sure if you would
> need to use 120VAC wall power to meet the requirements of the device
> you're considering building as you state further down I'd put it off at
> least until I was confident I had the theory down to come to a
> conclusion like that independently.
>
> You may get more help from other people here but this group gets a fair
> amount of questions on how to build things like stun guns, Tesla coils,
> death rays, etc. from folks who don't seem to have had much time
> learning which end of the soldering iron to hold and idk about other
> people but I personally consider it a breach of engineering ethics to
> give specific advice on projects like that to novices. Electronics/EM is
> an exciting field and once you learn a bit it feels pretty awesome and
> the tendency may be to want to "go big" but projects involving high
> voltages and currents aren't to be fucked with on a whim, I would
> consider carefully before continuing.
1) This isn't my first electronics project, I've done a few which involved soldering, including making time-sequence varying LEDs for my 2 year college's graduation cap (For fun and to be different). Granted, this isn't spectacular, like building a radio from spare parts without a kit. But it's at least something.
> into electronics/electrical design. If you're not even sure if you would
> need to use 120VAC wall power to meet the requirements of the device
> you're considering building as you state further down I'd put it off at
> least until I was confident I had the theory down to come to a
> conclusion like that independently.
>
> You may get more help from other people here but this group gets a fair
> amount of questions on how to build things like stun guns, Tesla coils,
> death rays, etc. from folks who don't seem to have had much time
> learning which end of the soldering iron to hold and idk about other
> people but I personally consider it a breach of engineering ethics to
> give specific advice on projects like that to novices. Electronics/EM is
> an exciting field and once you learn a bit it feels pretty awesome and
> the tendency may be to want to "go big" but projects involving high
> voltages and currents aren't to be fucked with on a whim, I would
> consider carefully before continuing.
2) This is just to demonstrate a physical principle, and from an electronics perspective is downright trivial. The circuit diagram would only consist of a 120V AC source and an inductor. I'm not looking to learn about inductance, I have my textbook for that. It's meant to be a toy, and is just for fun.
3) I've already run the numbers, and "did the maths". I'm just asking how to optimize the variables. For instance, I'm uncertain what material would have the highest inductance for the core, which appears to be the limiting factor.
bitrex
May 26, 2018, 2:05:25 PM5/26/18
to
On 05/26/2018 01:12 PM, Sarah Szabo wrote:
>> It doesn't seem like a particularly amenable project as a first outing
>> into electronics/electrical design. If you're not even sure if you would
>> need to use 120VAC wall power to meet the requirements of the device
>> you're considering building as you state further down I'd put it off at
>> least until I was confident I had the theory down to come to a
>> conclusion like that independently.
>>
>> You may get more help from other people here but this group gets a fair
>> amount of questions on how to build things like stun guns, Tesla coils,
>> death rays, etc. from folks who don't seem to have had much time
>> learning which end of the soldering iron to hold and idk about other
>> people but I personally consider it a breach of engineering ethics to
>> give specific advice on projects like that to novices. Electronics/EM is
>> an exciting field and once you learn a bit it feels pretty awesome and
>> the tendency may be to want to "go big" but projects involving high
>> voltages and currents aren't to be fucked with on a whim, I would
>> consider carefully before continuing.
>
>> It doesn't seem like a particularly amenable project as a first outing
>> into electronics/electrical design. If you're not even sure if you would
>> need to use 120VAC wall power to meet the requirements of the device
>> you're considering building as you state further down I'd put it off at
>> least until I was confident I had the theory down to come to a
>> conclusion like that independently.
>>
>> You may get more help from other people here but this group gets a fair
>> amount of questions on how to build things like stun guns, Tesla coils,
>> death rays, etc. from folks who don't seem to have had much time
>> learning which end of the soldering iron to hold and idk about other
>> people but I personally consider it a breach of engineering ethics to
>> give specific advice on projects like that to novices. Electronics/EM is
>> an exciting field and once you learn a bit it feels pretty awesome and
>> the tendency may be to want to "go big" but projects involving high
>> voltages and currents aren't to be fucked with on a whim, I would
>> consider carefully before continuing.
>
> I'm not looking to learn about inductance, I have my textbook for that.
"I'm guessing the limiting factor here is the inductance, and the higher
the better, but I could be wrong, my understanding of inductance is
rather limited."
So you're saying something different than you said before, now.
the better, but I could be wrong, my understanding of inductance is
rather limited."
Well, good luck and God bless.
bitrex
May 26, 2018, 2:14:13 PM5/26/18
to
On 05/26/2018 01:12 PM, Sarah Szabo wrote:
a lot if they show their work because then at least someone can look
thru it to see if it's vaguely correct or way off-base.
Without seeing the work nobody can do anything but speculate as to its
state of correctness and the crystal ball is out-of-order.
bitrex
May 26, 2018, 2:16:43 PM5/26/18
to
people say "I'll show you mine if you show me yours" trying to get other
people to do the work for them, I mean seriously you'd think Charlie
Brown would've learned that the football was gonna get pulled away at
some point.
Clive Arthur
May 26, 2018, 2:30:19 PM5/26/18
to
On 26/05/2018 08:18, Sarah Szabo wrote:
<snipped>
Here's a tip. If you're connecting something across the AC mains and
you're not completely happy that you fully understand things, put an
incandescent light bulb in series. That way, even a complete short
won't take out the building.
[I did an electrical safety demonstration in which I had no interest
whatsoever but had drawn the short straw. The faceless corporate droids
who mandate these things know nothing of any worth. I cooked
frankfurters by connecting them across the 230V mains, but made sure to
put a 500W lamp in series. Interesting. Nothing for a few seconds,
then the lamp starts to glow, then brighter and brighter. Fun as well as
pointless. Made the conference room stink too. If GE take over your
successful innovative company, leave as soon as you can, for they will
surely fuck it up and sell it at a loss.]
Cheers
--
Clive
<snipped>
Here's a tip. If you're connecting something across the AC mains and
you're not completely happy that you fully understand things, put an
incandescent light bulb in series. That way, even a complete short
won't take out the building.
[I did an electrical safety demonstration in which I had no interest
whatsoever but had drawn the short straw. The faceless corporate droids
who mandate these things know nothing of any worth. I cooked
frankfurters by connecting them across the 230V mains, but made sure to
put a 500W lamp in series. Interesting. Nothing for a few seconds,
then the lamp starts to glow, then brighter and brighter. Fun as well as
pointless. Made the conference room stink too. If GE take over your
successful innovative company, leave as soon as you can, for they will
surely fuck it up and sell it at a loss.]
Cheers
--
Clive
John Larkin
May 26, 2018, 4:03:48 PM5/26/18
to
--
John Larkin Highland Technology, Inc trk
jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
Sarah Szabo
May 26, 2018, 4:20:07 PM5/26/18
to
Wow, sorry to hear that about your company. I'll take that note about GE.
Using the typical Inductive Reactance formula, X_l = 2(Pi)*f*L, and using Ohm's law V=IR, we'll try to calculate the inductance needed for typical 120V sockets and at a maximum current of 15A. So, we solve for inductance and get L = V / (2(pi)*I*f), which when we insert the numbers is L = 120 / (2*(pi)*15*60) = .02H
This is mildly helpful. I need to calculate what material I need to fill a 3.81 cm diameter cylinder that is 1/3 of a meter high to obtain an inductance of .02H to impede the N turns of wire around the core. I don't know how many turns of wire are on the 500ft wire spool of 12AWG wire.
In the linked post, the author uses insulated steel welding wire for the inductor core. I need to know if there is a better alternative that I can realistically acquire.
Using the typical Inductive Reactance formula, X_l = 2(Pi)*f*L, and using Ohm's law V=IR, we'll try to calculate the inductance needed for typical 120V sockets and at a maximum current of 15A. So, we solve for inductance and get L = V / (2(pi)*I*f), which when we insert the numbers is L = 120 / (2*(pi)*15*60) = .02H
This is mildly helpful. I need to calculate what material I need to fill a 3.81 cm diameter cylinder that is 1/3 of a meter high to obtain an inductance of .02H to impede the N turns of wire around the core. I don't know how many turns of wire are on the 500ft wire spool of 12AWG wire.
In the linked post, the author uses insulated steel welding wire for the inductor core. I need to know if there is a better alternative that I can realistically acquire.
tabb...@gmail.com
May 26, 2018, 4:42:19 PM5/26/18
to
NT
Sarah Szabo
May 26, 2018, 6:09:37 PM5/26/18
to
> I'm happy to help. But what you say is not convicing. Fill in all the gaps, tell us what you've figured out & not. Not knowing what to use to maximise inductance is very basic, yet you want to put a big fat inductor across the mains. So tell us how you think that could create a major problem. So far I'm not convinced you know what the issues are, and I don't especially want to show you how to kill yourself.
>
>
> NT
I should state that I know how to maximize inductance. Just get a ferromagnetic object with a higher magnetic permeability and get more of it between your N loops of wire.
>
>
> NT
The set of potential problems is limited by type. The inductor itself is not necessarily dangerous. It's what happens when you try to open the circuit after the inductor is charged that can cause a dangerous situation. If you don't have a path for the inductor to discharge itself when you open the circuit, I'm aware that the inductor will do whatever it has to to keep the current constant, generating high voltages.
You can create a simple drain circuit by having a diode with a resistor in the reverse direction similar to https://electronics.stackexchange.com/a/21588/95654 thus the inductor always has a way to keep the current constant without generating high voltages until the magnetic field collapses.
Then there are the usual issues with strong electromagnets. They will induce strong oscillating magnetic fields in the region, which might effect any electronic devices in the area, including pacemakers, and the core itself is a solenoid, which generates a large nearly uniform magnetic field in the core, and can suck up anything ferromagnetic, including rings, possibly breaking the fingers of the wearer.
Then, there are the typical electronics hazards, such as touching mains voltage, fire, etc.
Sarah Szabo
May 26, 2018, 6:13:22 PM5/26/18
to
My question is more on what material would maximize the magnetic permeability. The original poster used steel welding wire for the inductor. Is this the best choice for a material that I can reasonably get my hands on?
Mike Perkins
May 26, 2018, 6:23:01 PM5/26/18
to
On 26/05/2018 23:09, Sarah Szabo wrote:
>> I'm happy to help. But what you say is not convicing. Fill in all
>> the gaps, tell us what you've figured out & not. Not knowing what
>> to use to maximise inductance is very basic, yet you want to put a
>> big fat inductor across the mains. So tell us how you think that
>> could create a major problem. So far I'm not convinced you know
>> what the issues are, and I don't especially want to show you how to
>> kill yourself.
>>
>>
>> NT
>
> I should state that I know how to maximize inductance. Just get a
> ferromagnetic object with a higher magnetic permeability and get more
> of it between your N loops of wire.
You might need to consider saturation. Have you sourced the material you
>> I'm happy to help. But what you say is not convicing. Fill in all
>> the gaps, tell us what you've figured out & not. Not knowing what
>> to use to maximise inductance is very basic, yet you want to put a
>> big fat inductor across the mains. So tell us how you think that
>> could create a major problem. So far I'm not convinced you know
>> what the issues are, and I don't especially want to show you how to
>> kill yourself.
>>
>>
>> NT
>
> I should state that I know how to maximize inductance. Just get a
> ferromagnetic object with a higher magnetic permeability and get more
> of it between your N loops of wire.
intend to used? Perhaps this is an ideal time to give us turns/SWG/dia
and material specs.
> The set of potential problems is limited by type. The inductor itself
> is not necessarily dangerous. It's what happens when you try to open
> the circuit after the inductor is charged that can cause a dangerous
> situation. If you don't have a path for the inductor to discharge
> itself when you open the circuit, I'm aware that the inductor will do
> whatever it has to to keep the current constant, generating high
> voltages.
>
> You can create a simple drain circuit by having a diode with a
> resistor in the reverse direction similar to
> https://electronics.stackexchange.com/a/21588/95654 thus the inductor
> always has a way to keep the current constant without generating high
> voltages until the magnetic field collapses.
DC excitation of a solenoid. Quenching using a diode across your
inductor or switch will result in tears.
More importantly, have you considered how much energy will be stored in
your solenoid, and how to dissipate this with an AC source?
> Then there are the usual issues with strong electromagnets. They will
> induce strong oscillating magnetic fields in the region, which might
> effect any electronic devices in the area, including pacemakers, and
> the core itself is a solenoid, which generates a large nearly uniform
> magnetic field in the core, and can suck up anything ferromagnetic,
> including rings, possibly breaking the fingers of the wearer.
likely to burn the skin than induce immense forces breaking a finger.
> Then, there are the typical electronics hazards, such as touching
> mains voltage, fire, etc.
--
Mike Perkins
Video Solutions Ltd
www.videosolutions.ltd.uk
tabb...@gmail.com
May 26, 2018, 7:24:08 PM5/26/18
to
Is 15A a good choice? Your winding will have both inductance & resistance, and the resistance R will get mighty hot on 15A. Do you know what your expected wire resistance is?
500' of 12AWG is 2.05mm dia = 3.14 square mm.
1mm2 is 22mΩ per m so 3.14 is 7mΩ/m
500' = 150m which gives 1.05Ω.
15A on 1.05Ω gives 15.75v & 236 watts of heat dissipation. It will soon get HOT.
Really though, your project raises enough questions that you're unlikely to get answers anywhere.
NT
Sarah Szabo
May 26, 2018, 7:52:41 PM5/26/18
to
I'm planning on using a typical 12AWG wire spool (Like one you could buy at big box stores). I would estimate 120 turns, although this is a very rough calculation at is not at all certain.
Sarah Szabo
May 26, 2018, 7:58:49 PM5/26/18
to
The actual r value I obtained from an online calculator (12AWG) was .079 ohms, which would make the energy dissipated around 17W. Calculator: https://www.cirris.com/learning-center/calculators/133-wire-resistance-calculator-table
bill....@ieee.org
May 26, 2018, 10:49:19 PM5/26/18
to
On Sunday, May 27, 2018 at 6:20:07 AM UTC+10, Sarah Szabo wrote:
> Wow, sorry to hear that about your company. I'll take that note about GE.
GE has been bad news on both sides of the Atlantic for quite a while now. The UK GEC was particularly bad news when it was run by Weinstock
> Wow, sorry to hear that about your company. I'll take that note about GE.
https://en.wikipedia.org/wiki/Arnold_Weinstock
He seems to have been a brilliant accountant, but when GEC took over an innovative company, they stopped spending money on innovating, and milked what they had for all it was worth, which isn't a recipe for long term success.
> Using the typical Inductive Reactance formula, X_l = 2(Pi)*f*L, and using Ohm's law V=IR, we'll try to calculate the inductance needed for typical 120V sockets and at a maximum current of 15A. So, we solve for inductance and get L = V / (2(pi)*I*f), which when we insert the numbers is L = 120 / (2*(pi)*15*60) = .02H
>
> This is mildly helpful. I need to calculate what material I need to fill a 3.81 cm diameter cylinder that is 1/3 of a meter high to obtain an inductance of .02H to impede the N turns of wire around the core. I don't know how many turns of wire are on the 500ft wire spool of 12AWG wire.
> In the linked post, the author uses insulated steel welding wire for the inductor core. I need to know if there is a better alternative that I can realistically acquire.
--
Bill Sloman, Sydney
bill....@ieee.org
May 26, 2018, 10:59:51 PM5/26/18
to
On Sunday, May 27, 2018 at 8:09:37 AM UTC+10, Sarah Szabo wrote:
> > I'm happy to help. But what you say is not convicing. Fill in all the gaps, tell us what you've figured out & not. Not knowing what to use to maximise inductance is very basic, yet you want to put a big fat inductor across the mains. So tell us how you think that could create a major problem. So far I'm not convinced you know what the issues are, and I don't especially want to show you how to kill yourself.
> >
> >
> > NT
>
> I should state that I know how to maximize inductance. Just get a ferromagnetic object with a higher magnetic permeability and get more of it between your N loops of wire.
That's not carefully stated. If you state off with a coil of wire - essentially a torus - you have to wrap your high-permeability material right around the torus to maximise the inductance.
> > I'm happy to help. But what you say is not convicing. Fill in all the gaps, tell us what you've figured out & not. Not knowing what to use to maximise inductance is very basic, yet you want to put a big fat inductor across the mains. So tell us how you think that could create a major problem. So far I'm not convinced you know what the issues are, and I don't especially want to show you how to kill yourself.
> >
> >
> > NT
>
> I should state that I know how to maximize inductance. Just get a ferromagnetic object with a higher magnetic permeability and get more of it between your N loops of wire.
With ferrites (which can be moulded, fired and ground) you use pairs of pot cores.
https://en.wikipedia.org/wiki/Magnetic_core
In general it is better idea to start off with a torus of the high permeablity material and wind your coil around that. There are ingenious machines for doing that quickly - essentially a split wire holder which you put together so it threads the torus, then wind wire onto that from a regular spool before winding it off again onto the torus.
Pot cores are easier.
<snipped the rest>
--
Bill Sloman, Sydney
Tom Gardner
May 27, 2018, 2:51:28 AM5/27/18
to
On 27/05/18 03:49, bill....@ieee.org wrote:
> On Sunday, May 27, 2018 at 6:20:07 AM UTC+10, Sarah Szabo wrote:
>> Wow, sorry to hear that about your company. I'll take that note about GE.
>
> GE has been bad news on both sides of the Atlantic for quite a while now. The
> UK GEC was particularly bad news when it was run by Weinstock
Ah yes, GEC.
> On Sunday, May 27, 2018 at 6:20:07 AM UTC+10, Sarah Szabo wrote:
>> Wow, sorry to hear that about your company. I'll take that note about GE.
>
> GE has been bad news on both sides of the Atlantic for quite a while now. The
> UK GEC was particularly bad news when it was run by Weinstock
While at university I was applying for jobs. I sent, IIRC, 6 to GEC
and was offered 11 interviews, and went to ~6.
One was in a Dickensian building, one was clearly riven by internal
politics, one (after, ahem, "listening" to what I had done) asked
me whether I was "really a hardware or software engineer". And at
one, when I was explaining to their security guard that milk round
process enabled me to see different companies, the guard said
"and I'm sure there are other places, aren't there".
I found the milk round very useful because it showed me I /never/
wanted to work at GEC.
Phil Allison
May 27, 2018, 3:18:29 AM5/27/18
to
Sarah Szabo wrote:
>
>
> 120V AC? What design choices would make it better?
>
> More importantly, what inductor material would be optimal for this
> situation that I can realistically get my hands on? I was thinking
> of using the steel welding rods, but was advised by a retired
> ***particle physicist to use insulated floral wire***.
>
>
> 120V AC? What design choices would make it better?
>
> More importantly, what inductor material would be optimal for this
> situation that I can realistically get my hands on? I was thinking
> of using the steel welding rods, but was advised by a retired
>
>
** Err - tell me, was that Dr Sheldon Cooper, PhD ???
FYI:
"floral wire" is used by florists to bundle flower arrangements.
The wire is made of aluminium.
.... Phil
amdx
May 27, 2018, 7:16:58 AM5/27/18
to
> https://en.wikipedia.org/wiki/Permeability_(electromagnetism)
Is there any reason to think about thickness of your material.
Why or why not. Why many rods instead of one nice 3.8cm 2/3 meter
long ferrous rod.
Answer could be technical, economic, or ease of construction.
bill....@ieee.org
May 27, 2018, 8:54:14 AM5/27/18
to
Making the core out of wire or rods is another way of limiting the size of the loop, provided - of course - that rods or wires are covered with insulating enamel (in the same way as laminations) to prevent current flow between adjacent conductors
--
Bill Sloman, Sydney
Chris Jones
May 27, 2018, 11:58:38 AM5/27/18
to
absent-mindedly held an old telephone exchange relay coil too close to
it, and inadvertently built a step-up transformer and burnt my thumb
with the arc - I didn't do that again.
I don't think very high inductance is necessarily what you want. If you
want to fire rings well, you want more voltage per turn, which means not
too many turns, but if there are too few turns, then the inductance may
be too low, (especially if the core saturates but maybe even if it
doesn't), and you may trip a breaker. From memory I think the coil I
made was with 1.7mm diameter wire, wound onto an old spool about 100mm
long, 100mm diameter. The core was about 35mm diameter and 400mm long,
made of a bundle of welding rods stuffed tightly into a PVC pipe.
For the coil, make sure you use enamelled winding wire, not ordinary
insulated wire, as the insulation needs to be thin in order to allow the
copper to be thicker (for a given overall wire diameter) and the
resistance to be as low as possible for a given number of turns. This
will minimise heating, though it will still only stay cool enough for a
few seconds at high power. If you want to run it for longer (which is
definitely interesting), use a variac or wire it in series with a heater
to reduce the current to a value that won't cause overheating.
You might find that for the core, dull steel wire for oxy welding is
better than shiny copper plated steel wire intended for TIG welding,
because the dirt and oxide on the surface of the oxy wire will help to
reduce eddy currents. The thick plastic coating of florists' wire may
use up too much space and reduce the iron that you would fit into the
core. The voltage between iron wires isn't much so you don't need very
good insulation, just a bit of dirt will do. If you were really
interested in finding the best possible material then there are special
materials intended for magnetic cores, such as grain oriented silicon
steel, but I don't think using these would add much to the educational
experience, and you could spend the effort instead on constructing other
models afterwards such as a linear induction motor:
https://www.youtube.com/watch?v=vxrUR_zZcmU
I recall that some of Eric Laithwaite's books contained instructions for
building the electrical machines. I would not pay too much attention to
his writings about gyroscopes though.
amdx
May 27, 2018, 12:10:56 PM5/27/18
to
Mikek
Neon John
May 27, 2018, 12:22:06 PM5/27/18
to
On Sat, 26 May 2018 13:20:03 -0700 (PDT), Sarah Szabo
<physici...@gmail.com> wrote:
>In the linked post, the author uses insulated steel welding wire for the inductor core. I need to know if there is a better alternative that I can realistically acquire.
Of the materials easily obtainable at reasonable cost, pure iron wire
<physici...@gmail.com> wrote:
>In the linked post, the author uses insulated steel welding wire for the inductor core. I need to know if there is a better alternative that I can realistically acquire.
would be a little better than steel. You can get it at a welding
supply store, Tractor Supply or most any farmer's co-op. It's called
steel worker's tie wire.
I suggest cutting it to length and then heating it red hot with a
welder. This will both straighten the wire and anneal it dead soft.
John
John DeArmond
http://www.neon-john.com
http://www.tnduction.com
Tellico Plains, Occupied TN
See website for email address
Sarah Szabo
May 27, 2018, 12:23:06 PM5/27/18
to
Sarah Szabo
May 27, 2018, 12:28:13 PM5/27/18
to
If it's already annealed, would it need to be heated again? I thought that's what annealed meant, where it was heated in an oven then allowed to cool.
Neon John
May 27, 2018, 1:03:40 PM5/27/18
to
back and forth several times. If it gets harder to bend (work
hardens), then it's not 100% pure iron.
Spooling it up, then your unspooling the wire will stress it if it can
work harden. It will have the best permeability when dead soft.
I anneal the wire by connecting an electric welder to lengths of the
wire and adjust the current to reach bright red heat. That anneals
the wire AND it becomes soft enough that a gentle tug will pull out
all the kinks and bends.
George Herold
May 27, 2018, 1:08:52 PM5/27/18
to
On Saturday, May 26, 2018 at 3:18:58 AM UTC-4, Sarah Szabo wrote:
> I'm interested in making a Thompson's Coil after seeing my University's physics II (EM) professor demonstrate Faraday's Law to us using it. It seems like a fun device to demonstrate various principles of Electromagnetism to lay people (Induced Voltage by Faraday's Law, Resistive Heating, Electromagnetic Levitation (Of rings), Conductivity, etc).
>
> I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
>
> How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
>
> I'm also well set up for woodworking/steelworking equipment for making various components, although I have more of a specialization in woodwork for now. I also have been trying to get into electronics ever since taking the physics II class. I have multi-meters (Including a clamp on one), but don't really have a power supply yet, I also have a 30W Weller soldering iron, and I've wired up a few outlets/switches, as well as all the wiring I did in my Physics II labs.
>
> Functionally, from what I've seen, a Thompson's Coil (Pictured Below)(Source: http://kossover.squarespace.com/journal/2012/5/1/improved-elihu-thomson-coil-jumping-ring.html), really just consists of a coil, with an insulated ferromagnetic iron core, such as this DIY Thompson's coil. I could copy this method outlined in the blog post of the person who made this Thompson's coil (He used the spool, with iron welding rods, which are used in TIG welding, if I'm not mistaken.), but I'm looking to make the best coil that I can, given the time and budget (Around $130-150) constraints, and I'm not sure if this is the design I should go with, hence my post here.
> [​IMG]
> Is this an acceptable design? Will it give good results for demonstrations? Will it run on 120V AC? What design choices would make it better?
>
> More importantly, what inductor material would be optimal for this situation that I can realistically get my hands on? I was thinking of using the steel welding rods, but was advised by a retired particle physicist to use insulated floral wire. Are there any other substances that would be better?
>
> What other optimizations could I make to make the project better? One consideration I was thinking about was thermal dissipation. It appears that it will overheat at some point due to thermal insulation and no cooling. That's alright for my application, as long as it doesn't overheat for about 30 seconds of use.
>
> I'm guessing the limiting factor here is the inductance, and the higher the better, but I could be wrong, my understanding of inductance is rather limited.
Hi Sarah, I've seen these 'jumping rings', but I've never bothered to
> I'm interested in making a Thompson's Coil after seeing my University's physics II (EM) professor demonstrate Faraday's Law to us using it. It seems like a fun device to demonstrate various principles of Electromagnetism to lay people (Induced Voltage by Faraday's Law, Resistive Heating, Electromagnetic Levitation (Of rings), Conductivity, etc).
>
> I should emphasize that this isn't for any university project, just as a fun project for introducing lay people to EM in a way that they can interact with it.
>
> How should I go about building this? I have a functioning knowledge of everything EM that I learned in class, although we skipped out on inductance unfortunately (Stupid school semester physics layout, god forbid we learn all the school covered-EM topics in the EM physics class right?) At a fundamental level, I get inductance, and am aware of inductive reactance, although I haven't reviewed that chapters in my Giancoli physics text book on it yet. I'm on break for the next month, having just finished a semester at the university. So I have plenty of time to plan and execute the project.
>
> I'm also well set up for woodworking/steelworking equipment for making various components, although I have more of a specialization in woodwork for now. I also have been trying to get into electronics ever since taking the physics II class. I have multi-meters (Including a clamp on one), but don't really have a power supply yet, I also have a 30W Weller soldering iron, and I've wired up a few outlets/switches, as well as all the wiring I did in my Physics II labs.
>
> Functionally, from what I've seen, a Thompson's Coil (Pictured Below)(Source: http://kossover.squarespace.com/journal/2012/5/1/improved-elihu-thomson-coil-jumping-ring.html), really just consists of a coil, with an insulated ferromagnetic iron core, such as this DIY Thompson's coil. I could copy this method outlined in the blog post of the person who made this Thompson's coil (He used the spool, with iron welding rods, which are used in TIG welding, if I'm not mistaken.), but I'm looking to make the best coil that I can, given the time and budget (Around $130-150) constraints, and I'm not sure if this is the design I should go with, hence my post here.
> [​IMG]
> Is this an acceptable design? Will it give good results for demonstrations? Will it run on 120V AC? What design choices would make it better?
>
> More importantly, what inductor material would be optimal for this situation that I can realistically get my hands on? I was thinking of using the steel welding rods, but was advised by a retired particle physicist to use insulated floral wire. Are there any other substances that would be better?
>
> What other optimizations could I make to make the project better? One consideration I was thinking about was thermal dissipation. It appears that it will overheat at some point due to thermal insulation and no cooling. That's alright for my application, as long as it doesn't overheat for about 30 seconds of use.
>
> I'm guessing the limiting factor here is the inductance, and the higher the better, but I could be wrong, my understanding of inductance is rather limited.
figure out how they work. If you search for "jumping ring physics"
you get tons of links.
https://arxiv.org/ftp/arxiv/papers/1404/1404.6024.pdf
lots more,
https://www.grinnell.edu/sites/default/files/documents/tjossem_and_brost_optimizing_thomsons_jumping_ring.pdf
I say ignore the nay-sayers and give it a try. AC is dangerous so use
caution, (and a lab partner) the incandescent bulb in series sounds
like a good idea. (at least to start.)
(lots of us got our start by building stuff according to a recipe.)
Since you are at a university, one thing you could try is to go and talk
to the 'lab/demo guy/ gal' in the physics department, (or wherever you saw
the demo.) You'll have to figure out who this person is.
Then go talk with them, they might be interested in helping you... again
I'm thinking it will work better if you can find a partner to help,
and stay safer.
There's a ton of literature, you should read a bunch of that.
(report back, tell me/ us what's any good. :^)
George H.
Cursitor Doom
May 27, 2018, 1:56:01 PM5/27/18
to
On Sun, 27 May 2018 10:08:48 -0700, George Herold wrote:
> I say ignore the nay-sayers and give it a try. AC is dangerous so use
> caution
Yeah, or use DC. DC by contrast is totally harmless as we all know. ;->
> I say ignore the nay-sayers and give it a try. AC is dangerous so use
> caution
--
This message may be freely reproduced without limit or charge only via
the Usenet protocol. Reproduction in whole or part through other
protocols, whether for profit or not, is conditional upon a charge of
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protocols constitutes acceptance of this condition.
George Herold
May 27, 2018, 2:59:05 PM5/27/18
to
On Sunday, May 27, 2018 at 1:56:01 PM UTC-4, Cursitor Doom wrote:
> On Sun, 27 May 2018 10:08:48 -0700, George Herold wrote:
>
> > I say ignore the nay-sayers and give it a try. AC is dangerous so use
> > caution
>
> Yeah, or use DC. DC by contrast is totally harmless as we all know. ;->
>
Right, by AC I meant the wall outlet. Here that's 120V and maybe a 20A
> On Sun, 27 May 2018 10:08:48 -0700, George Herold wrote:
>
> > I say ignore the nay-sayers and give it a try. AC is dangerous so use
> > caution
>
> Yeah, or use DC. DC by contrast is totally harmless as we all know. ;->
>
fuse.
GH
bill....@ieee.org
May 27, 2018, 9:39:04 PM5/27/18
to
--
Bill Sloman, Sydney
amdx
May 27, 2018, 10:46:00 PM5/27/18
to
99.5% iron wire annealed in Hydrogen, so I would go with Iron wire,
I don't know if the earlier suggested annealing process will oxidize
the wire enough to create an insulating layer.
Or you might find a trashed welder and disassemble the transformer
and use the laminations, the trade off, your filling a round section
with a square group of laminated wire whereas the wire could fill the
whole area. Also cutting and fitting the transformer laminations would
be a job. (I doubt you will be able to lift the welder transformer)
Go to an electric motor shop to get epoxy insulated wire, you don't
want the plastic insulation of house wiring. I would have my form all
ready with a proper exit for the internal lead and ask if the shop will
wind it for you. They need to wind it on something, might as well be
your form.
You probably should do some work to decide the dimensions of your coil.
Then you can find how many turns you can get with what ever size wire
you choose, using this.
> http://www.daycounter.com/Calculators/Coil-Physical-Properties-Calculator.phtml
You earlier suggested 0.02 Henries, Don't forget the resistance of
your wire,
Then you need to calculate the inductance.
> http://electronbunker.ca/eb/InductanceCalcML.html
Opps, you're going to install a core of magnetic material.
I would get my form built and install the magnetic material, then wind
50 to 100 turns of wire on it and measure the inductance and calculate
the A sub L (others may use a different term) from that you can find the
number of turns for the inductance you want.
I expect you will have several iterations, wire size vs number of turns.
Wire characteristics
> https://www.powerstream.com/Wire_Size.htm
nuff for now
Mikek
Phil Allison
May 27, 2018, 11:22:27 PM5/27/18
to
amdx wrote:
>
> You earlier suggested 0.02 Henries, Don't forget the resistance of
> your wire,
> Then you need to calculate the inductance.
> http://electronbunker.ca/eb/InductanceCalcML.html
> Opps, you're going to install a core of magnetic material.
> I would get my form built and install the magnetic material, then wind
> 50 to 100 turns of wire on it and measure the inductance and calculate
> the A sub L (others may use a different term) from that you can find the
> number of turns for the inductance you want.
>
>
** FYI: recently I disassembled a 6 inch loudspeaker on the bench. I removed the cone and voice coil from the magnet assembly. The VC was 28mm in dia, had four layers and measured 6.7 ohms. Next I measured it's inductance and found it to be a tad over 1mH.
>
> You earlier suggested 0.02 Henries, Don't forget the resistance of
> your wire,
> Then you need to calculate the inductance.
> http://electronbunker.ca/eb/InductanceCalcML.html
> Opps, you're going to install a core of magnetic material.
> I would get my form built and install the magnetic material, then wind
> 50 to 100 turns of wire on it and measure the inductance and calculate
> the A sub L (others may use a different term) from that you can find the
> number of turns for the inductance you want.
>
>
So I popped it back in the magnet gap and found the inductance had increased by no more than 50%, depending on the test frequency.
What can you conclude from this?
.... Phil
Mike Coon
May 28, 2018, 2:58:38 AM5/28/18
to
In article <ecfb0700-56ca-45c7...@googlegroups.com>,
palli...@gmail.com says...
permanent magnet is like a saturated core?
BTW is the measured inductance different if the coil is jammed so unable
to move?
Mike.
palli...@gmail.com says...
>
> ** FYI: recently I disassembled a 6 inch loudspeaker on the bench. I
removed the cone and voice coil from the magnet assembly. The VC was
28mm in dia, had four layers and measured 6.7 ohms. Next I measured it's
inductance and found it to be a tad over 1mH.
>
> So I popped it back in the magnet gap and found the inductance had increased by no more than 50%, depending on the test frequency.
>
> What can you conclude from this?
>
> .... Phil
My physics (like much else) is very rusty. But could it be that the
> ** FYI: recently I disassembled a 6 inch loudspeaker on the bench. I
removed the cone and voice coil from the magnet assembly. The VC was
28mm in dia, had four layers and measured 6.7 ohms. Next I measured it's
inductance and found it to be a tad over 1mH.
>
> So I popped it back in the magnet gap and found the inductance had increased by no more than 50%, depending on the test frequency.
>
> What can you conclude from this?
>
> .... Phil
permanent magnet is like a saturated core?
BTW is the measured inductance different if the coil is jammed so unable
to move?
Mike.
Phil Allison
May 28, 2018, 3:33:27 AM5/28/18
to
Mike Coon wrote:
>
>
> >
> > ** FYI: recently I disassembled a 6 inch loudspeaker on the bench. I
> removed the cone and voice coil from the magnet assembly. The VC was
> 28mm in dia, had four layers and measured 6.7 ohms. Next I measured it's
> inductance and found it to be a tad over 1mH.
> >
> > So I popped it back in the magnet gap and found the inductance had increased by no more than 50%, depending on the test frequency.
> >
> > What can you conclude from this?
> >
>
>
** The above Q was directed to amdx, but Mike got his reply in first.
>
>
> >
> > ** FYI: recently I disassembled a 6 inch loudspeaker on the bench. I
> removed the cone and voice coil from the magnet assembly. The VC was
> 28mm in dia, had four layers and measured 6.7 ohms. Next I measured it's
> inductance and found it to be a tad over 1mH.
> >
> > So I popped it back in the magnet gap and found the inductance had increased by no more than 50%, depending on the test frequency.
> >
> > What can you conclude from this?
> >
>
>
>
> My physics (like much else) is very rusty. But could it be that the
> permanent magnet is like a saturated core?
>
However, steel parts are magnetised to saturation so almost eliminating permeability.
As the aim of a Thomson Gun is to saturate the iron core ASAP, one can only rely on the air cored L value to limit AC current flow.
> BTW is the measured inductance different if the coil is jammed so unable
> to move?
>
.... Phil
Chris Jones
May 28, 2018, 8:08:15 AM5/28/18
to
already straight, and that would save a lot of straightening effort if
you want to make a dense bundle of them. They probably are steel and not
iron, but I doubt it makes much difference in this application where
losses in the iron are not going to be the limiting factor in how long
it can be left on.
As I understand it, mostly just the saturation flux density would be
important as the higher that is, the more volts per turn you can use on
the coil, but I think a bit of hysteresis or lower permeability might
not be important bearing in mind the huge air gap and the large copper
losses you have anyway.
amdx
May 28, 2018, 8:53:40 AM5/28/18
to
1 milliHenry. I'm experienced with 6" air cores with 35 turns
having 1/4 that.
Second, with the coil back in the gap and a 50% increase of
inductance, I'd say inductance increases with a core inserted.
That's why I suggested she measure it.
My experience is with Ferrite rods, and I see about a 6 to 1
increase in the inductance of a coil when the rod is inserted.
You mentioned that the aim is to saturate the core as fast as possible.
I did not know this.
If indeed the core is saturated, then I would assume measuring
inductance with the core is not a useful step as the core goes away
during the first 1/4 cycle.
How can she calculate that the flux produced will actually saturate
the core?
I found this paper, that may have info for Sarah. It is for a DC
Thompson Coil, but I think it has some relevant info.
> https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiP3K_HsqjbAhUEoVMKHV0fAsIQFggpMAA&url=https%3A%2F%2Fwww.rose-hulman.edu%2F~moloney%2FPh425%2F0143-0807_33_6_1625JumpingRing.pdf&usg=AOvVaw0Es1nAqRXBnnNSkRR-xlDw
I don't get the point of the last paragraph of section 2.
It seems the author lobbies for the short rod and then the long rod.
Which is it?
Mikek
George Herold
May 28, 2018, 1:22:45 PM5/28/18
to
pretty much coupled already.
George H.
>
>
> .... Phil
bitrex
May 28, 2018, 2:04:13 PM5/28/18
to
On 05/27/2018 01:55 PM, Cursitor Doom wrote:
> On Sun, 27 May 2018 10:08:48 -0700, George Herold wrote:
>
>> I say ignore the nay-sayers and give it a try. AC is dangerous so use
>> caution
>
> Yeah, or use DC. DC by contrast is totally harmless as we all know. ;->
>
>
>
One could design it systematically using math e.g.:
> On Sun, 27 May 2018 10:08:48 -0700, George Herold wrote:
>
>> I say ignore the nay-sayers and give it a try. AC is dangerous so use
>> caution
>
> Yeah, or use DC. DC by contrast is totally harmless as we all know. ;->
>
>
>
<http://www.bigel-labs.de/3.Physik/Thomson/web>
But oh no look at all them scary squiggles and vectors
Phil Allison
May 28, 2018, 11:20:56 PM5/28/18
to
amdx wrote:
Data: dia: 1.1 inches, turns: 220, length: 0.62 inches, depth: 0.044
Select "Inches" and "Multi-layer, multi-row coil".
You should get 1.26mH.
> Second, with the coil back in the gap and a 50% increase of
> inductance, I'd say inductance increases with a core inserted.
** No kidding ??
> That's why I suggested she measure it.
** Which cannot allow for the effect of saturation on permeability.
> My experience is with Ferrite rods, and I see about a 6 to 1
> increase in the inductance of a coil when the rod is inserted.
** Iron would usually produce even more.
.... Phil
>
> Phil Allison wrote:
>
>
>>
>
> >
> > ** FYI: recently I disassembled a 6 inch loudspeaker on the bench. I removed the cone and voice coil from the magnet assembly. The VC was 28mm in dia, had four layers and measured 6.7 ohms. Next I measured it's inductance and found it to be a tad over 1mH.
> >
> > So I popped it back in the magnet gap and found the inductance had increased by no more than 50%, depending on the test frequency.
> >
> > What can you conclude from this?
> >
>
>
> Phil Allison wrote:
>
>
>>
>
> >
> > ** FYI: recently I disassembled a 6 inch loudspeaker on the bench. I removed the cone and voice coil from the magnet assembly. The VC was 28mm in dia, had four layers and measured 6.7 ohms. Next I measured it's inductance and found it to be a tad over 1mH.
> >
> > So I popped it back in the magnet gap and found the inductance had increased by no more than 50%, depending on the test frequency.
> >
> > What can you conclude from this?
> >
>
>
> First, I'm surprised that a voice coil has an inductance near
> 1 milliHenry.
>
** http://www.66pacific.com/calculators/coil-inductance-calculator.aspx
> 1 milliHenry.
>
Data: dia: 1.1 inches, turns: 220, length: 0.62 inches, depth: 0.044
Select "Inches" and "Multi-layer, multi-row coil".
You should get 1.26mH.
> Second, with the coil back in the gap and a 50% increase of
> inductance, I'd say inductance increases with a core inserted.
> That's why I suggested she measure it.
> My experience is with Ferrite rods, and I see about a 6 to 1
> increase in the inductance of a coil when the rod is inserted.
.... Phil
amdx
May 30, 2018, 2:02:12 PM5/30/18
to
Sarah, Are you still looking at this project?
Mikek
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