Making a Thomson Coil?

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 f***ed with on a whim, I would consider carefully before continuing.

You'd essentialy be building a toy from plans. It wouldn't teach you 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

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 colleg e's graduation cap (For fun and to be different). Granted, this isn't spect acular, like building a radio from spare parts without a kit. But it's at l east something. 2) This is just to demonstrate a physical principle, and from an electronic s 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 inducta nce, I have my textbook for that. It's meant to be a toy, and is just for f un. 3) I've already run the numbers, and "did the maths". I'm just asking how t o optimize the variables. For instance, I'm uncertain what material would h ave the highest inductance for the core, which appears to be the limiting f actor.

"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.

Well, good luck and God bless.

Additionally in general when folks say they've "done the math" it helps 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.

And when asking for help at least show what work you've done. Lots of 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.

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 f*ck it up and sell it at a loss.]

Cheers

--
Clive

GE acquired and destroyed several of my VME competitors. Lov'em.

--

John Larkin   Highland Technology, Inc   trk 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com

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 = 12

0 / (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 inductan ce 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 in ductor core. I need to know if there is a better alternative that I can rea listically acquire.

d

s

d soldering, including making time-sequence varying LEDs for my 2 year coll ege's graduation cap (For fun and to be different). Granted, this isn't spe ctacular, like building a radio from spare parts without a kit. But it's at least something.

ics perspective is downright trivial. The circuit diagram would only consis t of a 120V AC source and an inductor. I'm not looking to learn about induc tance, I have my textbook for that. It's meant to be a toy, and is just for fun.

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.

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 th e 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 wan t to show you how to kill yourself.

NT

s, tell us what you've figured out & not. Not knowing what to use to maximi se 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 f ar I'm not convinced you know what the issues are, and I don't especially w ant to show you how to kill yourself.

I should state that I know how to maximize inductance. Just get a ferromagn etic object with a higher magnetic permeability and get more of it between your N loops of wire.

The set of potential problems is limited by type. The inductor itself is no t 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 c ircuit, 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

588/95654 thus the inductor always has a way to keep the current constant w ithout generating high voltages until the magnetic field collapses.

Then there are the usual issues with strong electromagnets. They will induc e strong oscillating magnetic fields in the region, which might effect any electronic devices in the area, including pacemakers, and the core itself i s a solenoid, which generates a large nearly uniform magnetic field in the core, and can suck up anything ferromagnetic, including rings, possibly bre aking the fingers of the wearer.

Then, there are the typical electronics hazards, such as touching mains vol tage, fire, etc.

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?

You might need to consider saturation. Have you sourced the material you intend to used? Perhaps this is an ideal time to give us turns/SWG/dia and material specs.

Up to now I thought you might understand the difference between AC and 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?

The only ferrous item I might have worn is a watch. A ring is more likely to burn the skin than induce immense forces breaking a finger.

Of course.

--
Mike Perkins 
Video Solutions Ltd 
www.videosolutions.ltd.uk

aps, tell us what you've figured out & not. Not knowing what to use to maxi mise inductance is very basic, yet you want to put a big fat inductor acros s 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.

gnetic object with a higher magnetic permeability and get more of it betwee n your N loops of wire.

not necessarily dangerous. It's what happens when you try to open the circu it after the inductor is charged that can cause a dangerous situation. If y ou 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 th e current constant, generating high voltages.

n the reverse direction similar to

21588/95654 thus the inductor always has a way to keep the current constant without generating high voltages until the magnetic field collapses.

uce strong oscillating magnetic fields in the region, which might effect an y electronic devices in the area, including pacemakers, and the core itself is a solenoid, which generates a large nearly uniform magnetic field in th e core, and can suck up anything ferromagnetic, including rings, possibly b reaking the fingers of the wearer.

oltage, fire, etc.

OK it's good you're aware of the risks. The diode won't work though.

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 expe cted wire resistance is?

500' of 12AWG is 2.05mm dia = 3.14 square mm. 1mm2 is 22m? per m so 3.14 is 7m?/m 500' = 150m which gives 1.05?. 15A on 1.05? gives 15.75v & 236 watts of heat dissipation. It will soo n get HOT.

Really though, your project raises enough questions that you're unlikely to get answers anywhere.

NT

Yeah, sorry, I was looking at a bunch of DC inductor problems and somehow g ot the idea that I was using DC. If you get close to the inductor with a ri ng, it might burn you. If you get close to the opening to the core of the w ire spool, you very easily could encounter a large magnetic force. I've see n it happen before in my EM lab with a similar set up.

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.

gaps, tell us what you've figured out & not. Not knowing what to use to ma ximise inductance is very basic, yet you want to put a big fat inductor acr oss 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 especial ly want to show you how to kill yourself.

magnetic object with a higher magnetic permeability and get more of it betw een your N loops of wire.

s not necessarily dangerous. It's what happens when you try to open the cir cuit 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 t he circuit, I'm aware that the inductor will do whatever it has to to keep the current constant, generating high voltages.

in the reverse direction similar to

a/21588/95654 thus the inductor always has a way to keep the current consta nt without generating high voltages until the magnetic field collapses.

nduce strong oscillating magnetic fields in the region, which might effect any electronic devices in the area, including pacemakers, and the core itse lf 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.

voltage, fire, etc.

, and the resistance R will get mighty hot on 15A. Do you know what your ex pected wire resistance is?

oon get HOT.

to get answers anywhere.

Yeah, I said that was the max current, and that the limiting factor was the inductance. The original author of the template project I was looking at ( The one I linked in the original post) didn't say how long he was able to r un for. The higher the inductance, the lower the current will be, and the l ess energy dissipated as heat by I^2 R losses.

The actual r value I obtained from an online calculator (12AWG) was .079 oh ms, which would make the energy dissipated around 17W. Calculator:

able

GE has been bad news on both sides of the Atlantic for quite a while now. T he UK GEC was particularly bad news when it was run by Weinstock

He seems to have been a brilliant accountant, but when GEC took over an inn ovative 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.

ng Ohm's law V=IR, we'll try to calculate the inductance needed for typic al 120V sockets and at a maximum current of 15A. So, we solve for inductanc e and get L = V / (2(pi)*I*f), which when we insert the numbers is L =

120 / (2*(pi)*15*60) = .02H

a 3.81 cm diameter cylinder that is 1/3 of a meter high to obtain an induct ance of .02H to impede the N turns of wire around the core. I don't know ho w many turns of wire are on the 500ft wire spool of 12AWG wire.

You can work out how long an average turn would be (half-way between the in ner and outer diameter) or write the equation for the length of a turn and integrate over the same range.

inductor core. I need to know if there is a better alternative that I can r ealistically acquire.

If the steel welding wire is mild steel and tolerably magnetic it might add extra inductance - not a lot since the magnetic path runs up through the c oil and back down the outside of the coil and you have to integrate over th e whole length.

--
Bill Sloman, Sydney

aps, tell us what you've figured out & not. Not knowing what to use to maxi mise inductance is very basic, yet you want to put a big fat inductor acros s 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.

gnetic object with a higher magnetic permeability and get more of it betwee n your N loops of wire.

That's not carefully stated. If you state off with a coil of wire - essenti ally a torus - you have to wrap your high-permeability material right aroun d the torus to maximise the inductance.

With ferrites (which can be moulded, fired and ground) you use pairs of pot cores.

In general it is better idea to start off with a torus of the high permeabl ity material and wind your coil around that. There are ingenious machines f or doing that quickly - essentially a split wire holder which you put toget her 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.

--
Bill Sloman, Sydney

Ah yes, GEC.

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.