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First Coil Build (w/pictures and a question)

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Charles73

Tue Jun 26 2018, 01:12AM

Registered Member #61343 Joined: Mon Dec 05 2016, 05:38AM
Location:
Posts: 18

Hey everyone,

My first TC build is coming along nicely. I still need to mount the Spark Gap, fabricate Primary support combs, and a few other odds and ends (including wiring the thing), but I'm really happy with it so far. It's finally looking like a Tesla Coil instead of a pile of parts, which has me really excited.

Here it is so far. Currently, it has a 12x3 toroid, but I'm saving up for an 18x4.5.

QSMR7kF

Spark Gap (not yet installed):

ZVNKyQ0

Beginnings of the Terry Filter beside the 15/60 Franceformer:

KgoBsIh

Cap Bank beside area for Spark Gap:

B2nDWwy

One thing I'm concerned about is the size of the capacitor bank. I was told that ten [942C20P15K-F] will work, but I see many builders putting 40 (or more) in there. Thus, I have reserved space for three more stacks of ten, just in case. *The brown standoff insulators will actually be going on 3" HDPE risers to accommodate that and the blower used for the spark gap.

The other question I have is about grounding. I know there have been many debates on this, so I want to make sure I have it all straight. Here's a sketch of one grounding scheme I have considered:

Sb2xODi

In this sketch, I am considering running two independent ground rods - one for RF Ground and one for NST and Terry Filter ground. Possibly leaving the EMI Filter on Mains ground. Or I could eliminate the second ground and bond the NST/Terry Filter/EMI Filter to mains ground. What are the opinions on this?

Doodlebug

Tue Jun 26 2018, 12:18PM

Registered Member #62084 Joined: Wed Jan 10 2018, 09:04AM
Location: Midlands UK
Posts: 12

What a beautiful looking coil. Antique looking and I love the mahogany looking bases and legs.

Charles73

Wed Jun 27 2018, 02:18AM

Registered Member #61343 Joined: Mon Dec 05 2016, 05:38AM
Location:
Posts: 18

Thank you so much! I'm really proud of this.

Charles73

Tue Jul 03 2018, 01:51AM

Registered Member #61343 Joined: Mon Dec 05 2016, 05:38AM
Location:
Posts: 18

Edited

hen918

Tue Jul 03 2018, 02:32AM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Charles73 wrote ...

Wow, either this forum is dead or no one cares about the beginners anymore. Either way, what a shame... This place used to be so interactive.

Not sure when you are referring to, but when there are no comments, usually you are on the right track.

Charles73

Tue Jul 03 2018, 03:29AM

Registered Member #61343 Joined: Mon Dec 05 2016, 05:38AM
Location:
Posts: 18

hen918 wrote ...

Not sure when you are referring to, but when there are no comments, usually you are on the right track.

That's encouraging - thank you. I guess no news is good news.

Dr. Slack

Tue Jul 03 2018, 08:57AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Grounding usually provokes a debate, as few people really understand it, but instead go by rules of thumb. You have to be aware of where current 'wants' to flow, at these frequencies, at these voltages, before deciding where to place the conductors. Grounding has to achieve several aims, including mains safety, and freedom from EMI, which emphasise different aspects.

At mains frequencies and impedance levels, current flows along wires, taking the path of least resistance, you can ignore capacitance. At Tesla frequencies and impedance levels, current flows along the path of least impedance, through sub-pF capacitances, setting up 10s of volts, 100s, or even multiple kV across long pieces of wire that have significant inductance (like a long wire to an earth spike in the ground).

The three scenarios that coils tend to get used in (from easiest to worst) are ...
1) In an open field, with or without a conductive counterpoise beneath the coil
2) In a garage or apartment, with a conductive counterpoise beneath the coil
3) In a garage or apartment, without a conductive counterpoise beneath the coil.

What is the loop that secondary current flows in? It starts at the secondary bottom terminal, through the topload, and then through the capacitance from topload to anything conductive near the topload. That's the ground, the counterpoise, wiring in the walls (earth, live and neutral conductors), drywall (at these impedance levels, oh yes). From all those grounds, it has to get back to the secondary bottom terminal. If there's a long wire in the way of that return, it will develop whatever voltage across it that it needs to to flow through it. If that voltage isn't where you want it, like between your mains earth and live conductors, then you'll inject EMI into your mains wiring, and interfere with (at best) or fry (at worst) anything connected to it.

As all the return current has to return to the secondary bottom terminal, put a common terminal at or very near that point, and we nominate this to be 'ground'. Connect that to your counterpoise if you're using one. That's where you ground your safety gaps. If you're in a field, that's where you attach your ground spike, on a short wire. That's where your mains filter grounds.

In a field is the easiest scenario to control. If you're in an apartment, there's always wiring in the walls and ceilings you can't control. Plug an RF filter into each socket, this shorts the L, N, and E wires together at RF frequencies. Take the ground of that filter to your nominated coil ground. This should minimise RF getting into the mains.

Wwhat the Tesla coil 'thinks of' as its ground is not the same as a mains ground. The RF ground is the point under the secondary, that connects to all those 'groundish' conductors, whatever words you use to try to pretend that mains ground or an earth spike is in fact the RF 'ground'. For mains safety, blowing fuses and all that, the mains ground and ground spikes are what's important. Connect the two grounds together at the TC's nominated RF ground point. The mains won't care about any long wires, the RF will.

Graham Armitage

Mon Jul 16 2018, 08:36PM

Registered Member #6038 Joined: Mon Aug 06 2012, 11:31AM
Location: Salado, TX
Posts: 248

Great looking first coil. Better than my first one :)

You asked about the capacitor bank. Not sure what size capacitance it is, but remember to impedance match the secondary of the NST to the MMC bank at 50/60Hz. That is so you get the maximum power transfer from the NST to the primary circuit. Once you have that capacitance value, use this calculator to get the right configuration -

Now that you have the right capacitance value, you can determine the correct primary winding to match resonant frequency with the secondary system.

Also noticed that the primary coil is sitting quite low below the bottom of the primary. Is it possible to raise it in line with the bottom as you may get better coupling. Check JavaTC for that. Look forward to seeing it running.

Gordon

Tue Jul 17 2018, 03:07PM

Registered Member #61983 Joined: Fri Dec 08 2017, 12:07AM
Location:
Posts: 22

Wow great job it looks amazing.
I agree with Graham, use javatc it will help figure out/get close to the capacitance that would be ideal and your MMC. As far as grounding from my testing having a dedicated ground rod that's close to the coil seemed to help with the performance, don't know if it was because the house had a poor ground or just a faster route to ground, even though I believe it was because it was a shorter distance that helped, but anyway I have always tied my Terry filter, nst, strike rail, and secondary to the same ground. Plus using the dedicated ground takes away the thought or worry of it effecting anything you have plugged in your house.

Charles73

Thu Jul 26 2018, 04:49AM

Registered Member #61343 Joined: Mon Dec 05 2016, 05:38AM
Location:
Posts: 18

Hey guys, thank you so much for the compliments and input! One thing I did want to clarify is that the primary coil was not in its final position for those photos. I will post some pics of its current progress below :). I'm still waiting on my 18" toroid. I'll probably end up using the 12" "stand-in" toroid as a ground/strike pole. I'm also going to be adding 30 capacitors to the MMC. I'll essentially add three layers to what I already have: 40 total; 2 strings of 20.

G8R7PWX

MMC/Spark Gap
Mxb74H1

NST/Terry Filter (all yet-to-be-wired)
BdprKP1

Primary Coil/Strike Rail
ApInSeu

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