I made a thing. It's a small part of a larger thing - updated

 Working on My Last Tesla Coil™ (AKA The Heirloom Coil) again, slowly.  One of many fiddly little things which need to be done on it is the connections to the primary coil.  Tesla coil enthusiasts have come up with half a hundred ways to make those connections, and nearly all of them suck. 

 I already went to extraordinary lengths to make it easier to bring good, short connections to the primary, which would not stick up above the primary (thus providing fewer targets for secondary strikes).  I've never seen any other coil builder do this, so naturally I've got to be speshul...

 So for some months I have been pondering some sort of connector / clip / interface gizmo which:

• could be easily installed in any of the radial slots
• provides a solid but easily changed connection to the primary from below
• provides a solid connection to the tank circuit cable and takes the weight of same off the primary conductor itself

I now have a conceptual design, I'm ordering materials - mostly phenolic rod and tube - to make the plunger assembly and the support, uh, thingummy / puck / module / unit / doohickey, which can be seen in sketch at the top of this image:

The wide part will sit on top of the deck to support the weight of the cable, the narrower part below that rides in the slot as a guide and mechanical support for the plunger. The hole through the center will actually be much larger than the one shown on the sketch, as originally I was thinking the plunger would be a brass bolt, but I have made it much larger.

 The hardware in the center of the photo is the prototype clip I made, which will go on the end of the plunger, and makes the connection to the copper ribbon of the primary coil.  I'm quite proud of that little thing.  It's nothing more than a .75" wide piece of copper strip, formed to fit in and around one of those little black steel "bull dog" paper clips, like this one:

 The spring steel of the binder clip maintains firm clamping pressure while the copper maintains a nice low-impedance path for the high RF circulating currents.

 Making that little bastard took nearly two hours, and I need two of them.  I suspect I won't need more than an hour to do the second one, now that I know how to do it.  The clips will be soldered to the ends of brass plungers made of .75" tubing, which in turn will slide inside phenolic tubes having closed ends with only a slot in the top, allowing the insulating tube to be fitted over the primary winding, like this:

 This somewhat over-engineered design is intended to cut down on corona and arcing between the primary connectors and adjacent windings.  I've never seen any other coil builder do this, so naturally I've got to be speshul... 

(wait, where have I heard that before?)

 I'm hoping to give this coil to a friend and brother, if he wants it. (he doesn't know that yet, and I haven't asked, and until just recently, he would have had no place to store or operate it - but he just moved into a bigger place with loads of room).  But he loves Tesla coils, he loves this kind of craftsmanship and attention to detail, and I suspect when he sees the finished primary taps he will lose his mind and that makes me happy.  I like it when grown men giggle.

 The thing is... I've built literally dozens of Tesla coils, ranging from a minimalist thing made with two transistors, two resistors, and a flyback from a TV all the way up to twelve kilowatt monsters that made arcs ten feet long.  When I decided to get out of the coiling hobby, I told myself I would build one more "really nice one" (just very general thinking at that point) either for myself, or if I needed the dough, it had to be something nice enough, and reliable enough, to sell for good money.

 So this thing is supposed to be one of a kind - something special.  I don't call it "museum quality" because what "museum quality" really means is that something rugged enough to stand up to being handled and operated either by the public or by unpaid volunteers, and built to last - but that does not mean it is the best of its breed.

 I mean for this coil to be as good as it can get without going to a solid state modern design - I'm a romantic at heart and I like spark gaps, although the consequence is that this coil isn't as efficient, and it will never sing music. 

 Call me a purist or a snob, but I don't really need my Tesla coil to make music.  They make terrible  loudspeakers anyhow, and I'm a music and hi-fi lover too.  Lots of big, long arcs and throat-searing quantities of ozone are music enough to this old-fashioned mad scientist's ears.

Tesla coil completion & "first light" tests

During the last week, I finished 'My Last Tesla Coil', at least insofar as it can be operated and is not an ugly mess to wire up. I was moved to push hard and get it working before Saturday March 23 (six days from today) which is the scheduled date for two grand opening parties for two businesses run by friends of mine.

The owner of The Concoctory wants the coil to be present and running as an attention-getter near the store.

Down the street and around the corner is a great little café called Cafe Crescendo, who are also opening that day. I gather that between them, they are trying to get the other local businesses to join in a sort of block party to draw attention further south to all of the existing and new businesses which are opening in that (newly renovated) south Broadway neighborhood.

Clever, fun, smart people are behind both operations and I hope I can add some sizzle and excitement to their opening day.

Yesterday, I set up the coil in the parking lot of Denhac, Denver's very own local hackerspace, and fired it up. After several extra trips to various places for forgotten parts and to put gas in the generator, and then perhaps fifteen minutes of the usual first-time tuning of the primary tap, adjusting the safety gaps in the power panel, and adjusting the main spark gap (an air-blast or "sucker" gap, the first of at least three gaps to be built for this coil) I obtained some reasonable results; approximately 36" streamers from the toroid.

I was expecting and hoping for closer to 60" streamers, however two problems rapidly became apparent during yesterday's tests:

1) the alleged "3,000 watt" generator (the only one readily available at no cost to me) is either failing to deliver its full rated power; or perhaps it is getting some RFI or spikes from the coil, causing its regulator to reduce the RPM; or -- and this seems the most likely cause to me -- the reactive load is causing a low power factor, resulting in more current being drawn from the generator than necessary and less "real power" being delivered to the load.

2) the spark gap was not quenching reliably (or at all). I don't have E/H field antennas for an oscilloscope which would confirm that theory, but I have enough experience with Tesla coils that I know a badly operating spark gap when I see and hear one. This gap (described here) uses an air blast to encourage the arc to extinguish (quenching the primary circuit) immediately after it has established. This is the desired "opening switch" operation of a spark gap, and it is much harder to achieve than the initial "closing switch" operation which precedes it in each firing cycle.

[aside: "opening switch" is a term of pulsed power jargon which refers
to switches -- there are a variety of methods -- which are designed to

interrupt current flowing in a circuit as quickly as possible. Opening

switches are frequently used to transfer energy between stages in a
pulsed power system.

A brief pulse of current is made to flow from a charged energy store
having a relatively long time constant into a following stage having a
shorter time constant, by way of passing electric current through an
already-closed opening switch. When most of the energy has been
transferred into the next stage, the switch is opened, causing the current
to cease very abruptly. This "traps"the transferred energy in the next
stage, whether the energy is being storedin an electric field (capacitance)
or a magnetic field (inductance).

When the energy is again transferred out of this second, "faster" stage
into either another power amplification stage or the load, the smaller
reactance of that stage causes the pulse to be delivered in a shorter time.
Because the same amount of energy is now being transferred in a shorter
period of time, the peak power increases proportionately, obeying the laws
of conservation of energy.]

While I have experimented with air blast gaps in the past, this gap was my first experience with the "sucker" design, which pulls air into holes in the electrodes, creating an axial shearing flow across the faces of the gap. While I was tuning up the coil, I noticed that the gap operation was not being affected much by the amount of air flow.

The gap did not work well at the original electrode spacing. With a conventional gap, if you want to increase the voltage at which the gap fires, you open the gap spacing. In a sucker gap, once the gap spacing exceeds the cross sectional area of the gas ports in the electrodes, the air speed across the faces drops dramatically, which spoils the quenching action.

The solution would seem to be opening the holes in the electrodes a bit (which I did after yesterday's test run) and reducing the gap distance, relying on the air flow to quench the gap rather than a long arc distance, which merely increases resistance in the gap and thus wastes power badly.

Some finessing may be required on one or both electrode faces as well.

The coil tuned up (the system resonates around 105 KHz) at 9 turns on the primary. I was shooting for 10 turns and there are 14 turns available, so that was agreeable. It would not hurt to have a slightly lower capacitance in the primary tank capacitor, which would allow (require) a few more turns on the primary. Counter-intuitively (because turns ratio in a Tesla coil doesn't matter as much as one might expect) increasing inductance in the primary tank circuit acts to reduce the peak current through the gap. Because gap losses increase as the square of the current, a small reduction in primary circulating current results in a large reduction in lost power. This improvement in efficiency completely swamps the small change in output which might otherwise result from reducing turns ratio.

So, before next weekend, I've got to find a slightly beefier generator. It's probably that some PFC capacitors on the line side of the HV transformer will reduce the amount of current being drawn from the 120V supply, but that's unlikely to happen in the next six days.

I also need a better-working spark gap. I have already modified the existing spark gap, but it will take a little experimentation before I can confirm whether the changes make enough of a difference.

It might actually be possible to build a Richard Quick -style multi-gap before next weekend, especially since I started work on one over a year ago; I have all the electrodes fabricated (but not yet drilled) and I probably have a suitable muffin fan in stock...

MLTC progress

I completed the HV section of the power cabinet for 'My Last Tesla Coil' last night. This morning I powered up the whole cabinet and verified that:

• no flashovers or evident leaks, no visible or audible corona at full volts

• full volts at both HV connector ports - no corona or leakage from HV rear panel connectors

• no breakdown problems with the RG-213 cable I'm using for HV leads between the power cabinet
and the coil

• the Terry Fritz filter section _appears_ be okay

In short, I wasn't really expecting everything to work fine the first time. There is no front panel on the power cabinet yet, so there is no way to control power to the HV transformer, but the coil is a LOT closer to First Light and tune-up testing than ever before.

There is an event in Denver at which this coil is wanted for a Grand Opening near the end of March. We'll see.

Tesla coil and "why so many projects?" also, "why don't you ever finish anything?"

1. Tesla coil
I am making headway on the Tesla coil, and have redoubled my efforts (in between trying to do real work for real money, about which more down below) because a friend is opening a very cool new art-nerd / techie arts & crafts type store in Denver, and very much wants to have an impressive Tesla coil at her grand opening in March, which is, um, roughly a month away. Oi. We'll see. I'm trying.

2. "Why do you have so many (unfinished) projects?"
I suffer from ADD - Attention Deficit Disorder, and have my entire life. It's been marginally worse since I had a protracted fever a few years ago. I now take Ritalin, and it has changed -- or I should say 'is changing' -- my life. Sadly, that's 45 years too late, but better late than never.

In the past, whenever I hit a snag in a project that I couldn't get around, I tended to find other things to occupy my hands while thinking about how I could get back to work on the other project, with the least added effort and expense. Quite often it's lack of an expensive part of material that holds me up. Whatever the reason that one, or two, or three projects are on hold, I need something to occupy my time.

Another reason for having multiple projects is simply that some of them are inter-related. I need a good working vacuum system (among other things) for several other, larger, experiments I'd like to do. The micro-Marx pulser is needed to trigger the experimental gas switch I've completed, but have not yet tested.

And while I have had a life-long tendency to take too long to finish projects, I am in fact finishing projects now that I am on the Ritalin. I have more perseverance and much more focus than ever I ever enjoyed before.

Unfortunately, having my job yanked out from under me due to a reorganization left me unable to pay for materials and parts. I also need to spend time looking for work AND trying to identify and reach my own customers for work that I can do with my own resources.

And finally, health problems of one sort or another continue to interfere with my ability to get things done.

All that said, more progress has been made on my various "mad science" / research / hobby projects in the last year than in the previous ten.

I've also been posting videos occasionally to my YouTube channel, which is HERE.

short update on Tesla coil

Haven't had much time or money for my science projects lately, but I am making plodding progress on the Tesla coil. The only remaining work is on the power panel (which, unusually, includes the HV transformer and its protection devices) and the enclosure for the primary cap.

Two additional spark gap designs are planned, but only one of the three has been finished.

"First Light" (ie, the first power-on tests and tuning) should occur some time before Christmas.

Here's a short video showing some parts I finished recently:

http://www.youtube.com/watch?v=MNoBmwaZFaQ

Tesla coil progress

Please see crummy phonecam pics below of nearly finished "MMC" primary tank capacitor (phenolic slab, to be set into rabbeted maple cabinet soon), an example low-corona primary tap (later to be replaced with a fancier brass blivet) main control cabinet with HV transformer and resonance spoiling resistors, and the beginnings of the front panel.