While successfully transmuting lead into gold with a small Solid State Tesla Coil (SSTC), it became apparent that a much larger Tesla Coil (TC) would be necessary to make a dent in the national debt. The new coil would need to have more output (500-700kV), the ability to run for long periods of time, and be relatively immune to mis-tuning (since the transmutation process causes considerable field distortions). After some consideration, a classic Spark-Gap Tesla Coil (SGTC) would fill the bill.
After absorbing the 20 years of Tesla Coil Builders Association Newsletters, which are now being hosted at TeslaUniverse, along with The Ultimate Design Guide to Tesla Coils, it became apparent that an eclectic mix of electro-mechanical components (and some fair amount of engineering) were going to be needed.
Desiring to get a larger TC up and running ASAP (since time IS money), I scoured the Internet (and Ebay, in particular) for parts. After firing off a list of questions to Alan Majernick at TeslaStuff about his “Fast Start” packages (see his site for what’s included), he responded with a set of plans (gratis), and thoughtful answers. Alan disclosed that he had sold a large number of these packages with NO failures, and at just under $1000, the price sure seemed right. Alan had all the parts in-stock, and I could take delivery within a week. A week after the order was placed, the parts arrived.
Now, just to set the proper expectation, Alan’s fast-start packages are not kits. They contain the hard-to-find, long lead-time, and more esoteric parts. General construction tools and materials are necessary to complete the coil. At the end of this post is a list of materials and costs for additional required bits & pieces. What follows is the 12-day “build-log” of the coil. Acquiring a copy of Alan’s plans from his store, and following along will help you get the most out of this build-log experience. If you want a spoiler for the (almost) completed coil, look here.
Day 1 – Lay of the land: After unboxing and checking the parts for damage, and buying wood & PVC parts for the base:
NOTE: The two 30ma 12kV transformers in the background are ones I already had. This blog entry covers their demise.
After testing the fan and Variac, I bought PVC tubing and end-caps for the base (stand) from a local hardware store, and ordered a sheet of 3/8″ XX phenolic from Amazon to mount the fan and spark-gap on (it should have been grade XXX, but more on that, later). I also ordered more ceramic stand-offs from Ebay to mount the second tier of (MMC) capacitors with. Finally, I purchased a polypropylene cutting board from a local grocery store that I later butchered to fabricate the primary coil supports.
Day 2 – Cutting up: Since I started with a plank that was cut into 18″ squares, and the plans call for circular discs, I cut, sanded, routed (and sanded again) the squares to shape. If I had “do-overs”, I would have left them square (more mounting area for assemblies):
I then purchased stain, polyurethane, brushes, sandpaper, etc. to finish the platform discs. Three of these discs are joined at roughly 1-foot intervals to create the base (with casters on the bottom disc). The discs were then fine sanded in prep for finishing. I bought more stand-offs from a local shop and electrical connectors for the MMC bank from a hardware store.
Day 3 – Whew, busy, busy: I applied the first coat of stain to the discs, and sanded the PVC endcaps flat on top so they could be bolted to the discs. The rest of the endcaps were sanded to remove gloss in preparation for painting. Screw holes were drilled in the end-caps (using the nubs on the inside for centering). The holes allowed me to lift & move the end-caps during painting, using a piece of 12-gage solid wire. The end-caps were cleaned with lacquer-thinner to remove markings, fingerprints, etc, wiped down with isopropyl, then painted (two coats):
The second coat of stain, and two coats of polyurethane were applied to the discs:
Lengths of PVC pipe were cut to 1-foot lengths, sanded, cleaned, and painted. They are the supports between the discs. After painting, the tubing wouldn’t fit nicely into the end-caps since they had an increased diameter (doh). The last 1.25″ of each end of each tube needed to be sanded down to fit easily into the PVC caps.
Day 4 – Base station complete: The painted plastic parts were coated with Rust-oleum crystal clear enamel, and the base construction completed with casters:
A trip to the hardware store yielded the Lexan and ten feet of copper tubing to fabricate the strike bar.
Day 5 – Zappy, Zappy: The 32-capacitor MMC array was fabricated:
The bleeder resistors are mounted below each capacitor, underneath the plastic. After this, the primary coil construction was started by drilling the large Lexan circle and mounting the large stand-offs.
Day 6 – Primary drive: The polypropylene cutting board purchased earlier was sliced-up and prepared for mounting the primary coil (copper tubing). The secondary end-caps and mounting hardware were then finished up:
The cut-outs for the primary coil are on 5/8″ centers. The plans detail how to create the mounts. The holes on the ends of the polypropylene are for mounting the strike-bar. At this point, I started gathering parts for the coil control console (box, switches, AC connectors, cable, etc) on a trip to the local surplus store (OEM parts).
Day 7 – Great progress: I wound the primary coil with some help from a friend (Jeff). 4-hands are VERY useful for this part. A hot-glue gun was used to secure a few “problem” mount points:
The Lexan strike-guard mounts were then cut, drilled, sanded, and installed for the strike-guard. This component is critical, as it keeps stray arcs from hitting and damaging the secondary (and other parts). Notice that the ends of the strike-guard tubing are joined with a small piece of flexible plastic tubing. This is important to keep the guard from altering the resonant frequency of the primary coil:
The secondary was then mounted to the base, connectors soldered to the primary coil & strike guard, and the toroid mounted:
Lastly, I started laying out the components for the Terry Filter. This filter is named after Terry Fritz, the designer, and well regarded Tesla Coil researcher. Some of his papers can be found here.
Day 8 – Pushing hard: I cut the plexiglass for the Terry Filter, finished the electronics, and mounted the components:
The safety gaps on the Terry filter were set just far enough apart so that the high-voltage from the neon sign transformers (NST) didn’t arc at the highest AC setting of the Variac. The transformers were then painted and sealed:
Brian then helped me with mounting the fan (arc quencher) and spark-gap on the phenolic board (as-well-as making another trip to the hardware store for nylon stand-offs):
Before firing up the coil, the primary needed to be approximately tuned by connecting one side of the MMC bank to a position on the primary coil. Alan’s plans specify somewhere around the 9th or 10th turn. A more accurate placement was determined by first measuring the resonant frequency of the secondary, then setting the tap on the primary for the same frequency.
Day 9 – First fire: We hurriedly finished up the spark-gap and fan board. In the rush, I neglected to cover the spark-gap bolts (bottom-side of the phenolic) with corona-dope as Alan outlines. The high-voltage wire was cut, tinned, and connected to all the components. A plexi-glass base was added to the MMC array for stability. An (RF) ground rod was driven into the earth, the TC carted outside, and initial (test) wiring of the coil completed. The ubiquitous aluminium ladder was then erected as a strike target:
The first-fire was performed at dusk, and the coil ran for about a second before the spark-gap shorted out. There was flash-over between the bolts on the bottom of the phenolic. So the carbonized trace was “dremmeled” out, and slathered with corona-dope.
Day 10 – Flash-fry and victory: The coil was fired-up, only to have arcing on the TOP of the phenolic board from under the insulators & stand-offs. My thoughts are that grade XXX phenolic might have prevented this:
Once again, the carbon path was cut-out with a dremmel tool, and covered with corona-dope. When the coil was fired-up again, the arc just ate through the dope. I replaced one of the metal bolts with a nylon bolt, and was able to get a successful run for a couple of minutes before arcing was noticed between the fan and the other spark-gap mounting bolt (still metal) at 6+ inches. A quick trip was made to the hardware store for another nylon bolt, and there has been no problem since. We shot a few pictures, and shut it down for the night (10PM, and it’s very noisy).
Day 11 – Safety first: Now that the coil was working, the final wiring needed to be completed. The control box parts:
There has been some controversy about whether to install AC line filters “backwards” to keep interference from getting “back” into the power mains. Alan has had no problems with any of his systems when installing them in the proper “forward” direction. After a bit of research, I am in agreement. The finished control box has Variac connections on the left, Coil connection on the right, and AC input/fusing on the back.
Once this was wrapped-up, I wrote a safety/operations manual for the coil.
Day 12 – In-to production: The final wiring was neatly run on the coil, and cables from the coil to the control box completed. After this, the coil was transported to the (secret) lab, where it has been creating copious amounts of shiny precious metals!
Ok, that last part about the precious metals, I just made up.
A costing of materials above and beyond the “Fast Start” package ran something like:
Remote Control power/control panel parts: $50
Wood: $25.00 (5’x18″ board)
Wheels: 2 locking, 2 not: $25.00
Paint, stain, brushes, sandpaper, polyurethane: $45.00
Pipe caps & PVC pipe: $20.00
Rust-Oleum crystal clear enamel: $4.00
Primary Coil mounting hardware:
Polypropylene cutting board (primary coil mounts): $10.00
Strike guard plastic and nylon (nuts & bolts) hardware: $7.00
Strike guard 1/4″ copper tubing (10′): $9.00
Strike guard copper lugs: $3.00
Plastic tubing to slip over strike guard ends: $3.00 (lots left over)
Phenolic Board for spark gap(s) & fan mounting: $35.00
Terminal strip for fan AC wiring: $2.00
(Threaded) ceramic stand-off’s for MMC (4-base, 3-top tier): $24.00
Misc Nylon nuts, bolts, screws, spacers: $30.00
Hot glue gun & glue for mounting primary coil
Polypropylene and stand-offs for mounting Terry Filter (& resistors)
Misc hookup wire
Grounding strap: $3
Grounding rod: $12
Special thanks to Jeff & Brian for their help on this project.
I would like to mention that Alan at TeslaStuff has been very supportive and responded quickly to my emails during the purchase/build process. Thanks Alan, for helping make this coil a reality!
Above all, be safe. This project generates potentially lethal voltages. If you have never worked with high voltage before, find someone who has, to help you. Never operate a Tesla Coil around someone who has a pacemaker or other biological implant. Never operate a Tesla Coil when drowsy or (self) medicated. All warranties void where prohibited, YMMV. Keep all pets at a safe distance. Never put food in the toroid to attract squirrels. Do not put a Tesla Coil near a gate or fence to keep the bear out.
This guide has lots of other useful information.