Well, unless I miss myguess, that time ofyear is comingagain.The time ofyear when it’s pos-

sible to let the real “mad scientist”in you out, and not worry about theneighbors having you committed.Atime when you can let your techni-cal skills place you where you reallybelong; not behind a computerscreen or over some smoky perfboard, but in the electrical wizard’srole!

This year is your time to cackle,throw back the curtains, and revealwild arcs of electricity surgingthrough your house!

Even though you find yourself ina burned lab coat, even though yourhair may be standing on end, andeven as you go wild with laughter,with two simple words with which

you CAN’T be blamed! Repeat afterme: “Happy Halloween!”

That’s right, it’s the perfectexcuse to build that wonderful gad-get you’ve always wanted to — aTesla Coil!

I warn you now, these coils aredangerous. Not so much becausethey produce large electrical arcs inopen air (that when properly han-dled are remarkably safe), butbecause these devices can be soexciting to build that they canbecome an OBSESSION.You maywell be at risk for continuing yourmad scientist activities beyond ...

Remember — using your TeslaCoil this Halloween will produceone other type of magic, one that ithas for more than 100 years ...

While the parents may jump outof their socks, the children will lightup with delight and interest!

Reprinted from September 1999 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 1

Outfitting Your“Mad” Scientist’s

Lair! Graphics byMatthew Roddy

bbyy WWaalltt NNoooonn

This Halloweenis your time to cackle,throw back thecurtains, andrreevveeaall wwiillddaarrccss of electricity surging throughyour house!

You and I can smile knowing thatwe may have just added some future“mad scientists” to our ranks!

The Tesla CoilThe coil featured in this article is a classic, and

a real performer for its size! In fact, though thesecondary coil stands at just 12” high and 3” indiameter, it will easily produce 70,000-volt sparksarcing 4” even with a LOW POWER input trans-former (such as an automotive coil or equivalent).

You can step the power up considerably witha larger input transformer and produce as much as250,000 volts! At these voltages, sparks are thick,brilliant, and noisy, and discharges of half a foot arepossible. Sparks of this order are suitable for terri-fying the staunchest of trick-or-treaters.

When operating, many special effects are pos-sible:The coil will light a florescent light bulb heldin your hand with no wires attached! It will driveplasma displays, and cause other florescent or tubelights in the room to flicker.

If you’re REALLY of the mad scientist variety,the arc can be taken to a metal object held in anoutstretched hand. (This coil is high frequency, andwill exhibit the “skin” effect in which the electricitycan travel over your skin without shocking you.However, you MUST read the safety tips for doingthis later in the article.)

Though you are free to build the coil “as is,”I’d like to briefly go over each component and giveyou some design philosophy. Significant increases inoutput and efficiency can be had with somethought on your part.And, that’s what these coilsare all about!

Important SourcesLater in the article, I’ll give some sources for

parts, and my web address where you can down-load free design software for altering the dimen-sions of your coil and even trying out your owndesigns on screen before building them!

How it WorksThere are only five basic components in sim-

ple Tesla coil design (see the schematic in Figure 1).These are: the line transformer, capacitor, sparkgap, primary, and secondary windings.

You’ll notice that in thedesign we’re using there arealso a pair of radio frequencychokes and a second spark gapfor safety. (The second sparkgap is not absolutely necessaryfor operation, in fact, many coildesigners leave it out.However, it can be importantfor coil longevity.The sec-ondary gap protects your linetransformer.)

Most of the componentsof the coil can be made byhand. I’ll give you a briefdescription of each part, whatit does in the circuit, and whatoptions are available.

The LineTransformer

The line transformerboosts the voltage from yourwall current to between 2,000and 10,000 volts depending onthe transformer you decide touse (2,000 volts is about aslow as you can go and stillhave a useful spark).Thingsdon’t really pick up with thiscoil until you get to around6,000 volts on your line trans-former.

Many Tesla builders feelthat the size of the secondarycoil and type of discharge ter-minal are the keys to a bigspark, but even with some ofthe interesting trade-offs you can make in design,you can’t escape the fact that you can’t get moreout than you put in, so, this is where you can makethe biggest difference.

A neon sign transformer rated at 9,000 voltsor better and around 30 milliamps is ideal. Neontransformers are nice because they can be dead-shorted without damage, though, transients in aTesla circuit can still harm them over time.Themore power you draw from your neon trans-former, the less efficient it becomes.This can costyou a little at the output side as well, and is whysome Tesla purists steer away from neon trans-formers.

People often use oil furnace ignition trans-

formers with similar ratings, and even automotivecoil type transformers (see details on this at theend of the article).

The automotive coil is nice because it’s cheapand the sparks are safe, yet still impressive andentertaining. I often operate my coil for extendedperiods of experimentation with an auto coil typeset-up. In a darkened room, the blue corona glowand subtle steamers of electricity are beautiful towatch. However — for special effects — yourcoil’s output will be modest if you use an auto coilas compared to a neon transformer.

New neon transformers are relatively expen-sive, however, by poking around the Internet andTesla groups (mentioned later), you can find somereal bargains. Big Tesla systems use distributiontransformers (as seen on your local telephonepole) which produce 17,000 volts or more, butyou’ll need a whole new design for that!

The Jacob’s Ladder!Before we go on, I should describe a quick

stunt with a neon transformer that could be“must-have” equipment for your Halloween’s lair.

Figure 2 shows a neon sign transformer.Connected to the transformer are two metal rodsangled close together at the base and then slantingapart. (I usually use welding rods.)

This is a classic “Jacob’s Ladder” in which aspark will form at the narrow point and rise with aloud crackle to the top and then repeat.

This is a simple, mesmerizing effect. Just makesure your transformer is grounded, and keep peo-ple clear of this somewhat dangerous spark. (Themetal rods can be placed inside a large plexy tubefor safety.)

The High Voltage CapacitorThe high voltage from the line transformer is

Reprinted from September 1999 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 2

needed to supply enough energy to the capacitorso that it can “kick” out pulses at a very highspeed (600 kHz is common) and not be depleted.The idea is that as a charge builds up in yourcapacitor, it eventually becomes large enough toarc across the spark gap.

For this coil, we’ll assemble a capacitor ratedat .0052 uF and at least 15,000 volts.

Commercial caps of this voltage are the best,but tend to be expensive. So, most builders createtheir own. See Figure 3A for a simple capacitorplan. (Figure 3B shows an exploded view.)

The capacitor is made by alternating fivesheets of .032” polystyrene and four sheets of 10”square metal. Note in the “top view” that eachmetal plate does not go all the way across thepolystyrene.

Copper or aluminum foil can be glued downand used for the plates. I personally use thin sheetsof aluminum such as those used to patch the roof.

To keep my capacitor together, I glue it andsandwich it between two pieces of wood mountedunder the coil.

Other configurations of this capacitor are pos-sible so that its size and dimensions can bechanged to fit your coil’s housing. Other home-made high voltage capacitors are also possibleusing everything from rolled plates in PVC and oilto beer bottles. Handy calculations for all thesecaps are provided in the free software.

The Spark GapThe spark gap acts as a high voltage switch

(Figure 4).When energy in the capacitor is suffi-ciently high, it arcs across the gap and suppliespower to the Tesla primary winding.This partiallydepletes the capacitor and thereby quenches itself,restarting the cycle.

The spark gap shown is the simplest, andworks well. It’s made from two bolts and tworounded screw-on caps. By threading the boltsback and forth, you can adjust the gap.The idealgap for this coil should be around one millimeter,however, changing the gap will get wildly differentresults and I encourage you to do so!

The spark gap is a key place where coil effi-ciency can be improved.The faster the spark isquenched after firing, the better the Tesla sec-ondary will oscillate! (A sloppy spark will cancelout some of the secondary coil’s output.)

To quench the spark, many experimentersapply a blast of air from a compressor across thegap to literally blow out the spark. Others use a“multi gap” spark gap by having several points thespark must leap to in crossing the gap(s). I haveheard of exotic spark gaps inside of vacuum cham-bers that increase efficiency by 50%!

I usually just use a gap as shown and it worksquite well. Due to the heat and damage that an arccan do to a steel bolt head over time, I often makea trip to the welding store and use Tungsten weld-ing rods instead of steel bolt heads.

The Primary CoilThe primary coil is just a few turns of heavy

gauge wire. I like RadioShack’s catalog #15-035.Since this wire is bare, you will be able to tune

your coil by sliding a wire along it until a point isfound where the coil fires most efficiently.

To get nice even circles, I first wrapped theheavy gauge wire around a cylinder, then removedit and threaded it through the PVC posts seen inthe photos.

In the photo, you’ll also notice I had 12 turnsof wire.This was simply for experimental purposesas I was playing with a wide variety of components.The coil was “tuned” with less than six windings,so I suggest you limit your primary to 6-½ or so

windings.The spacing between each windingwas approximately 2/16 of an inch.

The Secondary CoilIn my mind, this is where much of the

magic happens!Unlike a conventional transformer, a

Tesla coil’s output is not only related to theratio of turns in the primary and secondarywindings. In fact, the primary coil acts as atuned radio transmitter, and the secondarya tuned radio receiver.When the high fre-quency wave emanating from the primarystrikes the secondary — if they are proper-ly in tune — the secondary will begin tooscillate powerfully.

This has been described to be like theeffect of a child on a swing. If the child ispushed at just the right moment, the swingwill gain in amplitude. If pushed at thewrong time, however, the swing will bedeadened. (This is why quenching the gapand good tuning on the primary are soimportant.)

The secondary coil is simply a longwinding of wire (typically 500 turns) woundtightly on a cylindrical form.

PVC is typically used, or very dry card-board tubing with a few coats of shellac.Actually, the thinner and more electrical-ly inert your form can be, the better.Many Tesla purists have attempted (andsome succeeded) to wind a coil andremove the form altogether.

In the Tesla coil shown, I used a verythin butyrate tube from a local plasticsstore. It consists of 424 windings of #24enameled wire tightly wound along atube three inches in diameter and 12inches long.

The top of the coil will have highenergies so, the last few windings at thetop are spaced slightly apart and canoptionally be covered with a little coro-na dope.This prevents arcing betweencoils which can damage your secondary.

To protect the windings, I gave thecoil several thick coats of epoxy, rotatingit while the epoxy cured for an even fin-ish. Shellac or varnish can also be used.

Odds and EndsFor a top discharge terminal, I used

a smooth brass doorknob.All roughedges were coated with corona dope.Anoptimal discharge terminal should be atleast the same diameter as your sec-ondary coil, so I fell a little short here,but it worked well. Using a torroid-shaped top ter-minal instead of a sphere can make a dramaticimprovement, as well. For the radio frequencychokes, I simply used 21 turns of #18 enameledwire on a common 1-½ inch diameter PVC tube.

Final AssemblyAssembly is straightforward from the schemat-

ic in Figure 1, and components are placed asshown in Figure 5. I used simple PVC pipes withend caps, and screwed the end caps to the board.This included the Tesla secondary coil for which Ifound a three-inch end cap to seat it in

The primary coil should have at least 2-½inches of spacing between it and the secondarycoil all the way around. Electrical strikes from theprimary to the secondary can damage a coil overtime.A ground rod should be attached to allowsparks to have a place to fly. It can be connected

Reprinted from September 1999 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 3

to the wire leading from RFC 2 to the primary. Itcan be bent in, to around four inches from the topdischarge terminal.

If using a neon transformer, it is very goodelectrical practice to run your neon transformerfrom a variac (one rated at five amps would suf-fice) so that you can do low voltage testing, andcontrol the output of your coil.A variac is simply avariable transformer that connects between thewall and your transformer and allows you to con-trol power output. Several Nuts & Volts vendorsadvertise them, or look around the net to pick oneup for less than $50.00.

Firing it up!Now the fun begins! Your coil is complete

except for tuning, which is easy to do. One of the

wires attached to your primarycoil should be movable. Often analligator clip is used.Attach thiswire about 5-½ turns away fromthe other wire attached to yourprimary. Briefly run the coil andobserve the spark length and char-acter.

By moving this wire alongyour primary coil, you’ll find asweet spot where “spark” is at amaximum.This — and playing withspark gap distance — is all that isrequired to get the effect youwant.

Tip: In the schematic, thebottom of the secondary coil isshown grounded.You can increasespark length by instead attaching

this wire to the wire connecting RFC 2 and theprimary. However, this makes the spark dangerous.

Let the Experiments Begin!The stunts that can

be pulled with your Teslacoil are endless.The sim-plest and most fun forthis Halloween might beto hold a florescent tubein your hand and have itlight with no wires whenpassed near the coilwhich is blasting away!You can create a stunning“electric chair” withsparks flying from the coil

behind you while your victim’s scream!If you are using a low input coil like an auto

coil or equivalent driver, sparks of four inches canbe taken to the hand painlessly! Remember thatyou should have metal thimbles on your fingers orbe holding some metal object since the sparksthemselves can be warm.

Remember good electrical practice whendoing any high power work.Tesla wore thick rubber sole shoes, and kept one hand in hispocket!

If you get the Tesla bug, many serious andbizarre experiments are possible from wirelesspower transmission, to passing a million volts safelythrough a person! I have even read accounts oftemporarily, painlessly scrambling a person’s ner-vous system.

If you visit the web page soon, I’ll set up amailing list for Nuts & Volts readers to keep youinformed of upcoming Tesla events.

So, let’s get winding our coils, and give ourneighborhood friends a REAL shock thisHalloween! NV

Reprinted from September 1999 Nuts & Volts Magazine. All rights reserved. No duplication permitted without permission from T & L Publications, Inc. 4

My address is:walt@noonco.com The web address for free Teslasoftware and info from me willbe:http://www.noonco.com/tesla

For construction of the article,I have available:

• Precut polystyrene, $1.25 persheet.

• A “Wire Kit” which includesall the wires needed, including thewire for the primary, the sec-ondary, and the RFC chokes for$25.00.

• I also have a few of the “autocoil” line transformers for $34.00while they last.

For those who don’t haveaccess to the web, I’ll be happy tosend out a sheet of sources withmore Tesla info and experimentsto anyone who writes by E-Mail.

FREE CATALOGS/FURTHERTESLA INFO SOURCES

TCBA NEWS is a practicalnewsletter on homemade coilspublished quarterly by HarryGoldman, 3 Amy Lane,Queensbury, NY 12804.

Lindsay Books, Inc., has manyTesla and unusual electricalreprints.Write to P.O. Box 538,Bradley, IL 60915.

International Tesla Society, P.O. Box636, Colorado Springs, CO 80931.