Monthly Archives: September 2014

Special Notes

Note the optional current meter (Ml) can be used for an indication of fine-tuning by adjusting to a maxi­mum value. An initial operation where tuning may be way off can result in erroneous current peaks, espe­cially if coupling is too tight. Use a thermo couple device if available.

The secondary coil in the system acts similar to a quarter-wave antenna with top loading capacity. This means a current node at the base in amps. If you depend on the green wire of the line cord for ground­ing, you force your electrical wiring to become a pari of this system. This is not a good idea as a voltage gradient can result along the wiring run. This voltage value is determined by many complex factors such as frequency, harmonic content, and, of course, a varying

Special Notes

Fig иге 18-B Spark switch assembly and fan

amount of parallel and series complex impedances along this run. What this means in simple language is that you should ground the coil to earth with the shortest dircct lead possible. This can also eliminate a good part of interference coupled back to the power line.

The coil form used for the secondary coil should be an excellent insulator, plus be a relatively lossless dielectric at the operating frequency. A ruby mica coil form would be ideal if it existed. A material with this

property can be expensive. Thin-wall PVC tubing, while not the best, is a good compromise between cost and performance. Unfortunately, PVC is hygro­scopic (it absorbs moisture), but it can be treated by driving out the moisture with a heat gun and then sealing in orange shellac or an equivalent (do this on a dry day).

Caution: PVC tubing may give off undesirable gases under high-voltage stress. Lexan polycarbonate

1 Fabricate and verify pieces as per Fig. 18-7

2 Steel collars must be properly positioned and soldered to brackets Use a propane torch and ingenuity in this step. Holes must allow proper alignment of electrode faces.

tubing is preferred if you are planning to use your coil for continual use.

Not all the holes on the fabrication points are dimensioned. It is suggested that you trial-fit and fab­ricate as you go.

The CHK1 and CHK2 chokcs are designed to pro­vide a relatively high impedance to the resonant operating frequency and any of its associated har­monies. This is necessary to choke off these high fre­quencies from reaching the power transformer. Tl to T4, where damage to the secondary winding inevitably results. You may use 1К 50-watt wire – wound resistors in place of these chokes.

Special Notes

Figure 18-9 BTC FA В M fabrication and assembly of GRDPLT ground plate

The spark gap is connected across the transformer to limit voltage stress on their secondary windings. The gaps are fabricated from three pieces of 2-inch X 3/e-inch tool steel or tungsten rod. A muffin fan keeps the assembly cool (see Figure 18-13). Be cautious of any ultraviolet hazards. Spark gap discharges emit

hazardous ultraviolet emissions and must not be viewed directly. Observe them through a clear piece of plastic or protective eyewear.

Tungsten is recommended for long-term reliable coil operation. However, tungsten is expensive and those requiring short-term operation may use drill

rod/tool steel. It will be necessary to reface electrodes more often than if they were tungsten.

Use the remaining four feet of #14 wire to make a ground discharge probe that must connect directly to the ground plate (see Figure 18-11 ).This can be used for drawing sparks from the output of the coil.

Special Notes

Dashed lines show possible routing of tap lead when used with optional toroidal terminal. This is a rough adjustment of tap setting and will require repositioning to obtain maximum output It does, however, suffice as a starting point and should produce some impressive streamers into open air. You will note the routing of this tap lead is in the direction as the primary winding and actually adds a turn. Going the other way would effectively remove a turn. The routing and positioning shown will vary dependent on assembly.

Figure IB-10 Assembly of primary coil

Suggested labels if you intend to use your coil for demonstrations


Special Notes

Special Notes

Figure 18-12a BTCAS assembly and first-level wiring

Special Notes

BASE BOTTOM layout showing low – voltage wiring Note shown for 115 VAC.

DANGER as the above parameters can be lethal if Improperly contacted.

Special note on phasing The first step used in our laboratory is to initially phase Г1 and T2 to obtain 8,000 votts with a center point ground Repeat with T3 and T4 The second step is to now phase the above combinations for 8,000 volts at 60

Fi g иге 18-12Ь В TCBASP assembly aid for second-level wiring

Special Notes

Figure 18-13 Side view of spark gap and capacitor

Table 18-1 Thirty-inch lightning bolt generator parts

Ref. #





4000-volt, 30-mil liampere current-limited transformer

Cl, 2


Л mfd @ 630-volt capacitor


.022 mfd, 10 KVAC pulse capacitor


Fuse holder and 10-amp fuse


Three-wire, heavy-duty line cord


Line cord bushing


Crocodile clip for primary coil tap


Eight-foot section of #14 PVC stranded hookup wire


50 feet

3/i6-inch roll of copper tubing


(Optional) 12- x 3-feet or use stove pipe elbows



Large wirenuts


4,/2-inch 115 AC muffin fan (high output)



15-inch heavy nylon tie wraps for attaching C3



Assembled secondary coil as per Figure 18-3



Assembled chokes as per Figure 18-4


22- X 4.25-inch OD ‘/« wall PVC tube for LS10



5- X l-inch OD sked 80 PVC tube for CHK1 form



4’Л x 2 x.0625 lexan for primary bracket


4 x Ю x.063 aluminum for ground plate



14 x 14 x l/2 finished plywood (see Figure 18-5)



6- X l-inch OD PVC tube (see Figure 18-11)



2- x Vs-inch tungsten or too] steel


Fabricate as shown in Figure 18-7



Fabricate as shown in Figure 18-7



Fabricate as shown in Figure 18-7



fabricate for top and bottom of secondary coil as shown in Figure 18-3



6-32 X l-inch screws



6-32 X ‘A-inch screws



8-32 X ‘/2-inch screws



8-32 X l-inch screws



‘/4-20 x 8-inch threaded rod (see Figure 18-11)



#6 X ‘/-i-inch sheet metal


8-32 X 2-inch brass screw



6-32 nuts



8-32 nuts


#4 Kv/.ОЗ amp #.1 M/630 #.02 M/10 Kv

Table 18-1 Continued

Ref: #





‘/4-20 nuts



1Д-inch flat washers



#6 solder lugs



74-20 lugs



PVC end caps for bottom leet (see Figure 8-11)



< ID X 3Ia OD steel collars with set screws



6 X */2 brass wood screws



6-32 X 3/s-inch brass machine screws and nuts



74-20 X 172-inch brass machine screw



74-20 brass hex ruts for previous screws

Spark gap top view

Spark gap top view

Figure 18-6 BTC FA BP fabrication of plastic parts

blocks and readjusting all parameters. A round or square wooden block that fits inside the secondary coil will position and secure it in place. Always use brass screws for fasten­ing. You may have to remove the bottom bracket. Use your own ingenuity in perform­ing this experiment.

It is also a good idea to keep notes as you experi­ment.

Note that there will be a second-order differ­ential effect when the gap is opened due to changes in dynamic capacity resulting from space volume ionization. This effect will mani­fest itself as requiring slightly more induc­tance in the primary. We are currently developing an advanced program in MATH – CAD for those into the complex higher math and electrical physics of resonant high-voltage systems.

12 Experiment by using different values of cou­pling by raising the secondary coil on wooden

Testing Steps

If you live in a congested area, close to an airport, or near computers and other sensitive electronic equip­ment. it will be necessary to test this system within a Faraday cage (FAR1). It is also strongly advised to test this system in an area with wooden floors, as dan­gerous ground currents resulting from accidental contact will be reduced. To conduct the test, follow these steps:

1. Carefully position the secondary coil bottom bracket over the center screw and rotate until it sccures in place.

The wire in spark gap assembly is as shown in Figure 18-13. Note the mounting of C3 via two heavy tie wraps.

Figure 18-4 СИК1 choke protection coils

2. Verify the correct wiring, the proper clearance of high-voltage points, and a proper grounding to the GRDPLT ground plate.

3. Set the two spark gaps to about Vi6 of an inch.

4. Connect the tap lead to the outermost pri­mary turn. You will note that the flexible pri­mary tap lead is used as a full turn of the primary winding and adds another turn depending on the position of the tap connec­tion. This is important, as the system may not properly tune with the toroidal terminal with­out this added iurn.

5. Connect a meter to J1 or short (not necessary for a basic setup).

6. Attach a toroid or another similar terminal. Note that a metal bowl will suffice in a pinch. Screw on to the top secondary bracket and secure with a nut.

7. You may use a 2- to З-inch screw as an output terminal if not using the toroid. Attach and

Fabricate two pieces of.5" plywood for both top and bottom sections Note.25" holes placed on.625 centers from outside edges

grounding point

You may also bore out a.125"-deep section for nesting of the.825" PVC spacers. This step should be done prior to drilling the.25” through holes as shown on inset Figure 18-11.

Figure IB-5 Fabrication of both the top and bottom pieces BASTOP and BASBOT

screw into the center hole of the top bracket from the bottom. Note that maximum output will require the tap lead now being moved inwards several turns. Do not allow discharges to occur from the actual top winding as you may cause burning of the PVC coil form.

8. Place a grounded contact approximately 8 inches from the terminal and secure it in place.

9. Quickly plug the unit in and note a discharge occurring at the test contact. If not, recheck the system.

10. Separate the test contact from the point where the spark is erratic and connect the tap to the next inner winding on LPl. Reapply power.

11. Repeat the previous steps in an attempt to find the exact point on the primary tap for maximum output. Slightly open the spark gaps and repeat. Note that discharges into open air will be considerably longer than those from point to point. You may tune for this effect if the unit is for display purposes.

Material is.06" Lexan (polycarbonate) sheet PRIBKT Primary coil brackets (4 required)

4.50 ———————————————————

Slots are fabricated by first drilling.25" holes.5" centers. Use hacksaw and file remaining slot. Builders with more precise tools may want to taper slot so tubing snaps into place. Note tubing must fit tightly into slots.

Description of Major Components

The role main components perform in your Tesla coil.

LSI Secondary Coil

This is where the high voltage is produced. The coil form must be an excellent insulator and have a low dissipation factor to the high-frequency currents. It preferably should be of a material that will not read­ily “carbon track” in the event of spark breakover. Turns must be even and properly spaced. Turn crossovers or overlaps will always cause serious per­formance problems and must be avoided like the plague. The resonant frequency of the secondary coil can approximately be calculated by considering it to be a quaiter-wave section of the length equal to the actual physical length of the wire used. A reduction in this figure can be fudged due to extra capacitance as a result of ionization at the top of the coil when a dis­charge occurs.

Output Terminal

The output terminal of your system is shown as a 12- inch toroidal terminal. These are expensive and hard

LP1 Primary Coil

This coil is combined with capacitor C3 and must form a resonant circuit equal in frequency to that of the LSI secondary coil with its associated output terminal. It is made tunable via a tap that enables connection any­where along its spiraling turns. The wire used is heavy, bare copper or copper tubing and should be 3/i6 of an inch or thicker to accommodate the high-flowing pri­mary tank currents as a result of its high Q factor.


The secondary coil LSI is coupled to the LP1 primary coil and must be inherently tuned to the same fre­quency for efficient operation. The coupling of these circuits must not be too tight as beat frequencies can cause hot spots along the secondary coil. Coupling that is too loose, however, will not allow a proper energy transfer between the circuits. You may want to experiment by changing the position of LSI by plac­ing it on wooden blocks.

SPKGRP Spark Бар Suuitch

This is where energy stored in capacitor C3 is switched into the primary inductor LPl. The spark gap electrodes must allow for clean “makes” and
“breaks.” Adjustment is usually critical to allow C3 to charge sufficiently before a breakdown or switching occurs. Remember, system energy is a function of the square of the charging voltage across the primary capacitor. It is important that the gap cleanly shuts down before the secondary current reaches it maxi­mum value. The energy in the secondary current must not couple back into the primary one, as it will cause erratic spark gap operation, destructive voltage nodes, hot spots, and so on. The use of tungsten for the spark switch electrodes is recommended if the coil is to be frequently used.

C3 Primary Capacitor

This is where the energy is stored that is exchanged with the primary inductor ai a rate equal to the reso­nant frequency. It must be capable of handling high currents and have a low dissipation factor for efficient operation. Note a special capacitor must be used in this circuit and attention must be given to its dissipa­tion factor and reverse current-handling capability.


This part is necessary to block the high resonant fre­quency as well as the harmonic voltages and currents from feeding back into the transformer. These cur­rents can create destructive voltages that will most certainly cause premature breakdown of this part.

Rssembly Steps

The following steps are those used by our laboratory when assembling this device. You may implement your own ideas, but we cannot guarantee the per­formance claimed if circuit parameters and values are changed. The dimensions shown may also vary with different mechanical parts.

1. Study ail of the the plans, schematics, and figures.

2. Identify the parts and pieces if you purchase the kit. Important: The hardware located near the primary coil must be brass.

3. Assemble the secondary coil designated as LSI, as shown in Figure 18-3.

4. Assemble the chokes, designated CHKl, as shown in Figure 18-4 (two are required).

5. Add the top and bottom base sections, desig­nated BASTOP and BASBOT as shown in Figure 18-5. Note that not all holes are prefab­ricated because they are best determined by the actual placement of the components.

6. Fabricate the plastic parts (PRIBKT) per Fig­ure 18-6 (four are required). Then, fabricate the parts for a spark switch, as shown in Fig­ure 18-7. Note that the hole location on these pieces must be accurate, as shown. Also note the top and front view of the spark switch assembly, as shown in Figures 18-6 and 18-8.

7. Fabricate the metal parts designed GRDPLT (see Figure 18-У). Note the position of the holes for mountingTl, T2,T3, and T4.

8. Assemble the primary coil section designated BTCPRl (see Figure 18-10).This can easily be done because the Vicwnch copper tubing is usually neatly coiled up in its shipping con­tainer. Mount the PRIBKT brackets in place with small #6 brass wood screws. Carefully fit the coil turns of the copper tubing in place as shown. Connect a 12-inch piece of insulated #12 wire to the copper tube by inserting the striped end into the tube and soldering it with a heavy iron or propane torch. Note the end of the outside copper tube winding adjacent to the hole for the tap lead. Use some silicon rubber (room temperature vulcanizing [RTV] adhesive) and apply at slots in PR1BKTS to hold the copper tubing in place. Allow 24 hours to set. Cut a З-foot piece of the #12 wire for the coil tap lead and attach the crocodile clip for connection to the copper tube.

9. Assemble the parts to the bracket, designated GRDPLT, as shown in Figure 18-9. Note the fuse holder, strain relief, grounding screw (GRDSCR), and current monitor jack, as shown in Figure 18-11. Positioning is not criti­cal but should allow adequate clearance of the connection points.

The transformers are mounted to the bottom base (BASBOT) via suitable hardware. Use Figures 18-12a and 18-l2b and attempt to fol­low the layout as closely as shown. Note that

Holes for threading end leads

1. Position form on shaft using center holes of brackets and secure one end in a vice. Form will now easily rotate for winding on wire.

2. Position roll of #26 heavy magnet wire and thread into holes on one end of form Attach free end to bracket via one of the screws

3. Start to wind the turns, being careful to keep the wire tight and free of kinks and to avoid any overlaps. Do approximately

one inch at a time and shellac in place using orange shellac. Always secure lead with a piece of good adhesive sticky tape as unwinding of the lead would be disastrous Two people winding this coil makes this step much easier.

4. Completed coil should contain approximately 1.000 turns and should be tuned to around 200 kHz when free standing. Note that winding should be in the same direction as primary coil LP1

Special note: The coil form must be totally clean both inside and out. Use isopropyl alcohol and allow the form to completely dry. Coating with a layer of orange shellac should be done on a dry day or in a dehumidified area.

the inner mourning legs of the transformer are electrically contacted to the grounding bracket GRDPLT, providing a positive earth ground for the transformer frames.

Finally, assemble everything as shown in the remaining figures. Note the individual

Figure IB-3 Secondary coil assembly

Description of Major Components

An aluminum bracket with a 1 /4" center hole is placed at coil ends for initial winding and attaching to the base and top terminal. The coil winding leads are electrically attached via small brasa screws, as shown.

Description of Major Components

Description of Major Components

Description of Major Components

Connect to GRC earth grounding This is very impi

Connect to GRDPLT on Figure 16-12b for earth grounding ot secondary output coll This is veiy important for safety and proper operation Verify for connection integrity

schematic showing both 115 and 230 VAC operation. Note the wire nuts are shown con­necting to primary wires. You may use termi­nal strips or another more suitable means. Remember these points are al L15/220 VAC and must support at least 5 amps.

Description of Major Components

Description of Major Components

Note Space wind means using another same size wire and parallel winding together. You then remove the second wire, leaving the space between.


Note that ferrite cores are shown but are not necessary for normal operation.

3 x.5" ferrite core positioned

1" from base to enhance inductance of

bottom coil section; secure with RTV

Use a styrofoam peanut to position ferrite core


Description of Major Components

2. Continue and wind remaining 2"; close wound
and solder end to bottom lug as shown.

3. Shellac windings in place.

4. Assemble 3" x.5" length ferrite core into coil
form as shown. See note

5 Assembly is mounted by screwing retaining
plastic cap to bottom base. Coil assembly is
now tightly slid into cap for securing in place

6. Inductance should be around.1 to 4 mh.

Basic Points to Consider Before Building This Project

Your Tesla coil produces large amounts of electro­magnetic energy. It may damage computer systems and cause destructive interference to communication and sensitive electrical equipment. The system should be operated within a shielded enclosure, such as a Faraday cage, if near such sensitive equipment.

The primary circuitry, consisting of transformers Tl through T4. produces lethal currents. Human con­tact with these points, when the system is connected to a power source, can result in a dangerous and fatal shock or serious burns.

Never stand on a conductive surface such as cement or wet ground when operating this equip­ment. The proper grounding of the system is very important for safe and optimum operation. Omission of the line bypass capacitors С1 and C2 can create an unsafe condition with a voltage breakdown in the pri­mary feed lines.

Never operate the device in a flammable atmos­phere as sparks can cause ignition. Low, overhead wooden structures are also prone to fire hazards. Also, always provide adequate ventilation as the dis­charge produces ozone in large amounts.

It is often a merit of Tesla coil operation to make physical contact with the secondary spark discharge for demonstration purposes. An experienced and qualified person should only attempt to do such a demonstration. The secondary return of the output coil must be directly grounded to earth.

Never leave the system unattended where children or other unqualified personnel may turn it on. Also, there is no need to energize the coil for longer than 10 to 20 seconds at a time.

Basic Points to Consider Before Building This Project

Tesla lightning generator

Figure 18-1 The 30-inch-spark

This coil can produce up to 36-inch discharges. Therefore, it is suggested to position the main power
switch from a remote point as the sparks may jump toward you if you are standing too close to the output coil. All metal controls should be insulated because contact may cause irritating bums.

Do not use near pacemakers or other similar devices. Always warn spectators as to the possible danger of being near this device if wearing or using sensitive equipment. Also do not operate this device near computers.

Brief Theory of Operation

Transformers Tl through T4 step up the household 115 to 8,000 volts-cilternatmg current (VAC) and charges the “tank” capacitor C3.This capacitor now discharges through the spark gap switch (SPKG AP) on voltage peaks and steps a pulse of current into the primary coil (LP1 j. This sets up a resonant voltage of a frequency determined by the inductance of LP1 and the capacity of C3. Energy is now coupled into the secondary coil (LSI), also tuned to the resonant frequency of the primary circuit. The secondary energy now “rings down” with an exponential decay­ing waveform. The high voltage output produced in the secondary is now a function of the ratios of pri­mary LP1 to secondary LSI Q factors or capacities.

It is important to note that voltage is not depend­ent on turn ratios. The spark gap switch must turn off in order to not allow the “secondary ring down” energy to couple back into the primary circuit. The spark gap uses multiple gaps to enhance the positive turnoff and to prevent ionization from excessive heating. The spark gap electrodes can be brass or steel for limited use but should be tungsten for pro­longed operation. Input may be wired for 110- or 220-volt operation as shown in Figure 18-2.

Circuit Description


Basic Points to Consider Before Building This Project

Basic Points to Consider Before Building This Project

Figure lB~c? Schematic for both 115- and 220-volt operation

Figure 18-2 shows transformer T1,T2,T3, and T4 con­nected in a parallel series, parallel combination to produce 8,000 volts at 60-milliampere (ma) output. The secondary coils are connected to a common neu­tral point to provide a midpoint ground. This scheme provides 8 Kv between the transformer endpoints but only 4 Kv from any end point to ground. The primar­ies are wired using standard 115 VAC wiring tech­niques.

It is important to note the phasing dots shown adjacent to the windings. These must be followed in both primary and secondary circuits. Use Figure 18-2 for wiring points.

Caution: Note that the primary wiring must be iso­lated from the secondary. The secondary coil is con­nected directly to the ground plate bracket (GRDPLT).

The fuse (FS1) is rated for 10 amps and is neces­sary to prevent catastrophic damage from faults,

breakdown, and so on. A heavy three-wire line cord (COl) is strain relieved to the ground plate bracket. This bracket also serves as a connection point for all grounds of the system. It should be connected directly to a dedicated, solid earth ground. You will note capacitors Cl and C2 connected across the AC lines to the ground plate bracket. These capacitors bypass any “kickback" pulses from entering the house wiring where damage to sensitive electronic equipment is minimized (not eliminated). The system might be connected to a remote variable transformer for output adjustment.

The output of the unit can cause annoying burns and shocks from contact to the metal controls. Oper­ation can be controlled by simple removal and inser­tion of the power plug or a remotely located switch.

to find. You may use stove pipe elbows as a substitute at the cost of overall appearance.

The purpose of the terminal is twofold. First, it electrostatically shields the top winding of the sec­ondary coil from arcing into the open air. This bums the coil and can result in performance degradation. Second, the addition of electrical capacity to the top of a quarter-wave system will enhance current flow through the coil. This property will increase the spark energy at the cost of fewer discharges per unit time. Mathematically speaking, this capacity is unlimited, with the exception of the resonant frequency decreasing to an unworkable value. We are currently designing a computer program on this important property when it is used for voltage magnification and other nonmagnetically coupled resonant systems.

Basic Points to Consider Before Building This Project