Introduction: Pipe Dream: a Low Voltage Tesla Coil or 'Slayer Exciter'
Tesla's famous air-core transformer, the Tesla Coil, is rightly associated with blazing arcs, crashing spark gaps, and high voltage. The whole point of the Tesla coil was to serve as a source of high voltage, high frequency electricity, for Tesla's radio and wireless power experiments. But what if we could generate high frequency electricity without massive transformers or loud and angry spark gaps? What if we could build a coil that transmits radio frequency electrical power wirelessly, with enough power to light up a four-foot fluorescent tube? What if we could do all this with no more input power than a six volt lantern battery?
Turns out we can! By adapting the basic Tesla coil design we can turn it into something called a Slayer Exciter (more about the name later) which runs on low voltage sources like common dry cell batteries, produces no noise and no noxious ozone. We won't be generating violent lightning, but any Tesla coil can do that. Sometimes it's more interesting to be quiet.
Step 1: Totally Tubular!
Because we're dealing with high frequency electricity, we're going to avoid using metal or cardboard in our Slayer Exciter. High frequency electricity radiates from its source like a radio signal (it is a radio signal), and naturally collects on metallic objects in its path. You can actually get high frequency electrical burns from handling metal while the coil is operating--strange, initially painless burns that eventually hurt and make strangely colored scabs. As certain parts of the Slayer Exciter can also get hot (due to electrical resistance), we'll not use cardboard either. Fortunately, the perfect material is easily available for this project: PVC tubing.
PVC (polyvinyl chloride) is a good insulator. It has a dielectric constant of 3.19 (three times better than an equal volume of air) and a dielectric strength of 544 V/mil. See http://www.pvc.org/en/p/electrical-insulation-characteristics. It's also cheap, comes in many handy sizes, and is readily available in hardware stores and home centers. I frequently use it in my high voltage projects, such as the Tabletop Tesla Coil,Tesla's Candlestick, and the Asymmetrical Capacitor Thruster.
For the Slayer Exciter, I made a minor modification of the "Tesla Candlestick" design. To build the frame and coil form you will need:
--(4) 1/2 inch 90 degree PVC elbows, white Schedule 40
Don't use black tubing. It has carbon in it, and may prove to be conductive. Gray PVC, made for electrical conduits, is OK, but usually doesn't come in as many sizes or shapes as white Schedule 40.
--(1) 1/2 inch 'T' joint
--(1) 1/2 inch 'X' joint
--(1) 1/2 PVC plug
Make sure you get a plug and not a cap. The plug must fit tightly into one of the 90 degree elbows.
--about 2 feet of straight 1/2 inch PVC tubing
--(1) 3 inch straight PVC coupling. '3 inch' is the nominal size; the coupling is really 3 1/2 inches in diameter
--24 inches of '2 inch' PVC pipe
I actually used some nice, thin walled acrylic tubing, 2 inches in diameter, but '2 inch' PVC will do fine.
--(1) 1 1/2 inch PVC pipe cap
Ideally, this cap should fit inside the 2 inch pipe with a nice friction fit. If it is too small, you can wind on a few layers of electrical tape until the cap fits. You want the 2 inch pipe to stand up straight without wobbling.
--(1) 1/4-20 nylon bolt, 2 inches long or more, with nylon nut.
--(1) 1/4-20 nylon bolt, 1 inch long, with nylon nut
Try to get nylon bolts that require a slotted screwdriver, rather than cap bolts. Cap bolts will work, but they're harder to install.
--(6) 6 inch long white nylon zip ties
Tools: drill, 1/4 bit, 1/8 bit, pipe cutter or saw, screwdriver or box wrench
Step 2: Assembling the Frame
The frame is a simplified version of the one used in my Tesla's Candlestick Instructable. Start with the X joint. Drill a 1/4 inch hole through the center of the X, all the way through to the other side. Many PVC joint have nubs, or flat spots, where the piece was filled in the mold. These nubs are often in the exact center of the X and help make it easy to find the center.
Next drill a matching 1/4 inch hole in the center of the 1 1/2 inch pipe cap. Take your time and drill it dead center. Caps often have center mold spots too.
Put the 2 inch long nylon bolt through the X joint, then through the hole in the pipe cap. Fit a 1/4-20 nylon nut and tighten. You can use a nylon washer under the nut, but it isn't mandatory.
Next cut four pieces of 1/2 inch PVC tubing, each about 2 1/2 inches long. The exact length isn't critical, but it is important they all be the same length. Fit a piece of tubing into each opening of the X joint. On three pieces of tubing fit a 90 degree elbow. Turn the elbows so that the open ends face down, creating 'feet' for the frame to stand on. On the fourth piece of tubing push on a T joint, so that one open end points up, while the other open end forms the fourth 'foot.' See the pictures to understand how this all goes together.
Slip the '3 inch' pipe coupling onto the frame temporarily, center it around the pipe cap. Cut a piece of 1/2 inch tubing to fit in the upper open end of the T joint. The piece should be just long enough so that when the last elbow joint is added, the top edge of the elbow will be even with the top edge of the coupling. This may take some fiddling and fitting.
Take the 3 inch coupling off and drill a 1/4 inch hole along the upper edge, about 1/2 to 1/3 of an inch down. (This should be done by eye, as the exact spot is determined by the position of the upper elbow--see photos).
Drill a 1/4 inch hole in the center of the 1/2 plug. Fit the 1 inch long 1/4-20 nylon bolt through the inside of the 3 inch coupling and into the 1/2 inch plug. Put the nylon nut on the bolt (tricky, this puts it inside the plug!) and tighten. This joins the plug to the upper edge of the coupling. Jam the 1/2 inch plug into the open end of the elbow that sits atop the T joint. The coupling needs to be co-axial with the secondary form, that is, centered in it. If needed, trim the tubing where the T joint attaches to the X joint until the coupling is centered.
That completes the frame. Next we'll wind some wire.
Step 3: Primary & Secondary Coils
Transformers either step up or step down voltage by means of a pair or more of wire coils of differing gauges and lengths. The principle of voltage transformation by electromagnetic induction was discovered by Father Nicholas Callan in 1834. The basic method of building up voltage from low to high (sacrificing amps in the process) involves running the lower voltage into a coil of thick wire of relatively few turns, which induces high voltage in a larger coil made of longer, finer wire. Father Callan also invented a device that switched the power off and on in the thick coil. The collapsing magnetic field (created when the power was shut off) induces a high voltage surge in the longer, finer coil. The first coil of thicker wire has come to be called the Primary, and the lengthy small gauge coil is the Secondary. Father Callan and other 19th century scientists used soft iron as the core of the primary, relying on its ability to be easily magnetized. As time went on, inventors kept trying to increase the output of transformers, but they ran into a problem at very high voltages. The metal core of an induction coil can only de-magnetize so quickly, so often. This is because of a phenomenon called magnetic hysteresis. Think of it as the core gets tired of the rapid changes and can't keep up. The iron core can heat up too, due to resistance, and heat destroys magnetism. By the late 19th century experimenters like Paul Marie Oudin, Elihu Thomson, and Nikola Tesla were working on air core transformers--induction coils that did not have metallic cores. Unlike the older style induction coil, an air core transformer relies on the principle of resonance to boost voltage levels higher than is possible with a metallic core. No hysteresis interferes with the voltage rise.
The Slayer Exciter is an air core transformer adapted to operating at low DC voltages. It has a primary and secondary, like a Tesla coil, but it uses low voltage components--diodes and transistors--instead of spark gaps and tank capacitors to induce resonant rise in the coil.
Let's make the secondary first. This design calls for a two foot long, two inch diameter piece of PVC pipe. Slayer Exciters can be very small. Some designs I've seen use secondaries only a couple inches long, wound on pill bottles or plexiglass rods. Ours is bigger to have a more useful (and visible) power output.
We'll need copper magnet wire with an insulating coating. Wire is easily found on auction and electronics sites. In the USA, wire is rated by gauge, based on the diameter of the wire. The higher the gauge, the smaller the wire diameter. 40 gauge is thinner than human hair. Household wiring is often 10 or 12 gauge, depending on what load it is meant to carry. For our secondary, we want fairly fine wire, which will give us plenty of turns. The number of turns of wire determines the resonant frequency of the coil, and in general, more turns=higher frequency=more output, given the same power being put in.
For the coil in this Instructable, I used 1,018 feet of 24 gauge magnet wire, covering 22 inches of the 24 inch long tube. Sounds like a lot, but I wrapped it all by hand.
First, make sure your secondary tube form is clean and dry. One inch from either end, drill two small two small holes, about 1/4 inch apart and parallel to the ends of the pipe. (See photos). Take the end of your 24 gauge wire and thread it into one hole and out the other, leaving a generous amount (6-8 inches) coming out. Put a bit of electrical tape over the short length of wire visible inside the pipe. This will anchor the wire in place. Begin wrapping the wire in smooth, tight loops around the pipe. Keep the wire close together (no gaps) but don't let it overlap. My method, primitive as it is, is to sit on the floor with the secondary pipe across my knees. I thrust an axle through the reel of wire, something like a sturdy dowel or thick screwdriver, and place the reel between my stocking feet. Now I can wrap the wire by hand and control tension on the reel with my feet. It's easier (and less weird) than it sounds. It took me 70 minutes to wind this secondary. Many people build jigs and use drills or lathes to turn the form. That's fine, but building a rig can be as big a project as making the coil itself. I've wound about 15 or so secondaries, all by hand, in the last seven years. Do what suits you best.
When you get to the second set of holes in the pipe (at the opposite end), snip off the wire. Allow a long enough lead and weave it through the holes as before. Tape the inside. This method of anchoring the secondary was used by old time radio enthusiasts winding tuning coils a century ago. When finished, you will have a gleaming secondary 22 inches long, with an inch of open tubing at the top and bottom. Strip the insulation off both ends of the wire. This can be done by pulling it through a folded strip of sand paper until you see bright copper, or you can burn off the insulation with a lighter or candle flame. If you burn off the insulation, be sure to clean the soot from the wires when you're done.
For the primary, you'll need about 8 feet of heavier gauge wire. I used 12 ga. stranded house wire. This is enough for 5-7 turns around the primary form, the 3 inch coupling. Wrap the primary wire around the center of the coupling. As with the secondary, keep the turns tight together and don't overlap. Leave enough at the ends for decent, equal sized leads. Temporarily anchor the wire with rubber bands. then mark parallel spots around the primary with a marker pen. Take the wire off and drill 1/8 inch holes at each spot you marked. Re-wrap the primary wire and anchor with rubber bands. Next take nylon zip ties and thread them through the holes to permanently anchor the primary wire (see photos for the finished primary).
Slip the secondary over the pipe cap bolted to the frame. A good friction fit is OK, or you can attach the secondary with short nylon screws. Use no metal! Fit the primary over the secondary and push it in place on the short length of tubing connected to the top end of the T joint. Center the primary around the secondary. Let the secondary's ground lead (the bottom wire) trail away, preferably as far as possible from the primary leads. Gently straighten the secondary's top wire. The coil is finished. Time to make the circuit board.
Step 4: The Exciter Board
The heart of the Slayer Exciter is the spark-free, solid state circuit board used to drive the device. There are several Exciter circuits available on the web. I liked the one by 'FreeX periments' on YouTube, not only because it is lucidly explained, but also because of its modular design, which allows the ready exchange of components. This allows you to replace parts that are defective or damaged, and to experiment with different diodes, resistors, and transistors.
It's a very simple circuit. You'll need these parts:
--(1) 47K ohm resistor, 1/2 watt
--(2) UF4007 fast switching diodes. If you can't find UF4007, the more common 1N4007 will work.
--(1) a transistor. You can use a 2N2222 or a 2N3055. My best results came with a TIP 31C.
--(1) a wiring block with at least 10 double connections. I used a 12 connector from Radio Shack, leaving 2 connectors unused.
--a few feet of 22 gauge, plastic insulated bell wire
--(3) 1/2 inch 2-56 miniature screws, with nuts
--(3) crimp on ring connectors
--(2) miniature alligator clips
--a piece of perforated circuit board about 3 1/2 x 4 inches, or a piece of thin wood or plastic of similar size
Start with the wiring block. Attach it to the perforated board with three evenly-spaced 2-56 1/2 inch machine screws. We'll be using ten of the connectors, so if you get a 12-hole block, don't use the last two on the far right end of the block. The others we'll number 1-10, from left to right. Each connector has two openings 180 degrees apart. We'll start with wiring the bottom ones as you look at the circuit board. Study the photos for best understanding.
Cut a 3 inch piece of 22 gauge bell wire. Strip about 1/3 inch of insulation off each end of the wire. Put one end of this wire into the bottom side of the first wire block connector (the left end of the block, as you are looking at it). Tighten the screw just enough to hold the wire in place. Place the other of this wire into the sixth connector and tighten securely.
Cut a 1 1/2 inch piece of bell wire. Strip the ends as above. Insert one end in the second connector. Bend it sharply and put the other end in the third connector. Tighten lightly, just enough to hold the wires in place.
Cut a 4 inch length of wire, and strip both ends. Connect one end to the second connector and tighten securely. Put the other end in the eighth connector and tighten securely.
Cut a 1 inch length of wire. Strip ends. Connect securely between the third and fourth connectors.
Cut a 3 inch piece of wire. Strip the ends. Connect one end securely to the fifth connector. Insert the other end to the tenth connector, but only tighten enough to keep the wire in place.
Cut a 1 1/2 inch piece of wire. Strip the ends. Connect one end to the seventh connector, and the other end to the ninth. Tighten both screws securely.
All that remains of wiring this side of the block is to put in leads for the power supply or battery. Connect a longish piece of bell wire to the first hole and tighten firmly. Do the same with a wire into the tenth connector. Attach alligator slips to these leads. IMPORTANT: The wire in the first connector goes to the positive pole of your battery or power supply; the wire in the tenth connector goes to the negative pole. Connect this up wrong and you'll toast your transistor.
Next it's time to install the components in the other side of the wiring block. Start with the 47K Ohm resistor. Bend the leads and connect them to the first and second connectors on the open side of the block.
Take a piece of bell wire about 3 inches long. Strip both ends. Crimp a ring connector to one end. Insert the other end in the third open hole in the wiring block. Tighten the screw securely. Using the ring connector as a guide, bore out a hole in the perf board at the end of the wire. Insert a 2-56 machine screw from underneath, up through the perf board and ring connector. Put the tiny nut on and tighten down. Label this post 'Secondary.'
You'll need to link the two diodes in series. Carefully note the silver stripe on each diode. You want to join the diodes with the silver bands 'chasing' each other; in other words, the silver bands should face in the same direction. See photos of the circuit board for a clearer idea. Twist the leads of the diodes together--solder them if you like--and you should end up with this:
---- is the diode lead
's' is the silver stripe
'ooo' is the body of the diode
and --/-- are the twisted or soldered leads
Bend the open leads and insert the lead nearest the 's' into the fourth connector. The other lead should inserted into the fifth connector.
Attach a 3 inch length of wire with a ring connector crimped on to the sixth open connector. Drill a hole through the perf board where the ring connector falls and insert another 1 inch 2-56 screw. Add nut. Label this as the 'Primary Positive' post.
Insert a shorter (2 1/2 inch) piece of wire into the seventh open connector. Make a post for it as you did above and label it 'Primary Negative.'
The last three open holes in the wiring block (eighth, ninth, and tenth) are for the transistor. Label them from left to right B (for Base), C (for Collector), and E (for Emitter). If you use a TIP 31C transistor, this will line up nicely, as the transistor leads seen from the front are B, C, E. The TIP 31C has what's known as a TO-220 style case. Transistors of different shapes will work in the Slayer Exciter, but you must make the right connections. You may have to attach wire leads to other styles of transistors in order to connect them to the BCE connectors on the wiring block. In the photos you'll see the circuit board my daughter made using a 2N3055 transistor. It needed wire to reach the proper connectors.
If you run the Slayer Exciter for very long, the transistor may get hot. If it gets too hot, it will fail. To prevent that, common practice is to attach a heat sink to the transistor to help dissipate heat. I salvage finned heat sinks from old electronics (TVs, especially), but you can buy them new.
Step 5: Power!
The easiest way to power a Slayer Exciter is by dry cell battery. Small coils perform very well on as little 3 volts (2 AA batteries), but a coil the size of mine is better suited to more power. Once you've assembled the coil and circuit board, try testing it with a 6 or 9 volt battery. You'll need a fluorescent tube or two, of course. CFLs will respond to the exciter, but the most satisfying results come from traditional long tubes. I bought a couple of 48 inch tubes, and scrounged up an old ring fluorescent too. A small 1/2 inch diameter, 10 inch fluorescent works nicely with the smaller Slayer Exciter I made from an old Tesla coil.
Connect the secondary to the secondary's post on the circuit board with a jumper wire, or any suitable piece of wire with alligator clips on both ends. Connect the Primary Positive post to the bottom lead of the primary coil. This is important; the exciter may not work, or work poorly, if you reverse the primary connections. Clip the upper lead of the primary to the Primary Negative post on the circuit board.
Have your fluorescent tubes handy. Connect the Positive lead from the circuit board to the positive post of the battery. Finally, clip the Negative lead to the negative post. At 6 or 9 volts, nothing will happen. The Slayer Exciter is completely quiet, and no sparks spew from the top of the secondary coil. Now pick up a fluorescent tube and bring it near the secondary. At about 3-5 inches distance it will glow. Strange ripples appear at the ends of the tube. High frequency electricity is flowing through the tube, exciting the gas molecules inside. It's flowing through you too, but at this power level, it's essentially harmless.
If you have a pacemaker, this may not be a good experiment for you. I've not heard of a Slayer Exciter interfering with a pacemaker, but I wouldn't want to gamble on it, if it were me. The Slayer Exciter does energize metal objects within its field. I have heard of people getting high frequency burns from Slayer Exciter emanations. It hasn't happened to me, but I avoid touching metal when its running. All in all, the exciter is much safer than a conventional Tesla coil. There's no shock hazard, and it does not produce toxic gases, like ozone.
Play with the field. See how far it extends from the coil. At low voltages, I can light a 4 foot long fluorescent at a range of 6 inches or so. If you increase voltage to 12 or 18 volts, the tubes glow much brighter and at further away. The most power I ever ran through an exciter was 54 volts (using a 2N3055 transistor, which withstands higher voltage better than a TIP 31C) I lit up tubes five feet away. The drawback is, more power heats up the transistor a lot. I burnt out a handful of 2N2222 transistors (and others) this way, so be warned.
You can power exciters with 'wall wart' transformers. Find a likely wall wart, cut off the modular plug and separate the lead wires. ID which is positive and which is negative. You can do this with a multimeter, but the wires are often marked for polarity, such as having a white stripe on the positive lead.
Crimp on spade or quick-detach connectors, and your done. Clip these to your alligator battery clips and your coil should work well.
Step 6: Attitude Adjustments
Because the Slayer Exciter operates at low voltages but requires resonance, it may need tweaking before it gives its best performance. Some potential source of problems or adjustment include:
--the size of the primary coil. Fewer turns seems to increase coil output, but stresses the circuit components more.
--location of the primary coil. The coil I built worked best when the primary was sited 4 inches above the bottom of the secondary. I had to adjust the length of the PVC tubing that supports the primary (make it longer). Some experimentation may be necessary to find the sweet spot on your coil.
--the fixed resistor. The 47K resistor gives good performance, but less resistance will change the resonant point in the coil. So will increasing resistance. Watch out for over-heating if you mess with this.
--the transistor. I got best overall results with the TIP 31C. The 2N3055 works well with higher input voltages. Many websites tout the 2N2222 as the best choice, but I found the little 2N2222 vulnerable to burning out. According to engineer Mehdi Sadaghdar, the transistor in a Slayer Exciter ought to have a DC voltage gain of 100 or more. If you look at transistor datasheets, you'll see a cryptic reference to 'hFE.' This is DC voltage gain.
Strange side effects associated with the Slayer Exciter:
--Operating my coil at higher (24+) voltages cause my desktop computer to emit weird wailing sounds. Needless to say I backed off until I could screen my PC. The high frequency field extends much further that you think. You may not be able to light a fluorescent tube six feet away, but you might damage sensitive electronics.
--The base wire of the secondary emits HF too. Often you can place a glowing tube next to the base wire and it will glow brightly, even if you're not holding it.
--If you're using a heat sink on the transistor, the heat sink will radiate HF too.
--At higher operating voltages you can light up more than one tube.
--Using a portable radio, the operating frequency of the Slayer Exciter can be found by tuning the dial until weird squealing sounds are heard. By moving the radio in and out of the field, it sounds almost like a theremin.
--Once in operation, you can drain off the power from a Slayer Exciter's signal by touching the negative clip on the power source. Let go, and the light may return; touch, and it drains away through your body to ground.
Maybe you will discover other strange effects!
Step 7: What Does 'Slayer Exciter' Mean?
There's an online community of researchers, tinkerers, hobbyists, and yes, con-men who dream of finding a way of generating free energy. I'm not going into their methods or claims. They're not hard to find, if you're interested. One such researcher, a Dr. Stiffler, built a "Spatial Energy Coherence" device which lights ups LEDs wirelessly, etc. This seems to be the prototype of what we now call the Slayer Exciter. Another online experimenter who goes by the handle slayer007 popularized his own version of this device, which came to be called the Slayer Exciter. He sells kits now.
I don't believe the free energy claims. It seems pretty clear to me the low voltage Tesla coil relies on resonance to convert low voltage DC to high frequency electricity. This radiates from the coil like a radio signal, and excites gas molecules in fluorescent tubes. A very talented electrical engineer, Mehdi Sadaghdar, offers a woo free explanation of the Slayer Exciter. He's also a very funny man. You can check out his website at http://www.electroboom.com/.
Runner Up in the