Tesla Coil
I started playing with high voltages devices as a kid. The High voltage that is used to power Picture Tubes amazed me. I also took my share of shocks. I once saw the high voltage jump to the end of my screwdriver then up over the handle to my hand. The screwdriver ended up embedded in the wall behind me. Now I play with High Voltage devices like Tesla coils, Jacobs Ladders, and washer launchers. Maybe sometime I will experiment with can and coin crushers? My biggest Tesla coil is pictured at the right. Tesla Coils
Jacobs Ladder
Tesla Coils
I started playing with Tesla coils when I was only in my teens. I planned on zapping my brother so he would never walk into my room without knocking again. Someone knocked on my door so I turned it off and opened the door. My sister was standing there wanting to know what I was doing that was causing every TV and Radio in the house to go crazy.
Types of Tesla Coils
High Voltage Transformer Driven (best).
Multiple Microwave Oven Transformer (Dangerous!).
Vacume Tube based (Dangerous!).
Solid State.
Why the interest in Tesla coils? Most people do not know it, but Tesla was also working on a healing device. His first Tesla coil was made even before he moved to the United States. It was used to make Ozone as a treatment for diseases. Back then the technology did not exist for him to be completely successfull. Have you ever heard of someone being hit by lightning, and surviving to discover that all their diseases were healed? There is some sort of a connection there!
My first Tesla coil design used cardboard forms and rewound deflection yoke coils. For a transformer I used a 6KV transformer that was used to light some sort of Neon tube. The spark gap was two needles facing each other. The capacitor was a sheet of plastic with aluminum foil on each side. I used it to try to keep my annoying little brother from walking into my room without knocking!
Update on my big Tesla coil
I discovered that there was no picture on my web site of the parts behind by big Tesla coil. So here it is. It is powered by an Actown 12 KV 30 MA Neon Sign transformer (It cost me around $50.00). Front and center is the safety gap. The transformer leads go across it. The green wire is the ground from the bottom of the secondary coil. Behind that is the capacitor, it is .006uF at 30,000 volts. To each side of the capacitor is the RF chokes. They were salvaged from the crossover networks used in speakers. Behind that on the right is a 120 VAC fan and on the left is the multigap spark gap. It consists of 5 pieces of 1/2 inch copper pipe spaced about 1/16 of an inch appart. The gaps are not very precise, that is hard to do.
The primary coil is 12 turns 10 gague insulated copper wire with an inside diameter of 5 inches and an outside diameter of 12 inches. The secondary is about 1000 turns on a 2 foot long piece of 3 inch PVC. The top load is two aluminum pie pans glued together. The last run had it producing sparks well over 1 foot long. They were twice as long as the pictures of it show, the pictures were taken with a 10 KV 25 ma OBIT transformer.
My biggest Tesla coil yet
I have finally done it. I have made what some may call a "normal" Tesla coil. I purchased a 8 KV transformer that was removed from an air cleaner at the Rochester Hamfest for $5. Then I bought some .005, 8KV capacitors for $5 as well. For the primary I am using about 16 turns of Number 10 insulated wire on a 6 inch diameter sugar jar that I found at a yard sale for free. The secondary is about 1000 turns of #26 on a 3 1/2 by 2 feet piece of PVC pipe. The spark gap is pictured in the MOT tesla coil. It consists of two bolts through a piece of 2" PVC with Brass round nuts on the ends of the bolts. I am using two of the .005 capacitors in series for .0025 at 16 KV.
The transformer had lots of problems with arcing at first so I covered the areas where it arched over with RTV glue. Then it happened, the first firing of the new Tesla coil. There were lots of sparks around 4 to 5 inches in length, and streamers coming off the top windings. It works! The next problem is that after less than 10 seconds the capacitors seem to overheat and shut the coil down. I guess they were not made for this kind of use, or should I say abuse. Now to start refining the design. I have tried adding a torroid consisting of an aluminum pie plate. With the plate you need a ground rod to get some sparks, they are about 6 inches in length.
Next I tried using the 10 KV 25 Ma Oil Burner Ignition Transformer (OBIT) that I used for the Jacobs Ladder shown below. The arcs to a ground rod were close to ONE FOOT in length! Blue streamers were shooting off the pie plate top load. That lasted for all of about 10 seconds then one of the capacitors blew up! Pieces of glass bounced off the walls of the room. Then I rebuilt the capacitor bank using 24 .0033 uF 3 KV Ceramic capacitors in 4 parallel groups of 6 in series to handle 18 KV. Acording to the meter it was .0028 uF in capacitance. The sparks are back to 6 inches, and it only runs a few seconds before the transformer shuts down.
The next thing I purchased was a .0053 at 15KV Door Knob Capacitor on Ebay. The really big sparks are back! They are shown in the picture at the top of this page. The top load is two aluminum pie plates glued together. What you see at the bottom of the coil is two big RF chokes in front of the door knob capacitor, they are all being lit up by the arc from the spark gap located from just below them. I am getting lots of primary to secondary arcs that are charing the primary's form, so I need to go to a flat or angled primary to keep it running.
Microwave Oven Transformer Tesla Coil
My current design uses two microwave oven transformers set up 180 degrees out of phase. That gives about 4000 volts AC. The capacitor bank is over eight .01, 1000 volt capacitors in series and parallel to form .005 at 4000 volts. The spark gap is two bolts facing each other with a 12 volt fan to cool them. This arrangement needs some help. The primary is 10 turns of 12 gauge electrical wire on 1/2 of a Metamucil jar. The secondary is 1000 turns of 24 gauge wire on 18 inches of 1 1/2 inch PVC pipe.
The first problem I encountered was that every time it sparked it blew the fuse. First I added two chokes consisting of 16 turns of number 20 enameled wire on a ferrite core. One was added to each output leg of the transformers. Next I used a third transformer in series with the primaries with its secondary shorted. That is an idea I picked up by searching the internet.
The design needs lots of improvement like mostly a better spark gap. I tried a spark gap consisting of 3 - 1/2 inch copper pipe segments evenly spaced. I thought that would spread the sparks out and make them run cooler. Instead it sparked the whole length of the pipes and really overheated. I also tried two steel needles but they quickly melted. Next I need a bigger capacitor by adding more to get at least .01 uF total. Also the doorknob on the top of the secondary needs to be mounted somehow. The picture shows the sparks at about 2 to 3 inches.
Quad Microwave Oven Transformer Tesla Coil
Once again I am making a Microwave oven transformer based Tesla coil. This one will use a total of five MOTS, four to produce output voltage and one to work as a current limiter. Not much has changed except the use of the four transformers, and the coils. The primary coil is 12 turns of number 12 wire wound on a CD spindle cover. The secondary is about 1000 turns of number 24 wire wound on 2 feet of 3 inch PVC pipe. If you leave out the current limiting transformer the other four will eat 15 amp fuses for lunch. With the current limiting transformer added the output voltage is reduced slightly from about 9 KV to about 7 KV. The outer transformers were chosen as ones that had extra insulation as their secondaries start at 2 KV.
When I first fired it up I did not have the transformers cores grounded. The outer transformers lit up blue as they were running at 2 KV. So I took a piece of 12 gague wire and grounded all of the transformer frames. In the picture you can see where I disconnected the secondary grounds of the outer transformers and connected them via High Voltage wire to the secondary output of the middle two transformers. These connections were then covered with clear RTV to prevent arcing. The yellow wire nuts are connecting all of the transformer primaries together. This way I can change the phase of the transformers untill I reach 4 KV on each of the secondary or outer transformers. I used a high voltage probe to verify correct wiring. Then a loud nasty arc confirmed that the two sets of transformers were in fact out of phase for 8 KV across the spark gap.
Next I need bigger caps, perhaps some Microwave oven caps in series? I have heard warnings about them blowing up unless they are vented. Another improvement will be some kind of rotary spark gap. The sound of the current gap is way too loud. The arc never stops. It needs to be quenched or stopped so the coils can run free between sparks. Another possible solution is to use multiple spark gaps. The primary coil could also use some improvements.
The quad microwave oven transformer tesla coil has burned up several times. First the capacitor bank fried. Never try mounting ceramic capacitors next to each other like in the picture. They arc between themselves and burn up. They must be spaced at least 1/4 inch apart. Next one of the MOT's developed a secondary short. The 2,000 volts on the inside of the secondary winding is just too much for the little amount of insulation. The final straw was when the secondary developed a break. I had only heard of this happening but now I have seen it. Somehow weeks after being wound the wire just snaps! I have rewound the secondary and the polyurathane is drying. Now to redesign the rest of the tesla coil. What I am thinking of is going back to just two transformers but using a rotary spark gap and or voltage doublers to get the 8 KV. The best option is to buy a 10,000 volt transformer on ebay!
Vacume Tube Tesla Coil
My latest addition is a Vacume tube based Tesla coil. This coil setup produces a two to three inch spark. I used an 812 tube because I had two laying around from another experiment. The first sparks were dismal at best. Then I started playing with parts values. When I added more capacitors in series with the plate capacitors the spark started growing. I had stated with three 3300 at 3 KV caps in series for .001 uf at 9 KV. When It was increased to ten capacitors in series the spark was at it's best. That is how I arrived at 330 Pf at 30 KV. These capacitors will get warm at it runs. The resulting frequency is about 1 Mc.
The first problem is in the coil design. The more turns the lower the frequency, but then there will be less voltage per turn. The tube is not supposed to work very well at higher frequencies. I finally decided on 30 turns of #14 on a 3 1/2 inch piece of PVC. The grid coil is another 15 turns of #14 on the same form. The secondary coil is the same as the one used above on the MOT tesla coil. It is about 1000 turns of 24 gauge wire wound on 18 inches of 1 1/2 inch PVC pipe. I like to reuse what I have laying around.
The power supply is, once again, a Microwave Oven Transformer (MOT). This time I removed the two metal shims and added three turns of #14 in series with the three turns already there for the filament power of about 6.5 volts AC. A 6.3 volt 5 amp transformer could also be used. For the plate circuit at first I center tapped the coil. To do this you carefully pull a wire out of the glue around the middle of the high voltage coil. It will likely break. Then solder a jumper wire to connect it to ground. Be sure to disconnect the factory grounded end of the coil as that is now at about 1000 volts. This does not show up very well in the picture. Then for the fun of it I used the entire 2000 volt secondary. I thought the whole thing would blow up as this far exceeds the maximum plate voltage of the 812 tube. It did not! The spark went from 1 inch to about 3 inches in size! I did not have a tube cap so I soldered the wire onto the cap of the 812 tube. The grid coil has a 10 K ohm 10 watt resistor in series and a .001 uF 9 KV capacitor in parallel with the resistor. When I vary the capacitor it makes little or no difference. However if the resistor is reduced to 5 K ohm the output spark turns white!! My latest problem is that the end of the wire at the top of the secondary coil likes to melt!
Dual Vacume Tube Tesla Coil
The plate of the one tube tesla coil glows red hot while it is running, if we used two tubes there should be less of a strain on the tubes. Hopefully two tubes would add more power as well. The two tube version will even use two Microwave oven tubes for more power and a full wave rectifier for less AC on the output. Another advantage of using two microwave oven transformers is that the filament voltage of 6 volts can be reached by connecting the two 3 volt windings already on the transformers together. The primaries hould be wired out of phase and the 3 volt windings in series to reach the needed 6 volts for the tubes to light up.
The two tube tesla coil has burned up several times while the design was being perfected. There has been problems with arcs between the grid and the plate coils, as well as between the plate coil and the secondary coil. The grid coil was eventually replaced with 20 turns of #18 3/4 of an inch below the plate coil. This resolved arcs from the grid coil to the plate coil. The secondary coil was raised up about 1 inch to reduce the amount of high voltage present close to the plate coil. A bigger plate coil, perhaps on a 5 or 6 inch diameter form would be a better solution.
Solid State Tesla Coil
Most solid state tesla coils are really more like a radio transmitter. They use the power from the outlet rectify it then pulse it through some 200 volt FET's into the primary coil. You can get some big sparks that way, but is it really a tesla coil? To really be a tesla coil you need a high voltage source, a spark gap, a capacitor, and of course, the coils.
I have all the parts laying around so I threw them together and built a simple solid state tesla coil. First I used the car ignition coil driver circuit to produce about 10 KV. Then I used some .0033 3KV Capacitors in series for the capacitor. Next I used a spark gap made out of two sharp wires spaced about 1/4 inch apart. For a primary coil I used about 12 turns of #12 wire wound on a 5" CD spindle cover for a form. The secondary coil was my coil of 1000 turns on a 1 1/2 piece of PVC. The frequency generator that fed the car ignition coil worked best at around 120 HZ. The output sparks were just under 1 inch in length. To get a picture I turned the lights off and took a time lapse picture. That is not really a powerfull spark, but it is a real Tesla coil.
Jacobs Ladder
I purchased a 10 Kilovolt Oil Burner Ignition Transformer (OBIT) on Ebay for my experiments. It does not mount to anything real well but it is set up nicely for a Jacobs ladder. I used two 1 foot long pieces of 10 gague copper wire. The gap at the bottom is 3/8 inches and it grows to 1.5 inches at the top. Once the wires are shaped correctly the spark will start at the bottom just as it disappears at the top. I had started with longer wires but the spark would only travel about 10 or 11 inches up the wires. I made a video of it but space limitations keep me from posting the video here. The sound the Jacobs Ladder makes is awsome!
