COLUMBUS OHIO |
UNITED STATES OF AMERICA |
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LOCATED IN GRANDVIEW HEIGHTS, COLUMBUS, OHIO |
Hal's 4 Inch Tesla Coil Project | ||
Updated February 21, 2007 | ||
Coil Plans Coil Assembly Transformer Assembly Control Panel | ||
July 1, 2006 |
January 10, 2007 | |
Click on photos above for an enlargement. | ||
Click here to see video of my coil. |
Coil Plans
Coil Schematic
Click on image above for an enlargement. | Here is the schematic for my 4 inch Tesla coil. The basic design is from Gary Lau's site (with
permission) but I have made substantial change. Note that the schematic reflects 3 separate sections to the coil assembly's overall construction:
the "Control Panel", the "Transformer Assembly" and the "Coil Assembly. Three lines of thought
go into this modular construction: inevitable future changes will be easier, the power source lies outside the strike zone and,
breaking down and transporting the coil will be easier and faster.
I got most of my information, concerning the construction of my coil, from Gary Lau and his Web site. For more about EMI Filters, and the correct way to connect them, see http://www.laushaus.com/tesla/emifilter.htm. For more about Terry's NST Protection Filter, see http://www.laushaus.com/tesla/protection.htm. For more about Power Factor Correction Caps, see http://www.laushaus.com/tesla/pfc.htm. For more about MMC Tank Capacitors, see http://www.laushaus.com/tesla/mmc_cap.htm. The photos and info that follow are categorized to reflect the 3 sections of my coil design, starting with the "Coil Assembly". |
Coil Assembly
Click on photos above for enlargements. | After finishing the rest of the coil assembly and running the coil's dimensions through Bart Anderson's JavaScript Tesla Coil Designer program, I found that I needed only 7.8 turns to match the secondary coil. After firing the coil for the first time on July 1, 2006, I found that those calculations were very precise. On July 5th, I trimmed the outer loops of the primary, leaving only 8.5 turns. |
Sucker Gap (Version 1)
Click on photo above for an enlargement. | I built my sucker gap after a trip to Home Depot. It is attached to the suck end of my shop vac
during coil operation. The gap is fully adjustable, since the PVC pieces are not cemented together. The pieces of the
gap fit well enough that none of the pieces shift during coil operation. Another advantage to not cementing the pieces
together is that the brass fittings, that I used as the gap electrodes, get tarnished rather quickly from use. Being able
to easily remove them for cleaning and polishing is a plus.
WARNING Spark gag systems emit ultraviolet radiation that WILL permanently damage your eyes. Never look at a sucker gap or rotary gap system during operation. UV sun glasses do not provide enough protection. As proof of my claim, the WHITE PVC pipe, that my sucker gap is made of, turned YELLOW from being exposed to the light from gap operation. Comparison photos to be posted shortly. | |||
Sucker Gap (Version 2) | My first sucker gap made long hot streamers but it had one major drawback: it only functioned at full voltage. In January 2007, I attended my first Teslathon, the Western Winter Teslathon. There I met Jeff Mullins and saw his series spark gap system. I decided then that I would make my own series gap. Since the sucker system had worked well on my first gap, I chose to incorporate suction in my series gap design. It took a month to accumulate the parts, finalize my design and build the thing. On February 19, 2007, I fired my series sucker gap for the first time. After several hours of testing and adjusting, I achieved some very good results, including the ability to turn the power down. Now, I can run the coil on input voltage ranging from 50 to 135 volts, which makes the coil much more versatile. I will be able to perform experiments and demonstrations that would not have been possible at full power. | |||
I made the base of my gap from 4 layers of 3/16" white Lexan. Phenolic would have worked just as well. The power tools I used to make it were a drill press, a router, a grinder and a jigsaw. | ||||
The electrode holders are made of 1/2" threaded couplers. I drilled a 1/2" hole in each, perpendicular to its length, to accommodate the electrodes. The electrodes are Miller Welder points, part #020603. The body of these points are 1/2" diameter steel, tipped with 3/8" diameter tungsten. To hold the electrodes in place, I used 1/2" hex set screws. The five grooves in the PVC pipe were drilled on a drill press using a 1/2" drill bit. Each set of electrodes fit snugly into the grooves in the PVC pipe. Flat washers are used as spacers to adjust the electrode holders to the proper height. | ||||
Half inch bolts secure each electrode holder to the top layer of Lexan. The electrical connection between each set of electrodes is made with 3/4" wide by 1/16" thick brass strips. Two layers of Lexan are required to match the height the heads of the 1/2" bolts, after the bolt heads are ground down by 1/16". The fourth layer of Lexan (not shown in this photo), is a solid piece that covers the entire bottom of the series sucker gap and acts as insulation. | ||||
Click on photos above for enlargements. | After several hours of testing, burn marks are seen on the PVC pipe, adjacent to each gap. Much of
this was caused by running the gap with the suction turned off, so to make comparisons. My testing proved that the gap runs much
more efficiently with the suction turned on, resulting in longer and stronger streamers.
In March 2007, I will build my own version of a Terry Blake style asynchronous rotary gap, to take the place of this gap. Toward the end of 2007, I will build a table-top Tesla coil and use my series sucker gap with it. |
Tank Capacitor
Click on photos above for enlargements. | I built the tank capacitor from 22 Multi-Mini Polypropylene Capacitors (MMC). They are
0.15 uF 2000 VDC Cornell Dubilier caps, Part Number 942C20P15K-F. The "F" in the part number means that the caps are RoHS
compliant: lead-free terminations. I purchased them from Eilene at Richardson Electronics, phone number 1-888-735-7358. If you
try to order them from their Web site, you have to purchase a minimum quantity; not so if you call directly.
My Neon Sign Transformer array (NSTs) consists of four 15,000 volt 30 mA NSTs, with the secondaries connected in parallel, for a total current of 120 mA: more than enough to kill you DEAD!! This amount of power requires the tank capacitor to have a mains-resonant value of 0.0159 uF. Using the "Larger Than Resonant" premise (LTR), the tank capacitance value is multiplied by a factor of 1.5 to 2.0. When the mains-resonant value of 0.0159 is increased by a factor of 2.0, the tank capacitance rises to 0.03 uF. For more information concerning LTR, see Gary Lau's "Steps to designing your own coil". Configuring the MMC array with two strings of eleven caps each, wired in series, with the two strings connected in parallel (see schematic), the capacitance becomes 0.027 uF. There is a 10M ohm 1/2 watt resistor connected in parallel to each capacitor in the array, as a safety precaution to drain the caps once the coil has been shut off. Each string of caps is mounted on separate clear Lexan panels. The two Lexan panels have been mounted vertically, in 1/2 inch deep slots, on a 3/4 inch thick, 6 ply plywood board. The sucker gap is mounted on the same plywood board. The board sits on the lower shelf of the table that supports the coil assembly. Gary Lau checked out my MMC strings and pointed out that there should be some space between each cap, to avoid them from arcing between each other. To avoid a complete rebuild of my MMC strings, I purchased .030 inch clear polyester plastic sheeting from my local hobby store and slid a piece between each cap. During the first firing of the coil, I didn't seem to have any problem with arcing. However, I did notice that several caps on the power supply end of both strings were perceptibly warmer than the others. This may be caused by my sucker gap design; it may not be quenching the plasma arc sufficiently. I really don't know. If any experienced coiler has an idea what's causing this, please email me. FYI, when running four 15KV NSTs for a total of 120mA, with a variac output of 135 volts, the current draw is steady at 11 amps. |
Transformer Assembly
Click on photo above for an enlargement. |
Before my second test firing on July 5, 2006, I added a fourth 15KV @ 30mA transformer which brought the total current up to
120mA. The results were dramatic. The coil spat out more vicious looking streamers that made regular strikes at four
feet. Video of my first and second test can be seen on my "4 Inch
Tesla Coil Video Page". My
"Terry's NST Protection Filter"
is mounted on top of the transformers. Fortunately, Terry designed his filter to withstand 120mA, so no modification was needed to
the filter when I added the fourth transformer. The four large capacitors sitting to the right are the "Power Factor
Correction Caps". Each is rated at 60uF @ 370 VAC, for a total of 240uF @ 370 VAC.
In January 2007, my nephew Craig made me a stout platform for my transformer assembly. The platform has casters, which makes moving the assembly a breeze. I have used this transformer assembly to power my Jacob's Ladder. To see a video of it in WMV format, click HERE. In November 2006, I connected the same Jacob's ladder to my 15KVA pole pig. To see a video of it in WMV format, click HERE. |
Terry's NST Protection Filter
Click on photos above for enlargements. | Terry's NST Protection Filter is designed to protect the secondaries of the Neon Sign Transformers (NSTs)
from being damaged during coil operation. The original schematic can be found
HERE.
Gary Lau made a variation of this filter for his coil. You can see it by clicking HERE and scrolling to the bottom of the page. I copied an innovation that Gary Lau designed to give warning if the ZNRs (MOVs) start to heat up. I have siliconed a 120 degree Fahrenheit thermostat switch (Stancor STC-120) to the end of one of the two ZNRs closest to ground. If the ZNRs heat up to 120 degrees, the thermostat switch will activate a 120dB siren (Radio Shack 273-079) that is powered by a 9 volt battery. I have mounted the siren and battery to the bottom of the filter board, as shown in the last photo. |
Control Panel
Control Panel
Click on images above for enlargements. | Here is the control panel. The box is a rectangular aluminum parking lot lamp housing: the type you see
shining down upon you from a tall pole in your WalMart parking lot. I took the glass out of its access door and replaced it with
translucent white 3/16 inch Lexan. The volt and amp meters I purchased online at
Action Electronics. The main power
switch in the lower right corner is keyed. The toggle in the lower left corner is a SPDT momentary that controls the variac.
The white knob on the left controls the RPM of the shop vacuum that will be connected to the sucker gap. Note that the unit is
operating in the top photo: the meters showing voltage and current flow. At the moment the photo was taken, the control panel was
being used to operate my Jacob's Ladder.
The second and third photos show the interior of the box. The variac, contactor and EMI occupy the right third of the interior, leaving the rest of the box for storage. The gray metal box mounted in the middle of the open space holds the tools that will be needed to maintain the coil. The space around the box is storage for the wires used to connect the three separate components of the coil. A clear Lexan panel separates the circuitry from the storage area. Mounted in the upper left corner of the interior of the box, is a 15 amp micro-switch, from a microwave oven door assembly, that shuts off the power to the entire box when the access panel is opened. In the schematic, this switch is labeled "Safety Switch". The schematic shown below depicts the physical layout of the control panel box. The simplified electrical schematic of the Control Panel, as well as the entire coil can be found here. |
EMI
Click on photo above for an enlargement. | I bought this 30 Amp Electro Magnetic Interference Filter (EMI) for $5.00 from Southwest Liquidators, Inc. in Tucson. See Gary Lau's EMI page for how best to use this type of unit. |
I fired this coil for the first time on the afternoon of July 1, 2006 and a second time on July 5, 2006. Video of both days can be
seen on my "4 Inch Tesla Coil Video Page" in Media Player format (wmv).
Many of the ideas for the construction of my coil came from Gary Lau. His coil circuitry and Terry's NST Protection Filter, are the basis for my coil's wiring. For tons of great info and insight, read Gary's entire site carefully, especially "Gary's steps to designing your own coil". Another great source for Tesla coil information is the "Tesla Coil Mailing List". There you can communicate with the worldwide community of Tesla coil enthusiasts. |
Hal's Physics page 4" Tesla coil video page Hal's Lifter page Hal's Van de Graaff page Hal's NST Repair page |
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