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Step 5The spark gap
The spark gap is made entirely of brass hardware and HDPE (polyethylene) plastic. The base is a HDPE cutting board 8 by 6 inches. My first spark gap was a simple two electrode model, but it quickly overheated in use, so I put together the four post model you see here. You will need 4 90 degree brass brackets( 2 x 2 inches), 2 0.75 inch 6-32 brass bolts, 2 2.5 inch 6-32 brass bolts, two 6-32 brass nuts, 4 6-32 brass thumb nuts, and four 0.4 inch (10 mm) solid brass balls, drilled and tapped for 6-32 threads. These balls are sold as lamp repair parts in many hardware stores and home centers. You will also need 6 short machine screws.
The two center posts are mounted on the HDPE base with a single machine screw in the rearmost bracket hole. The screws should be short enough they do not pass all the way through the plastic base. If they do you will have arcing through them when the coil is energized--not a good idea. Using one screw in each bracket allows you to pivot them slightly to adjust the spark gap.
A 0.75 inch long bolt is put through the top hole of each of the center brackets and a nut is turned on tight. Add a brass ball to each post.
The other two posts are adjustable as to length and spacing. Place one at right angles to the center posts and screw it down with two machine screws. Put on thumb nut on one of the long brass bolts. A high voltage wire from the power supply will attach here, and the wire going on to the capacitors. Put the second thumb nut on after the bolt has passed through the bracket. Tighten, then add the ball electrode. Repeat this assembly for the last post, which is mounted at a 45 degree angle to the rest. (This angle is strictly a matter of convenience due to the size of the base. If you have a larger base, you can set the last post perpendicular to the center posts). The other lead from the power supply goes here, and the HV line going on to the primary coil.
Adjust the four electrodes so that they line up and have about 1/16th inch gap between them to start with--about 1mm or slightly less. Adjust as necessary to get good output.
In operation the multi gap still gets warm. When the air is ionized, it adversely affects the rate at which the spark gaps fires. The result is fluctuating power levels and poor output. The gap can be cooled by a stream of air from a vacuum cleaner with its hose reversed, a hair dryer set on unheated air, or even a converted computer cooling fan. Quenching the gap will greatly improve the performance of your coil.
Do not look at the spark gap when it is operating. It gives off intense UV light, like a welder, so avoid looking at it or else shield it in some way. When the coil is operating there is lethal voltage going through the spark gap--do not touch it!
Update 6-25-09: Spark Gap Mark III. I rebuilt the four post spark gap with much larger components. (See pictures). Instead of the little 10 mm brass balls, I installed four brass knobs designed as drawer or cabinet pulls. The two egg shaped knobs are lacquered brass; the spherical knobs in the center are satin nickel plated brass. The brackets and supporting bolts are the same as before
The larger knobs work very well and handle the heat of spark gap operation better. They are superior to the smaller electrodes, and and being threaded for the same 6-32 bolts, they are easily exchanged.
Update 8-3-10: For even better performance, try making a pressurized spark gap, as described here: http://www.stephenhobley.com/blog/2008/09/10/petes-quick-hyperbaric-spark-gap-tm/. I used smaller components than shown--half-inch copper pipe and a half-inch sized PVC junction box--and it works very well when connected up to a small vacuum cleaner. See this video for example.
The two center posts are mounted on the HDPE base with a single machine screw in the rearmost bracket hole. The screws should be short enough they do not pass all the way through the plastic base. If they do you will have arcing through them when the coil is energized--not a good idea. Using one screw in each bracket allows you to pivot them slightly to adjust the spark gap.
A 0.75 inch long bolt is put through the top hole of each of the center brackets and a nut is turned on tight. Add a brass ball to each post.
The other two posts are adjustable as to length and spacing. Place one at right angles to the center posts and screw it down with two machine screws. Put on thumb nut on one of the long brass bolts. A high voltage wire from the power supply will attach here, and the wire going on to the capacitors. Put the second thumb nut on after the bolt has passed through the bracket. Tighten, then add the ball electrode. Repeat this assembly for the last post, which is mounted at a 45 degree angle to the rest. (This angle is strictly a matter of convenience due to the size of the base. If you have a larger base, you can set the last post perpendicular to the center posts). The other lead from the power supply goes here, and the HV line going on to the primary coil.
Adjust the four electrodes so that they line up and have about 1/16th inch gap between them to start with--about 1mm or slightly less. Adjust as necessary to get good output.
In operation the multi gap still gets warm. When the air is ionized, it adversely affects the rate at which the spark gaps fires. The result is fluctuating power levels and poor output. The gap can be cooled by a stream of air from a vacuum cleaner with its hose reversed, a hair dryer set on unheated air, or even a converted computer cooling fan. Quenching the gap will greatly improve the performance of your coil.
Do not look at the spark gap when it is operating. It gives off intense UV light, like a welder, so avoid looking at it or else shield it in some way. When the coil is operating there is lethal voltage going through the spark gap--do not touch it!
Update 6-25-09: Spark Gap Mark III. I rebuilt the four post spark gap with much larger components. (See pictures). Instead of the little 10 mm brass balls, I installed four brass knobs designed as drawer or cabinet pulls. The two egg shaped knobs are lacquered brass; the spherical knobs in the center are satin nickel plated brass. The brackets and supporting bolts are the same as before
The larger knobs work very well and handle the heat of spark gap operation better. They are superior to the smaller electrodes, and and being threaded for the same 6-32 bolts, they are easily exchanged.
Update 8-3-10: For even better performance, try making a pressurized spark gap, as described here: http://www.stephenhobley.com/blog/2008/09/10/petes-quick-hyperbaric-spark-gap-tm/. I used smaller components than shown--half-inch copper pipe and a half-inch sized PVC junction box--and it works very well when connected up to a small vacuum cleaner. See this video for example.
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What is your capacitor? Have you tested it for correct function?
How wide is your spark gap? A too wide gap will prevent the coil from working.
How is your secondary wound? How big is it? What gauge of wire?
How is your primary wound? What gauge? How many turns? Is it wound the same way as the secondary, or in the opposite direction? Opposite winding will keep the coil from working properly.
How big is your transformer (how many volts, how many amps)? What kind is it? If it is a modern sign transformer it will have Ground Fault Interrupt (GFI), which prevents it from working in a spark gap circuit. This, I suspect, may be your problem.
Paul
My spark gap is set up so each knob is extremely close to touching but is not touching.
My secondary is 24 gauge magnet wire gauge wire with approximately 443 windings.
My primary is 12 gauge wire with 5 windings. I think it might be in the opposite direction.
My transformer is a Pro Series Low Glow neon sign transformer. The input is 12-15VDC at 5 amps (max.). The output is 9500V; the output amperage is 30 mA. It also has an 8 amp fuse.
Paul
Try a local sign shop. A lot of businesses are switching from old style neon transformers to the transistorized type with GFI. Go to a shop that sells or services neon signs and ask if they have any old type transformers. They may just give you one to get rid of it.
Try a heating contractor and ask if they have any oil burner ignition transformers. Specify you want one without GFI!
Good luck!
Paul
http://www.mylampparts.com/Departments/BALLS/BRASS-BALLS/2---PIECE-BRASS-BALL.aspx
for example
Paul