This 6 inch coil has been a dramatic performer with sparks reaching 8 feet.
For more details and photos:
The 8 foot (96 inch) spark is exactly 3 times as long as the 32 inch secondary coil that generates it. This has a large topload and a tank capacitance of 92 nF (0.092 uF) at a power in excess of 5 kVA. A lot of smoke comes from my spark gap at runs of over 5-10 seconds at the highest powers. I suspect it is metal oxide from the tungsten stationary electrodes and the brass dome nuts and steel bolt heads that form the rotary electrodes. There was no sign of any polycarbonate frame or Tufnol wheel overheating. Despite the leaf blower cooling, the tungsten rods become hot enough to have a visible glow though the yellow polypropylene box after turn off.
Predicted maximum spark length by John Freau’s formula for 3 kW is 1.7 x sqrt 3000 = 96 inches. For 5 kW it is 120 inches. These seem to be most accurate for large (24 inch diameter) coils. A recently proposed correction by the late D. C. Cox gives spark length for a 6 inch coil = 0.85 x {1.7 x sqrt (power)}. This would suggest spark lengths of 79 inches at 3 kW and 100 inches at 5 kW.
Earlier photos reaching up to 6 feet with a capacitor of 48 nF and a smaller topload at a power of about 5 kVA. They are 10 second exposures showing a variety of types of sparks and streamers. Lots of ground rail strikes resulting in arc-overs from the primary (the bright spot in the right photo). These improved with a smaller toroid under the larger one. In these early photos, It is all supported by a stylish barstool and is precarious, particularly as the toroid is supported by a heavy 12 inch loudspeaker frame including magnet.
This 10 second exposure of the Tesla coil 6-inch demonstrates the shaping of the high electromagnetic fields around the main coil that directs away them from the axis of the coil. The strong wind at the time shows the multiple sparks going down the initial ionized path of each main strike (banjo effect). This is best seen on the enlarged view.
Related pages
Try something else
External links
Photo Date: Feb 2, 2006