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UK Teslathons
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My High Point......Ten Foot + A Personal Record |
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A nice 10 foot+ strike. (taken from a video) The toroid break-out point height was 74 inches high, while the distance to the strike screen (located to the right and horizontal to the toroid) measured 97 inches (8 foot 1 inch). |
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Once again, the city of Cambridge acted as a magnet to those with an interest in tesla coils, as for the eleventh time it hosted the annual Cambridge Teslathon. I therefore decided to lug a lot of what is basically, copper wire, vinyl and heavy iron, 170 miles up the motorway network, swearing that I will never do it again, exactly as I had said last year, and, no doubt, as I will say again next year. |
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The coil has recently had an extra 30nF added to the MMC, as has been explained here, and this extra capacitance seemed to have improved the intensity and ferocity of the sparks. I ran the coil initially with a break-out point and found no difficulty at all constantly hitting an earthed screen erected 8 feet away (measured distance) Unfortunately the overhead lighting conduits were also at an 8+ foot distance and they acted as a limiter on what I could achieve. Most of the runs on the second day of this two-day event were done without a breakout point (BP). This changes considerably how the coil behaves at start-up. With a BP fitted, the coil would start to fire when the variac was inputting just 50V. (250v normal mains voltage - UK) Without the BP fitted, I found the coil would only breakout when 200v to 210v was inputted. This shows how the larger minor diameter of the new the toroid was doing its job and holding back the charge nicely. When the coil did eventually break out, it was violent and loud, like a firecracker going off. |
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The resonant frequency of the secondary was 81 kHz in the hall, as the overhead lighting conduit was having minimal effect on the frequency on this occasion. Whilst tuning the secondary with the oscilloscope I did find that once the display showed resonance (display shows maximum amplitude) that this could be altered by anyone approaching anything closer than eight or nine feet. This would also apply it seems to its vicinity to other objects, hence my concern about the overhead lighting conduit. With my previous 6 x 24 inch toroid, you could approach within six feet without any effect. I presume from this behaviour that the larger toroid creates a much broader field. I next ran a couple of artificial streamers from the toroid to simulate the capacitance of real streamers and found that the frequency then dropped down to the region of 70 kHz, dependant on the streamer length. I therefore tuned the primary to 70 kHz to allow for this. This meant the coil should be closely in tune when a streamer forms. Prior to that happening the coil is obviously slightly out of tune, but it does not seem to be too critical of this, and in fact seems to benefit more by being in tune when a streamer is created. |
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The Low Points It was not an event entirely without incident however. At one time, a fluorescent lighting tube decided to commit suicide by falling on someone's head whilst they were filming a run of my coil. The said person though is the tesla coil world's equivalent of an 'Ambulance Chaser', as the first sign of any smoke will always be well documented on his website. (See here for the gory details) Prior to this, I had managed to badly burn the winding of the variac I use for the Phase Controller. This was caused it seems by a dirty contact between the wiper and its winding, creating a high resistance point that heated up. Fortunately, Derek (aka 'The Ambulance Chaser') came up with the simple solution of using the variac reversed. This was possible because in the arrangement for a phase controller, the variac is wired simply as a variable inductor. (See Phase Controller link above). |
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