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Re: Re:High speed Tesla spark photographs - A summary of developments



Original poster: "Peter Terren" <pterren@xxxxxxxxxxxx>

Just an update summary for those who came in late in this field that is only just over a month old. Current state of art (in my part of Australia) is that I have a rotating mirror (10 x 15cm, 2000RPM) to look at Tesla coil sparks. Taking a spark photo through this results in a smeared image, or would normally, except that sparks are for most purposes instantaneous events and appear sharp. Anything that happens a few microseconds later will be displaced and visible separately on the photo. Typical events that can be made visible by this technique are streamers that develop over perhaps 5 or 10 cycles (ringing up) and can be seen to progressively lengthen until a spark connects. Other events such as the oscillation that takes place after a spark to ground (ringing down) are also seen clearly which occuur at the TC resonant frequency of about 100kHz. Superimposed on this, and predicted by Terry's models, is an oscillation of longer frequency which in my case is perhaps 8-10kHz and probably due to the difference between primary and secondary resonance. It is seen best with streamers as bunches of oscillations of perhaps 10 cycles as streamers develop, diminish and redevelop. Current flow can be monitored with surprisingly hardy red LED's and the polarity of each resonant ring at 100kHz can be seen. Current can be estimated similarly. Even more sensitive but non polarised indicator of current flow can be shown with a small sprk gap arrestor or a small xenon flash lamp from a disposable camera. This can indicate current flow even below the light level of the camera and shows for example that the ring down can extend for many cycles. Unusual effects of polarity are seen as as well. For example a streamer branch showing alternate ring up pulses going in different directions eg positive to the left, negative to the right. Also have a shot of a streamer developing into a weak ground strike because it fell into a low voltage region of a harmonic. Curently, I am working on a better mirror mount with less flex stress bending the mirror and this seems to help. I have ordered new "proper" mirrors as suggested by Terry below. Also need to work out why the LEDs vary in effectiveness and some of the voltage dividing stuff for a current meter.
Starting to work on my new "secret weapon" soon too.
Terry has made up his own superfast rotating mirror unit (10,000 RPM) and is also getting great results. He is planning a voltmeter/current meter for his unit as below.
Peter
http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark%20photography

Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx>
Hi Peter, ....
Looks like the back surface mirror causes a few little problems after all. This guy has big front surface mirrors that go real cheap!!
http://stores.ebay.com/vette4jja30
.. I just got the parts on order for a 20 element voltage bar graph that uses 5 LM339s, high-brightness LEDS, etc for +-5V. It will be able to run off standard current monitors, DigiKey cheap CTs, or across a resistor. Three green LEDs at +5, 0, -5 will provide a bit of a vertical "grid" and it will be a "bar" graph so it might be fairly accurate.

If you can, you might try surface mount power resistors like the 1W ones. I found they we much more tame back in the fiber optic probe days. They are a bit fragile and hard to solder using them as discrete parts, but they perform very well (like they are supposed to) at RF.

Cheers,

        Terry