Original poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx> Hi Peter, Cool as always ;-)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 Apparently they are easy to chop to size with a glass cutter.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
At 09:55 AM 10/2/2006, you wrote:
Well, I've taken well over 500 photos today and have whittled them down to 100 for a closer look.There is a little mirror aberration giving ghosting due to flex of the mirror in the support giving horizontal displacement. Seemed to get worse during the day so needs a new design with no stress and epoxied in place. Possibly a proper mirror. I now have had full 2 foot spark with a spark that is 3 pixels wide (1 pixel per microsecond in these shots). This was a daytime shot and in retrospect was probably sharper than the night shots as it was f18 and 1/10 sec. Night shots were f3.5 and longer duration. I got quite interested since almost all of my photos showed the negative LED firing well, but I expected it was due to some asymmetry in the LED's as it seems to be just happening today. Makes you wonder though as I was using slow ASRG rates today. I did try a current meter but I have had problems with it. Possibly overvolting the metal film 1.8 W resistors. Certainly looks like one resistor is open circuit here. They should fire at 0.01, 0.1, 1 and 10 amps respectively but the 1 amp LED is firing too readily. The 100A and above LED's never fired. (but did with a capacitor on a rectified ignition coil setup). I was intrigued by a streamer shot showing a second and possibly third group of streamers following. I added a spark arrestor and a disposable camera xenon flash in series with unprotected LED's and got an interesting but blurred streamer shot showing a remarkble 6 streamer groups that the camera and LED's weren't picking up. Seems like there is a another frequency superimposed of perhaps 8-10kHz. I presume that this is the difference between primary and secondary resonances (the "notch"). I am running it a bit out of tune still so that may account for that. It could actually explain a row of negative only ring down sparks as well.Pics here http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark%20photography%20-%20large%20mirror PeterOriginal poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx> Hi,Nice Peter! Just mounting a single mirror close to the spinning axis is a nice way to go. My block mirror does get along "aerodynamically" better though since it is less of a flying wing. Back surface mirrors should not be too bad since we always take the pictures at a significant angle where direct reflections are not a problem. Common mirror distortions and some lens effects will be there, but I don't think we would really notice for this work. A common cheap plate glass mirror might do perfect fine!"I" have not made any progress these last days due to other stuff going on... Cheers, Terry At 10:38 AM 10/1/2006, you wrote:I have been a bit busy with other pursuits such as picking up some big old discarded physics equipment and attending the Tesla exhibition. A week without new developments has been a long time in the high speed Tesla photography field. I was however able to obtain a new higher quality mirror of 10 x 15 cm which although rear silvered, does not show any distortion visibly when viewed from a distance. It is well centered but moves a fearsome amount of air and has some vibration at 3000 RPM (250 VAC) but 2000 RPM (85 VAC)seems comfortable. It is a big mirror to spin fast but the aluminium supports seem to hold it firmly without adding too much weight or obstructing the view. The reduced revs should be countered by the much clearer and wider view. Still needs to be tested in use though.http://tesladownunder.com/HighVoltage.htm#High%20speed%20Tesla%20spark%20photographyI have also done some testing on a 7 stage LED meter to get the feel for how it will work. Now have to make a reverse copy to indicate the opposite polarity then run things with the new mirror.PeterOriginal poster: Vardan <vardan01@xxxxxxxxxxxxxxxxxxxxxxx> Hi Peter, .......The mirror was spinning at 7500 RPM in those photos but "cheap cam" made it look "still"... I have been pushing higher RPMs now to separate the lead up leaders... If anything gives way, I get to go buy a "new" camera ;-))...... Cheers, Terry-- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.407 / Virus Database: 268.12.11/460 - Release Date: 1/10/2006