Although my basic coil is now finished, that doesn't mean that I can't keep improving it! This page will keep you up to date with my latest tinkerings.
- August 11, 2001: Recently I was lucky enough to find another 15kV/30mA NST made by Standard Electric Works of Hong Kong exactly the same as my other NST. As soon as I can, I will try hooking the new NST up in parallel with the old one so that I effectively have a 15kV/60mA (900VA) power supply. I will also add another eight beer bottles in parallel to bring my tank capacitance up to 0.012uF (from 0.006uF). Hopefully, this will solve my breakout problem and provide me with longer streamers to boot!
- August 20, 2001: Success! I hooked up the extra NST and bottle caps last weekend and tested it out, with great results. Now I am getting bright, multiple streamers around 12" long, whereas before I could only manage one single streamer using a breakout point. Next, I think I'll try making a bigger topload to stack on top of the one I'm using at the moment this should give me one or two long streamers rather than lots of smaller ones
- September 10, 2001: After battling with flashover problems on the tank cap for several weeks, I've finally got my coil up and running again. In the meantime, I've built a larger 4" x 19" toroid from aluminium foil and corrugated drain pipe, which is now stacked on top of the smaller 4.5" x 10" one. Maximum streamer length is 14" to a grounded aluminium ladder. Primary is tapped at turn eight. Although they seem to have gone out of favour in the past few years, I'd like to try building some rolled or flat plate stacked polythene caps an MMC would be ideal but is still out of reach for me
- September 16, 2001: I've added a plot of my coil's electric field (generated using Terry Fritz' E-Tesla6 program and Microsoft Excel). This shows me where breakout is most likely to occur on my coil click here to see it (49KB GIF). I've decided to go with Marc Metlicka's party cup capacitor instead of a polythene unit price and simplicity of construction were the determining factors here. This should be built in the next few weeks watch this page for updates
- October 7, 2001: The party cup capacitor is built:
Unfortunately, it didn't fare too well when connected in parallel with my beer bottle caps (major flashover problems through the polystyrene dielectric). Perhaps the cups weren't quite thick enough.
In other news I recently obtained another microwave oven transformer (MOT), a 1uF 2000VAC capacitor, and a 12kV microwave oven diode out of a dead microwave oven, so I decided to experiment with drawing arcs off the MOT secondary using my other MOT as inductive ballast (WARNING: A MOT in inexperienced hands is positively LETHAL !) Here is the result:
As you can see, the MOT gives a very hot, flamelike arc. I tried a Jacob's Ladder arrangement, but I found that the relatively low voltage (about 2000 VAC) of the MOT stopped the arc from starting reliably.
- January 12, 2002: Well, I spent the $AUD150 or so to build an MMC, and I can say that it is definitely worth it. Pictures are coming soon.
- February 9, 2002: As promised, a picture of the MMC is up on the specifications page. I used a perspex microwave door to mount them on, which unfortunately had a black (read CARBON) surround bonded to it. After running the coil with the MMC for the first time, I discovered that the ends of the aluminium L-extrusion I was using as buss-bars were surface tracking to the black surround on the microwave door. Although this was not affecting the spark length too dramatically (I guess the HV just saw the surround as a high-value carbon film resistor), it demonstrates that insulators often turn out to be conductors where HV is concerned!
In other news: I lucked into three old NSTs the other day, all at least 60mA units (which is pretty rare here in Australia), and all but one functioning perfectly (even the 'bad' one has one good leg). There must be some truth in the claim that 60mA units are more reliable then 30mA ones, as these ones are all pretty old.
This one is running fine, and has some writing on the side opposite to the camera saying it tested OK in 1971!
- April 4, 2002: In a splurge of coiling activity during the Easter break, I have built a new 4" x 20" toroid for my coil using flexible aluminium ducting and two pizza pans. Apart from looking nicer than my previous toroid, it also yields slightly longer streamers due to the smoother finish. A photo of it can be found on the specifications page.
I am also working on a new vacuum gap similar to those on Greg Hunter's and Gary Lau's sites. It will use a 900W vacuum cleaner I picked up for $AUD10, plus some 3/4" PVC fittings, and a couple of 3/4" brass all-thread segments. Pictures of the gap, plus some more recent photos of the coil in operation will be up soon.
- April 5, 2002: I have added a picture of the coil running with the new topload and MMC on the results page. More to come once the vac gap is completed!
- April 19, 2002: A photo of the vacuum gap is up on the specifications page. Also, a new shot of the coil running with the vac gap can be found on the results page.
- June 1, 2002: After a bit of experimenting with my digital camera, I have finally got a decent shot of my coil running. It can be found on the results page.
- February 8, 2003: A flurry of activity on the ol' website, including the new hints and tips page, a diagram of my MMC on the specifications page, and some more shots of the coil doing its things on the results page.
- March 22, 2003: Thanks to some friends who have a digital camera that can record video footage, I now have a clip of the coil in operation on the site. You can get it on the results page.
It was my lucky day last week. I came across some more NSTs, courtesy of the friends whose camera I used to record the video clip. As well as the old-style units potted in tar (these included a Leda 15/30 and a Standard Electric Works 10/30), there was also a resin-potted Siet 10/30. I also came across a resin-potted Tecnoservice 7.5/30 on the same day... when it rains it pours :-)
Of interest to some people may be the OCMs (Open Circuit Monitors) I found on the newer Tecnoservice and Siet units - this is the first time I have encountered these. I had heard from the Pupman list that these can cause problems in Tesla coil use, but luckily they were separate modules that were not potted in the resin and were hence quite easy to disable. In the case of the OCM on the Techniservice NST, the connection was made using three sockets that fitted over the terminal posts on the NST for active, neutral, and earth - to take the OCM out of the circuit, it was simply a matter of undoing one screw and pulling the unit off the NST :-) Photos are coming soon...
I'm thinking that one of the 10/30s or the 7.5/30 might be good for a tabletop coil or even a compact Jacob's Ladder... only time will tell. I also haven't upgraded the main coil for a while (/me eyes off the 15/30)...
- May 24, 2003: Fixed up the video of the coil so that it's not so !@#$ big (it's encoded with DivX now, bringing it down to 2.9MB). The original clip also had trouble playing under Linux mplayer, but that's fixed now as well.
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