Arcs at about 1/3th power. Did not continue further yet.
I'm glad I'm able to post here, that's for sure. This thread is a) to show off and b) to provide data about my working coil. Also some kind of worklog to dump data for myself and anyone else, I guess. As of this moment I have to wait for my USB oscilloscope, so I can't provide 100% detailed information about this working coil just yet.
Building
I got my coil about three weeks ago, and I started soldering the same day. I got both of them done a few hours later, soldering is such a calming and satisfactory job, really. It was with the low power testing stuff went wrong. I mounted the 5V voltage regulator the wrong way around, causing the full 15V of the 15V regulator to unleash its fury on my HCT chips. They did not survive and smoke got out. Electronics work on smoke, once it gets out it's broken, so I just went on with the rest of the build. Something to put in the manual: Test the voltages before putting in the IC's, that's basic electronics right there, and even I got tricked by the manual saying otherwise. I also had problems with the green LEDs in both the main board and the interrupter. The green LEDs are manufactured backwards. Check if the cathode (the big dish) inside the LED is on the negative side, that should do it.
Building the rest wasn't hard, but I think the primary coil could have a more nifty way of applying it to the acrylic cylinder. Trying to wrap it around with the clips in place and everything moving all over the place isn't really my thing. I'm thinking of designing something better, but also for tuning the primary circuit better somehow, by varying the coil turn amount.
When I got my replacement chips I could proceed with testing the GDT. By the way, the normal LS versions do not work. At first my local supplier only had these so I tried them anyway. The GDT buzzed happily so the next test up was the IEC power test, which it passed. Another thing for the manual: during the high power test, do not touch the top of both capacitors to feel if they're hot. The manual states to check if those get hot, in case of reverse polarity. Unfortunately, there was in my case 150VDC between the tops of those caps. Was a nasty surprise, but I'm probably used to it.
Startup problems
After the tests the only thing I could do was proceed with the full test: applying power and starting the thing. I did this outside, with a counterpoise of aluminum foil underneath the coil, on a table. The coil and counterpoise were grounded to a port under the attic. I was under the carport, but it was a rainy day, so the humidity must have been high. The resistance from top to ground was measured at all times.
When turning on, buzzing was heared, but no sparks seen. I've turned it up until 1/3 power, and the buzzing got louder, but no sparks. After that, I tried more grounding by connecting everything to a metal pin in the ground, but that did not improve the thing further. I detached the topload, and it turns out that my coil was arcing on the inside. After this, the GDT also stopped buzzing, so I figured that the gate drivers also must've died
I've moved the wire in the photo, but before the arcing it was vertically down from the nut in a little loop. I eventually fixed it by doing a few simple stuffs. First of all, I let the wire run on the outside of the coil to the topload. I used lot's of hot glue to isolate the exposed nut on the inside of the coil. My best guess is that this at least prevents the arc form entering the inside of the coil. I also ordered some more silicon.
Working coil
So yesterday, With a complete package of IC's, gate drivers, IGBT's and a lower value tank capacitor. I tried testing again. This time inside.
With this setup I went for testing. One tesla coil standing on my counterpoise of aluminum foil. The foil is connected to the ground on my IEC cable, and both of those grounds are connecting to a pipe under my sink just on the left. The breakout point was aimed at the foil sticking out the most. When turning on, a little blue/violet spark was visible on the breakout point. Finally output!
Unfortunately that didn't last long. When I was bathing in a nice smell of ozone and pushing beyond 1/3th power, the spark was maybe 5-7cm long, before it suddenly stopped It still buzzed a little when turning the power knob, but no output. Closer inspection showed that the top half of the bridge was damaged. This IGBT showed no resistance between collector and emitter.
Today I installed the new bridge IGBT's, and also the default 68nF tank capacitor, as I had the suspicion this wouldn't hurt my primary resonance. Throughout this last 2 weeks, while reading this forum, I got more and more convinced that the secondary circuit had a larger frequency than the primary. A post of one of the oneTesla members told that to increase the primary oscillation, a smaller value tank capacitor could be used instead of adding more topload, or decreasing primary windings.
Time for some testing again. I also had a power meter connected to the outlet where the coil was connected to. I am measuring the current draw from the mains, so I can see what happens. This is a pic of it:
When firing up, a tiny spark again. Oh well, output at least:
Turned it up to 1/4th power:
This runs stable, so I've even tried 1/3th power. The sparks are getting so much longer and fatter I did not dare to go higher, breaking one bridge is costly enough as it is, let alone the repair work itself turn out to be a pain in the *ss.
Specs and measurements so far
- Original oneTesla coil
- 230V edition
- 47nF tank capacitor, instead of default 68nF cap
- 6 primary windings, close together
- Secondary resistance: 221 Ohm
Current draw vs power setting vs spark length:
Coil off:
0%: 0,006A - no sparks (obviously), this seems to be the idle current draw
Coil on:
0%: 0,058A - 1cm tiny sparks and corona visible
25%: 0,207A - 5~7cm sparks
33%: 0,512A - 20+cm sparks
50%: 0,765A - 30+cm sparks
75%: 1,052A - 35+cm sparks
100%: 1,574A - 35+cm sparks
Will try to fill in some more data when I dare to run higher.
The noise level is high! Even at a third of the power I'm not keeping it up for long, because it gets late here. For now I can experiment and try out stuff. I'm waiting for my scope to take some better measurements, because I still feel it's a little out of tune.
All in all, it's a nice kit. I would see some more protection around the IGBT's, as burning them out is expensive, and a hassle to replace. Also, be prepared to spend some more money on replacement parts. I'm happy to have some in stock, in case stuff goes wrong again. I'd like to use this coil as a stepping stone to a bigger tesla coil, with spark gaps and stuff, but first I'd like to tune this to behave well.
Yet a few questions remain here:
- My arc sounds like crackling or popping sometimes, is this normal behavior? Deemed normal, it has something to do with the interrupter coding
- I tried running some MIDI files, but the software seems buggy and freezing. The USB adapter is recognized only half the times, and 1 or 3 seconds in the song, the sounds freeze on the last played tone. I don't know if this is my interrupter, or the software. Fixed, the electric field was disturbing the midi cable
- Does anyone know an acceptable mains draw of this 230V edition when in full power mode? This way I can aim for something. Got it