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Well, I was working on my coil yesterday, and I was trying to tune my coil. I've been doing it by trial and error. After getting the proper capacitors (big thanks to Killa-X and Kizmo), I was able to get a decent spark gap arc (previously it didn't make my ears ring for an hour afterwards. Now it does, so I know that works! :P), and now that I have a slightly more decent primary (instead of looking like a 3 year old wound it, it looks like a 7 year old wound it), I think that it's going to be as good as I can get it at the moment. If I get a summer job, I might pay someone to make one for me. But until then, I was curious to see how the coil worked. The arc looks similar to the last time, but at that time, my secondary was in a lot better shape than it is now, and I had used a different topload of which I couldn't find this time. (about an inch, inch and a half only with a grounding stick). I am just wondering how to tune the coil. I know my primary is the second worst ever built (second only to my first one) but with a 1 inch turn spacing about of 1/8 inch solid copper tubing (no place carried 1/8 inch piping) and I don't know the number of turns at the moment. The power supply is a 7.5kV 30mA NST, cap bank around 16.9 nF. I will rewind a new secondary with similar specs, but this time using 26awg much better wound around a 3.5inch diameter 16 inch long PVC form. I don't know about the inductance or the capacitance of the topload, nor how to calculate it. But approximately what turn do I tap the primary on? I know I won't be able to do anything until summer, but I want to get a good idea of what I have to do. If I missed out on a spec, I'll add it later. :D Thanks
Also: I learned yesterday that you should try and secure your topload in a way that a grounding stick won't accidentally knock it over, causing you to jump back in surprise, and hit your tailbone on the sharp part of the open car door. Also, I don't know how to ground the secondary without the wire touching the primary. I used plastic drink lids to sort of hold it up, but it really looks ghetto, heh. If someone can tell me a way to hold it up properly until I get a form, I'd be happy :D
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
I use a small battery operated signal generator and dump a signal into the secondary and watch for peaks on the oscilliscope but there is another way.
I believe this little device was Terry Fritz's tesla coil tuner, I have used it and it works quite well. What I do is connect one lead to GND and the other to the secondary base wire( the wire from the bottom of the secondary and then scan through the frequencies by rotating the POT until the LEDS are the brightest. That is going to be Fro of the secondary.
Now leave the POT in that position. Connect Your primary in series with your secondary. Connect one lead from the tester to the other lead of the cap bank and the other lead of the tester to the different tap positions on your primary. when the LEDS are at their brightest you have found the correct primary tap spot to match your secondary.
I haved used this device many times over and over and it works really well. Whats nice is you dont even have to know what frequency your tuned too. I usully check the frequency it lands on either with my Fluke meter or the scope just so I know where I am tuning too. Here is a link to the tuner:
Registered Member #3324
Joined: Sun Oct 17 2010, 06:57PM
Location:
Posts: 1276
Dr. Brownout wrote ...
I use a small battery operated signal generator and dump a signal into the secondary and watch for peaks on the oscilliscope but there is another way.
I believe this little device was Terry Fritz's tesla coil tuner, I have used it and it works quite well. What I do is connect one lead to GND and the other to the secondary base wire( the wire from the bottom of the secondary and then scan through the frequencies by rotating the POT until the LEDS are the brightest. That is going to be Fro of the secondary.
Now leave the POT in that position. Connect Your primary in series with your secondary. Connect one lead from the tester to the other lead of the cap bank and the other lead of the tester to the different tap positions on your primary. when the LEDS are at their brightest you have found the correct primary tap spot to match your secondary.
I haved used this device many times over and over and it works really well. Whats nice is you dont even have to know what frequency your tuned too. I usully check the frequency it lands on either with my Fluke meter or the scope just so I know where I am tuning too. Here is a link to the tuner:
--Brian
Wow, i read what you were saying about the tuner and thought the circuit would be rather complex so i went and had a look at it, Wow, theres almost nothing too it!, hmm, how did Terry work out that circuit anyway, how does it work?
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
Baiscally its a oscillator ciruit with an adjustable output. The ouptut is connected to a couple of LEDS through a coupling capacitor, the LED diodes are connected anti parallel to each other so one or the other comes on with either a positive or negative signal swing.
The variable resistor or POT controls the frequency, in the configuration it has more than enough frequency swing for most of the coils.
So it is an adjustable signal generator so to speak so sweeping the pot back and forth until the LEDS light up the brightest gives you your Fro.
I have tuned SGTC coils and DRSSTC coild with this. If you build one I would suggest using a 10 turn pot. I used a fairly low budget pot and I think I am going to change it because with a 10 turn it will give you much better control of finding the sweet spot.
Registered Member #2405
Joined: Fri Oct 02 2009, 12:59AM
Location: Wisconsin
Posts: 140
I can say that I am driving my LEDS a little hard in mine and it is difficult to see the parallel resonance. That is why I connect everything in series when I use it even when checking the primary tap position. You figure in series resonance the resistance is at a minimum and that allows the most current to flow through the LEDS and lights them the brightest.
In parallel resonance the resistance would be at max and that would reduce the current going to the LEDS and they would be at their dimmest. But my Blue LEDS are being driven to hard (they are in spec but these LEDS are bright) to realy see that so I series connect everything and then just reconnect it up the right way once I find the tap postition.
And so far its been right on. I am sure you could use a scope with this as well and then just watch for maximum amplitude on the scope. But this little gadget is really handy out in the field.
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How do you tune a SGTC?
