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PLEASE HELP! No output on my tesla coil

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lokeycmos

Sun Jun 24 2012, 09:46PM

Registered Member #2553 Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97

so i finally got my coil ready to fire it up. but im not getting any output from it. ive double checked everything, but no luck. im hoping someone more experienced than me can help me figure this out. do i have the grounding wrong? let me know if you have any questions or need more information. THANK YOU!!

Here is the video of it in action:

brandon3055

Sun Jun 24 2012, 10:26PM

Registered Member #4548 Joined: Mon Apr 23 2012, 03:52AM
Location: tasmania
Posts: 271

Might be a tuning problem what are the specs

Sigurthr

Sun Jun 24 2012, 10:35PM

Registered Member #4463 Joined: Wed Apr 18 2012, 08:08AM
Location: MI's Upper Peninsula
Posts: 597

1) your spark gap is WAY too wide and it doesn't look like you set your gap like you need to.

2) You NEED to ground the secondary return, steel of a garage door is NOT an RF ground source.

3) You will need to tap at not just whole turns of the coil but also as incrementally as 1/8 of a turn.

4) It is very possible you are using a topload which is much too large. It looks like you have about 12 turns on your primary, depending on secondary self-capacitance you may need far more turns than that for such a large topload. For example, in my similarly sized coil I need 14 turns for a much smaller topload of 4 inches in diameter, because my secondary has so much self-capacitance.

The larger the capacitance of the secondary and the larger the topload, the more turns you need on your primary.

Okay, now lets address each issue.

Fix #2 immediately. Run an insulated copper wire to your nearest cold water pipe if you have to, the thicker the wire the better, and stranded is better than single conductor.

Now, Fix #1 by properly setting your spark gap, the procedure is simple:

- Disconnect the primary and tank capacitor completely. You should ONLY have the NST connected to the spark gap now. It is important you are not using the incorrect schematic going around where the spark gap is in series with the NST. The Spark gap should be ACROSS the NST terminals, and the tank cap should be in series between one spark gap terminal and one primary terminal. Set the gap by adjusting it to be closer so that the arc jumps across the gap every time you turn the power on and it stays arcing while the power is on. Widen the gap as much as you can get with it still igniting and staying lit every time you turn the power on. That is it, your gap is set. Reconnect your primary and tank capacitor.

Now lets tackle #3. Set the primary tap to the most turns you can get. This means the farthest point (longest tube length point) on the outside of the spiral from where the pipe comes up on the inside of the spiral. Fire up the coil and see if you observe any output now.

If you do see output, try different tap locations via guess-and-check method to get best performance.

If you do not see output or it is very very weak output it is time to correct #4.

Your primary is essentially a fixed variable, in other words, it isn't worth it to heavily modify it to work with the cheap and easy to change topload. So, turn your attention to the topload. Remove the dryer duct topload and get say a softtball (or similarly sized round object) and wrap it with aluminium foil. Place this on top of the secondary and give it a shot. You'll have to use guess and check to find the needed tap point, as drastically reducing topload size will drastically change the tap point needed.

Keep in mind when selecting a topload it isn't the overall size that is important but the surface area, so a bowl can have a very large surface area even though it is visually "less than half a sphere" when looking at it from the side.

Finally, I am curious about your TC's specs. What is the NST rating (voltage out, current out, voltage in, mains frequency)? What are you using for your tank capacitor? These only affect the maximum output you'll get and have nearly no bearing on just getting -some- ouput. I recently proved that with a very badly designed thrown-together style untuned coil of less than 100VA you can get decent output with the right topload/primary combination.

lokeycmos

Sun Jun 24 2012, 10:51PM

Registered Member #2553 Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97

thank you for the detailed information! yes my gap is very wide. i will readjust that next. my primary is 14 turns. i do have a couple different top loads to experiment with. yes i am using the circuit with the spark gap across the output of the NST. My nst is 15kv 30Ma. 120v in, 60Hz. im using 10nF 50Kv(total) doorknob cap as my tank.

Ben Solon

Sun Jun 24 2012, 11:44PM

Registered Member #3900 Joined: Thu May 19 2011, 08:28PM
Location:
Posts: 600

That's a very small cap. You can make a homemade cap with a larger capacitance by making a few with al foil and overhead trancparencies and it'll easily withstand the voltage with 3-4 layers of dielectric.

PhilGood

Mon Jun 25 2012, 01:27AM

Registered Member #3806 Joined: Sat Apr 02 2011, 09:20PM
Location: France
Posts: 259

You could also add a break out point to your topload to help arcing out during tuning process.

Put a fluorescent tube near the topload to see if HV builds up. If not, check secondary continuity between bottom ground connection and topload.

Herr Zapp

Mon Jun 25 2012, 03:57AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

lokey -

How did you "design" all your coil's electrical parameters to ensure that it can be 'tuned" to achieve resonance? Did you use a Tesla coil design program, or run all the calculations "manually"?

What is the required inductance of your primary and secondary coils, what is the resonant frequency of your tank circuit (primary coil and primary capacitor bank), and what is the resonant frequency of your secondary with your selected topload?

If you don't have the answers to the above, use JAVATC (a "CAD" program for designing TCs) to determine the electrical parametsrs for each of the components of your coil, and make sure that it can be "tuned". Once we know that it (at least theoretically) should be able to achieve resonance, then we can work through a step-by-step troubleshooting process.

JAVATC is available at

Additionally:
1. Your NST is a non-GFI unit, correct? Does it say "UL 2161" on it anywhere?

2. Close your spark gap down to around 1/4" for initial tuning. Be advised that a single-segment gap will never achieve peak performance; build a mult-segment copper pipe gap with at least 4-5 segments (search "TCBOR gap" or "RQ gap").

3. Your garage door framing is NOT an earth ground, and if you try to use it as an RF ground the only ground path may be back through the electronics of your garage door opener to the AC line ground (in other words your garage door opener is at risk of being fatally fried). Move your coil to a location within a few feet of where you can pound a piece of 1" copper pipe at least 2' - 3' into moist earth.

4. To maintain decent pri-sec coupling, the "fixed" connection to your primary must be at the innermost turn, and your variable "tap point" moves radially outward for tuning.

After you get your JAVATC output file, post it here for review.

While you're working with JAVATC, post some good-quality photos here, showing all the main components of your coil and the interconnections, etc.

Herr Zapp

lokeycmos

Tue Jun 26 2012, 05:02PM

Registered Member #2553 Joined: Fri Dec 18 2009, 01:36PM
Location: St Cloud Minnesota
Posts: 97

here is a follow up video with specs. at the end of the video i have math and TeslaMap results

Tetris

Tue Jun 26 2012, 08:18PM

Registered Member #4016 Joined: Thu Jul 21 2011, 01:52AM
Location: Gainesville, FL
Posts: 660

Try it without the topload. Mine works a bit better without one, maybe yours will too. Calculate it for without a topload.

Herr Zapp

Tue Jun 26 2012, 10:46PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

lokey -

When you've got the tank circuit set up properly, the spark gap (set initially at 3/16" or 1/4") will make a continuous "sizzle" sound, not the erratic blasting shown in your video. There is no indication that your spark gap is actually firing, it looks like you are having arcing somewhere on the upper deck, possibly between primary and secondary?? This is a classic symptom of an ungrounded secondary.

Also, something's wrong with your measured vs calculated resonant frequency for your secondary. You say you "measured" it to be 325 KHz, but Teslamap claims it should be 281 KHz. That's a considerable discrepancy, so there may be some error somewhere in your inputs to Teslamap, or some variation in your construction. What's the resonant frequency of your primary circuit (or rather, the RANGE of resonant frequency adjustment, from two primary turns out to max)? Obviously, the primary circuit needs to be capable of being adjusted to the same resonant frequency as the secondary circuit, whether its actually 281 KHz or 325 KHz.

Do yourself a favor, re-enter all your coil's physical parameters into JAVATC (

), it will provide more useful information than Teslamap.

Just looking at your videos shows some serious mechanical design flaws, without even getting into the electrical parameters. Correct these problems first:

1. You apparently have BOTH sides of your capacitor bank bolted directly to the wooden baseplate. What's the spacing between screws, maybe 1-1/4" or 1-1/2"? At tens of thousands of volts, wood is nearly worthless as an insulator. Do some searching on the web under "surface tracking". I've seen similar construction fail several times, sometimes with surface tracking, sometimes along the gluelines in the interior of the plywood (if plywood is used). All HV connections need to be insulated from the wood by using plastic or ceramic standoff insulators.
2. Likewise your spark gap is bolted directly to the wood.
3. It looks like you have used galvanized steel pipe-strap to connect your capacitors together. Galvanized steel is a terrible conductor at the high peak currents in your tank circuit. Replace this square array of 8 individual straps with two long pieces of 1/2" wide copper strap. If you can't find copper strap, make it by carefully flattening 3/8" or 1/2" copper tubing or pipe.

4. Your "hubcap" topload won't work (at least not well) because of the sharp edges at the end of the big radii. The maximum breakout voltage of a topload is dictated by the minimum radius. The hubcaps have a large center radius, but almost a sharp edge at the end of the big R. You will have lots of corona leakage from these edges, limiting topload max voltage and limiting max streamer length. It might look cool, but won't generate long arcs.

Herr Zapp

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