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Thu Apr 19 2018, 08:40PM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
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Posts: 10

Hi all,

After a couple of years I've decided to start working on my SGTC again.
I stopped working on it because I could never get it to output anything more than an electric fly swatter and it started to get frustrating.

First, some specs (measurements in centimeters)
7.6 cm diameter secondary, 41 cm in height. ~820 windings
21cm high, 42cm diameter (~6.9pF) topload made of aluminium flexible ducting
12nF, 8000V MMC (2 string of 8 47nF 1000v axial pulse capacitors)
~4.4Kv dual antiparallel MOT powersupply (core grounded), limited to 52W by a lightbulb in series with the primaries (lightbulb is interchangeable)
Single static sparkgap, currently set at ~0.06 cm
2 different primaries (for testing):
Inverse conical (5 deg) primary, ~4.5 windings of 12mm copper tubing, inner diameter ~9cm, outer about 54cm, 3cm spacing, tapped at ~3.5 turns
Cylindrical (90 deg) primary, ~10 windings of 2.5mm2 (13AWG)insulated copper wire, no spacing, 12cm diameter, tapped at ~8.7 turns

Pictures, schematics, etc. can be provided if needed.

After some calculations in JavaTC and a lot of testing I still can't get anything more than ~1-2 mm sparks out of it (sparking to a set of pliers).

I'm completely out of ideas as to why this doesn't work, as calculations in JavaTC seem to suggest this setup should output about 100Kv so I'm open to any suggestions.
I'd like to finally get this first (10+ years!) project working and it's frustrating to see some people just slap together a bunch of microwave parts and have a working coil

KUN

Fri Apr 20 2018, 02:03PM

Registered Member #61824 Joined: Mon Oct 02 2017, 05:38PM
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Posts: 40

Hi. JavaTC calculations may not be correct always, as there can be some parameters that you forgotten. Also, try adding another lightbulb in series with the first one to provide more wattage to the transformers. When you ensure that you have at least 100 wats, as 50 wats may not be enough for that settup, then try changing primary tap as you experiment with the coil, try connecting your coil to different spot in mmc. If it seems to make arcs longer, move in that direction until it no longer gets better. So try changing mmc, primary tap, and maby the height of the primary to change impedence. Make sure that there is no conductive things inside of your secundary. 2 mots may be tricky power supply for tc as they output reletively low voltage, so you need to provide more wattage to them so that they give their best, but not as mutch to trip the bracker(if you have variac it would help...

termination

Sat Apr 21 2018, 10:30AM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
Location:
Posts: 10

I did input all parameters into JavaTC, strange that it's calculation were off.
Anyhow, as per your advice, I've changed the ballast to a 1400W heating element and that did make a big improvement in corona discharge but still no breakout.
Since I didn't have a good ground plane and the bottom of the secondary was forming corona to the floor I used some chicken wire as a ground plane, added a drill bit to serve as a breakout point and used a vacuum cleaner to quench the sparkgap, and presto! ~30cm discharges. Finally!

KUN

Sun Apr 29 2018, 07:26AM

Registered Member #61824 Joined: Mon Oct 02 2017, 05:38PM
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Posts: 40

Nice, but for 1400 wats input, you should be able to get much more. I have really small coil wich at 160 wats, outputs 20 cm arcs. With 1400 wats you could get atleast 0.5-1 m arcs. Try grounding your coil to mains ground. Now when you have some output try changing amount of primary windings to see if it makes a difference, try changing the topload(try both round ball and toroid), and maby change amount of capacitors in primary capacitor bank.

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Tue May 01 2018, 08:17AM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
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Posts: 10

Yeah, it should be able to output more but it needs tuning.
I'm currently rewinding the inverse conical primary to better match the rest of the coil, changing it to 30deg ~7 windings.
Also, I'm upgrading the sparkgap. The whole setup was basically to see if it would actually work, now It's time to make it look nice.

You say connect the bottom of the secondary to mains ground, but I'm reading this is a really bad idea with all the RF feeding back in to the mains wiring.
As I live in a 3rd floor apartment, I think I'd upset my neighbours if I did that.

Since the chicken wire groundplane is way too small, some other electronics in the apartment don't respond that well to the coil running (the nearby microwave goes crazy, for instance) so I'm looking at building a faraday cage.
That is where I run into a new question: How should that be grounded? Connect it to the TC secondary base, ofcourse, but connect it to mains ground as well?
Should there be any filtering on the wires powering the MOT stack (230VAC) feeding into the cage? If so, how should that be connected to the cage?

I understand RF filters and chokes, I just can't get my head around how one would feed that into the cage and how the cage should then be grounded.

KUN

Fri May 04 2018, 01:17PM

Registered Member #61824 Joined: Mon Oct 02 2017, 05:38PM
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Posts: 40

Hi, other electronic equipement going crazy is pretty mutch normal. You can only prevent that if you put your whole coil in faraday cage. As for ground, you can atleast try grounging it to mains, and see what happens, i had my coil grounded to mains ground for a 1 year, and nothing blew up. Except for Electromagnetic waves radiated in air and causing television to work badly, internet crashes and so on, so mains ground will not be the biggest problem to your neighbours :D.

termination

Mon May 07 2018, 09:25AM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
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Posts: 10

That's exactly the idea, put the entire coil in a faraday cage. The problem is, how to connect to mains as just running a wire through would create a "leak" in the cage.

I'll try connecting it to mains ground, will shut down and unplug my PC just to be on the safe side though.

medved

Mon May 07 2018, 12:30PM

Registered Member #4338 Joined: Sun Jan 15 2012, 10:19AM
Location: Slovakia
Posts: 21

I have all my tesla coils (SGTC, SSTC, VTTC) ground into the mains ground for 10 years. I don't have any problem. The problem, however, is to radiate from the tesla coil - PC, TV, router... freezing my mouse and keyboard on PC, sometimes a TV signal failure... it's normal, but I've never damaged anything and never left any electronics. Okay, once I destroyed the washing machine, but it was a direct discharge into the front panel (SGTC)

.. but never through ground or at a distance from tesla coil. I currently have in my room a large VTTC with GU-5B just about 2 meters from my PC. My PC sometimes sends random characters on the FB or freezes mouse, keyboard, but the rest of the house is OK ! .. the only problem is the blinking of bulbs throughout the house every pulse of the VTTC

Anyway ... my friend is running big VTTC with 80cm discharges in the apartment and the neighbors do not know anything yet!

by the way, my little SGTC knew very well to disturb the TV signal, but at that time we had an analogue and not a digital one. Fortunately, the digital is a bigger problem to cancel

termination

Mon May 07 2018, 07:48PM

Registered Member #1559 Joined: Mon Jun 23 2008, 10:17AM
Location:
Posts: 10

Ok, that took away most of my concerns on grounding the secondary to mains ground.
So what about mains filtering? I'm currently using a stabdard RF filter (salvaged from a microwave). Would that do until I can cook ul something better?
Don't have a way of measuring RF on the mains (yet) so I'm being a bit (maybe overly) cautious.

Really thankful for the help so far though!

medved

Mon May 07 2018, 08:07PM

Registered Member #4338 Joined: Sun Jan 15 2012, 10:19AM
Location: Slovakia
Posts: 21

I don't know... I don't use any filters... and my PC is in the same socket where I also connect all my tesla coils. Directly from a 230V socket, usually on a regulated transformer (variac) and on the tesla coil. I didn't have a problem with this, so I didn't use any filters...

RF filter from microwave oven is better than nothing, but what is better... maybe someone else will know better in this advice, I would also like the experience of others in this...

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