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Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Hi All,
First, I have to say this site is so useful and informative. I've been reading it for the last week while I built my first TC. Hopefully someone here can help my figure out somethings...
My first (Ver. 1A) TC was a bust, probably rushed a few things. I rebuilt half of it (Tank Cap / Spark Gap / Primary Coil) to slightly different specs, and I have a working TC. Can I tell you how gratifying it was to finally have a working TC? My Plans are attached...
Now for some help (hopefully...)
I can't get the Top Load to break out alone. I have to bring the Earth-Ground within 4" of the TL. I'm going to guess that my Tank Cap (MMC) is not big enough.
5kV 30mA NST - nF rating of TC approx 22.3 nF. My TC is 4x2 2000V 47nF Caps (4 Series, 2 parallel strings) for 8000V 23.5nF
To stay at the 23.5nF TC, using the same (readily available) Caps, I can go 6x3 (12kV), 8x4 (16kV), or 10x5 (20kV).
Second "interesting" thing - When the Earth Ground is ~4" from the TL, there are some strikes, but there are also small 1" streamers running from the Ground to the TL??!!?? I would expect it to go the other way. Any Ideas?
Registered Member #1732
Joined: Thu Oct 02 2008, 02:34PM
Location: Huntsville, AL
Posts: 112
First you should check that the coil is properly in tune. Put a breakout point on the topload and move the tap on the primary until you achieve the longest streamers. If the coil is in tune than your topload may be too large for the coil to have spontaneous breakout.
Registered Member #160
Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938
Your cap bank is the right size, I wouldn't go any bigger but don't expect too much from a 150VA power supply. The arcs coming from your ground to the topload tells me that the voltage at the ground is higher than the voltage at the topload, which means you are out of tune. Try it at about 5 turns to get the best results, but by the sound of it you have only certain tapping options on each turn. You will have to play with that. I notice you don't have a safety gap on your transformer either, you might have damaged the transformer. The secondary on the NST has two legs centre tapped to ground, check if they are both arcing to ground. Good luck.
Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Ok, so I changed a few things, and got some better results, but still shy of what I expected.
- Connected the secondary ground to a newer copper pipe, and that caused the top load to break out on its own. :) - Moved the primary tap in and out, found the "sweet-spot" to generate more streamers, 5 turns.
- Reduced the top load size - fewer and smaller streamers (2") - Original top load - 3" streamers - Double size top load - 3" - 3.25" streamers - but what appears to be twice as many.
Top Load Issues? I think So. The TL is a 1"x6" torid. simply a hard foam "wreath ring" from a craft store. I wrapped it in aluminum tape, made a flat foam centre out of foam covered in aluminum foil to short-out all the tape bands, which works. My problem is the tape is not entirely smooth. There are wrinkles, which create dozens upon dozens of little points. These points are where my "multiple streamers" originate from.
I'd like to fashion a 2"x6" torid TL, or buy something equiv. Any Suggestions?
Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Coronafix wrote ...
I notice you don't have a safety gap on your transformer either, you might have damaged the transformer. The secondary on the NST has two legs centre tapped to ground, check if they are both arcing to ground. Good luck.
True-No Safety gap. I'll look into building one.
My NST is potted. Yay me. It's an Allanson 5kV 30mA unit with a pull chain on/off switch. Box says Model/Type is 2231. Between the HV leads from the case, there is a solitary screw which is grounded. I have a second identical NST, both were purchased new from a sign shop for $30 each. The University takes all the bigger NST's. I've thought about un-potting the sucker, but skiddish about roasting the thing and doing more harm than good.
Dr. Spark wrote ...
30ma should be able to get at least 6 to 7 inches spark.
Got a pic of your spark gap? Remember the most efficient spark gap is still only around 60% as the rest is wasted in heat. You can lose a great deal of power in your spark gap if not built or cooled properly.
Yes put a low pass filter w/ safety gap on the power supply (2K resistors and caps to ground @ ) to protect the first few windings of the xformer from RF and over voltage. RF will break down the insulation of the xformer wire (very thin) and one day it will just stop working.
No pic of the gap, but I will describe it (pic later tonight...)
Single Gap. Two 1" D x 3" L copper pipe sections, capped at one end, directed capped end to capped end. Left side stationary, right side adjustable. Gap is set to ~3.5mm. Smaller gap and only the gap fires, larger and the gap may not fire at all. Cooling/quenching performed by standard computer-case fan, 12V DC 0.5A, positioned (centered) 1.5" behind the gap. Standing 5' from the coil, I can still feel the fan blowing on me. It has it's own wall-wart PS.
Still looking for a new top load. I also found another problem. The bottom of my secondary is arcing about 3/4" from the bottom of the coil (not to the primary, just within the secondary.) There is a 2.5mm hole in the polyurethane coating. I'm in the process of winding a new secondary anyway, so that's not a big deal.
Registered Member #1733
Joined: Thu Oct 02 2008, 03:17PM
Location: Hamilton, ON, Canada
Posts: 100
Yep, works great. Took a bunch of tuning, but I got it. The SG fires nicely, no arcing from primary to secondary or within the secondary. Top load is two 5" stainless steel bowls (from Ikea) forming a sphere. Streamers are around 8 or 9", and I can arc to a grounding rod at over 12". I demo it when people come over. I have an 18" and a 48" fluorescent tube, and various other bulbs, for demo purposes. Other than the board it's on (ugly ply) I'm happy.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Zenador wrote ...
Yep, works great. Took a bunch of tuning, but I got it. The SG fires nicely, no arcing from primary to secondary or within the secondary. Top load is two 5" stainless steel bowls (from Ikea) forming a sphere. Streamers are around 8 or 9", and I can arc to a grounding rod at over 12". I demo it when people come over. I have an 18" and a 48" fluorescent tube, and various other bulbs, for demo purposes. Other than the board it's on (ugly ply) I'm happy.
Very nice! Gotta video somewhere? I have never seen a tesla coil with less than 6kv.
Registered Member #480
Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644
Zen -
Can you provide the details on the primary coil, so we can also evaluate the primary-secondary coupling factor?
Is it a flat spiral primary, or a helical cylindrical primary, or a conical primary?
We need ID, OD, conductor diameter, and winding pitch (center-to-center distance betwee turns).
I strongly recommend that you install a low-pass filter between the saprk gap and the NST (Terry filter), or you increase the risk of NST death.
Breakout from a nearby grounded object before the topload breaks out is common. Usually, the grounded object has a smaller radius of curvature than a properly-constructed topload, and therefore the first streamers will originate from the grounded object. On my 6" X 42" spark-gap coil, with a 6" X 24" commerciallly-made spun aluminum toroid, I cas get 10"-12" streamers from the point of a grounded wire 40" away from the toroid before there is any breakout from the toroid itself.
I think you will be able to get better performance if you go to a larger, smoother topload, like a 2 X 12 or a 3 X 14 toroid, or something similar. Or, you can try a 10" diameter stainless-steel "gazing ball", but you may have to add a copper tubing "corona ring" above the top turn of the secondary to prevent excessive corona or streamers from originating from the top turn.
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