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RE: [TCML] Questions on grounding
Yes, you need a dedicated earth ground for the bottom of the secondary.
(you've probably already heard this 10 times by now) Any sort of metal
rod pounded into the ground will do. Mine is about 2.5 feet long 1/2"
thick with some thick wire wound tightly around it, which is all wrapped
tight with tape. All but about 3 inches are in the ground. Its
half-as*ed, but it works fine. The ground is always soaked here in
Or-e-gone. In a drier climate you would probably need something more
One strange phenomenon that I've recently noticed about spark length
involves which way you wind your wire around the primary to get to your
I should mention for clarification that I'm using a vertical primary,
which will make what I'm describing make more sense, at least in terms
of how I'm describing the setup. Strange as it sounds, going in one
direction totally detunes the coil, whereas going the other direction
gets maximum sparks. The tap spot is on the direct opposite side of the
primary relative to where the wires come up through the enclosure. Your
site is unavailable from my work internet access, but just thought I'd
throw that out there in case you were using a similar setup. And does
anyone know why this would be so?
As a point of reference, I'm using a 12kv 30 ma nst, a .009 cde mmc, a
4.5x17" secondary with 24 gauge, and a 7.5" primary former that is wound
with some thickly insulated monster cable. 12" ikea sphere on top with a
small semipointed breakout on the top. The spark length in free air is
I haven't tested it to ground.
Sounds like your topload needs a long breakout point somewhere along the
outer circumference of your toroid. Otherwise it just breaks out
wherever the electrostatic intensity is greatest, which will be all
along ridges on your ducting. All of those ridges will keep you from
getting a significant amount of energy built up on the toroid before it
breaks out. You might try wrapping the toroid with aluminum tape. That
will help a bunch. Smoothing the whole thing with bondo and putting
aluminum tape over that is better yet, as with the tape alone you will
still have hills and valleys around those ridges.
I'm betting that just getting a good earth ground to your secondary is
going to make a serious improvement to your spark length.
From: jocatch [mailto:jocatch@xxxxxxxxxxx]
Sent: Tuesday, April 14, 2009 6:35 AM
Subject: [TCML] Questions on grounding
Hello. I have built my first coil using standard parts and dimensions
and have fired it up and so far I am producing sparks but only about 12"
long. I am using a 12KV nst with .0125uf mmf, 13 turns of copper tubing
as primary and 20" of #28 magnet wire on a 4" form with aluminum cloths
dryer ducting for the toroid
My questions concerning grounding. I have read alot about discharge
spark length but not much regarding how to measure it. Above I said 12"
discharge spark length, that was to a key ring held at the end of a boom
stick handle. Should the metal object that I am drawing the spark to be
grounded? To earth ground? Right now nothing is grounded to earth or
electrical ground. The bottom side of the secondary coil is connected to
the metal case of the nst. Should the secondary coil and nst be grounded
to earth ground?
Lastly, the aluminum toroid is discharging all around its circumference.
I know the fewer discharge points on the top load, the bigger the
discharge length will be. If I tape the toroid with aluminum tape to
produce a smoother surface, will it help?
I have a web page showing photos of my first tesla coil before I
recently updated it to copper tubing and new toriod. The web page shows
the old primary wire coil and old topload. I will post new pictures of
the update soon.
Thanks for your help.
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