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Re: [TCML] Treating RF feedback
On 3/17/13 3:01 PM, w5als wrote:
HI Brandon Being a ham operator and tesla coil, I will tell you what
I would do.
Bear in mind that what's effective at 2-30 MHz (HF radio) and 100kHz or
100 MHz might be quite different.
If you can get at lease 4ft in the ground that will work
but do 2 ground rods at lease 4 ft apart. you have to be the length
of the ground rod apart from each other min. More the 4 ft. would be
better. Done not run one wire and go from one to another. Run 2
separate wire's to each one, with them coming to a common spot. I
mounted a wall outlet in my shop with nothing hook to it but the
ground wire's only. Than when I use my Tesla coil I plug my ground in
that outlet only. If you use 3 short ground rod's use 3 separate
wire's. But the deeper the ground rod the better. alton w5als
Are you saying that the bottom of the secondary coil is connected to the
"greenwire" ground pin at that receptacle, which is then connected to
your three rods?
Or do you have 3 rods driven surrounding your TC, you have wires from
the rods to the TC location, and then hook that to the bottom of the
secondary coil.
And have a dedicated outlet for the TC power.
I'm not sure there's any good physics behind this suggestion. Not that
it doesn't work, but I suspect that if it does work, it's because of
factors other than the ground rods, per se.
WIthout knowing more about how your house is wired and where your TC is
relative to those ground rods (and more important the wires going to
them) it's hard to say whether this is an effective strategy. Or, more
to the point, measuring the RF current in those ground wires.
For EMI/EMC and tesla coils, there's two factors to bear in mind..
there's the 100-300 kHz frequency from the coil itself.. but that
doesn't propagate very well, and the "antenna" (e.g. the coil) is a very
tiny fraction of a wavelength. So all the 100kHz fields tend to be
close to the coil, and you don't have to get very far away before they
are "small". (if you're 10 coil heights away.. e.g. 30 feet from a 3
foot high coil) I'll bet they're almost negligible.
For EMI, I think a bigger problem is the transients from the actual
sparks, and those radiated from the wires going to the spark gap. The
latter typically radiates at VHF sorts of frequencies (think of the
wires going to the spark gap as a dipole radiator, with the spark gap at
the center). Several coilers have measured substantial radiated fields
from this source, and since VHF receivers are pretty sensitive, it's
easy to jam them. Whether it could "false trigger" is another story..
Then there's the wide band transients from when the spark "fires". You
have a very high di/dt, so you get a fairly big magnetic field radiated
from a loop that's fairly large (ground, secondary coil, topload, spark,
wherever the spark hits, conductor from spark end to ground). This is
why you *don't* want to run a coil indoors with a 50 foot wire to the
ground outside. You're making the transient transmitter more effective
by making the antenna bigger.
some analysis from a few years ago is here
http://home.earthlink.net/~jimlux/hv/tcemi.htm
The problem with things like garage door openers is that they have
unshielded wires going to the photosensors and limit switches, so you
could easily get a pretty big receiver loop (with "capacitive coupling"
being part of the loop). In my garage case, the opener is about 10 ft
from the door, and there's a wire that goes down to each side of the
door where the photosensors are, and then a ground through the plug in
the ceiling for the opener. So there's this huge 8 footx15foot
rectangular loop to pick up signals (the wire from the photosensor runs
along side the metal track of the door, and has significant capacitance
to "earth ground" since that track is connected at the slab with an
anchor bolt. It's kind of like it was designed for poor emi performance.
Sprinkler systems are worse. They are very cost sensitive, so the
output is typically a bunch of triacs connected right to the
microprocessor switching the 24VAC to the valves, and there's a common
ground wire for all valves. It's easy to get a big loop between "valve
hot" and "common ground" depending on how it's wired. And if there's
much induced voltage on the control wires, then the triac will switch on
(or, simply that the triac is a 50V part, and it just avalanches when
there's a spike). Your TC is emitting pulses synchronized with the
power line, so it's optimally timed to trigger the triacs with an
induced gate pulse.
Since people want to save money, the valve wiring is often sort of a
point to point daisy chain, rather than a single twisted pair to each
valve (the latter would be ideal for EMI), and the wires are buried and
often have some conductitivty to the surrounding soil. I had terrible
trouble with EMI on my first sprinkler timer.
On 3/17/2013 3:45 PM, Brandon Hendershot wrote:
Hi All,
With the renovation of my coil nearly complete, I'll need to
address the old issue of electrical appliances going haywire
whenever I run my coil. At the time I didn't have a proper RF
ground, only a counterpoise. On separate occasions, I'd have the
jacuzzi tub turning on or the sprinkler system switching the
sprinkler heads like pinball paddles. My hunch was RF interference
which the list seemed to support. I'm currently attempting to
install a 10' ground rod but that's proving difficult with my dry
rocky soil. Since my deadline is fast approaching I may need to
rely on the counterpoise once again and I want to make sure I don't
go fizzling all the fancy electronics we've acquired in the past
years since I retired my coil.
On a separate topic, any bright ideas on getting a 3/4" copper pipe
backed with city water pressure through a boulder?
Thanks, Brandon H. _______________________________________________
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