Idea for a ground..
Subject: Idea for a ground..
From: richard.quick-at-slug-dot-org (Richard Quick)
Date: Sat, 4 Mar 1995 02:24:00 GMT
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Quoting Rob Bicevskis:
RB> Since a Tesla coil can be thought of as an antenna (?), -
RB> or more specifically as a 1/4 wave vertical -
It sounds logical doesn't it? But it does not really work this
way. You are better off looking at the coil with one foot
standing in coupled RF resonators, and the other in transmission
line theory. In the long (and short) run, these models give
better practical and mathmatical overviews.
RB> - wouldn't it be almost as effective to just use a metal
RB> sheet under the coil as a ground plane?
Ground planes are very effective platforms for a coil to resonate
off of. The problem is that ground planes are radiant antennas in
this application and will contribute greatly to RFI. I do not
recommend using one frequently unless you are operating in a
properly grounded Faraday cage.
RB> One could approximate this with just radial wires - or use a
RB> mat of link fence or 'chicken' fence.
I have done this. Trust me, a dedicated RF ground is more
effective in the long run, if for no other reason than the
reduction in RF interference. However some experimentation with
ground planes is a very valuable teaching tool considering the
knowledge and experience that can be gained with them.
RB> By the way, I have never connected the 'bottom' of my
RB> secondary to earth ground - just to the bottom of the
RB> primary - which goes directly to one side of the transformer
RB> - so it is 'floating.' Any comments on this practice???
RB> (This is a 2 KVA system - (secondary is a 4" diam by 1 meter
RB> long coil.) currently throwing 1 meter long sparks.)
Well Rob, you left the barn door open so I am going to drive in
the truck. :-) It has been awhile (at least a week) since I
climbed up on the soapbox and preached the preach.
First off, this connection opens a direct pathway for potentially
lethal 60 cycle components to enter into the secondary discharge.
In my opinion this reduces the safety of the system, and I would
not advise that this discharge be experimented with, especially
allowing sparks to the body. There is a shock hazard. I will
admit that the chance of receiving a lethal shock directly
through the secondary here is very remote, but the shock can
easily be enough to cause a lethal accident after receiving it;
we are taking about high energy systems from the breaker box to
the discharge terminal are we not? Lots of exposed HVAC wiring?
Secondly, while the coil can obviously be resonated to produce
some spark with this connection: where is the heavy RF current
from the base wire going? Without a low impedance pathway to
remove the current from the base of the coil, the VSWR (voltage
rise) in the coil is severely limited. The more current taken
away by the base wire, the higher the VSWR. This works both ways.
Third, I get closer to six feet of spark at 2 kVA. Ed Sonderman
(who just completed his new 6" coil system last weekend relying
heavily on my advice and assistance) is getting 32 to 36 inches
of spark length with only 720 VA (less than 3/4 of 1 kVA).
I submit that there is a better way that produces significantly
higher efficiencies. This way is also much safer.
... If all else fails... Throw another megavolt across it!
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