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Re: [TCML] Strike rings - to use or not to use; was: Newbie Grounding Question

Hi David,

Regarding this photo on your page:
http://www.teslauniverse.com/members/drieben/100a2.jpg
I have to wonder if the strike rail caused it. I agree with Jeff that the RF grounded rail acts like a magnet to the sparks. Strike rails will tend to take the spark abuse away from the primary in most instances, but it also draws the spark to it. A catch 22 situation.
My old big coil had many rail hits. It was actually that coil that made me remove the strike rail. Even though the strikes would hit the rail, there were occasions when it also arced to the primary. That's when I thought I would remove it to see how the coil ran without it. It did much better without the strike rail. There were still hits now and then to the primary, but downward strikes were minimized and that is what I was after. As you know, I don't have that coil any longer. These days I add a plexi sheet over the primary which seems to help. 

Take care,
Bart

David Rieben wrote:

Hi Jeff,

Although a properly desinged coil should see a noted decrease
in strikes to the primary and secondary coils as opposed to an
improperly desinged one, I do not see any practical design com-
pletely eliminating this issue. My toroid was (still is) 56" in diame-
ter and the outermost turn of my primary is about 40" in diameter.
The strike ring is only slightly larger in diameter than the outermost
primary winding (probably around 41" diameter) but sits about 3.5"
above the plane of the primary. "I" would consider this to be proper
coil design geometry to minimize primary or secondary strikes and the
strike ring sticking up ~4" higher and closer to the toroid would be the
only possible "Achilles heal" that I could see in my design. Yet because
of fairly high winds, I still had a streamer to "blow" back into the side
of the lower part of the primary on that day. You can see my coil setup
at: http://www.teslauniverse.com/members/drieben/  for further details.
Although I have done a few modifications to my control panel since
posting these pics, the basic coil tank circuit and the 15 to 20 kVA
power feed is still the same.

David Rieben
----- Original Message ----- From: "Jeff W. Parisse" <workshop@xxxxxxxxxxxxx> 
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Saturday, December 29, 2007 1:30 PM
Subject: Re: [TCML] Strike rings - to use or not to use;was: Newbie Grounding Question
A strike ring is just an invitation for the arcs to travel downward. A properly designed Tesla coil, geometrically speaking, will not hit its own primary or secondary coils. Sometimes, all that is needed is a larger toroid. I switched from a 48" to a 59" toroid (5.5" more overhang) on my 20kVA coil and solved all coil strikes.
The tried and true method for protecting old equipment (i.e. Tesla coils) from overvoltage is to employ ball gaps set to fire just above the circuit's operating voltage. I use 1" brass balls (McMaster-Carr or others) because the old ball gap charts that are used to determine gap spacing usually use a common ball diameter such as one inch. I place the gap between ground and the circuit section I'm trying to protect. 

Jeff



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