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Re: [TCML] Questions on grounding

Hey Joe, I don't remember who came up with this gap design originally so please forgive but a static gap I have used on smaller coils in the past was made of several pieces of 1 inch copper pipe bolted to a non-conductive backing. They get warm and pull air up through the middles of the individual pieces which helps cooling a little. The gaps were 3/16s each if I remember right. I've long since forgotten all the details but you can adjust the gap spacing by varying the number of pipes in the gap. You can later add to the efficiency by using the fans you mentioned. I'm sure some of the more experienced guys can fill in the details but that should help you get started on a little better gap that the two carriage bolts and angles we all start out with. ;)

From: jocatch <jocatch@xxxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Wednesday, April 15, 2009 1:01:07 PM
Subject: Re: [TCML] Questions on grounding

Hello to everyone who has responded so far. Thank you!

Today I went and got a 4' ground rod and banged it into the ground and ran a wire to the secondary coil and nst case. I used a 4' rod because my ground here has lots of rocks and I have never been able to go more than about 4' with ground rods. As you can see from my photos that the coil is on my rear deck, there is no concrete floor. The wire from the coil to the rod is less than 20' long. Tonight after dark I will power it up and see if it helped. I will also connect the ground wire to the end of a pole and see how long of a spark I can get.

Regarding my spark gap, I always go for the easiest, simplest solution as I am not that mechanically inclined. I do have some 12v computer fans I was thinking about placing near the gap to see if it helps. But I wanted to try the grounding, tuning and adjusting the gap width before adding a fan. Besides, I have no place right now to add the fan on the base; I will have to move the gap to somewhere where there is more room. Regarding a 'sucker' gap, I am not sure what that is, I will have to research that.


----- Original Message ----- From: "Lau, Gary" <Gary.Lau@xxxxxx>
To: "Tesla Coil Mailing List" <tesla@xxxxxxxxxx>
Sent: Wednesday, April 15, 2009 10:36 AM
Subject: RE: [TCML] Questions on grounding

Hi Joe,

When you say that "Right now, nothing is grounded to earth or electrical ground", this is REALLY bad!  The secondary base needs a ground connection. If there is not a good, direct ground connection, the RF current will travel through your hot & neutral wires and wreak havoc with household appliances.

I agree with Bart's reply - that the secondary base is typically connected to the NST case, and that this case connection should go to a dedicated RF ground, not the mains ground.  For low powered coils, the mains ground is often used, but the definition of "low" is subjective.

Regarding the sparks discharging all around the toroid, this may be due to having a ragged surface on the toroid, so smoothing it out may help.  If the toroid is simply too small for the power level you're running at, no amount of surface prep is going to help, but yours appears to be reasonable in size.

Looking at your web site, I think the weak link in your coil is the 2 carriage bolt spark gap.  It needs forced air flow directly through the arc (more than just a gentle breeze from a fan), and should be designed to arc not at just a single point as yours will.  I recommend using a sucker gap, as it's easy to build and works very well.

Regards, Gary Lau

> -----Original Message-----
> From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
> Behalf Of jocatch
> Sent: Tuesday, April 14, 2009 9:35 AM
> To: tesla@xxxxxxxxxx
> 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.
> http://www.joecool.org/joe_s_tesla_coil.htm
> Thanks for your help.
> joe

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