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Author Topic: Tesla Grounding Issue  (Read 10785 times)

Jeg

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Tesla Grounding Issue
« on: March 05, 2014, 11:47:03 AM »
Hi@all

I have made a Tesla coil which needs grounding. What i'd like to ask is what about the length of the ground wire from the bottom of the coil up to the ground point. To my understanding, this length is added to the main coil wire length, and affects my overall wave length calculations. How can i get over this factor? My ground which is in my garden is many meters from my coil bottom, and i'd like to cancel this extra cable affection. What is your opinion on this? If i put 2 diodes in parallel to the bottom of my coil, one facing upward and the other facing downward, will this cancel the extra cable length affection to my wavelength calculations?

Thanks
Jeg :)

TinselKoala

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Re: Tesla Grounding Issue
« Reply #1 on: March 05, 2014, 07:50:25 PM »
You can try it of course but I think you will need some pretty hefty diodes if you don't want them to blow out. Both ends of your TC will be swinging through the same peak relative voltages. The purpose of the ground at the bottom of the secondary is to "pin" the voltage there at ground potential. This doesn't mean nothing is happening there! The ground acts as an infinite source/sink for electron charges, and ultimately the power of the secondary discharge makes a current loop, just like any other current loop. You just can't see most of the TC loop because it is happening through the big capacitor made of the local environment.... and the Earth itself. Draw current from the top of the secondary, and you also "suck" current from the ground into the bottom.

If I were you I'd string a fairly heavy cable conductor out by the shortest path to the real Earth ground. The length of this cable/wire won't matter in terms of being a good ground, as long as the ground end is done properly. Drive a piece of 1/2" copper plumbing pipe, not too expensive, cheaper than copper rod, 3 or 4 feet into soft moist soil and secure the cable to it with a hoseclamp.  Yes, this will affect the tuning of your coils, but the coils will run much better when tuned and grounded like this. It sounds like you already have a good ground like this.

I confronted this issue in several places I have lived. Some of my early work is on YT, where I lived in a small basement apartment; I was actually underground with the entire coil and the Earth ground I used actually ran to a level above me. If you are in a tall apartment building or something like that, you could try the cold water plumbing pipes in your kitchen or bathroom but much newer construction doesn't even have metal pipes, and there may be other things that would make the cold water pipe not usable as well. Whatever you do, don't use the "ground" conductor in the mains wiring! This will cause noise on the line for everyone else and could actually be very dangerous if there is a ground fault in the building's wiring, or if an arc forms between the ground connection and one of the other mains wires.

Also, as you know, the "effective length" of the ground wire can be very different from the actual physical length, so don't be surprised if the calculated frequency differs from the actual resonant freq when the ground is connected. The proper way to compensate is with a LC network that stays connected to the ground wire, and you take your TC ground from that. But that kind of compensation is of course frequency dependent.

Jeg

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Re: Tesla Grounding Issue
« Reply #2 on: March 06, 2014, 11:44:38 AM »
Hey Tins nice to see u again:)

You made a good point about this LC network on ground side. I'll keep it in mind for later consideration. First i'll try the diodes as i hope that they will cut this extra ground cable effectiveness to the system.  Perhaps a few picofarads cap. will do the job either. I just want the system to work on any ground cable without the need of re-calibration!
What is your opinion on RF grounds? I will also try a big metal plate between that bottom of the coil and the ground rod. I hope the coil will 'see' this plate as a ground, with only a meter of cable connecting them together.

Tnks
Jeg

TinselKoala

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Re: Tesla Grounding Issue
« Reply #3 on: March 06, 2014, 05:18:50 PM »
Oh yes, for a full Tesla system the RF ground is important. Most people building small coils neglect this aspect for portability purposes but the "real deal" includes the RF ground plane, the overhead surroundings and more. Take a look at my favorite TC design software, it even gives you a little diagram of your coil and capacity.
http://www.classictesla.com/java/javatc/javatc.html

Jeg

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Re: Tesla Grounding Issue
« Reply #4 on: March 06, 2014, 06:04:43 PM »
It looks great. I'll give it a try..thanks   ;)

TinselKoala

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Re: Tesla Grounding Issue
« Reply #5 on: March 06, 2014, 06:18:13 PM »
I forgot to mention: I used that software in the design of my MOT-DC coil with the stationary 2-element blown sparkgap.

tim123

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Re: Tesla Grounding Issue
« Reply #6 on: March 07, 2014, 09:31:09 AM »
Hi Jeg,
  I recently discovered this product, which is an 'artificial ground' for radio... It provides that LC network that TK mentioned...
http://www.mfjenterprises.com/Product.php?productid=MFJ-931

It can work in 2 modes:
 1) To 'tune' a ground lead - so it's length appears to be zero.
 2) To provide an artificial ground plane (counterpoise) using a short length of wire.

There is some great info on how to homebrew one online, such as:
http://www.remeeus.nl/english/hamradio/artificial_ground.htm

Regards, Tim

Farmhand

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Re: Tesla Grounding Issue
« Reply #7 on: March 07, 2014, 10:31:43 AM »
I live on a hill top which has very dry rocky ground, our house grounds are a bit sus in the dry months which is a concern but there is two of them.

For my Tesla coil ground I located the main "vein" of the septic tank underground drain off, I divined it with two pieces of wire but I did know where it was in general. Then I drilled a hole with the tractor auger about 4 feet deep which got me into "clay" hehehe, then I drove a 6'6" galvanized fence picket into the bottom of the hole till there would be only about 3 or 4 inches above ground after I filled in the hole, then I filled the hole with layers of ash/charcoal and dirt, I also placed one end of a piece of poly pipe in the bottom of the hole and the other end is above ground and folded over, I can use that to check the ground moisture with a long piece of wire and/or put water into the ground 4 feet down by connecting a hose to it. It's also right next to a grounded steel fence so I can connect to that as well but I don't.

It's much better than the house grounds and has a great deal more surface area than a rod but maybe less surface area than a pipe if the center of the pipe is also contacting the ground.

It works good I think, the voltage difference between it and the house grounds is not much.

Cheers 

Jeg

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Re: Tesla Grounding Issue
« Reply #8 on: March 07, 2014, 10:41:44 AM »
That's fantastic Tim!!! I have to learn more about this trick!
Tnks a lot! ;)

Jeg

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Re: Tesla Grounding Issue
« Reply #9 on: March 07, 2014, 12:03:11 PM »
Good work Farmhand! I just wonder if dc grounds like that can stand frequencies up to some decades of MHz. I think this virtual ground would fit better to my needs!

Thanks for sharing
Jeg

Farmhand

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Re: Tesla Grounding Issue
« Reply #10 on: March 07, 2014, 02:46:51 PM »
A virtual ground might be good. You should note that the virtual ground device is for certain frequency bands and needs adjusting within that band to get your frequency. A regular ground is not really DC or AC, the house ground is for the AC system, the virtual ground has a certain power rating as well.

Another way to go is to just make two identical coils and connect them together by the bottom of the secondaries.
The second coil kinda acts as the counterpoise but it can be used as well.

Counterpoise (ground system)
http://en.wikipedia.org/wiki/Counterpoise_(ground_system

Or a bipolar coil (sphere each end) requires no ground.

A good stake in the ground has a high power rating I think,  ;D I forgot to mention I planted a tree right next to the ground stake which is now about 12 feet high, I guess I should trim it down in case of lightning. Looks to me like the Earth stake and the tree both have a pretty good grip on the same bit of ground. A strike to the tree might go to the ground stake then inside my hut to the coil and ping the coil so that flames leap from it. hahahaha That could be scary. Virtual ground sounds good.

Cheers

TinselKoala

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Re: Tesla Grounding Issue
« Reply #11 on: March 07, 2014, 10:49:33 PM »
The bipolar coil with spheres on both ends will work a treat if you ground the center winding and tune in that condition.

Farmhand

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Re: Tesla Grounding Issue
« Reply #12 on: March 08, 2014, 09:17:03 AM »
Yes Tinsel it sure will, and in that condition it would be tuned like two opposing 1/4 Wave resonators wouldn't it ? Which might require additional tuning of one side to match the other precisely, this might only require a grounded capacitor plate to be placed in some proximity to the higher frequency side.

Cheers