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Teddosan

Thu Apr 20 2006, 06:08PM

Registered Member #401 Joined: Thu Apr 20 2006, 04:03PM
Location: Wisconsin
Posts: 4

Hi all... I am building my first Tesla Coil, and I have a question about grounding.

I have seen people say that the RF ground should NEVER be tied to the primary ground or mains ground; I have also seen TC designs where the RF ground is tied to one or both. What is the truth here?

As a bonus follow-up: I have also seen a couple of people say that the strike rail should not be a closed loop. Why is that?

the_anomaly

Thu Apr 20 2006, 06:22PM

Registered Member #19 Joined: Thu Feb 02 2006, 03:19PM
Location: Jacksonville, FL
Posts: 168

The rf ground really shouldn't be connected to the mains or primary ground but it is sometimes for convenience. If your coil is small you could get away with using the mains ground but its would be much safer to use a rod in the earth as an rf ground. Never use the primary ground because the secondary streamers could be attracted and strike the primary.

vasil

Thu Apr 20 2006, 06:24PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

The truth depends by where are you living. If it is a 9-th floor apartment, the mains ground is the only avalaible ground for you.
If you use the mains ground you inject a lot of RF noise in the mains frame when the TC strikes to the tank components.
If you use a different RF ground (another than the mains ground) you need a strike ring because any strike to the primary turns can break down your HV transformer (secondaries floating at high voltage versus primary).
If the strike ring is a closed loop it will steal energy from the RF field (current induction in a closed turn).

Teddosan

Thu Apr 20 2006, 07:00PM

Registered Member #401 Joined: Thu Apr 20 2006, 04:03PM
Location: Wisconsin
Posts: 4

Thanks for the replies...

Assuming I ground the RF to mains ground as you said "for convenience."

I am using a NST for the power supply. The NST is case-earth grounded through the mains. The case ground is also, I believe, tied to the center-tap for the HV side. So, if I ground the RF to the mains as well, then isn't that basically tying all three grounds togther?

Will the noise injected from the RF damage other appliances, etc. on my mains?

vasil

Thu Apr 20 2006, 07:05PM

Registered Member #229 Joined: Tue Feb 21 2006, 07:33PM
Location: Romania
Posts: 506

It would be ok for low power coils.
The raports vary frequently for higher powers. Some coilers accuse RF noice in the appliances and neighbours disturbing, others not. Just disconnect all the home electronics when you run the coil for safety.

HV Enthusiast

Thu Apr 20 2006, 07:12PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

If your first coil is going to less than say 300W, then by all means use the third prong ground.

Self Defenestrate

Thu Apr 20 2006, 07:23PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

I wouldn't tie the secondary to the primary if the primary rises up the coil any good amount, such as on smaller coils(see my thread on the "1kv spark gap/tesla coil", its an example of what I'm talking about.). What I mean is, if you ground the secondary to the primary, you'll get primary strikes from the lower part of the coil. On the other hand, I'm gounding my secondary to my primary, but I had to put my coil under oil to keep it from arcing. Never use a closed loop for a strike ring, it wastes energy that could be transfered to the secondary. And keep the ends of the strike ring pointed down and smooth, it will keep unwanted corona from sprouting.

Hazmatt_(The Underdog)

Thu Apr 20 2006, 07:52PM

Registered Member #135 Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735

Strike rings should not be a connected turn because it acts as a secondary to your primary. In my previous ~300 watt systems I had the split in the strike rail so close that I had it sparking between the gap, something like 2KV!! If you short this out you will have a loss of power which will not get coupled to the system secondary.

In a large system you really wouldn't want your RF and system grounds tied together. From a single strike to the primary you would couple your RF gnd return wire through the transformer and back to the arc. The transformer would see a horrendous hv pulse across its terminals and ground causing a dielectric breakdown.

Using a large sheet alone as the RF ground, which I do for my ~700W systems, can also be a problem. Even though the grounding is isolated, and the line protected with a filter, stray RF currents affect solid state devices in large radii. RF blocking on the transformer is advisable here, but I have to work that one out still such that it doesn't cause overcurrent conditions on the hv side.

coaster_chris

Sun Apr 23 2006, 06:02PM

Registered Member #359 Joined: Sat Apr 01 2006, 09:27AM
Location: Utrecht, The Netherlands
Posts: 16

I have used a counterpoise in my 360 VA coil, consisting of an aluminum sheet of 1 square meter, placed under the coil. I had the coil running in an apartment so I had no posibility of using a coper grounding rod.
I prefered this above using the mains ground, I wasn't realy feeling in the mood of killing my computer, tv etc. Sleight Img

It isn't the best way of grounding, but... it worked.

Chris

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