Questions about tesla coil grounding, rf interference, etc.

Discussion in 'General Electronics Chat' started by skydivecarl, Nov 15, 2013.

  1. skydivecarl

    Thread Starter New Member

    Nov 15, 2013
    I'm getting ready to build my first tesla coil, most likely from a kit. I've done a lot of reading and research, and feel comfortable overall, but there is one thing that I couldn't find much solid info on.

    How concerned should I be about any electrical voltage or interference potentially traveling back through my households electrical system and damaging things elsewhere in the house? For example...

    1. What would happen if a stray spark happened to strike the main power cord, or the primary coil or something else? A quarter million volt arc, striking or otherwise getting introduced into a 120 line just sounds bad, could this potentially fry things across the house? Are there any simple affordable steps that can be taken to prevent this (if it is indeed a concern)? Perhaps some sort of choke or filter to prevent any voltage/current being back fed?

    2. What about RF interference? I've heard that tesla coils can potentially produce RF interference on the household ground line, potentially interfering with other things plugged in. I once saw it advised not to have a computer plugged in while a tesla coil is running due to RF interference. Is this really a concern? Can anyone elaborate a little more about what exactly causes this RF interference. And also, are there any steps that can prevent this?

    Just brainstorming, perhaps if I ran the tesla coil off a modified extention cord which had a splice or pigtail coming off its ground cable, going to a completely seperate ground rod I would pound into the ground nearby. That way it would still be connected to the main ground, but there would be a second ground rod as sort of a first line of defense to hopefully catch the vast majority of anything bad, before it even reaches the main ground. Or perhaps a better idea?

    I might be over paranoid, I've seen people running tesla coils in their living rooms, around all sorts of electronics, with no major precautions seemingly taken, and no major issues. However I don't want to take chances, I want to gain the skill and knowledge to fully understand this, and make my safety system as bullet proof as possible, so any input would be appreciated.

  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    The RF coil ground should be earthed with the copper rod as you describe.

    The power supply section can utilize your normal household power ground system.
    A RFI filter on the power supply would not hurt anything.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    Google it. See what others have done.
  4. skydivecarl

    Thread Starter New Member

    Nov 15, 2013
    So I'm not familiar with RFI filters, did some googling and found this one

    Assuming the tesla draw is under 10 amp, should that work good?

    I'm making a guess, would a working solution to cut an electrical cord in half, install this RFI filter on the hot and neutral wires, and on the ground wire, install perhaps a 2 foot copper rod which I would pound into the ground?

    That way the mini ground rod is a first line of defense, to hopefully eliminate anything harmful before reaching the main ground. And the hot and neutral will have this filter preventing anything harmful?

    I am very new to all of this.

    As far as the person who said just google it. Well, I have done a bit of googling, without much luck which is why I'm asking. In my googling, at actually seems like the majority of people just plug theirs in and go, without even thinking about any of this stuff. I want to be safe, and have a full understanding of the potential issues and solutions.
  5. killivolt

    Distinguished Member

    Jan 10, 2010
    Draw a schematic of what you plan to do? You'll get a lot more help that way.

    Improperly handling this will kill you e.g. wet soil grass and standing to close could electrocute you or someone else. The more reading the better, you need a full understanding of what your doing or you and someone else will get killed.

    I don't know your background or experience, I just think if your asking these questions your need a lot more reading. There are some good tesla books out their. You get what you pay for.

    Edit: FYI, kermit2 doesn't have over 2000+ post for nothing, if he say's google it, then spend some more time trying to find the answers.
  6. DerStrom8

    Well-Known Member

    Feb 20, 2011
    I have built numerous Tesla coils in the past, so I do have a fair amount of experience in this matter. First of all, do not ground your secondary to mains ground. I think you already know this, but you should pound a long metal stake into the ground and connect the bottom of your secondary to it. Second, create a strike rail. All you need is a piece of tubing about the size of the widest turn of the primary coil. Bend it into a ring, but make sure the ends don't touch. Set it up above the primary on standoffs and connect it electrically to the same ground post you stuck in the ground for the Tesla coil secondary. This strike rail will attract any arcs that get close to your primary coil. Your transformer and power cord should be a good 10 feet (at least) away from the coil, just for safety. And to prevent harmful high-frequency voltage spikes from flowing back through your transformer and into your mains, wind two chokes connected to the output of the transformer. They will allow the 60Hz current go to the tesla coil, but they will prevent the several hundred KHz current from your tesla coil from flowing backwards through the tank circuit and into your transformer.

    Does this make sense, or is there something I need to clarify?

    As always, with high-voltage Tesla-coil-related threads, I feel the need to provide the obligatory safety warning:


    Tesla coils use and produce very high voltages with high-current parts. One touch of the tank circuit can, and probably will kill you. Please take every possible precaution to prevent damage to you, other people, pets, and property. It is also very important to have someone with you at all times when working with such high voltages and currents, as they could save your life if something goes wrong.

    And now that that's out of the way, good luck, and PLEASE--if you have any questions, don't hesitate to ask. It's better for someone here who knows what they're doing to help you than for you to continue without knowing the answer.

    (Tesla coil enthusiast)
    shortbus and killivolt like this.