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Herr Zapp

Thu May 28 2009, 05:57AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Blitzorn -

Identifying different branch circuits is easy if the various circuits are not clearly labeled in the breaker box. Each "branch circuit" is served by one circuit breaker.

Select your candidate outlet #1, and plug something into it, like your shop vac. Turn the vac on, go to the breaker panel and start turning breakers off and on. When the vac shuts off, you have found the breaker for that branch circuit. Leave this breaker turned "off".

Now, go to the next candidate outlet and see if it is "live". If its live, then you have found an outlet on another branch circuit. If the outlet is "dead", then you know it is on the same circuit as outlet #1.

Regards,
Herr Zapp

Blitzorn

Fri May 29 2009, 02:33AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Thanks much, will do :)

I'm working on my primary and am trying to come up with a good way of attaching my strike rail - this is what i'm planning on doing, but i need to know if the copper straps are going to be a hazard or cause reduced performance.

I can also move the rail in or out (change the diameter) with no difficulty at all, so before i put it on the outside, should it be closer to the primary?

StevenCaton

Fri May 29 2009, 03:20AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

but i need to know if the copper straps are going to be a hazard or cause reduced performance.

Hazard? Well, the only problem I could see would be that you could place the straps too close to the primary and it would arc. The straps will not cause reduced performance of the strike rail or the coil.

Firstly, the strike rail should not be a closed loop, it should have a break in it somewhere. Second, you should have adequate spacing between your primary and the strike rail. I've had my primary arc out to the strike rail, even though it was pretty far away. (maybe 2+ inches) I would suggest you keep your strike rail at a minimum of two inches away from your primary everywhere. The strike rail is connected to either RF ground, or mains ground. (RF ground preferably) It really doesn't matter how you connect to the strike rail, as long as your connection maintains adequate spacing to prevent arcing. An alligator clip would be fine, or a small wire soldered to it, screwed in, etc.

Blitzorn

Fri May 29 2009, 03:32AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Alrighty, can do.

Yeah i'm pretty clear on how to make the strike rail there were just a few niggling questions. But this is good.

That brings me to another question though... how exactly does one achieve an RF ground? is there a piece of equipment to be built/bought? what kind of wire do i need for grounding?

Herr Zapp

Fri May 29 2009, 04:49AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Blitzorn -

Securing your strike rail to the tops of your strike rail stands with copper strap & epoxy adhesive is complicated, time-consuming, & messy. Forget the epoxy and the copper strap.

Just drill a horizontal hole through the side of each strike rail stand 1/4" below the top and secure the strike rail with a nylon cable tie. Cheap, easy, and takes about 15 seconds to drill & secure each location.

Your RF ground IS important. Ideally, drive a 2' or longer length of copper-clad ground rod (or a piece of copper pipe) into moist earth as close to the coil as possible. For a coil of your size, #12AWG wire is plenty big enough to connect the coil to the ground rod. Keep the ground wire as short and direct as possible. A ground-rod clamp (used to connect the wire to the ground rod) can be bought at Home Depot for $2-$3, or you can just drill a hole through the rod and use a through-bolt to secure the ground wire to the rod.

If you can confirm that your house's cold-water supply line is copper all the way out to the water meter, you can also use a nearby cold water pipe as an earth ground.

If for some reason you absolutely cannot create a good earth ground, you can create a "counterpoise" ground plane under the coil, using thin sheet metal, metal window screening, or even large pieces of aluminum foil electrically tied together. Make the counterpoise at least 1-2' larger in diameter than your primary coil diameter, and tie your coil's RF ground tie point to the counterpoise.

Regards,
Herr Zapp

StevenCaton

Fri May 29 2009, 05:03AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

An optimal RF ground would be a copper ground rod driven around 6 feet into the ground. The deeper the rod, the better. The wetter the ground, the better. The larger the rod size and the larger the wire size from the rod to your coil, the better.

First, I would suggest you smack some kind of rod into the ground near your house that you will clamp to for testing purposes. If you can, go to a hardware store and buy a ground rod, if you can't then any copper pipe will work. (even a piece of re-bar or galvanized pipe would work) This will serve as your RF ground. Use a 8 gauge wire (the size really isn't critical, any wire would work ok, like a 10 or 12) and connect this to your ground rod via ground clamp. So one end of your wire is connected to the rod. Now you will connect the other end of the wire to the base of your secondary coil (meaning you physically connect the small magnet wire to the ground rod's wire) and connect it to your strike rail. So the base of your secondary and strike rail will be electrically connected to earth ground.

So that's how its done. However, you need to assess whether or not you will have time or be able to drive a ground rod at the location of the science expo. (or whatever it is)
If you can, go to your expo early and find some dirt patch to smack that rod into. If you are demonstrating your coil in a science classroom, you could just connect to a nearby water pipe that goes to ground. (I have done this) It is not extremely critical to have a super nice ground rod connected into wet soil driven 15 feet into earth, but you do need a somewhat solid connection.

If making some kind of RF ground at the expo really isn't possible, then you could use the mains ground on an extension cord. This method, however, is really not recommended.

Blitzorn

Fri May 29 2009, 05:44AM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

I have a suitable rod, but i wonder if i'll be able to drive it in where i'm presenting... i'll see if i can find out tomorrow. In any case, there'll probably be a nearby door to the outside, through which i could run the RF grounding wire, but how short does it really have to be to function? Should it be insulated or stripped?

and that reminds me, what is the best way to discharge my caps after use?

Herr Zapp

Fri May 29 2009, 07:24PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Blitzorn -

DO NOT attempt to use the AC line ground from an outlet for your RF ground!!!

A coil with a 60ma power supply is capable of injecting enough RF noise and high-voltage spikes into a building's AC wiring to damage other other electronic devices (computers, TVs, alarm systems, etc). Worst-case, you can cause arcing in the wall behind the outlet or in remote junction boxes that could conceivably cause a fire. A tiny desktop coil powered by a 4/20 NST MIGHT get away with using an AC line ground, but it's NEVER a good idea.

If you can't find or make a decent RF ground, then you'll need to select another location to demo your coil. If you are in an auditorium or classroom, and can't run a ground wire to an earth ground rod, see if there is any exposed structural steel that is anchored in concrete (vertical I-beams or columns, etc). A ground wire can be clamped to clean, bare steel with a vise-grip pliers or a C-clamp.

Remember that a metallic counterpoise (especially if it's laid directly on bare concrete) will work OK if you have no other other grounding options.

Also, you didn't mention if you have an AC line filter in your feed to your transformer(s), but you certainly should.

Your ground wire can be bare or insulated.

Regards,
Herr Zapp

Blitzorn

Fri May 29 2009, 08:44PM

Registered Member #2128 Joined: Thu May 21 2009, 03:17AM
Location: Seattle, Washington, USA
Posts: 58

Herr Zapp -

Have no fear, when i saw that a huge red battle standard went up in my head and i didn't even consider it. I have established a location for the demo where i can easily drive in a 5-1/2' copper tube <10 feet from the coil. It is a dark room with plenty of room to cordon off a safety area, and i think it will do marvelously. There's even a supply closet only yards away that somehow got its own branch circuit and will power the shopvac. With regards toward safety, how far away should onlookers be kept, and please note that they will mostly be somewhat obnxious, relatively clumsy, undoubtably curious classmates of mine. I'm thinking 15 feet is not unreasonable.

No, i do not have an AC line filter. I understand that this is a relatively important security measure, i've read up on what can go wrong - but i also read that most neon sign transformers have rudimentary filtering built in... am i off my rocker here? and if the system is unprotected, how big of a problem will it be?

Herr Zapp

Sat May 30 2009, 02:25AM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

Blitzorn -

If your ground rod location is in anything but dead dry desert sand, then driving 2' - 2.5' of ground rod underground will be fine. Trying to pound 5.5 feet of copper tube into the ground would be a challenge, and don't forget you'll have to remove it when you're done.

I'm not aware of ANY conventional NSTs that have any sort of internal filtering on the AC input side. I'd try to find a line filter if at all possible. You may be able to salvage one out of some piece of discarded electronic equipment. They are pretty common at electronics surplus stores, electronics recycling outfits, etc. Anything rated 5A or greater will be better than nothing.

Keeping everybody back 10-15' will be fine. With some luck & tuning, you may be able to squeeze 24" streamers out of this setup fairly easily.

Regards,
Herr Zapp

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