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Building first Tesla Coil

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EvilTesla-RG

Sat Jun 07 2008, 02:36PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

I have been wanting to build a Tesla coil since elementary school, and now I finaly belive I have enough knowlage to finaly build one, but I still need to know alot.

I'v already build three "Tesla Coils" but they wern't true Tesla coils, becouse they wernt tuned. I just kinda slaped them together in a few minuets. They worked, but not very well.

First question I have is the Primary coil.
What matierial should the coil itself be? Pipe is expensive, and doesn't bend.
Normal wire can't be tapped easily.
Would electric fencing wire work? becouse I have miles of that.
Does the angle of the coil REALY matter? I heard something about dubbing, but I don't know what that is.

My most important question concerns capacitors. Currently, I use something I call a scroll capacitor. Which is just a rolled capacitor, with two sheets of polyethaline (don't remeber the thickness) It holds a realy good charge, but it has two problems.
1) charge time. takes about one intire second for the capacitor to fully charge, doesn't this prevent the Coil from working at high frequency??
2) measuring it. How do you measure the capacitence with a capcitor like this?? I can't use the normal methods, becouse I don't have teh money to buy a DMM that can measure capacitence, and most other methods require the capacitor to work at 120 v, which these do not. Would just calculating the capacitence be accurit enough?

Where online is the best place to buy a NST? I had a 7.5 kv 40 MA transformer, but my last experement fried it. It was sad, that thing has served me since early elementary days, I'll probably organize a small funeral for it......
I live in North Idaho, so finding a Neon sign store is out of the question.

Also, I have heard something about filters. WHat are these? do I need them? If I do, where do I get them? and how do they interfere with coil operations

Also about wire connections, at this high voltage I know it is easy to create leaks. Is just wrapping wires together good enough for connectins two wires? Or should I take the time to solder it? or what?

I also heard something about grounding. I don't understand it. Said something about not connecting the HF ground and the common ground?

Does that mean that I shouldn't connection my secondary coil's ground to the third prong in the wall socket? Why not? A Store bought coil I have does it.

If thier is anything else I should know, pls tell me. I realy want to build a Tesla Coil, it's becoming an addiction.

Avi

Sat Jun 07 2008, 03:23PM

Registered Member #580 Joined: Mon Mar 12 2007, 03:17PM
Location: Melbourne, Australia
Posts: 410

The primary coil must be made of heavy duty wire that will be capable of huge peak currents without resistive loss (as would happen with thin wire).
As for the capacitor charge time, as you may already know 50/60hz is way below the operating frequency anyway! so the charge time only determines the average power output (how often it will resonate), but when it fires, it will resonate until the capacitor is discharged.

Arcstarter

Sat Jun 07 2008, 03:44PM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

Well a high frequency choke is suggested or you may burn another supply out. What i use is really easy to make. All i did was make two choke which were just 1 inch pvc pipe with around 100 turns of 28 awg. I also use a safety spark gap which just consisted of two screws in close proximity to each other that is JUST large enough so that the transformer will not fire it when running normally. It will protect from over voltage and the chokes, A.K.A hf (high frequency) chokes will keep any high frequency oscillations out of the fragile windings of the transformer. And yes, your capacitor is MUCH too big. If you have any money buy some of these capacitors:

These are each 150 nanofarads(nf). Depending on your power source you typically need 20nf to as low as a few nf with a typical nst. If you want, download tesla map(i use visual) and you just type in the frequency of your transformer and current and voltage and it will give you the correct capacitance you need. Use ltr(larger than resonance) to run it. Also at the top of the tesla map page, it has the symbol of 4 capacitors and that is a capacitor calculator. Just type in the capacitance of the capacitor you are going to use, as well as voltage. It will show you how many capacitors it will take to get you to the right value. Oh and with those capacitors i showed you, you generally want to use them as 1000 volt capacitors. If you use them for the full voltage they are rated for they will ruin themselves, because that is the dc rating, not ac.

flannelhead

Sat Jun 07 2008, 03:45PM

Registered Member #952 Joined: Mon Aug 13 2007, 11:07AM
Location: Finland
Posts: 388

EvilTesla-RG wrote ...

My most important question concerns capacitors. Currently, I use something I call a scroll capacitor. Which is just a rolled capacitor, with two sheets of polyethaline (don't remeber the thickness) It holds a realy good charge, but it has two problems.
1) charge time. takes about one intire second for the capacitor to fully charge, doesn't this prevent the Coil from working at high frequency??
2) measuring it. How do you measure the capacitence with a capcitor like this?? I can't use the normal methods, becouse I don't have teh money to buy a DMM that can measure capacitence, and most other methods require the capacitor to work at 120 v, which these do not. Would just calculating the capacitence be accurit enough?

1) Depends on your HV supply you're using. More current = faster charging time.
2) Calculating the capacitance should be accurate enough as you don't need to know the exact capacitange. The fine tuning is done with the primary.

EvilTesla-RG wrote ...

Where online is the best place to buy a NST?

Everyone is buying NSTs from Ebay. Maybe you should check it out?

EvilTesla-RG wrote ...

Also, I have heard something about filters.

I suppose you mean RFI filters. These are needed (or not) if you ground the secondary to the mains ground.

EvilTesla-RG wrote ...

Also about wire connections, at this high voltage I know it is easy to create leaks. Is just wrapping wires together good enough for connectins two wires? Or should I take the time to solder it? or what?

Absolutely use solder. Make nice connections without sharp points to minimize corona leakage.

EvilTesla-RG wrote ...

I also heard something about grounding. I don't understand it. Said something about not connecting the HF ground and the common ground?

The secondary base has to be grounded to a RF ground. It means, if you are operating it outdoors, just a rod you push to the Mother Earth. Or it could be grounded to the mains ground.

EvilTesla-RG wrote ...

If thier is anything else I should know, pls tell me. I realy want to build a Tesla Coil, it's becoming an addiction.

JavaTC is good for planning your coil. Some other useful links:
Jan Wagner's theory site
HvWiki SGTC article
Google

And good luck with your coil!

HTH,
Dr. 2N3055

EvilTesla-RG

Sun Jun 08 2008, 10:17PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

Awsome!!

Thnxs for all this info!!!!

I do have Tesla Map. So that is good knowing I should use something larger than resonate....

Fencing wire is designed for high voltages, even though this is significantly higher, it should work.

I hate soldering, but I guess I'll do taht.

I realy do not want to build an MMC. I am not very good at soldering, and capacitors arn't easy to solder.
What is the best way to build a home-made capacitor?

And yes, I can do Ebay, I was looking at that.

Once again, thnxs for all the info, I'll get back if I have anymore questions. Which I'm pretty sure I will.

Mon Jun 09 2008, 01:01AM

Registered Member #1415 Joined:
Location:
Posts: 21

This is essentially where I got all the information to build my first tesla coil.
The site has a place where you can plug in numbers for various parts of the coil and make sure everything is in tune.
Maybe you will find it useful.

I am relatively new with tesla coils as well, but I worked all the numbers out with this website and my first coil gave 30 inch sparks.
good luck

Patriot

Mon Jun 09 2008, 02:43AM

Registered Member #1507 Joined: Tue May 27 2008, 04:05PM
Location: el paso, texas
Posts: 39

I wouldn't use electric fencing wire for your primary, Its small diameter would lead to loses in your primary circuit. Like avi said you need a heavy gauge conductor which will handle the high peak current, the thin strand of electric fence wire will ionize the air around it and be "lossy". If you could at least get 1/4 in copper tubing or even some 10 gauge multistrand wire you'd be better off. You can make your coil more efficient by using heavy wire and making sure your connections don't have sharp points or edges on them. And keeping connections short also helps too. Good luck and have fun.

Firefox

Mon Jun 09 2008, 06:36PM

Registered Member #1389 Joined: Thu Mar 13 2008, 12:50AM
Location: Pittsburgh, PA
Posts: 346

If you don't want an MMC, try building plate glass, PET rolled, or beer bottle capacitors.

For the plate glass cap, just put two pieces of tin foil on either side of a piece of plate glass, then connect your circuit to each plate like you would a capacitor lead. This is good for caps in the .5-3 nF range, because the glass is electrically strong, so it won't break down given you use the right thickness to hold back your primary's voltage. Breakdown voltage of glass is about 8kV/mm.

To find the capacitance of your build, use the equation C=(kÎµ(n-1)A)/d where C is the capacitance, k is the dielectric constant (glass is about 3.7, PET film is about 3.2), n is the number of conducting plates, A is the area of one plate, and d is the distance between the plates (or the thickness of the dielectric).

In a rolled PET (polyethylene terephthalate, a.k.a. overhead slides, and some types of ground tarps) you just double the capacitance of of a parallel plate cap like the one above. The procedure is outlined here: 60kV, 3.5nF Rolled Cap. You don't need to hot glue and melt the ends together, and I believe mates even recommends against it now. At the very least, I've never had problems when I haven't fused them shut. The breakdown voltage of PET film is about 300kv/mm IIRC. I've put 10kV across a .1 mm piece of PET and it held up just fine, even after being repeatedly charged and discharged.

I've never made a beer bottle cap before, so I can't help you with them.

Andyman

Mon Jun 09 2008, 07:09PM

Registered Member #1083 Joined: Mon Oct 29 2007, 06:16PM
Location: Upland, California
Posts: 256

The most simple, quick capacitor is the beer bottle/mason jar cap. I personally use a mason jar, and it has held up at 12 kV even during my occasional 5-10 minute runs. I fill the jar with saltwater, put a long bolt on the lid, and put it in a tupperware container filled with saltwater.
It's low capacitance, around 1nF so you would need at least 10 of them in parallel. The only problem is that glass has high losses at the RF frequencies.
If you want to build something nicer, use the overhead projector sheet capacitor. I have found that the sheets are VERY expensive brand new, so I have just used brand new, unseparated sheet protectors.

For the primary, if you're coil and nst are small, you can get away with using 10 AWG stranded wire. I've used it on a medium sized coil with a 9kV 60ma nst and it seems to work just fine.
I have a 500 foot spool of white insulated 10 awg, and I could send you some if you want

Hit me up with a PM.
Good luck!

EvilTesla-RG

Tue Jun 10 2008, 08:29PM

Registered Member #1523 Joined: Sat Jun 07 2008, 02:05PM
Location:
Posts: 97

once again, thanks for the replies.

Steve C- Yes, Just looked at that site, looks like it will help alot, thnxs.

Patriot- Thnxs, guess I'll have to find something else....shouldn't be too hard. And I guess I'll have to strive for better connections.

FireFox- I'v made a version of the PET rolled, so I'll stick with them. Thnxs for the EQ, I was hoping thier was a way to directly measure the capacitence, but I guess thiers not.

Andyman- yea, I'v build a mason jar cap b4. It made an insane amount of ozone, yea, not going thier!! lol. Thnxs for your offer, but I'll find something on my own, it can't be TOO hard!!

One other question. Arcstarter recomended building some small 100-coil coils for chokes. But wouldn't these produce alot of resistence and inductence? that would throw off the frequence?

Also I'm wondering, if I go with pipe for my primary, how do I bend it?

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