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Blitzorn

Thu May 21 2009, 09:17PM

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

First post here, what i've seen so far is promising, so maybe i can get some quick feedback.
I'm 17 and am working with my father in designing and constructing a tesla coil.
He is a veteran electrical engineer and a good resource for knowledge on many subjects, but is HV experience is fairly limited. Mine is too, i have never built or operated HV devices for home or commercial purposes. The trick is that despite his knowledge i will be doing all of the assembly, all of the shopping, and most of the research because he has a fairly advanced case of ALS (lou gehrig's disease).

I believe i am more than capable of creating a quality product essentially solo, but there's a kicker. I see myself progressing up through different designs of varying complexity and configuration throughout my coiling career, but in the short term i really need to build a coil FAST. My school is hosting a youth science expo and i've put just about all my eggs in the SGTC basket. And i have about two weeks to make it happen. I don't need a big, showy, expensive coil. As a matter of fact that's the opposite of what i want. Optimally components will be cheap, even hand assembled. I have plenty of time to spend on things like winding and sanding but can't afford a lot of delays - waiting for shipments, going back to the drawing board, etc. Nothing needs to last for hours and hours of operation, just long enough to get it tuned and tested and do a few short demos.

Here's what i have so far as basic components:

7200v/35mA xformer
Bank of saltwater bottle caps (quantity not yet established)
Static sucker SG, multiple or simple
Flexible aluminum ducting toroid

BUT I NEED EXPERT INPUT

I don't know the specifics on assembling saltwater caps, i don't know if they're the best choice for a small demo, and i don't know what my fallback alternative would be.
I don't know the specifics on winding the primary or secondary, how large they should be, etc.

But one thing at a time.

My first question is, IS THIS EVEN POSSIBLE? I think with the right equipment i could get a coil working in two weeks but that seems like a lot to bite off for a first timer. I can check back often, post pics of progress, etc, but i'm going to need a lot of backup from pros in order to get a suitable result.

StevenCaton

Thu May 21 2009, 10:29PM

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

IS THIS EVEN POSSIBLE?

Everything is possible.

Well, it sounds like you've got everything you need. Just follow a basic spark gap coil schematic and your coil will work fine.

I don't know the specifics on winding the primary or secondary, how large they should be, etc.

It sounds like you want the coil done quickly and cheaply, so if I were you, I would just wind a coil on the nearest piece of pvc or cardboard you can get your hands on. You probably have some wire for the secondary already, don't you. Wind about 800 turns on it. A 3 inch diameter form would be fine.

For the primary, about 12 turns will do, but the # of turns of course depends on the Fo of your secondary + topload. You will have a *tap* point on your primary that you will adjust (change the #of turns) until the ouput is the best. Once again, just use whatever you have access to for the primary. A good material for your coil would be 1/8 inch Cu tube, but you don't seem like you want to spend $ so any reasonably sized Cu wire or aluminum tube.
Google "deep fried neon" and go to the website.
Also, don't plug anything in if you are not doing it in a safe manner. I know you want the coil built quickly, but don't sacrifice safety for a project deadline.

Good luck

syntroniks

Thu May 21 2009, 10:45PM

Registered Member #1530 Joined: Tue Jun 10 2008, 03:34PM
Location:
Posts: 32

Two weeks is possible, I built my SSTC when I was 18, took much longer though (because I am a turtle and didn't have parts).

I wouldn't recommend saltwater caps, or any capacitors that are homebrew. Spending the $$ on a MMC will most likely give you better performance.

You could probably get away with out the fancy copper tube primary. Go get some PVC and start winding that secondary then. ---EDIT SteveC posted right before me. If he says use tube, go ahead and use tube.

I see winding secondary and getting a capacitor setup as being your biggest challenge. Also, make sure everything is ncie and safe at the expo. Get a variac and make sure things are fused correctly. And good luck!

Coronafix

Thu May 21 2009, 11:19PM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

I would suggest making your secondary smaller than you want to. Your transformer is only small so if you go making a big secondary you will get little sparks if any at all.
My first TC was on a 69mm former with about 1300 turns of wire scrapped from a microwave oven fan. This is cheap and works well. I ended up pumping 900W into the little thing, it looked great! Sparklength was longer than the coil.
My latest coil is a MOT monster that puts out 1.5m arcs and I'm still tuning it.
For my first primary I used 3mm solid copper wire that I got from a salvage place for 5 bucks. It was actually a piece of fat cable that had a whole heap of the 3mm wire twisted together. Another option would be pulling the copper tubing out of an old fridge.
For a capacitor you really can't beat an MMC, but the saltwater caps will work or you can check out Mates 60kv rolled caps in wiki.

I will assume you are on 60Hz mains, so your resonant cap will be 13nF, to be safe you should use larger than resonant (LTR) usually 1.4-1.5x =18nF

oucivileng

Fri May 22 2009, 02:30AM

Registered Member #1772 Joined: Tue Oct 21 2008, 05:23AM
Location: Athens, OH
Posts: 71

this is what i did initially - saltwater in the bottles, saltwater in the tub, long bolts hanging into the bottles, and a wire hanging in the tub. it worked pretty well i think. Just try to space the bottles out a little better than what you see in the pic. if they're too close, they start sparking more and you just wind up with more losses. I used 12 bottles filled to almost to the neck and got around 6-8 nF if I remember correctly. It kind of varied from day to day

Blitzorn

Fri May 22 2009, 02:50AM

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

I'm currently working out some calculations on the secondary winding and i can't seem to find a straight answer anywhere - does the wire go on bare or insulated? Logic tells me insulated, but i keep seeing pictures with that gorgeous coppery shine and have second thoughts.

Coronafix

Fri May 22 2009, 04:32AM

Registered Member #160 Joined: Mon Feb 13 2006, 02:07AM
Location: Melbourne, Australia
Posts: 938

Always use insulated wire otherwise it will all short out and just be a pipe. :)

Blitzorn

Fri May 22 2009, 04:55AM

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

So the ones that i'm seeing which are coppery in color appear that way because the insulation is an enamel that is clear. This all sits well :D
I've made more progress today thanks to these few replies than all of last week - thank the internet!
(and thank you guys of course)

More to come as it comes!

Herr Zapp

Fri May 22 2009, 06:20PM

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

Blitzorn -

Designing, building and tuning a Tesla coil in two weeks will be a BIG challenge. Do you have two weeks that will be dedicated ONLY to building a coil, or will this be a spare-time activity after school, etc?

First, don't even think of buying parts or starting assembly of anything until you have a complete design "on paper". A Tesla coil will only work if the resonant frequency of the primary and secondary circuits are the same. The only way to get matched resonant frequencies is to very carefully design and construct the primary and secondary so they have the same natural frequency.

There are several Tesla coil design calculators that make it very easy to determine the parameters of every component of the coil so the resonant frequency will be correct. One of the easiest to use for a first-time coil builder is WINTESLA, which can be downloaded free from R. Scott Coppersmith's site at:

To start, you will need to know the following parameters:

1. Diameter and length of your secondary coilform (suggest 3" or 3.5" dia PVC pipe, or acrylic tubing);
2. Shape and dimensions of your secondary topload (suggest toroid made from 2" dia convoluted aluminum ducting);
3. Diameter of the enameled magnet wire you will use to wind the secondary coil (recommend #26 to #28 AWG);
4. Diameter and length of your primary conductor (suggest #10 or #12 AWG solid house wiring, or 1/8" diameter copper tubing);
5. Value of your tank capacitor;
6. Output voltage and current rating of your HV supply transformer.

WINTESLA will allow you to enter the parameters, perform the calculations, and show you what dimensions, etc are required to get both primary and secondary circuits to resonate at the same frequency.

Also, since you are starting out with very limited knowledge of Tesla coil design and theory of operation, I strongly recommend that you first spend several hours reading about spark-gap Tesla coils at what's still the world's best TC technical website, Richie Burnett's site at:

What you are trying to do CAN be done in the available time, but it will require intense focus and attention to detail. Don't start assembling ANYTHING until you understand how a Tesla coil operates, and you have the complete design laid out on paper.

Regards,
Herr Zapp

Dr. Drone

Fri May 22 2009, 06:50PM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

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