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Blitzorn

Sat May 23 2009, 08:14PM

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

Thanks much, i'm going to make a round of calls about transformers and then probably jump on this one.

Two other speed bumps -

PVC - the only 4" and 6" dia PVC i could find at my hardware store for the secondary form and spark gap housing was sold in 20 foot lengths that could not be cut down pre-sale. Are there any good alternative sources of PVC? I was told plumbers and contractors, and that's probably a good choice but i'm just looking for other fallbacks. Where did you guys get yours?

Secondary wire - i'm having trouble finding a big enough spool, and i was thinking i might be able to cannibalize some from another appliance... what sort of devices could i hack open for some approx. 0.5mm enameled copper wire?

I'll get my hands on a transformer pronto and build a jacob's ladder rig right away so that i can relax and know that if worst comes to worst i still have a presentation.

rp181

Sat May 23 2009, 08:39PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529

Here is a place for pipe:

Its about 5$ a foot for 4". If you wan't to go fancy, they have clear PVC pipe. If you don't like that, check out mcmaster-carr, they have almost everything imaginable, from urinals to magnet wire.
You would be hard-pressed to find enough wire in one appliance that long, best bet is a motor.

Blitzorn

Sat May 23 2009, 09:12PM

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

Is there any reason not to buy the much cheaper PVC Sewer piping? It looks like it has thinner walls but i read that that is a good thing...

Andri

Sat May 23 2009, 10:57PM

Registered Member #1533 Joined: Wed Jun 11 2008, 02:13PM
Location: ReykjavÃk, Iceland
Posts: 46

Any piping that does not conduct any electricity will do. I say that because some piping is tainted with carbon. Stay away from black pipes or any dark color. I'd spend a bit more effort on finding magnet wire if I were you. It will probably save you some labour.

Herr Zapp

Sun May 24 2009, 01:06AM

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

Blitzorn -

Your first "transformer" is definitely a solid-state unit with GFI, and is not suitable for powering a conventional AC spark-gap Tesla coil.
The second transformer is definitely a conventional iron-core NST without GFI, and would be fine. However, it is relatively expensive, and you have no guarantee that it will arrive on time.

I'd hit all the local neon sign shops, and sign maintenance shops. If you can do a little verbal salesmanship, and make it sound like you know exactly what you are doing, there is a good chance that you can get a used 30ma transformer free, or for $10 or so.

Next, I'd focus on getting the wire for your secondary. Trust me, trying to salvage enough wire to wind a secondary will be difficult, and salvaged wire will invariably have nicks in the insulation, kinks, etc, etc. It's just not worth the probable nightmare that salvaged wire will cause. Just get a small spool of virgin wire and avoid the hassle. Remember, enameled magnet wire is what is usually used for secondary coils, but ANY small gage insulated wire will "work".

The secondary coilform can be any grade of PVC or ABS pipe (ABS pipe is black, by the way, and doesn't contain any "carbon"). Many Home Depot stores carry 2 foot lengths of 4" and 6" diameter PVC and ABS pipe. Stop by any construction site and ask the site foreman (or any plumber) for some scrap 3", 4", or 6" diameter PVC or ABS pipe. 2-4 foot lengths are ALWAYS lying around as remnants that will be thrown out. Any plumbing contractor will likely have small lengths of PVC and ABS pipe available for free.

If you just can't find a plastic coilform, even a cardboard core from a roll of carpet can be used. It's not ideal, but will certainly "work". Every carpet shop will have loads of cardboard cores in the dumpster.

You are on a very tight schedule, so you're going to have to be creative and hone your "scrounging" skills to get materials that will work. Later, you can re-build the coil using pristine materials so it looks more presentable.

Regards,
Herr Zapp

Blitzorn

Sun May 24 2009, 05:45AM

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

Thanks for the tips, i'll call up some sign stores tomorrow and immediately get my hands on some wire and piping, i found a good web site for the wire, thanks to RP181, and i know just the place to get the piping thanks to all who suggested plumbers/contractors, one of my friend's dads is a plumbing installer. One change, I'm thinking about making my topload out of a styrofoam ball coated in aluminum at this point though.

Herr Zapp

Sun May 24 2009, 06:07AM

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

Blitzorn -

For your topload, I'd recommend a toroid over a sphere for several reasons.

One of the most important is that a sphere will (usually) not provide adequate electrostatic shielding of the top turn on the secondary. You will get lots of corona and small streamers from the top turn, which reduces the length of the main streamer. Also, a toroidal topload will help direct streamers up and out, reducing the potential for primary strikes (the streamer reaching down and hitting the primary conductor).

A very functional and inexpensive toroid can be made from flexible convoluted-aluminum duct material from the hardware store. This is sold in compressed lengths about 24" long that can cut to length and formed into a donut, Depending on the diameter of your secondary coilform, 3" or 4" diameter duct would be perfect when formed into a 12" to 16" diameter donut. This material typically costs $5-8 per segment. Most Home Depot stores carry this material in 3" to 8" diameters.

Use self-adhesive aluminum (metal) HVAC duct tape (again from Home Depot) to hold the ends of the duct material together, and to cover and secure a cardboard disk that creates the "center" of the toroid.

Regards,
Herr Zapp

Blitzorn

Mon May 25 2009, 10:01PM

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

Alrighty! Yesterday i made a hardware store visit and two garage raids, and am now in possession of all my needed materials except for some epoxy which i will get tomorrow, and my transformer and magnet wire, which are both in the mail.

I spent about seven hours yesterday working and about 4 so far today, my top load is complete, i went with a 5" ducting toroid held together with aluminum tape, and it should be nicely functional - if not a bit ugly, and my spark gap is coming along nicely. I'm just beginning work on my primary coil now, as the secondary has been postponed until i actually have wire to wind it!

In any case, progress is being made! More to come soon.

Herr Zapp

Mon May 25 2009, 11:06PM

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

Blitzorn -

OK, all sounds well and good.

May we assume that you have used WINTESLA, or JAVATC, or some other tool to determine all the dimensions and parameters that will allow your coil to be tuned to achieve resonance in the primary and secondary circuits?

I'm not sure how you can be assembling your primary coil unless you know how many turns you will need.

It sounds like you know the gage of magnet wire that you will be using, and that you know the dimensions of your secondary coilform, and that your topload is already completed. I assume that you have plugged these dimensions into one of the Tesla coil design tools, and that you now know what the resonant frequency of your secondary coil (with topload) will be. Knowing the resonant frequency of your secondary system, you then know what the resonant frequency of the primary system needs to be: that is, the capacitance value of your salt-water capacitor, and approximately how many turns will be required in your primary coil.

The only reason I keep repeating this "design it first" mantra is because many, MANY first-time coil builders see a Tesla coil on the web, and think that it is just a few turns of heavy wire in the primary, another coil with many turns of fine wire, a spark gap, a capacitor, and a transformer. They throw something together that looks (pretty much) "just like" the one they they saw on the web, but when they're finished they find it doesn't work at all: zero output. The main spark gap may fire like crazy, but there are no streamers or any evidence of high voltage output. They didn't understand that THE key characteristic of a Tesla coil is RESONANCE, and they didn't understand that each part of the coil has to have very specific inductance and capacitance values to achieve resonance.

Now if you did really study Richie Burnett's website, and really understand Tesla coil resonance, and know how to achieve it, then all this talk is unnecessary. However, you were "99.9% sure" that your solid state gaseous tube power supply was a conventional iron-core NST......

So, if you've "run the numbers", and know the target inductance of your primary and secondary coils (in microhenries and millihenries, respectively) and how many turns of wire are required to achieve these inductance values, and you know the required capacitance value (in microfarads or nanofarads) of your salt-water capacitor, then just keep moving forward at full speed.

If you don't know what any of this "millihenry" or "microfarad" talk is about, then STOP building and do some calculating!

(It might be a good idea to post all your dimensions and parameters [from WINTESLA or JAVATC], along with the details of your spark gap design, for everyone to review before you get too far into construction. That way, if there are any fundamental errors or likely problems, the experienced Tesla coil builders on this forum can spot them and provide corrections or improvements, and you won't have to "learn the hard way".)

Regards,
Herr Zapp

StevenCaton

Mon May 25 2009, 11:40PM

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

Blitzorn, do you have a variac? (variable voltage transformer)

If you don't have a variac, then its ok, but then you should be very meticulous in your design and calculations because applying full power to a coil that is badly out of tune is not a good thing.

Good luck and keep us posted.

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