How To Build A Spark Gap Tesla Coil (SGTC)

Step 2: Gather Materials

The materials that you will need for this project should cost you no more than $200 and you can easily spend less than $100 if you invest some time into searching for good deals. Here is how I distributed my money:

Electrical Parts:

$35 - (1) 9kV 30mA Neon Sign Transformer
$35 - (100) 1.5kV 0.01uF Polypropylene Film/Foil Capacitors (the type of capacitor, in addition to it's value, is critical)
$5 - (100) 10M 1/2W Resistors (I actually bought 200, but didn't use half of them)
$20 - 680 Feet of 23 AWG Enameled Wire

Hardware Parts:

$15 - Wood from Home Depot - I cut a large piece into (2) 13" x 16" x 3/4" pieces for the base
$3 - 20" Long 3.5" Diameter PVC pipe for the secondary coil former
$2 - (1) 2' long 1" diameter PVC pipe for the primary coil former
$2 - (8) Nuts and bolts to hold the primary formers down - I used #8-32 x 1 - 1/4" Machine Screws
$0 - Primary Coil Wire - I used some relatively thick insulated wire I found at a recycling center, one could easily use flexible copper tubing or thick speaker wire for this purpose
$0 - (1) 1' by 1' piece of acrylic - I had some extra pieces from a laser project, but any moderately-sized sheet of plastic will do
$0 - (2) Metal objects to form a spark gap - I used a pair thick nuts and bolts for this
$3 - (1) 6" Styrofoam ball for the topload former
$0 - Aluminum foil to cover the topload
$0 - Spray-on Polyurethane Varnish or Shellac

TOTAL COST: $120

Coil Specs.

Power Supply: 9kV 30mA NST (270W)
Primary Capacitor: 10nF 15kV MMC
Spark Gap: Single static gap made from a bolt and a washer
Primary Coil: Flat spiral coil made from 9 turns of 10AWG wire tapped every quarter turn with 0.25" spacing
Secondary Coil: 3.5" by 18" winding of 23AWG enameled wire
Topload: 6" Styrofoam sphere covered in aluminum foil
Max. Spark Length: 14" to ground, 11" to air

Comments

[sciencetor2]

found these capacitors on ebay, they're from a supplier so they should be around for a while.

http://www.ebay.com/itm/380266725123?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649#ht_1854wt_811

all the info you would need isn't there, but with a bit of research done after i recieved my order, they appear to be the crimped version of these

http://www.panasonic.com/industrial/includes/pdf/ECW-H_C_New_Product_Introduction_Sheet.pdf

which should(probably) be suited for coil use, though the specs are slightly different from the instructable, so you would need to change your MMC configuration. i will probably go with a 12x8 setup(12 per string, 8 strings in paralell) which yields a capacitance of 0.01uF and a voltage rating of 19200v(19.2kV). i will let you know how it goes when i finish my coil.

[The MadScientist]

Hi. I am just wondering whether these capacitors would also work?

Cheers

[agod]

could you give a link for the resistors you used. Thanks.

[sciencetor2]

yep :) here you go! happy coiling!

http://www.ebay.com/itm/10-Meg-Ohm-Bleed-Resistors-Tesla-Coil-Capacitors-/360313237049?pt=LH_DefaultDomain_0&hash=item53e457ae39

[sciencetor2]

ok, just finished my tesla coil and ran it, these capacitors work great! highly reccomend them for their price, amount, and continuous availability.

[seraine]

I need 17 0.15 uf capacitors, and these appear to be perfect for my Tesla Coil

http://www.digikey.com/product-detail/en/B32023A3154M/495-3802-ND/1648119

Can a MMC use polypropylene metallized film capacitors?

[Xellers]

Yes - those are precisely the kind of cap you'd want to use (unless you can afford CDEs).

Good luck!

[seraine]

Thanks for the speedy reply!

[agod]

my transformer is the same as yours but 60ma. what will i need to change in the cappacitor bank? THanks

[Xellers]

See the step on building the capacitor - I discuss how a value is selected there. You'll need to run the calculations yourself. Good luck!

[Electrodude]

would an electrolytic capacitor work?

[Xellers]

Nope

[intellectualbean]

Would ceramic disc capacitors work (http://www.opentip.com/Musical-Instruments/Capacitor-Ceramic-Disc-p-1620763.html)? Or are Polypropylene Film/Foil Capacitors the only type that should be used?

[Xellers]

Unfortunately, ceramic disc capacitors will not work. I know this because I tried it with one of my low power coils and they all started exploding and because it's basically common knowledge in the high voltage community that ceramic capacitors are not coil worthy.

[intellectualbean]

Well then I'm glad I asked before I purchased them. Thank you for your fast reply.

[Gone_Phishing]

Hey I was wondering if I could use a 15 kV 30 mA NST instead, or do I have to change other specifications? Thanks! I really like your project

[Xellers]

You would need to change the specifications; you NST has a higher output voltage and can provide more power than mine. Recalculating can be as simple as finding a new resonant capacitance value and voltage rating and then slightly adjusting primary inductance and secondary size, or it can involve ScanTesla and various other Tesla coil optimization methods; it's up to you.

[Gone_Phishing]

Oh ok thanks a bunch! Those are detailed in the instructable right, there were equations I think.

[Legoman132]

I'm building my first coil, and i'm looking at different types of caps (MMCs and bottle caps mostly), an I was wondering where you got yours. Nice idea with the washer on the spark gap, by the way.
Thanks in advance

[Xellers]

I got my MMC caps from eBay. Don't search for "tesla capacitor", it only returns cheap metalized polystyrene capacitors that won't work for Tesla coil duty and super-expensive CDE film capacitors that are unnecessary for this project. Try searching for polypropylene capacitors or high voltage capacitors to see what you can find.

As for bottle capacitors, I haven't experimented too much with them so I can't really say much. All I know is that they have a reputation for having high losses and low performance. I have yet to see a truly effective low power design that utilized bottle capacitors.

However, I have seen bottle capacitors being used in large numbers in high power coils with some success. Greg's Garage Tesla Coils is a great example of this. Remember though, if you pump huge amounts of energy into your coil, then even major power losses will still yield decent results. With 4.4kW in, Greg was able to make 4' sparks, while the theoretical maximum spark length at this power is in excess of 9'. On the other hand, bottle capacitors are dirty cheap and can take a huge beating without failing.

Good luck with your project!

[Legoman132]

Do these look like the right type? http://cgi.ebay.com/0-68UF-250V-Metallized-Polypropylene-Film-Capacitor-ECW-/120660620766?pt=LH_DefaultDomain_0&hash=item1c17eef5de

[anurag130]

I looked at those and they are only 250VDC. Also the price is for one capacitor, not the whole bag.

[Legoman132]

I thought they were WAY cheap, but according to the MMC calculator the 250V rating didn't make the number of caps to high, it just put less in parallel because of the capacitance.

[Xellers]

That's definitely the type of capacitor you should be looking for, but you should get capacitors with a higher voltage rating and lower capacitance. That way, it will be cheaper and your MMC will have more than one series string, increasing the current that it can handle.

At the moment, the best deal I see is this: http://cgi.ebay.com/Assorted-Radial-Film-Capacitors-High-Voltage-Assortment-/120712257419?pt=LH_DefaultDomain_0&hash=item1c1b02df8b

The capacitors aren't all the same, which might make it more difficult to find the best combination, but at only $18 for 80 high voltage capacitors, I'd say it's worth buying just to experiment with.

[Legoman132]

Thank you so much. At this stage, I'm just concerned with just getting it working, so i was willing to accept the losses and upgrade later, But now I'll go straight to an MMC. Thank you.

[anurag130]

(removed by author or community request)

[Xellers]

See the reply I posted to Legoman132's comment.