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New Tesla Coil - Capacitor advice

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LAN_403

Xplorer

Thu Aug 05 2010, 10:22AM

Registered Member #2416 Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91

Hey guys,

So I'm going to build a new SG TC with a 15/60 and I need a cap bank of .0106uf. However my budget for this project is limited. BTY I'm using Deep Fried Neon's calculator.

A couple of these in series will give me .01uf at 30kv

Pretty good right? Do they hold up?

OR

Should I get the Cornells? They're .15uf but only 2000v so I'll need 14 of them in series to get .0107uf.

Any opinions are appreciated! Thanks!

-Tony

Herr Zapp

Thu Aug 05 2010, 06:22PM

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

Tony -

If you are going to use a 15/60 NST to power your TC, you definitely DO NOT want to use a tank capacitor with a value of .0106uF.

If you aren't familiar with the dangers of "resonant rise", which can very quickly destroy both your NST and your tank capacitor, study the section on resonant rise and missed firings at:

Also, Google "LTR capacitor value", and learn why a larger-than-resonant tank capacitor value is the best overall solution to obtaining optimum coil output along from freedom from resonant rise.

Regards,
Herr Zapp

quicksilver

Thu Aug 05 2010, 06:51PM

Registered Member #1408 Joined: Fri Mar 21 2008, 03:49PM
Location: Oracle, AZ
Posts: 679

I found some old material on the construction of Leyden Jars. These are simple graphic scans from a very old book but could be helpful. They are not the easiest thing to read but not impossible. Their age is indeterminate. The original text many no longer exist.
]leyden-jar.zip[/file]

Xplorer

Fri Aug 06 2010, 02:15AM

Registered Member #2416 Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91

Herr Zapp wrote ...

Tony -

If you are going to use a 15/60 NST to power your TC, you definitely DO NOT want to use a tank capacitor with a value of .0106uF.

If you aren't familiar with the dangers of "resonant rise", which can very quickly destroy both your NST and your tank capacitor, study the section on resonant rise and missed firings at:

Ok I used JavaTC and the SG LTR cap size is .0199uf. You're right. BTY, I'm actually going to use a 12/60 not a 15/60.

So I need .0199uf for a 12/60, how about two of these in series?

That's .02uf at 20kv. Is 20kv enough? I know the capacitor voltage should be higher than the supply voltage right? Like I said I really only have about 40 bucks to spend on my caps.

Now for my frequency of LC calculations do I use the LTR cap size or the resonate cap size? Thanks for your help, really, I appreciate it!

-Tony

Arcstarter

Fri Aug 06 2010, 03:15AM

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

Never buy the kind on eBay, to answer the question. CDE all the way, every time.

And you need more like 28 capacitors for a 15/60. And then, for what would be considered life long and with a safety margin, you would need like 100 caps O_O. Tesla coil caps are usually way under rated what the actual voltage in the tank cap is.

Herr Zapp

Fri Aug 06 2010, 03:24AM

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

Xplorer -

I think you may want to do some additional research on the operating conditions that a tank capacitor sees in a spark-gap Tesla coil circuit, what types of capacitor construction can survive these extreme conditions, and how an MMC array is physically constructed.

The operating life of your "two-caps-in-series", polyester-dielectric MMC would likely be measured in seconds.

See the MMC design guides at:

and:

For your resonant frequency calculations, you would of course use the actual capacitor value (preferably measured, rather than calculated) as most capacitors will have large tolerance (typically +/- 20%) on their value.

Regards,
Herr Zapp

Xplorer

Fri Aug 06 2010, 03:53AM

Registered Member #2416 Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91

Man... Well there is no way I can spend hundreds on a huge capacitor bank and I'm already invested in this project.

-Tony

Herr Zapp

Fri Aug 06 2010, 04:09AM

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

Xplorer -

"....hundreds on a huge capacitor bank" ........

If you'd read the links I provided, you'd see that 32 Cornell-Dubilier 942 series film-foil caps would be adequate for your 12/60 power supply. These can be purchased for around $3.50 each if you look for best pricing. 32 X $3.50 = a little over $100.

Otherwise, you can build a salt-water cap bank for near zero cost, and still make sparks, although you won't match the performance of an MMC assembled with the proper capacitors.

Regards,
Herr Zapp

Xplorer

Fri Aug 06 2010, 04:27AM

Registered Member #2416 Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91

I did look over the pdf. Thank you for that.

But the outlook is bleak if I'm going to expect to pay 3.50 each, and that doesn't include shipping....

There is someone selling them on eBay for 4.50, so I'm looking at about $150 at best.
*sigh*

-Tony

Herr Zapp

Fri Aug 06 2010, 07:13AM

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

Xplorer -

The only people selling CDE caps for Tesla coils are the ones that buy them from distributors for $3.00, and then mark them up to sell to dummies who can't use the Internet to find better pricing.

Go to the Cornell-Dubilier website (cde.com), click "services", then "stock check". This will give you a complete listing of all CDE distributors who have stock of the particular cap you are after. A very commonly used model is the 942C20P15K-F, .15uF at 2KV. The .10uF model can also be used.

But, ("sigh") if money's a problem, or all the CDE distributors are temporarily out of stock , there's no reason not to build a salt-water capacitor out of a dozen beer bottles, some aluminum foil (or a plastic bucket) and a pound of salt. This will allow you to learn how to set up and tune a coil. Then, ("sigh"), after you've saved more of your pennies, you can buy some suitable capacitors and assemble a MMC. If your coil runs OK with the salt water capacitors, you will be pleasantly pleased with the performance improvement you'll get with a good capacitor. With a properly assembled and tuned coil, your 12/60 NST can generate 28-32 inch arcs, or better.

Herr Zapp

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