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Re: [TCML] Tuning, Capacitors, and Spark Gaps

Joel -

Before delving into a detailed troubleshooting process, please provide some additional information on your coil.

Did you use a Tesla coil design program to determine all the electrical & mechanical parameters? If so, please post the output file, showing ALL the parameters for ALL the components. This will allow List members to perform a quick "design review" and look for any obvious design problems.

You mentioned that your tank capacitor is made from a large number of microwave oven capacitors. This may be a problem, because they probably will not be capable of withstanding the peak current seen in a Tesla coil tank circuit.

Also, you stated that your target tank capacitor value is .0088uF, for a 9kv/30ma NST. This capacitor value yields a resonant condition with this particular NST, which can cause extremely high voltage conditions that can instantly destroy either (or both) your NST and your tank capacitor. What you want for a static-gap system is a "larger than resonant" (LTR) capacitor value, typically 1.3 - 1.5X the resonant value.

A few additional questions on your capacitor array:

1. Are all 80 of the capacitors connected in a single series string?
2. Are all the capacitors the same capacitance value?
   a)  If so, please provide the value.
b) If there are various values, please list the values, and how many capacitors of each value are used.

Unless your capacitors all have a value of 0.7uF, I don't see how you achieved your .088uF target value.

Herr Zapp

----- Original Message ----- From: "Joel Torgeson" <joeltorgeson@xxxxxxxxx>
To: "Tesla Mailing-list" <tesla@xxxxxxxxxx>
Sent: Saturday, August 22, 2009 3:19 PM
Subject: [TCML] Tuning, Capacitors, and Spark Gaps


I've now built my tesla coil, and am very disappointed that it fails to work. My transformer is a 9,000v 30ma NST. I have tailor-built my capacitor out of capacitors from microwave ovens. They are internally resisted, and with 80 of them in series i hit my target capacitance of .0088 uf. My primary consists of 1/4 inch copper tubing spaced 1/4 inch between each winding. there are 15 turns of tubing in a flat pancake configuration. My secondary consists of approximately 760 feet of 24 AWG magnet wire wrapped around 3.26 inch outside diameter PVC pipe. The topload is of the tubing and pie-pan variety, using 3 inch aluminum tubing/ducting. This makes a ~ 15 inch toroid on the top. i am using a 8 ft grounding rod that isn't attached to anything important. There is no metal inside the secondary, so that isn't a problem. My biggest concern is the spark gap. It's a static gap, not split up into multiple gaps, just one big one. it is 5.6mm wide, and has a hair drier running on cool temp, high velocity blowing on it for quenching.

There's all the numbers i have, now i need some advice. I have been trying to tune it in for 2 days, and all i can get is the occasional 3/4 inch spark (usually no more than 1/2 in for rapid sparks). It does light up a broken fluorescent bulb, and as i said, it makes some small sparks, but i didn't spend all that time and effort to create something my Van de Graaff can beat! So, does anyone see anything obviously wrong? Any suggestions, comments, tips, or (yes) criticisms would be much appreciated.

Joel Torgeson

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