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

Dear coilers,

     Thanks for all of your replies! I was afraid that you would say that the caps wouldn't work. After i posted last night, i made some adjustments (mostly to my grounding rd and object i was attempting to strike). I was able to get a nice little corona off a sharp point and 1 1/2 inch sparks. But that still is much smaller than i would like.
It is really unfortunate that they won't work, because i was able to pick them all up for free! all together weigh about 26 lbs and fit on a 1.5 x 1.5 piece of plywood. 
Yes, like i said, they are ALL in series. they range from .55 uf to .77 uf. I realize that the .55's are taking more voltage then, but almost all of these are rated at 2100 WVAC, and with 80 in series, certainly the voltage is dropped sufficiently, correct? I did in fact do the math on how to set up the bank, using the formula :   1/C(t)  = 1/C(1)  + 1/C(2) + ... 1/C(80)  (parenthesis  indicating subscript).
I'm not exactly sure how to "give you output file". I used the calculators at deepfriedneon. If you would like, i can put my numbers back through, and give you all the info. Also, what do you mean that this cap value leads to a resonance problem? Please explain, as i would not like to have to find another NST.

There is another option for a capacitor. Before building a MOC bank, I built a plate capacitor. I kind of need something to show tomorrow (I'm going to the state fair, although thats not the reason i built it) so my father (I'm 15) thinks it would be an amazing idea to rebuild it, because it failed when we tried it the first time. Its problem is that it was filled with mineral oil, but sprung a leak. We decided to test it dry (I smack myself every time i think of it) and one plate arced on the surface of the glass to the lead on an another plate. We were able to refill it with oil, but even so, there must have been a carbon path still conducting, because the spark gap wasn't firing, and there was a faint glow in the capacitor (we made the sides out of plexi-glass, so it was see-through). If we cleaned of the plates, and remade the container so as to be oil-tight, do you think it would be a viable option?
Again, thank you for taking the time to read this, and please ask if there is any information i may have forgotten to give you.
One last question: I forget, how do you post picture links in these mailings? A picture is worth 1000 words, and i have a lot of pictures of various parts of my tesla.
Thank you!
Joel Torgeson

From: Quarkster <quarkster@xxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Saturday, August 22, 2009 10:21:45 PM
Subject: 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

> Alright,
>     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.
> Sincerely,
> Joel Torgeson
> _______________________________________________
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> Tesla@xxxxxxxxxxxxxx
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