Herr Zapp wrote ...

Enyuki -

First, my humblest apologies - the correct "larger than resonant" capacitor value for your 15/60, 60 Hz system is .015uf, not .15uF. (Don't know where the missing zeros went....)

Responding to your specific questions:

1. Yes, it is highly recommended that you use a "larger than resonant" capacitor value. See the section on uncontrolled resonant voltage rise on Richie Burnett's website for much background on this phenomonon:

2. There are many options for constructing home-made toroids, depending on what materials you have access to. One of the most commonly used is flexible, convoluted aluminum duct material used for home heating and air-conditioning systems. This is relatively thin corrugated aluminum tubing that can be formed into a circle and secured with aluminum foil tape. In the US, this material is available in 1" diameter increments from 3" to 8". It comes in "compressed" sections about 3 feet long that can be stretched out about 1.5X the initial length. Look at many of the coils on the teslacoilwebring for examples of this construction.

3. There are two areas in WINTESLA that "calculate" the required capacitor value. First, the "Trans/Cap Match" tab calculates the RESONANT cap value for a given transformer's output voltage, current, and AC line frequency. This is just a "theoretical" value, and NOT what you want to actually use. Multiiply this value by 1.4 or 1.5 to determine a "safe" LTR value that will not be subject to extreme resonant voltage rise.

The second area where WINTESLA calculates the cap value is in the "Primary Coil" section. This calculates the actual "required" cap value to tune the resonant frequency of your primary circuit to match the resonant frequency of your secondary coil + topload. The capacitor value shown here will change (to maintain resonance) if you make any changes to the number of turns in the primary coil, or if you make any changes to the secondary circuit that changes its resonant frequency.

4. You still didn't tell us anything about the design of the spark gap. Are you using a single gap, with two 1.5cm spherical electrodes? If so, this won't quench well at all with a 60ma power supply. Consider changing to a gap design using multiple pieces of 17mm-25mm diameter copper pipe 75mm to 100mm long, mounted parallel to each other, to provide at least 5-6 series-connected spark gaps. This should be cooled with a small fan. The "single-gap" concept can work, but it requires a supply of high-velocity air at moderate pressure, or a fairly powerful vacuum-motor. See Gary Lau's "Sucker-Gap" design at: for a typical vacuum motor design. However, this type of gap is usually annoyingly noisy.

5. An MMC for a 15/60 NST-powered coil consisting of 300+ caps is absurd, both from a cost standpoint, and from physical size and mounting complexity. I'd go back and review your design (and your cap ratings) to find a more efficient solution. An MMC with 300+ individual capacitors is just not rational (or cost effective) for this coil.

The number of parallel "strings" of caps required in an MMC is determined by the peak current in the primary circuit. JAVATC and other Tesla coil design tools will calculate the peak current and help you determine the required number of strings.

Or, simply go to Terry Fritz' "MMC cap chart" at: , which will show you the required number of caps in a string, and the number of parallel strings required. (This is based on the C-D 942 series cap, .15uF at 2kV.) For your 15/60, static-gap system,, with the MMC designed to have a reasonable safety factor, you will need two strings of 20 caps each, or a total of 40 caps. This is FAR more reasonable than 300+ caps. This chart was designed with actual measurements of cap heating in an RF test setup.

You mentioned that the CDE 942-series caps are hard to find. If you go to the Cornell-Dubilier website (cde.com), you will find a "Services" tab at the top of the home page. Click this, and in the drop-down menue is a "Stock Check" option. Enter the model of the capacitor you are interested in, and it will display a listing of all the C-D distributors that have these caps in stock. Also, these capacitors are almost always available from certain eBay sources. The C-D 942C series caps are well-proven in Tesla coil service, and the RMS and peak current ratings of the 942C20P15K-F model (13.5A and 432A) are among the highest of all similar caps offered by various manufacturers.

I found the datasheet for the "RS Components" caps you are considering, which are actually the Arcotronics A72 series:

Note that the "Maximum Current vs Frequency" graphs show that the .047, 1500V cap has a maximum RMS current rating of around 5A, much less than the 13A rating of the .15uF C-D cap.

Your NSTs sound like conventional iron-core transformers, and should work well when the secondary outputs are paralleled. You will need to "phase" them correctly to get the full 60ma output.

You should also consider adding a simple R-C filter array (knoiwn as a "Terry Filter", after its developer Terry Fritz) to protect the NSTs from the high voltage "spikes" that will be generated in the primary circuit. Many, many NSTs have been destroyed in Tesla coil systems because they were not adequately protected from HV spikes & RF harmonics in the primary circuit.

Regards,
Herr Zapp

eniyuki wrote ...

hey my friend, whats up.
when you answer my question, i feel dumb that needs a lot of reading again!. haha

that LTR issue, i noticed that too. no big deal.
i understand LTR now after i read the link you gave.

for my toroid, im still finding the right materials. so il stick at the moment with my 3x12 toroid.

"The second area where WINTESLA calculates the cap value is in the "Primary Coil" section. This calculates the actual "required" cap value to tune the resonant frequency of your primary circuit to match the resonant frequency of your secondary coil + topload. The capacitor value shown here will change (to maintain resonance) if you make any changes to the number of turns in the primary coil, or if you make any changes to the secondary circuit that changes its resonant frequency."

okay okay. so what i need to do is match the primary and secondary's frequency but LTR is applied. is that correct?

i just got interested in that 2 round shiny balls and popped out in my mind that i can use it as a spark gap. but well
i think i'll fabricate new spark gap like how you describe it above. is it okay if it is noisy? i like my tesla to be very noisy (happy new year!) LOL

for my MMC, i always use deepfriedneon to calculate values.
still looking for 942c

i read some articles about terry filter but i can't understand how to construct since they explain it very briefly.
can you provide more on how to construct?i'll google some too!
i have AWG # 13,18,21,26,28 and 31 magnet wires. i dont know what,size and length of my former and how to connect them!

i'll google how to phase transformer.

thank you!

eniyuki wrote ...