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Re: MMC Question



Original poster: "huil888" <huil888@xxxxxxxxxxxx>

Mark -

A few questions on your TC:

1. Are you absolutely sure that your HV transformer is rated 15kV at 20ma?? This is an extremely unusual rating for a NST, in 10 years of Tesla coil building I have never heard of a NST with this rating in North America, Europe, or the UK. Or is it not a NST? There are some relatively small (8" X 8" X 8") DC power supplies for air ionizers that have similar ratings, but these may not be suitable for driving a Tesla coil. Double check the nameplate, let me know who the manufacturer is and what the nameplate says.

2. How did you determine that 0.0042uF was a "resonant" capacitor value for your transformer? My data indicate that 0.0035uF would be the resonant value with a 15/20 transformer.

In any case, these variations in tank capacitor "value" (technically more correct than "size") have no significant affect on eventually tuning your system. The inductance of the primary coil is "adjusted" (via variable tap point) to make the resonant frequency of the tank circuit match the resonant frequency of the secondary coil with topload.

Are you using one of the Tesla coil design programs to design all the critical parameters of your coil? If you don't have an oscilloscope and RF signal generator, it is VERY important to carefully calculate the dimensions and values for each component, or you will have a very difficult time "tuning" your coil to achieve resonance.

WINTESLA is a very simple but useful program, JAVATC is even more powerful but slightly more complex. I would suggest that you design your coil COMPLETELY on paper before you proceed with any more construction. The biggset single source of failure with tesla coils is not having the primary and secondary circuits tuned to EXACTLY the same resonant frequency. This will not happen by lucky accident; these circuits need to be very carefully designed and constructed to achieve resonance. Without resonance, there will be no sparks. Period.

Regards,
Scott Hanson
Costa Mesa, California
USA
----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Monday, April 23, 2007 12:26 PM
Subject: MMC Question


Original poster: mark@xxxxxxxxxxxxxxxx
Hi,

I've just built my MMC for my first Tesla coil, and I have yet another question
regarding its construction and use.  From what I've read the MMC makes part of
a tuned circuit. My original question, was regarding the size of MMC required,
and someone from the list recommended making it 1.5 - 2x bigger than required.

so my original size was

0.0042uF for a 15Kv 20mA 50hz xfmr

so timed this by 1.5 and got 0.0063uF

However I mucked up the calculation and didn't realize until after I built my
MCC, I've ended up with 0.0055uF

So my question really is, will this still work correctly or do I need to start
again ??

And if this needs to be in tune with the rest of the circuit, surely even
increasing this 1.5 would muck the tuning up??

Any comments appreciated.

Mark