Hi Yesn (?),
A 9/60 NST is perfectly suitable for a coil, beginner or otherwise. I'm
not sure I agree with the opinion that 9kV might be too low a voltage, I
built a damn fine coil with a 4/20 NST. I don't know if I would consider
195 eur a good price, but as conventional core and coil NST's are becoming
increasingly uncommon, perhaps this is the way of the world.
The .15uF/2kV caps are a good choice as they're something of a sweet spot
for best HV capacitance for the buck. The target capacitor value is chosen
after deciding on the transformer rating, the mains frequency, and the
spark gap type. The .15 and .1 uF caps are so commonly used that a design
chart was created, a link to the chart is here:
https://drive.google.com/open?id=1obSs-BEquvANQK5BCRTzzMDatnFTsU6W If
you're using a static gap, you should use the "Static gap LTR Cap" column.
Assuming you have 50 Hz power, for your 9/60 NST, the chart suggests that
you target a 0.0318 uF cap value. Unfortunately it's difficult to
series/parallel 0.15uF caps to achieve this value, and the best and most
economical approximation to this at a suitable voltage rating would be to
use 0.1uF/2kV caps - 2 parallel strings of 7 - fourteen 0.1 uf caps total.
After the cap is chosen, you can choose a secondary and top load, and
primary configuration. I've not used it but JavaTC comes highly
recommended and it will match the pri/sec turns to achieve resonance.
Yes - be very mindful of the spark gap width. There's no formula to
predict the proper width, and too wide WILL kill your NST. Multi-gap
cylinder gaps work well but they're difficult to adjust. For this reason
and for performance issues recommend a "sucker gap" which has a single gap
with forced airflow provided by a vacuum cleaner motor. Mine is documented
here: http://www.laushaus.com/tesla/onegap.htm
The "proper" width of a static spark gap is determined by applying the NST
output directly to the gap, with no capacitor connected. Adjust the gap
width so that with the Variac set to max if you have one, the gap *just*
begins to fire, and perhaps a smidge wider if you're feeling lucky.
The secondary aspect ratio is not at all critical and what you suggest is
fine.
A Terry filter IS a good idea, but the most important thing is to be
mindful of the gap width and avoid the temptation to go wider, even though
wider will always make for better performance. Also remember that Terry
filters for different NST voltages require differing numbers of varistors.
A Terry filter designed for a 15kV NST won't do any good for a 9kV NST, and
setting the safety gaps on the filter is also done the same way as the main
gap width. My Terry filter is documented here and explains why it's
useful: http://www.laushaus.com/tesla/protection.htm.
Hope this helps, Gary
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On Mon, Dec 11, 2017 at 5:19 PM, YESN via Tesla <tesla@xxxxxxxxxx> wrote:
> Hi all
>
> I am (still) busy designing my first Tesla Coil.
> I have found a reasonable 9kV 60mA NST for 195 eur. Is this reasonable for
> a first build?
> Or is it way too much to begin with?
> I have been sent this website for designing my MMC. Bart Anderson uses
> 150uf 2kV caps.
> How exactly is the capacity of a cap chosen? Are there formulas to
> calculate the total capacitance of your MMC? If so it does depend on the
> amount of strings you use right?
> (The one that in my mind were reasonable were hese:
> https://nl.mouser.com/ProductDetail/Cornell-Dubilier-CDE/940C20P15K-F/?qs=
> 11kF6y5Z3OhbthK%252bpYczHA%3D%3D)
>
> Also how is the resonant frequency between the two circuits calculated? I
> have also heard about tapping your primary coil, (much like finding the
> frequency with an old radio right?) does anyone have a description of how
> this process is done? About the spark gap. As someone on this list luckily
> pointed me out placing the spark gap too wide can cause your NST to
> overvolt and die. How do you decide the starting width of the spark gap?
> (Do you gradually increase it or leave it at a certain length?)
> I recently came across a static spark gap which where multiple ones across
> copper tubes. Is this advisable for a beginner?
>
> The PVC pipe I have already bought is 11,5 cm in diameter. Therefore it's
> length should be around 58 cm right?
>
> I really care about the state of the components and do not want them to be
> harmed? Therefore a Terry-Filter is necessary right?
>
> P.S. Are these questions normal for someone starting?
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