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Re: [TCML] first coil help
From reading your post, I would say you are well acquainted with
the mathematics and theory behind coiling, therefore I am going to
assume you have good values for all of your components (someone like
Bart Anderson will go over them in detail with you I am sure). So with
that said, I have two pieces of advise for you.
1. The RF ground should be grounded to a stake in the dirt, not to the
mains ground. Since you don't have that option, I would suggest you use
a counterpoise, and ground that. Simply put it is a large flat sheet
laid on the ground, and the energy form the coil is transferred
capacitively, instead of directly to ground.
2. We need more details of your spark gap, that is probably the most
important part of a coil. You could have everything else perfect, and a
lousy spark gap will kill your performance. We need details if we are
to help you, you are probably not quenching properly, or are just out of
tune (but given your mathematical background, I'm going to assume it is
your spark gap). I hope this helps, and I am sure you will hear form
others, who may be a bit more helpful soon.
Ryckmans, Thomas wrote:
> I am building my first Tesla coil, but having issues - sparks are
> pathetic - about 1 cm from topload to a grounded object. Help is much
> I am adding the same document as a Word attachement, in case the pics
> don't make it. <>
> First of all here is a picture of the thing on my kitchen table; scale
> is provided by the yellow yardstick sitting on the primary (21 cm). In
> the background there is a crate of the best beer in the world -
> My first problem is that I find books and internet references on "RF
> ground" a bit confusing. Several books (e.g electronic gadgets for the
> evil genius, gadgeteer's goldmine) show a RF ground connected to the
> mains ground as here (evil genius):
> Other references state that the RF ground should be distinct from the
> mains ground, to avoid frying electronic equipment etc.
> Unfortunately I live in an apartment, so I would find it difficult to
> drive an iron rod into the ground to create my own RF ground...
> What would you recommend?
> I am using a 6kV 50 mA NST to power
> Here are some values for the coil; the calculated values are provided by
> Primary is
> Salt water bottle caps, 24 bottles for a total of 10 nF (measured)
> Copper tubing (8 mm) with inside diameter 189 mm, spacing 25 mm
> Measured values are
> 4 turns 1uH
> 5 turns 5 uH
> 6 turns 9 uH
> 7 turns 14 uH
> Secondary is using a 130 mm (diameter) black tube, 320 mm high, with
> (about) 14 turns/cm hence (about) 450 turns.
> Measured value for the secondary coil is 3.53 mH
> Calculated value for the top load is 7.3 pF and self capacitance of the
> coil (calc) 5 pF assuming spherical top load with R=65 mm. In reality
> the top load is cylindrical and I expect its capacitance to be a bit
> This gives me a calculated resonance frequency of 767 kHz.
> Using a signal generator with a LED indicating max current I get a
> maximum current at 833 kHz - not too far away from calculated values.
> Using a signal generator and an oscilloscope I get a resonance value at
> 909 kHz.
> With my primary's capacitor at 10 nF I would need my primary inductance
> around 3.5 uH to give a similar resonance frequency of about 850 kHz -
> this turns out to be just between 4 and 5 turns of the primary coil.
> Using the signal generator at 833 kHz and the oscilloscope, I get a
> maximum voltage value for the primary coil+cap in parallel at around 3.5
> turns - again, not too bad.
> So far, so good. However when firing the coil, I get pathetich sparks
> (about 1 cm long) between the top load and a (insulated) screwdriver I
> hold above it.
> What am I doing wrong?
> I am using this configuration:
> I tried the other configuration (cap and primary in series, below) I get
> the same kind of results... which configuration would you recommend? The
> series one (below) is said to offer more protection to the NST
> apparently - I will add a Terry filter soon anyway.
> Many thanks for your comments!
> Thomas Ryckmans
> P Pfizer Discovery Chemistry
> Office 500.1.177A Lab 500.1.109
> Global Research and Development ipc 351
> Sandwich Kent CT13 9NJ
> Phone +44 1304 643 735 Fax +44 1304 651 817
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